WO2017095152A1 - Cathode active material for secondary battery, and secondary battery comprising same - Google Patents

Abstract

The present invention provides cathode active material comprising lithium composite metal oxide particles expressed by the chemical formula 1 below and a secondary battery comprising the cathode active material. [Chemical formula 1] Li_aNi_1-x-yCo_xM1_yM2_zM3_wO₂ In the chemical formula 1, M1 is a metallic element having surface energy (ΔE_surf) of -0.5 eV and higher as calculated by the mathematical formula 1 below, M2 is a metallic element having surface energy (ΔE_surf) of -1.5 to - 0.5 eV as calculated by the mathematical formula 1 below, and M3 is a metallic element having surface energy (ΔE_surf) of -1.5 eV and lower as calculated by the mathematical formula 1 below, where 1.0≤a≤1.5, 0<x≤0.5, 0<z≤0.05, 0.002≤w≤0.1, and 0<x+y≤0.7 [Mathematical formula 1] ΔE_surf = E_surf2-E_surf1 = (E_slab2-E_bulk)-(E_slab1-E_bulk) In the mathematical formula 1, E_surf2 indicates the degree to which the metallic element is oriented toward the outermost surface in the lithium composite metal oxide particle, E_surf1 indicates the degree to which the metallic element is oriented toward the center in the lithium composite metal oxide particle, E_slab1 is the slab model energy of the lithium composite metal oxide particle when the metallic element is in the center thereof, E_slab2 is the slab model energy of the lithium composite metal oxide particle when the metallic element is on the surface thereof, and E_bulk is the energy of the bulk model corresponding to each slab model.

Description

Cathode active material for secondary battery and secondary battery comprising same

[Citations with Related Applications]

This application claims the benefit of priority based on Korean Patent Application No. 10-2015-0168676, filed on November 30, 2015 and Korean Patent Application No. 10-2016-0161895, filed on November 30, 2016. All content disclosed in the literature is included as part of this specification.

[Technical Field]

The present invention has an interfacial stability between the electrolyte and the active material with improved surface stability and stability of the internal structure of the active material particles, including a cathode active material for a secondary battery that can exhibit excellent battery safety and life characteristics even under high temperature and high voltage conditions It relates to a secondary battery.

As technology development and demand for mobile devices increase, the demand for secondary batteries as a source of energy is rapidly increasing. Among such 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.

However, a lithium secondary battery has a problem in that its life is rapidly decreased as charging and discharging are repeated. In particular, this problem is more serious at high temperatures. This is a phenomenon caused by decomposition of the electrolyte or deterioration of the active material due to moisture or other influences inside the battery, and increase of internal resistance of the battery.

Accordingly, the positive electrode active material for lithium secondary batteries currently being actively researched and developed is LiCoO ₂ having a layered structure. LiCoO ₂ is most commonly used due to its excellent lifespan characteristics and charge and discharge efficiency. However, LiCoO ₂ has a low structural stability and thus is not applicable to high capacity technology of batteries.

As a cathode active material to replace this, various lithium transition metal oxides such as LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , Li (Ni _x1 Co _y1 Mn _z1 ) O ₂ have been developed. Among them, LiNiO ₂ has an advantage of exhibiting battery characteristics of high discharge capacity. However, LiNiO ₂ Simple solid phase reactions are difficult to synthesize and have low thermal stability and cycle characteristics. In addition, lithium manganese oxides such as LiMnO ₂ or LiMn ₂ O ₄ have the advantage of excellent thermal safety and low price. However, lithium manganese oxide has a problem of low capacity and low temperature characteristics. In particular, in the case of LiMn ₂ O ₄ but a part merchandising products to low cost, since the Mn ^{+ 3} structure modification (Jahn-Teller distortion) due to the not good life property. In addition, LiFePO ₄ has a low price and excellent safety, and a lot of research is being conducted for hybrid electric vehicles (HEVs). However, LiFePO ₄ is difficult to apply to other fields due to the low conductivity.

Due to this situation, LiCoO ₂ is a lithium anode manganese cobalt oxide, Li (Ni _{x 2} Co _{y 2} Mn _{z 2} ) O ₂ (At this time, X2, y2, and z2 are atomic fractions of independent oxide composition elements, and 0 <x2 ≦ 1, 0 <y2 ≦ 1, 0 <z2 ≦ 1, and 0 <x2 + y2 + z2 ≦ 1. This material is less expensive than LiCoO ₂ and has the advantage that it can be used for high capacity and high voltage. However, lithium nickel manganese cobalt-based oxides have disadvantages of poor rate capability and poor life characteristics at high temperatures.

On the other hand, the lithium secondary battery using the positive electrode active material is a problem that the safety of the battery is deteriorated or the lifespan characteristics rapidly decrease due to the exothermic reaction accompanied by the deterioration of the surface structure of the active material and a sudden collapse of the structure as the charge and discharge repeatedly There is this. This problem is particularly acute under conditions of high temperature and high voltage. This is because the active material deteriorates due to the decomposition of the electrolyte due to moisture or other influences inside the battery or the instability of the surface of the positive electrode, and the interface resistance between the electrode and the electrolyte including the active material is increased.

In order to solve this problem, methods for improving the structural stability and surface stability of the active material itself by doping or surface treatment of the positive electrode active material, and to improve the interface stability between the electrolyte and the active material has been proposed. However, the situation is not satisfactory enough in terms of effects and fairness.

In addition, as the demand for high capacity batteries increases recently, the necessity for the development of a cathode active material that can improve battery safety and lifespan by securing internal structure and surface stability is increasing.

The first technical problem to be solved by the present invention has the surface stability of the active material particles and the stability of the internal structure, along with improved interfacial stability between the electrolyte and the active material, showing excellent battery safety and life characteristics even under high temperature and high voltage conditions It is to provide a cathode active material for a secondary battery.

In addition, a second technical problem to be solved by the present invention is to provide a secondary battery positive electrode, a lithium secondary battery, a battery module and a battery pack including the positive electrode active material.

According to one embodiment of the present invention to solve the above problems, there is provided a cathode active material for a secondary battery comprising a lithium composite metal oxide particles represented by the following formula (1).

[Formula 1]

Li _a Ni _1-xy Co _x M1 _y M2 _z M3 _w O ₂

In Chemical Formula 1,

M1 is -0.5 eV to more than the surface energy (△ E _surf) calculated by the equation (1) metallic elements, M2 is -1.5 eV is more than -0.5 eV surface energy (△ E _surf) calculated by the following equation (1) Metal element of less than, M3 is a surface element (ΔE _surf ) calculated by the following equation 1 is a metal element of less than -1.5 eV, 1.0≤a≤1.5, 0 <x≤0.5, 0 <y≤0.5, 0 <z ≦ 0.05, 0.002 ≦ w ≦ 0.1, 0 <x + y ≦ 0.7.

[Equation 1]

△ E _surf = E _surf2 -E _surf1

= (E _slab2 -E _bulk )-(E _slab1 -E _bulk )

In Equation 1, E _surf2 represents the degree to which the metal element is directed to the outermost surface in the lithium composite metal oxide particles, E _surf1 represents the degree to which the metal element is directed to the center of the lithium composite metal oxide particles, E _slab1 Silver is the energy of the slab model of the lithium composite metal oxide particles when the metal element is in the center of the lithium composite metal oxide particles, and E _slab2 is the lithium composite when the metal element is on the surface of the lithium composite metal oxide particles. The energy of the slab model of the metal oxide particles, and E _bulk is the energy of the bulk model corresponding to each slab model.

According to another embodiment of the present invention, there is provided a cathode for a secondary battery, a lithium secondary battery, a battery module, and a battery pack including the cathode active material.

Other specific details of the embodiments of the present invention are included in the following detailed description.

The positive electrode active material for a secondary battery according to the present invention has an improved interfacial stability between the electrolyte and the active material with excellent particle surface stability and stability of the internal structure. Since the secondary battery according to the present invention includes a cathode active material having the above characteristics, it may exhibit excellent battery safety and life characteristics even under high temperature and high voltage conditions.

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

The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

A cathode active material for a secondary battery according to an embodiment of the present invention,

To include lithium composite metal oxide particles represented by the formula (1).

[Formula 1]

Li _a Ni _{1 -x- y} Co _x M1 _y M2 _z M3 _w O ₂

In Chemical Formula 1,

M1 is a metal element whose surface energy (ΔE _surf ) calculated by the following Equation 1 is -0.5 eV or more,

M2 is a metal element whose surface energy (ΔE _surf ) calculated by Equation 1 is -1.5 eV or more and less than -0.5 eV,

M3 is a metal element whose surface energy (ΔE _surf ) calculated by Equation 1 below is less than -1.5 eV.

1.0 ≦ a ≦ 1.5, 0 <x ≦ 0.5, 0 <y ≦ 0.5, 0 <z ≦ 0.05, 0.002 ≦ w ≦ 0.1, 0 <x + y ≦ 0.7.

[Equation 1]

△ E _surf = E _surf2 -E _surf1

= (E _slab2 -E _bulk )-(E _slab1 -E _bulk )

In Equation 1,

E _surf2 indicates the degree to which the metal element is directed to the outermost surface in the lithium composite metal oxide particles.

E _surf1 indicates the degree to which the metal element is directed toward the center of the lithium composite metal oxide particle.

E _slab1 is the energy of the slab model of lithium composite metal oxide particles when the metal element is in the center of the lithium composite metal oxide particles.

E _slab2 is the energy of the slab model of lithium composite metal oxide particles when the metal element is on the outermost surface of the lithium composite metal oxide particles.

E _bulk is the energy of the bulk model corresponding to each slab model.

In the present invention, when manufacturing a cathode active material for a secondary battery, the position preference on the cathode active material particles according to the amount of surface energy of the element is investigated, and based on this, the element has an optimized concentration profile from the surface of the cathode active material particle to the center section. As a result, the surface stability and the internal structure stability of the active material particles may be improved, and thus the interface stability between the electrolyte and the active material may be improved. As a result, the secondary battery, a final product, can exhibit excellent battery safety and life characteristics even under high temperature and high voltage conditions.

In the cathode active material according to an embodiment of the present invention, the lithium composite metal oxide may include a compound of Formula 1 below.

[Formula 1]

Li _a Ni _{1 -x- y} Co _x M1 _y M2 _z M3 _w O ₂

In Chemical Formula 1,

M1 is a metal element whose surface energy (ΔE _surf ) calculated by the following Equation 1 is -0.5 eV or more,

M2 is a metal element whose surface energy (ΔE _surf ) calculated by Equation 1 is -1.5 eV or more and less than -0.5 eV,

M3 is a metal element whose surface energy (ΔE _surf ) calculated by Equation 1 below is less than -1.5 eV.

1.0 <a <1.5, 0 <x <0.5, 0 <y <0.5, 0 <z <0.05, 0.002 <w <0.1, and 0 <x + y <0.7.

In the present invention, the surface energy calculated by Equation 1 (E _surf ) May indicate the degree to which the metal element is directed toward the outermost surface or the center of the lithium composite metal oxide particles.

[Equation 1]

△ E _surf = E _surf2 -E _surf1

= (E _slab2 -E _bulk )-(E _slab1 -E _bulk )

In Equation 1, E _surf2 represents the degree to which the metal element is directed toward the outermost surface in the lithium composite metal oxide particles, and E _surf1 represents the degree to which the metal element is oriented toward the center, that is, the center of _gravity in the lithium composite metal oxide particles. E _surf1 and E _surf2 represent the _difference between the energy of the slab model and the energy value of the bulk model when the metal element is located at the center and the outermost surface of the lithium composite metal oxide particles. In addition, E _slab1 is the energy of the lithium composite metal oxide particle slab model when the metal element is in the center of the lithium composite metal oxide particle. E _slab2 is the energy of the lithium composite metal oxide particle slab model when the metal element is on the outermost surface of the lithium composite metal oxide particle. E _bulk is the energy of the bulk model corresponding to each slab model and is calculated stoichiometrically regardless of the position of the metal element in the lithium composite metal oxide.

As the surface energy value ΔE _surf calculated by Equation 1 indicates a positive value, it indicates that the metal element has a property of being located at the center of the lithium composite metal oxide particle. On the contrary, a negative surface energy value indicates that the metal element has a property of being positioned on the surface side of the lithium composite metal oxide particle. Therefore, the metal element whose surface energy exhibits a positive value diffuses to the center of the lithium composite metal oxide particle. In addition, the metal element having a negative surface energy penetrates into the surface of the lithium composite metal oxide particle. In addition, the closer the surface energy value is to 0, the less the directivity toward the surface or the center portion. That is, as the surface energy value approaches 0, it may be uniformly distributed at a constant concentration throughout the lithium composite metal oxide particles. In the present invention, the surface energy value of the metal element may be determined through modeling calculation by the method of the Discrete Fourier Transform DFT.

In the present invention, the concentration profile refers to the content of the metal element according to the depth of the center portion at the surface of the lithium composite metal oxide particle when the X axis represents the depth from the particle surface to the center portion and the Y axis represents the content of the metal element. Meaning graph. For example, the mean slope of the concentration profile is positive means that the center portion of the lithium composite metal oxide particles is located relatively more than the surface portion of the particle, and that the mean slope is negative means that the center portion of the lithium composite metal oxide particles is central. More means that more metal elements are located in the particle surface portion. In the present invention, the concentration profile is X-ray photoelectron spectroscopy (also referred to as XPS (X-ray Photoelectron Spectroscopy) or ESCA (Electron Spectroscopy for Chemical Analysis)), electron beam microanalyzer (Electron Probe Micro Analyzer, EPMA), inductively coupled plasma- It can be confirmed using methods such as Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-AES), or Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Specifically, in the case of confirming the profile of the metal element in the lithium composite metal oxide using XPS, the active material is etched from the surface of the lithium composite metal oxide particle toward the center part, and the atomic ratio of the metal is etched by etching time. It is possible to determine the concentration profile of the metal element therefrom.

Specifically, in the positive electrode active material according to an embodiment of the present invention, the surface energy (E _surf ) is a metal element of -0.5 eV or more of the M 1 is a single concentration value, that is, the concentration profile of the entire lithium composite metal oxide particles The slope may be included at the same concentration of 0 or the average slope of the concentration profile from the surface of the lithium composite metal oxide particles to the central section may be positive. More specifically, M1 may be one having a surface energy of -0.5 to 0.5eV. As a result, the internal structure stability of the lithium composite metal oxide particles may be exhibited by being included in a uniform content throughout the lithium composite metal oxide particles, having little directivity toward the particle surface or the center.

M1 satisfying the surface energy condition may include any one or two or more selected from the group consisting of Al, Mg, Y, Zn, In, and Mn. In the case of M1 can improve the crystal stability of the active material to improve the battery life and high temperature characteristics.

In addition, in the lithium composite metal oxide of Chemical Formula 1, M1 may be included in an amount corresponding to y, that is, 0 <y≤0.5. If y is 0, the improvement effect due to the inclusion of M1 cannot be obtained. If y is greater than 0.5, the output characteristics and capacity characteristics of the battery may be deteriorated. In consideration of the remarkable effect of improving the battery characteristics according to the inclusion of the M1 element, M1 may be included in a content of 0.1 <y ≤ 0.2 more specifically.

In the cathode active material, M2, which is a metal element having a surface energy of -1.5 eV or more and less than -0.5 eV, more specifically, -1.5 eV to -1.0 eV, has an average slope of the concentration profile from the surface of the cathode active material particles to the center portion. It can be distributed to be negative. M2 whose surface energy meets the above conditions has surface directivity. However, compared to M3, the surface directivity and the central directivity are low, and the absolute value of the average slope of the concentration profile may be smaller than that of M3.

M2 satisfying the surface energy condition may be present at a position where these elements should be present by substituting a part of Ni, Co or M1 in the crystal structure of the lithium composite metal oxide. Or doped to the lithium composite metal oxide. In addition, the M2 may react with lithium present on the surface of the lithium composite metal oxide to form lithium oxide. More specifically, M2 satisfying the surface energy condition may include any one or two or more selected from the group consisting of Zr, Ti, Ta, Hf, Sn, Cr, Sb, Ru, Gd, and Os, More specifically, it may be Ti or Zr.

In the lithium composite metal oxide particles of Chemical Formula 1, M2 may be included in an amount corresponding to z, that is, 0 <z≤0.05. When the M2 content is 0 or more than 0.05, it is not easy to implement the surface stability and internal structure of the lithium composite metal oxide. As a result, the improvement of output and life characteristics may be insignificant. In addition, when considering the surface stability of the lithium composite metal oxide particles according to the control of the M2 content and the remarkable effect of improving the battery characteristics, more specifically, the M2 may be included in more specifically 0 <z≤0.02.

In the cathode active material, M3, which is a metal element having a surface energy of less than -1.5 eV, more specifically, -1.8 eV to -4.0 eV, has large surface directivity. Therefore, the M3 is present at a high concentration on the surface side of the lithium composite metal oxide particles, thereby improving the surface stability of the lithium composite metal oxide.

M3 satisfying the surface energy condition is specifically an element corresponding to the Group VI (Group VIB) of the periodic table, and may be introduced on the surface side of the lithium composite metal oxide particles to rearrange the crystal structure during the production of the lithium composite metal oxide particles. have. As a result, the lithium composite metal oxide may have a more stable crystal structure, and may also play a role of suppressing particle growth during the firing process. In the crystal structure of the lithium composite metal oxide particles, M3 may be present at a position where these elements should be present by substituting a part of Ni, Co, or M1, or reacting with lithium present on the particle surface to form lithium oxide. You may. Accordingly, it is possible to control the size of the crystal grains by adjusting the content of M3 and the timing of addition. More specifically, the M3 may include any one or two or more selected from the group consisting of W, V, Nb, Nd, and Mo, and more specifically, may be at least one element of W and Nb. Among them, when M3 is W, it may be excellent in terms of output improvement, and in case of Nb, it may be superior in terms of high temperature durability.

In the lithium composite metal oxide particles of Chemical Formula 1, M3 may be included in an amount corresponding to w, that is, 0.002 ≦ w ≦ 0.1. If the M3 content is less than 0.002 or more than 0.1, the surface stability of the lithium composite metal oxide particles may not be easily implemented, and as a result, the effect of improving output and life characteristics may be insignificant. In addition, when considering the surface stability of the lithium composite metal oxide particles according to the control of the content of M3 and the remarkable effect of improving the battery characteristics, more specifically, the M3 may be more specifically included in 0.005 <w≤0.5.

In the lithium composite metal oxide particles of Chemical Formula 1, Li may be included in an amount corresponding to a, that is, 1.0 ≦ a ≦ 1.5. If a is less than 1.0, the capacity may be lowered. If a is more than 1.5, the particles may be sintered in the firing step, and thus the production of the active material may be difficult. Considering the remarkable effect of improving the capacity characteristics of the positive electrode active material according to the Li content control and the sinterability in the preparation of the active material, the Li may be more specifically included in a content of 1.0≤a≤1.15.

In addition, in the lithium composite metal oxide of Chemical Formula 1, Ni may be included in an amount corresponding to 1-x-y, that is, 0.3≤1-x-y <1. If 1-x-y is less than 0.3, the capacity characteristics may be deteriorated, and if it is more than 1, high temperature stability may be deteriorated. In consideration of the remarkable effect of improving the capacity characteristic according to the inclusion of Ni, the Ni may be included in a content of more specifically 0.35≤1-x-y <0.8.

In addition, in the lithium composite metal oxide of Chemical Formula 1, Co may be included in an amount corresponding to x, that is, 0 <x≤0.5. If x is 0, the capacity characteristic may be lowered, and if it is more than 0.5, there is a fear of an increase in cost. Considering the remarkable effect of improving the capacity characteristics according to the inclusion of Co, the Co may be included in a content of 0.1≤x≤0.35 more specifically.

On the other hand, the lithium composite metal oxide particles according to an embodiment of the present invention may have a structure of a core-shell including a core and a shell formed on the surface of the core.

Specifically, in the lithium composite metal oxide particles according to an embodiment of the present invention, the core refers to a region existing inside the lithium composite metal oxide particles and close to the particle center except for the surface of the particles. In addition, the core may be a region present inside the lithium composite metal oxide particles and may maintain a regular crystal structure. Specifically, it may be an area corresponding to a distance r _in from the particle center to the surface, that is, a distance of 0% or more and less than 100%, more specifically 0% or more and 70% or less from the particle center with respect to the semi-diameter of the particle. . In addition, in the present invention, the 'shell' means a region close to the surface except for the center of the particle or the inside of the particle. The shell may also be an area where the regular crystal structure is not maintained due to its geometric constraints. Specifically, the shell is at a distance from the surface of the particle to the center (r _sur ), i. It may be a corresponding area.

More specifically, the lithium composite metal oxide particles having the core-shell structure may include the core and the shell in a volume ratio of 50:50 to 80:20. When the volume ratio of the core and the shell exceeds the above range, the effect of improving the active material stability due to the position control of the metal element may be insignificant.

In the present invention, the core and the shell can be classified using the X diffraction analysis results for the lithium composite metal oxide particles.

More specifically, in the lithium composite metal oxide particles having the core-shell structure, the surface energy (ΔE _surf ) is -0.5 eV or more, more specifically -0.5 eV to 0.5 eV metal element M1 is a lithium composite It can be included at a single concentration throughout the metal oxide particles.

In addition, the surface energy is a metal element of more than -1.5 eV but less than -0.5 eV, more specifically -1.5 eV to -1.0 eV M2 is in the concentration of 1 to 25 mol% in the core, 75 to 99 mol% in the shell May be included. Metal elements whose surface energy satisfies the above conditions have particle surface directivity, but have a low surface directivity and a high central directivity compared to the M3. When included in the lithium composite metal oxide particles in the above content condition, it can exhibit the surface stability and internal structural stability of the lithium composite metal oxide particles.

In addition, M3, which is a metal element having a surface energy of less than -1.5 eV, more specifically, -1.5 eV to -4.0 eV, may be included at a concentration of 1 to 10 mol% in the core and 90 to 99 mol% in the shell. M3 having a surface energy satisfying the above conditions has a large particle surface directivity, and when included in the lithium composite metal oxide particles under the above content conditions, may exhibit excellent surface stability of the lithium composite metal oxide particles.

In addition, in the cathode active material according to an embodiment of the present invention, at least one metal element of nickel and cobalt contained in the lithium composite metal oxide of Formula 1 may increase or decrease in the cathode active material particles. The concentration gradient can be expressed.

Specifically, in the positive electrode active material according to an embodiment of the present invention, at least one metal element of nickel and cobalt may have a concentration gradient in which the metal concentration continuously changes throughout the active material particles, and the metal element concentration The gradient slope may represent one or more values. By having such a continuous concentration gradient, there is no abrupt phase boundary region from the center to the surface, so that the crystal structure is stabilized and the thermal stability is increased. 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. In addition, by varying the concentration of each metal in the active material particles through the concentration gradient, it is possible to easily utilize the properties of the metal to further improve the battery performance improvement effect of the positive electrode active material.

In the present invention, "showing a concentration gradient in which the metal concentration continuously changes" means that the metal concentration exists in a concentration distribution that gradually changes throughout the particle. Specifically, the concentration distribution is 0.1 atomic% to 1 micron, more specifically, 0.1 micron, based on the total atomic weight of the metal included in the lithium composite metal oxide particles. 30 atomic%, more specifically, 0.1 atomic% to 20 atomic%, and more specifically, there may be a concentration gradient, that is, a concentration difference that varies from 1 atomic% to 10 atomic%.

More specifically, in the lithium composite metal oxide, the concentration of nickel contained in the lithium composite metal oxide may decrease while having a continuous concentration gradient from the center of the lithium composite metal oxide particles toward the surface of the particles. . At this time, the concentration gradient slope of the nickel may be constant from the center of the lithium composite metal oxide particles to the surface. As such, when the concentration of nickel maintains a high concentration at the center of the particles in the lithium composite metal oxide particles and includes a concentration gradient that decreases toward the particle surface side, thermal stability of the lithium composite metal oxide may be improved.

In addition, in the lithium composite metal oxide, the concentration of cobalt contained in the lithium composite metal oxide may increase while having a continuous concentration gradient from the center of the lithium composite metal oxide particle toward the surface of the particle. At this time, the concentration gradient slope of the lithium composite metal oxide may be constant from the center of the lithium composite metal oxide particles to the surface. As such, when the concentration of cobalt is maintained at the center of the particles in the lithium composite metal oxide particles and has a concentration gradient that increases with the concentration toward the surface side, the capacity and output characteristics of the cathode active material can be improved while reducing the amount of cobalt used. Can be.

In addition, in the lithium composite metal oxide, nickel and cobalt may each independently exhibit a varying concentration gradient throughout the lithium composite metal oxide particles. The concentration of nickel may decrease while having a continuous concentration gradient from the center of the lithium composite metal oxide particles toward the surface. In addition, the concentration of the cobalt may be independently increased while having a continuous concentration gradient from the center of the lithium composite metal oxide particles toward the surface. As such, the capacity characteristics of the lithium composite metal oxide are included by including a combined concentration gradient in which nickel concentration decreases and cobalt concentration increases toward the surface side of the lithium composite metal oxide particles throughout the lithium composite metal oxide. It can improve thermal stability while maintaining

In addition, the lithium composite metal oxide according to an embodiment of the present invention, the surface of the lithium composite metal oxide particles by diffusion to the surface of the lithium composite metal oxide particles according to the surface directivity of the M2 and M3 in the manufacturing process On the at least one metal element selected from the group consisting of M2 and M3; Or it may include a coating layer comprising a lithium oxide produced by the reaction of at least one metal element and lithium.

When the lithium composite metal oxide further includes a coating layer including M2 or M3 diffused to the surface, the lithium composite metal oxide may include a lithium composite metal oxide having a composition represented by Formula 2 below:

[Formula 2]

_{Li a Ni 1 -x- y Co x} M1 y M2 z M3 w O 2 · M2 'z' M3 'w'

In Formula 2, M1, M2, M3, a, x, y, z, and w are as defined above,

M2 'and M3' are M2 and M3 respectively located on the lithium composite metal oxide surface,

w 'and z' are the coating amounts of M3 'and M2', respectively, w 'is 0.01 to 10 atomic% based on the total amount of M3, and z' is 5 to 30 atomic% based on the total amount of M2.

If the coating amount is too small, the improvement effect due to the coating is insignificant, and if the coating amount is too large, there is a fear that the structural stability is lowered by a decrease in the amount distributed in the lithium composite metal oxide particles relatively. In addition, in the present invention, the coating of the metal element means that the metal element is physically adsorbed or chemically bonded to the surface of the lithium composite metal oxide.

In addition, when the coating layer comprises a lithium oxide by the reaction of a metal element of M2 or M3 and lithium, the lithium oxide may specifically include a compound of formula (3):

[Formula 3]

Li _m (M2 _p M3 _1-p ) O _{(m + n) / 2}

In Formula 3, M2 is any one or two or more elements selected from the group consisting of Zr, Ti, Ta, Hf, Sn, Cr, Sb, Ru, Gd and Os, M3 is W, V, Nb, Nd and Any one or two or more elements selected from the group consisting of Mo, 2≤m≤10, n is the sum of the oxidation number of M2 and M3, 0≤p≤1.

The cathode active material according to an embodiment of the present invention having the structure as described above may have an average particle diameter (D ₅₀ ) of 4 ㎛ to 20 ㎛. If the average particle diameter of the positive electrode active material is less than 4 μm, the structural stability of the positive electrode active material particles may be lowered. If the average particle diameter is more than 20 μm, the output characteristics of the secondary battery may be reduced. In addition, in consideration of the remarkable effect of the improvement of the concentration distribution of the metal element in the positive electrode active material particles and the average particle diameter of the active material, the average particle diameter of the positive electrode active material may be 5㎛ to 18㎛. In the present invention, the average particle diameter (D ₅₀ ) of the positive electrode active material may be defined as the particle size at 50% of the particle size distribution. In the present invention, the average particle diameter (D ₅₀ ) of the positive electrode active material particles is, for example, electrons using a scanning electron microscopy (SEM) or a field emission scanning electron microscopy (FE-SEM). It can be measured by microscopic observation or by laser diffraction method. When measured by the laser diffraction method, more specifically, the particles of the positive electrode active material are dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring apparatus (for example, Microtrac MT 3000) to irradiate an ultrasonic wave of about 28 kHz to an output of 60 W after that, it is possible to calculate the mean particle size (D ₅₀₎ of from 50% based on the particle size distribution of the measuring device.

In addition, the positive electrode active material according to an embodiment of the present invention may be one having a BET specific surface area of 0.3m ² / g to 1.9m ² / g.

When the BET specific surface area of the positive electrode active material exceeds 1.9 m ² / g, there is a fear that the dispersibility of the positive electrode active material in the active material layer and the resistance in the electrode are increased due to aggregation between the positive electrode active materials, and the BET specific surface area is 0.3 m ² / g. When less than g, there exists a possibility of the dispersibility fall of a positive electrode active material itself, and a capacity fall. In the present invention, the specific surface area of the positive electrode active material is measured by the Brunauer-Emmett-Teller (BET) method, specifically, nitrogen gas at liquid nitrogen temperature (77K) using BELSORP-mino II manufactured by BEL Japan It can calculate from adsorption amount.

In addition, the positive electrode active material according to an embodiment of the present invention may exhibit excellent capacity and charge and discharge characteristics by simultaneously satisfying the above average particle diameter and BET specific surface area conditions. More specifically, the cathode active material may have an average particle diameter (D ₅₀ ) of 4 ㎛ to 15 ㎛ and a BET specific surface area of 0.5m ² / g to 1.5m ² / g. In the present invention, the specific surface area of the positive electrode active material is measured by the Brunauer-Emmett-Teller (BET) method, specifically, nitrogen gas at liquid nitrogen temperature (77K) using BELSORP-mini II manufactured by BEL Japan It can calculate from adsorption amount.

In addition, the positive electrode active material according to an embodiment of the present invention may have a tap density of 1.7 g / cc or more, or 1.7 g / cc to 2.8 g / cc. By having a high tap density in the above range, high capacity characteristics can be exhibited. In the present invention, the tap density of the positive electrode active material can be measured using a conventional tap density measuring device, and specifically, can be measured using a SEISHIN Tap-tester.

The cathode active material according to an embodiment of the present invention having the above structure and physical properties may be prepared by wet precipitation, and in detail, may be prepared by coprecipitation according to the method of forming the precursor.

Specifically, the method for producing a positive electrode active material by the coprecipitation method, nickel raw material, cobalt raw material, and M1 raw material (wherein M1 is M1 is a metal element having a surface energy (E _surf ) of -0.5 eV or more, specifically, Is an at least one selected from the group consisting of Al, Mg, Y, Zn, In, and Mn), and an ammonium cation-containing complex former and a basic compound are added to the metal-containing solution and reacted to form a precursor. Preparing a step (step 1), and mixing the precursor with a lithium raw material and then firing at 700 ° C. to 1,200 ° C. (step 2), wherein the preparation of the metal-containing solution or the precursor and the lithium raw material M2 raw materials and M3 raw materials when mixed with materials (where M2 is a metal element with a surface energy of more than -1.5 eV and less than -0.5 eV, specifically Zr, Ti, Ta, Hf, Sn, Cr, Sb, Ru) Lines in the group consisting of, Gd and Os M3 is a metal element having a surface energy of less than -1.5 eV, and specifically, any one or two or more elements selected from the group consisting of W, V, Nb, Nd, and Mo). Can be.

The metal-containing solution is an organic solvent (specifically, alcohol, etc.) capable of uniformly mixing nickel raw material, cobalt raw material, M1 containing raw material and optionally M2 or M3 containing raw material with a solvent, specifically water or water. It may be prepared by dissolving in a mixture of water and water, or may be prepared by preparing a solution containing a raw material of each of the metals, specifically an aqueous solution, and then mixing them. In this case, the mixing ratio of each raw material may be appropriately determined within a range to satisfy the content condition of each metal element in the final cathode active material.

As a raw material including the metal element, acetate, nitrate, sulfate, halide, sulfide, oxide, hydroxide, or oxyhydroxide may be used, and the like, and it is not particularly limited as long as it can be dissolved in water.

For example, the cobalt raw material may be Co (OH) ₂ , CoOOH, Co (SO ₄ ) _{2 ,} Co (OCOCH ₃ ) ₂ 4H ₂ O, Co (NO ₃ ) ₂ ㆍ 6H ₂ O, CoCl ₂ or Co ( SO ₄ ) ₂ .7H ₂ O, and the like, and any one or a mixture of two or more thereof may be used.

In addition, as the nickel raw material is Ni (OH) _2, NiO, NiOOH, NiCO ₃ and 2Ni (OH) ₂ and 4H ₂ O, NiC ₂ O ₂ and _{2H 2 O, NiCl 2, Ni} (NO 3) 2 and 6H ₂ O, NiSO ₄ , NiSO ₄ .6H ₂ O, fatty acid nickel salts or nickel halides, and the like, and any one or a mixture of two or more thereof may be used.

Further, as the manganese raw material, manganese oxides such as Mn ₂ O ₃ , MnO ₂ , and Mn ₃ O ₄ ; Manganese salts such as MnCO ₃ , MnCl ₂ , Mn (NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganese dicarboxylic acid, manganese citrate and fatty acid manganese; Oxy hydroxide, and manganese chloride, and the like, and any one or a mixture of two or more thereof may be used.

In addition, the aluminum raw material may be AlSO ₄ , AlCl ₃ , Al-isopropoxide (Al-isopropoxide) or AlNO ₃ and the like, any one or a mixture of two or more thereof may be used.

As the M2 raw material, acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide containing M2 may be used. For example, when M 2 is Ti, titanium oxide may be used.

As the M3 raw material, acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide containing M3 may be used. For example, when M 3 is W, tungsten oxide may be used.

In addition, the ammonium cation-containing complexing agent may specifically 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 the like. Species alone or mixtures of two or more may be used. In addition, the ammonium cation-containing complex forming agent may be used in the form of an aqueous solution, and as the solvent, a mixture of water or an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water may be used.

The ammonium cation-containing complex forming agent may be added in an amount such that the molar ratio of 0.5 to 1 per mole of the metal-containing solution. In general, the chelating agent reacts with the metal in a molar ratio of at least 1: 1 to form a complex, but the unreacted complex which does not react with the basic aqueous solution may be converted into an intermediate product, recovered as a chelating agent, and reused. In addition, the chelating usage can be lowered than usual. As a result, the crystallinity of the positive electrode active material can be increased and stabilized.

In addition, the 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 one or more of these may be used. The basic compound may also be used in the form of an aqueous solution, and as the solvent, a mixture of water or an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water may be used.

In addition, the coprecipitation reaction for forming the precursor may be carried out under the condition that the pH is 11 to 13. If the pH is out of the above range, there is a fear to change the size of the precursor to be prepared or cause particle splitting. In addition, metal ions may be eluted on the surface of the precursor to form various oxides by side reactions. More specifically, the pH of the mixed solution may be performed at 11 to 12 conditions.

In addition, the ammonium cation-containing complexing agent and the basic compound may be used in a molar ratio of 1:10 to 1: 2 to satisfy the above pH range. At this time, the pH value means a pH value at the temperature of the liquid 25 ℃.

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

In addition, in the case of forming a concentration gradient of the metal element in the positive electrode active material, the nickel, cobalt and M1-containing raw materials and, optionally, M2 and M3-containing raw materials are prepared at different concentrations from the metal-containing solution. After preparing a second metal-containing solution, the transition metal solution such that the mixing ratio of the metal-containing solution and the second metal-containing solution is gradually changed from 100% by volume to 0% by volume to 100% by volume. It can be carried out by adding the second metal-containing solution to the reaction, and at the same time reacting by adding an ammonium cation-containing complex forming agent and a basic compound.

As such, by continuously increasing the amount of the second metal-containing solution to the metal-containing solution and controlling the reaction rate and the reaction time, nickel, cobalt, and M1 are independently from the center of the particle to the surface in one coprecipitation reaction process. Precursors with continuously varying concentration gradients can be prepared. At this time, the concentration gradient of the metal in the precursor and its slope can be easily controlled by the composition and the mixed feed ratio of the metal-containing solution and the second metal-containing solution, and to make a high density state with a high concentration of a specific metal It is preferable to lengthen the reaction time and to lower the reaction rate, and to shorten the reaction time and increase the reaction rate in order to make a low density state having a low concentration of a specific metal.

Specifically, the speed of the second metal-containing solution added to the metal-containing solution may be carried out continuously increasing in the range of 1 to 30% compared to the initial charging speed. Specifically, the input speed of the metal-containing solution may be 150ml / hr to 210ml / hr, the input speed of the second metal-containing solution may be 120ml / hr to 180ml / hr. In the input speed range, the input speed of the second metal-containing solution may be continuously increased within the range of 1% to 30% of the initial input speed. At this time, the reaction may be carried out at 40 ℃ to 70 ℃. In addition, the size of the precursor particles may be adjusted by adjusting the supply amount and the reaction time of the second metal-containing solution to the metal-containing solution.

As a precursor, particles of a composite metal hydroxide are generated as a precursor and are precipitated in a reaction solution. Specifically, the precursor may include a compound of Formula 4 below.

[Formula 4]

_{Ni 1 -x- y Co x M1 y} M2 z M3 w (OH 1-a) 2

(In Formula 4, M1, M2, M3, x, y, z and w are as defined above, 0≤a≤0.5)

In addition, the precipitated precursor may be selectively carried out after separation in a conventional manner.

The drying process may be carried out according to a conventional drying method, specifically, may be carried out for 15 to 30 hours by a method such as heat treatment or hot air injection in the temperature range of 100 ℃ to 200 ℃.

In the manufacturing method for the production of the positive electrode active material, step 2 is a step of preparing a positive electrode active material by mixing the precursor particles prepared in step 1 with a lithium-containing raw material and optionally M2 and M3 raw material and then calcined . At this time, M2 and M3 raw materials are the same as described above.

As the lithium-containing raw material, lithium-containing carbonate (for example, lithium carbonate), hydrate (for example, lithium hydroxide I hydrate (LiOH, H ₂ O), etc.), hydroxide (for example, lithium hydroxide, etc.) , Nitrates (e.g., lithium nitrate (LiNO ₃ ), etc.), chlorides (e.g., lithium chloride (LiCl), etc.), and the like. One of these alone or a mixture of two or more thereof may be used. In addition, the amount of the lithium-containing raw material used may be determined according to the content of lithium and transition metal in the final lithium composite metal oxide, specifically, the metal element included in the lithium and precursor contained in the lithium raw material (Me ) And the molar ratio (molar ratio of lithium / metal element (Me)) can be used in an amount such that 1.0 or more.

On the other hand, the firing process may be performed at 700 ℃ to 1,200 ℃.

If the temperature at the time of firing is less than 700 ° C, there is a risk of lowering the firing rate, and if it exceeds 1,200 ° C, there is a fear of generation of side reactions due to oversintering. More specifically, the firing process may be performed at 800 ℃ to 1,000 ℃.

In addition, the firing process may be performed in an air atmosphere or an oxygen atmosphere (for example, O ₂ ), and more specifically, may be performed in an oxygen atmosphere having an oxygen partial pressure of 20% by volume or more. In addition, the firing process may be performed for 5 hours to 48 hours, or 10 hours to 20 hours under the above conditions.

In addition, a sintering aid may optionally be further added during the firing process.

The addition of the sintering aid can easily grow crystals at low temperatures and minimize the heterogeneous reaction during dry mixing. In addition, the sintering aid has the effect of making the rounded curved particles by dulling the corners of the lithium composite metal oxide primary particles. In general, in a lithium oxide-based positive electrode active material including manganese, manganese elution occurs frequently from the edges of the particles, and the manganese elution reduces characteristics of the secondary battery, particularly at high temperatures. In contrast, when the sintering aid is used, the elution portion of manganese can be reduced by rounding the corners of the primary particles, and as a result, the stability and lifespan characteristics of the secondary battery can be improved.

Specifically, the sintering aid is boron compounds such as boric acid, lithium tetraborate, boron oxide and ammonium borate; Cobalt compounds such as cobalt oxide (II), cobalt oxide (III), cobalt oxide (IV), and tricobalt tetraoxide; Vanadium compounds such as vanadium oxide; Lanthanum compounds such as lanthanum oxide; Zirconium compounds such as zirconium boride, calcium zirconium silicate and zirconium oxide; Yttrium compounds such as yttrium oxide; Or gallium compounds such as gallium oxide, and the like, and any one or a mixture of two or more thereof may be used.

The sintering aid may be used in an amount of 0.2 to 2 parts by weight, more specifically 0.4 to 1.4 parts by weight relative to 100 parts by weight of the precursor.

In addition, the moisture removing agent may be optionally further added during the firing process. Specifically, the water removing agent may include citric acid, tartaric acid, glycolic acid or maleic acid, and any one or a mixture of two or more thereof may be used. The moisture remover may be used in an amount of 0.01 to 2 parts by weight based on 100 parts by weight of the precursor.

The positive electrode active material prepared by the above process has an improved interfacial stability between the electrolyte and the positive electrode active material together with excellent particle surface stability and internal structure stability, and thus exhibits excellent battery safety and life characteristics even under high temperature and high voltage conditions. Can be. In addition, the distribution of the transition metal in the cathode active material can be additionally controlled, as a result of which the thermal stability can be improved to minimize performance degradation at high voltage.

Accordingly, according to another embodiment of the present invention provides a cathode and a lithium secondary battery including the cathode active material.

Specifically, the positive electrode is formed on the positive electrode current collector and the positive electrode current collector, and includes a positive electrode active material layer containing the positive electrode active material.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, carbon, nickel, titanium on the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with silver, silver or the like can be used. In addition, the positive electrode current collector may have a thickness of about 3 to 500 μm, and may form fine irregularities on the surface of the current collector to increase adhesion of the positive electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

In addition, the cathode active material layer may include a conductive material and a binder together with the cathode active material described above.

In this case, the conductive material is used to impart conductivity to the electrode. In the battery constituted, the conductive material may be used without particular limitation as long as it has electronic conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more thereof may be used. The conductive material may typically be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

In addition, the binder serves to improve adhesion between the cathode active material particles and adhesion between the cathode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC). ), Starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubbers, or various copolymers thereof. One of these alone or a mixture of two or more thereof may be used. The binder may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the positive electrode active material described above. Specifically, the positive electrode active material and optionally, a composition for forming a positive electrode active material layer including a binder and a conductive material may be prepared by applying a positive electrode current collector, followed by drying and rolling. In this case, the type and content of the cathode active material, the binder, and the conductive material are as described above.

The solvent may be a solvent generally used in the art, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or acetone. Water, and the like, one of these alone or a mixture of two or more thereof may be used. The amount of the solvent is sufficient to dissolve or disperse the positive electrode active material, the conductive material, and the binder in consideration of the coating thickness of the slurry and the production yield, and to have a viscosity that can exhibit excellent thickness uniformity during application for the production of the positive electrode. Do.

Alternatively, the positive electrode may be prepared by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating the film obtained by peeling from the support onto a positive electrode current collector.

According to another embodiment of the present invention, an electrochemical device including the anode is provided. The electrochemical device may be specifically a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

At this time, the operating voltage of the lithium secondary battery may be 2.5V to 4.6V. This is because it is possible to operate at a relatively high voltage as the safety of the battery is improved due to the structural stability of the positive electrode active material including the lithium excess composite metal oxide of the formula (1). More specifically, the lithium secondary battery according to an embodiment of the present invention may be a high voltage driving battery of 3.1V to 4.6V, and more specifically 3.4V to 4.6V or 3.5V to 4.35V high voltage driving battery Can be.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is as described above. The lithium secondary battery may further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

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

The negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material. For example, the negative electrode active material layer is coated with a negative electrode active material, and optionally a composition for forming a negative electrode including a binder and a conductive material on a negative electrode current collector and dried, or casting the negative electrode forming composition on a separate support It can also be produced by laminating a film obtained by peeling from this support onto a negative electrode current collector.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; Metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; Metal oxides capable of doping and undoping lithium, such as SiO _x (0 <x <2), SnO ₂ , vanadium oxide, lithium vanadium oxide; Or a composite including the metallic compound and the carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the anode active material. As the carbon material, both low crystalline carbon and high crystalline carbon can be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is amorphous, plate, scaly, spherical or fibrous natural graphite or artificial graphite, Kish graphite (Kish) graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, petroleum coke and coal coke High-temperature calcined carbon such as tar pitch derived cokes is typical.

In addition, the binder and the conductive material may be the same as described above in the positive electrode.

On the other hand, in the lithium secondary battery, the separator is to separate the negative electrode and the positive electrode and to provide a passage for the movement of lithium ions, if it is usually used as a separator in a lithium secondary battery can be used without particular limitation, in particular to the ion movement of the electrolyte It is desirable to have a low resistance against the electrolyte and excellent electrolytic solution-moisture capability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer or the like Laminate structures of two or more layers may be used. In addition, conventional porous nonwoven fabrics such as nonwoven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be optionally used as a single layer or a multilayer structure.

In addition, examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery. It doesn't happen.

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 may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolanes may be used. Of these, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can improve the charge and discharge performance of a battery, and low viscosity linear carbonate compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate and the like is more preferable. In this case, the cyclic carbonate and the chain carbonate may be mixed and used in a volume ratio of about 1: 1 to about 1: 9, so that the performance of the electrolyte may be excellent.

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 0.1M 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 move effectively.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoro ethylene carbonate, pyridine, tri, etc. for the purpose of improving battery life characteristics, reducing battery capacity, and improving discharge capacity of the battery. Ethyl phosphite, 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 be included. In this case, the additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

As described above, the lithium secondary battery including the cathode active material according to the present invention may exhibit excellent battery safety and life characteristics even under high temperature and high voltage conditions due to the excellent stability of the cathode active material. Accordingly, the present invention is useful for portable devices such as mobile phones, notebook computers, digital cameras, and electric vehicle fields such as hybrid electric vehicles (HEVs).

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 the battery pack is a power tool (Power Tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

[ Reference Example  1-1: Of positive electrode active material  Produce]

2L of distilled water was charged into the 3L wet reactor tank, and nitrogen gas was added to the tank at a rate of 1L / min to remove dissolved oxygen. At this time, the temperature of the distilled water in the tank was maintained at 45 ℃ using a temperature maintaining apparatus. In addition, distilled water in the tank was stirred at a speed of 1,200 rpm using an impeller connected to a motor installed outside the tank.

Nickel sulphate, manganese sulphate and cobalt sulphate were mixed in water at a molar ratio of 0.6: 0.2: 0.2 to prepare a metal containing solution at a concentration of 1.5 M, and a separate 3 M aqueous sodium hydroxide solution was prepared. The metal containing solution was pumped continuously to the tank for the wet reactor at 0.18 L / hr with a metering pump. The aqueous sodium hydroxide solution was pumped variable so that the distilled water in the wet reactor tank was maintained at pH 11.5 in conjunction with the control equipment for pH control of the distilled water in the tank. At this time, 30% aqueous ammonia solution was continuously pumped into the reactor at a rate of 0.035 L / hr.

By adjusting the flow rates of the metal-containing solution, the sodium hydroxide aqueous solution and the ammonia aqueous solution, the average residence time of the solution in the wet reactor tank was 6 hours.After the reaction in the tank reached the steady state, the metal ion and hydroxide of the metal-containing solution were A nickel-cobalt-manganese composite metal precursor prepared by continuously reacting sodium hydroxide ions of sodium and ammonia ions of an aqueous ammonia solution for 20 hours was continuously obtained through an overflow pipe installed at the top of the tank. The obtained composite metal precursor was washed with distilled water and dried in a 120 ° C. constant temperature dryer for 24 hours.

Then, 0.998 mol of the composite metal precursor is 0.002 mol of Al ₂ O ₃ and Li ₂ CO ₃ Dry mixing with 1 mole and firing at 900 ℃ for 10 hours to prepare a cathode active material (Li (Ni _0.6 Mn _0.2 Co _0.2 ) _0.998 Al _0.002 O ₂ ).

[ Reference Example  1-2 to 1-21: Of positive electrode active material  Produce]

Mn, Mg, Y, Zn, In, Ti, Hf, Sn, Cr, Zr, Sb, Ta, Ru, Gd, Os, V, Nb, W, Mo, or in place of dopant Al in Reference Example 1-1. A positive electrode active material was prepared in the same manner as in Reference Example 1, except that each was doped with Nd.

[ Experimental Example  One]

In order to predict the positional orientation of metal elements in the positive electrode active material, surface energy values (E _surf ) and dopants are preferred through modeling calculations using the DFT method for the positive electrode active materials prepared in Reference Examples 1-1 to 1-21. The location was predicted. The analysis results are shown in Table 1 below.

[Equation 1]

△ E _surf = E _surf2 -E _surf1

= (E _slab2 -E _bulk )-(E _slab1 -E _bulk )

In Equation 1, E _surf1 , E _surf2 , E _slab1 , E _slab2 , and E _bulk are as defined above.

division	Dopant Type	△ E surf	division	Dopant Type	△ E surf	division	Dopant Type	△ E surf
Reference Example 1-1	Al	0.720	Reference Example 1-8	Hf	-0.673	Reference Example 1-15	Gd	-1.171
Reference Example 1-2	Mn	0.420	Reference Example 1-9	Sn	-0.906	Reference Example 1-16	Os	-1.497
Reference Example 1-3	Mg	0.384	Reference Example 1-10	Cr	-0.913	Reference Example 1-17	V	-1.505
Reference Example 1-4	Y	0.223	Reference Example 1-11	Zr	-1.074	Reference Example 1-18	Nb	-1.531
Reference Example 1-5	Zn	-0.052	Reference Example 1-12	Sb	-1.083	Reference Example 1-19	W	-2.072
Reference Example 1-6	In	-0.164	Reference Example 1-13	Ta	-1.137	Reference Example 1-20	Mo	-2.273
Reference Example 1-7	Ti	-0.633	Reference Example 1-14	Ru	-1.155	Reference Example 1-21	Nd	-2.566

When the surface energy of the metal element in the positive electrode active material is positive based on 0, it means that the metal element penetrates into the center of the positive electrode active material particle. If the surface energy shows a negative value, it means that the metal element has a property to diffuse to the surface of the cathode active material particles.

As a result of calculating the surface energy value ΔE _surf from Equation 1 from the surface energy change values of the metal elements of Table 1, Al, Mn, Mg, Y, Zn and In have a surface energy of -0.5 eV or more. In particular, Mg, Y, Zn, and In were 0.5 to 0.5 eV, showing values close to zero. From this, it can be seen that Mg, Y, Zn, and In do not exhibit particle center or surface directivity, and it can be expected that the mean slope of the concentration profile in the positive electrode active material is zero or a value close to zero. In addition, it can be seen that Ru, Gd, Os, V, Nb, W, Mo, and Nd exhibit negative surface energy values, specifically, surface energy values of less than -1.5 eV, indicating surface directivity of the positive electrode active material particles. In addition, Ti, Hf, Sn, Cr, Zr, Sb, and Ta exhibit surface energy values of -1.5 eV or more and less than -0.5 eV, compared to Ru, Gd, Os, V, Nb, W, Mo, and Nd. It can be seen that represents a low surface directivity.

[ Example  1-1: Of positive electrode active material  Produce]

2L of distilled water was charged into the 3L wet reactor tank, and nitrogen gas was added to the tank at a rate of 1L / min to remove dissolved oxygen. At this time, the temperature of the distilled water in the tank was maintained at 45 ℃ using a temperature maintaining apparatus. In addition, distilled water in the tank was stirred at a speed of 1,200 rpm using an impeller connected to a motor installed outside the tank.

Nickel sulphate, manganese sulphate and cobalt sulphate were mixed in water at a molar ratio of 0.6: 0.2: 0.2 to prepare a metal containing solution at a concentration of 1.5 M, and a separate 4 M NaOH aqueous solution was prepared. The metal containing solution was pumped continuously to the tank for the wet reactor at 0.18 L / hr with a metering pump. The aqueous sodium hydroxide solution was pumped variable so that the distilled water in the wet reactor tank was maintained at pH 11.5 in conjunction with the control equipment for pH control of the distilled water in the tank. At this time, 30% aqueous ammonia solution was continuously pumped into the reactor at a rate of 0.035 L / hr.

By adjusting the flow rates of the metal-containing solution, the sodium hydroxide aqueous solution and the ammonia aqueous solution, the average residence time of the solution in the wet reactor tank was 6 hours.After the reaction in the tank reached the steady state, the metal ion and hydroxide of the metal-containing solution were A nickel-cobalt-manganese composite metal precursor prepared by continuously reacting sodium hydroxide ions of sodium and ammonia ions of an aqueous ammonia solution for 20 hours was continuously obtained through an overflow pipe installed at the top of the tank. The obtained precursor was washed with distilled water and dried in a 120 ° C. constant temperature dryer for 24 hours.

Thereafter, dry mixture of Li ₂ CO ₃ , tungsten oxide (WO ₃ ) and titanium oxide (TiO ₂ ) together with 1.05 mol, 0.005 mol and 0.01 mol, respectively, in 0.935 mol of the precursor, under an oxygen atmosphere (20% oxygen partial pressure), Firing at 850 ° C. for 10 hours to prepare a cathode active material (Li _1.05 (Ni _0.6 Mn _0.2 Co _0.2 ) _0.935 W _0.005 Ti _0.01 O ₂ ).

[ Example  1-2: Of positive electrode active material  Produce]

Except for using the same amount of zirconium oxide (ZrO ₂ ) in place of titanium oxide (TiO ₂ ) in Example 1-1 by the same method as in Example 1-1 to the positive electrode active material (Li _1.05 ( the _{Ni 0. 6 Mn 0. 2} Co 0. 2) 0.935 W 0. 005 Zr 0. 01 O 2) was prepared.

[ Example  1-3: Of positive electrode active material  Produce]

Except for using niobium oxide (Nb ₂ O ₅ ) in the same manner as in Example 1-1 instead of tungsten oxide (WO ₃ ) in the same manner as in Example 1-1 to the positive electrode active material (Li a _{1.05 (Ni 0. 6 Mn 0} . 2 Co 0. 2) 0.935 Nb 0. 005 Ti 0. 01 O 2) was prepared.

[ Example  1-4: Of positive electrode active material  Produce]

A positive electrode active material (Li _1.05 (Ni _0.6 Al _0.2 Co _0.2 ) _{0.935 was} prepared in the same manner as in Example 1-1 except that aluminum sulfate was used in the same amount instead of manganese sulfate in Example 1-1. W _0.005 Ti _0.01 O ₂ ) was prepared.

[ Comparative example  1-1: Of positive electrode active material  Produce]

2L of distilled water was charged into the 3L wet reactor tank, and nitrogen gas was added to the tank at a rate of 1L / min to remove dissolved oxygen. At this time, the temperature of the distilled water in the tank was maintained at 45 ℃ using a temperature maintaining apparatus. In addition, distilled water in the tank was stirred at a speed of 1,200 rpm using an impeller connected to a motor installed outside the tank.

Nickel sulphate, manganese sulphate and cobalt sulphate were mixed in water at a molar ratio of 0.6: 0.2: 0.2 to prepare a metal containing solution at a concentration of 1.5 M, and a separate 4 M NaOH aqueous solution was prepared. The metal containing solution was pumped continuously to the tank for the wet reactor at 0.18 L / hr with a metering pump. The aqueous sodium hydroxide solution was pumped variable so that the distilled water in the wet reactor tank was maintained at pH 11.5 in conjunction with the control equipment for pH control of the distilled water in the tank. At this time, 30% aqueous ammonia solution was continuously pumped into the reactor at a rate of 0.035 L / hr.

By adjusting the flow rates of the metal-containing solution, the sodium hydroxide aqueous solution and the ammonia aqueous solution, the average residence time of the solution in the wet reactor tank was 6 hours.After the reaction in the tank reached the steady state, the metal ion and hydroxide of the metal-containing solution were A nickel-cobalt-manganese composite metal precursor prepared by continuously reacting sodium hydroxide ions of sodium and ammonia ions of an aqueous ammonia solution for 20 hours was continuously obtained through an overflow pipe installed at the top of the tank. The obtained precursor was washed with distilled water and dried in a 120 ° C. constant temperature dryer for 24 hours.

Thereafter, 1 mol of the precursor was dry mixed together with 1.05 mol of Li ₂ CO ₃ , and calcined at 850 ° C. for 10 hours under an oxygen atmosphere (20% oxygen partial pressure) to obtain a cathode active material (Li _a (Ni _0.6 Co _0.2 Mn _0.2 ) 0 ₂ ) was prepared.

[ Comparative example  1-2: Of positive electrode active material  Produce]

Example molybdenum oxide instead of titanium oxide in the 1-1 (MoO _3), and a positive electrode active material is carried in the same manner as in Example 1-1 except that the same amount (Li _1.05 (Ni _{0. 6} the _{Mn 0. 2 Co 0. 2} ) 0.935 W 0. 005 Mo 0. 01 O 2) was prepared.

[ Comparative example  1-3: Of positive electrode active material  Produce]

The positive electrode active material of Reference Example 1-1 was used.

[ Comparative example  1-4: Of positive electrode active material  Produce]

The positive electrode active material of Reference Example 1-7 was used.

[ Example  2-1 to Example  2-4, Comparative example  2-1 to Comparative example  2-4: Fabrication of Lithium Secondary Battery]

A lithium secondary battery was manufactured using the cathode active materials prepared in Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-4, respectively.

Specifically, the positive electrode active materials prepared in Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-4, carbon black as a conductive material and PVDF as a binder, N- Methyl-pyrrolidone was mixed in a weight ratio of 95: 2.5: 2.5 to prepare a composition for forming an anode (viscosity: 5,000 mPa · s), which was applied to an aluminum current collector, dried at 130 ° C., and then rolled To prepare a positive electrode.

In addition, natural graphite as a negative electrode active material, carbon black as a conductive material and PVDF as a binder are mixed in a ratio of 85: 10: 5 by weight in N-methyl-pyrrolidone as a solvent to prepare a composition for forming a negative electrode, which is copper It was applied to the current collector to prepare a negative electrode.

An electrode assembly was manufactured between the positive electrode and the negative electrode prepared as described above through a separator of porous polyethylene, the electrode assembly was placed in a case, and an electrolyte solution was injected into the case to prepare a lithium secondary battery. At this time, the electrolyte is prepared by dissolving 1.0M concentration of lithium hexafluorophosphate (LiPF ₆ ) in an organic solvent consisting of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mixing volume ratio of EC / DMC / EMC = 3/4/3). It was.

 [ Experimental Example  2]

In order to confirm the distribution of the metal element included in the lithium composite metal oxide with respect to the cathode active material particles according to Example 1-1 and Comparative Example 1-2, the active material is etched for various times using HCl, and ICP The amount of element elution according to the etching time or dissolution time was analyzed through the analysis, and the composition of the lithium composite metal oxide in the active material particles was confirmed from the results. The results are shown in Table 2 and Table 3.

Dissolution time (minutes)	division	Distance from Particle Surface (μm)	Example 1-1 (molar ratio)
			Ni	Co	Mn	Ti	W
0	Selbu	0	0.561	0.215	0.209	0.010	0.005
One		0.1	0.575	0.208	0.205	0.008	0.004
5		0.3	0.593	0.201	0.197	0.006	0.003
10		0.8	0.595	0.200	0.199	0.005	0.001
30	Core part	1.1	0.599	0.200	0.199	0.002	0
120		3.6	0.600	0.200	0.200	0	0
240		4.9 (particle center)	0.600	0.200	0.200	0	0

Dissolution time (minutes)	division	Distance from Particle Surface (μm)	Comparative Example 1-2 (molar ratio)
			Ni	Co	Mn	Mo	W
0	Shell	0	0.560	0.218	0.207	0.010	0.005
One		0.1	0.575	0.212	0.201	0.008	0.004
5		0.3	0.592	0.202	0.197	0.006	0.003
10		0.8	0.597	0.201	0.196	0.005	0.001
30	Core part	1.0	0.600	0.200	0.198	0.002	0
120		3.5	0.600	0.200	0.200	0	0
240		4.8 (particle center)	0.601	0.200	0.199	0	0

[ Experimental Example  4: evaluation of positive electrode active material]

The average particle diameter, specific surface area, and tap density were measured for the cathode active materials prepared in Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-4, and the results are shown in Table 4 below. Shown in

(1) Average particle diameter (D ₅₀ ): 50% of the particle size distribution in the measuring device after being introduced into a laser diffraction particle size measuring device (for example, Microtrac MT 3000) and irradiating an ultrasonic wave of about 28 kHz at an output of 60 W. The average particle diameter (D ₅₀ ) at the reference was calculated.

(2) BET specific surface area: The specific surface area of the positive electrode active material was measured by the BET method, specifically, it was calculated from the amount of nitrogen gas adsorption under liquid nitrogen temperature (77K) using BELSORP-mino II manufactured by BEL Japan. .

(3) Tap Density: Tap density under 2tonf / cm ² pressure was measured using a tap density meter (HPRM-A1, manufactured by Hantec Co.).

In addition, a coin cell (cathode: Li metal) prepared using the positive electrode active material prepared in Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-4 was 0.1C at 25 ° C. The battery was charged until the constant current (CC) of 4.25V, then charged with a constant voltage (CV) of 4.25V, and the first charge was performed until the charging current became 0.05mAh. After standing for 20 minutes, the battery was discharged to a constant current of 0.1C until 3.0V, and the discharge capacity of the first cycle was measured. Then, the charge and discharge capacity, charge and discharge efficiency and rate characteristics were evaluated by varying the discharge conditions at 2C. The results are shown in Table 4 below.

division	Average particle diameter (D 50 ) (㎛)	BET specific surface area (m 2 / g)	Tap Density (g / cc)	First charge and discharge			2C rate
				Charge capacity (mAh / g)	Discharge Capacity (mAh / g)	Charge / discharge efficiency (%)	Capacity (mAh / g)	2.0C / 0.1C (%)
Example 1-1	9.8	0.35	2.4	196.5	181.4	92.3	165.8	91.4
Example 1-2	9.6	0.41	2.3	195.4	179.2	91.7	164.3	91.7
Example 1-3	9.8	0.38	2.4	194.2	179.4	92.4	165.2	92.1
Example 1-4	10.2	0.31	2.4	197.6	180.8	91.5	165.6	91.6
Comparative Example 1-1	10.4	0.43	2.4	196.5	177.6	90.4	161.3	90.8
Comparative Example 1-2	9.6	0.44	2.4	195.5	177.1	90.6	159.6	90.1
Comparative Example 1-3	9.8	0.51	2.3	197.1	175.6	89.1	155.8	88.7
Comparative Example 1-4	9.9	0.47	2.2	195.3	176.2	90.2	157.2	89.2

As a result of the experiment, the coin cells containing the positive electrode active materials of Examples 1-1 to 1-4 were compared with the coin cells containing the positive electrode active materials of Comparative Examples 1-1 to 1-4. In terms of the rate characteristics and the capacity characteristics, the effect was improved.

[ Experimental Example  5: Battery Characteristic Evaluation of Lithium Secondary Battery]

Lithium secondary batteries (Examples 2-1 to 2-3, Comparative Example 2-) containing the positive electrode active materials in Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-4, respectively. 1 to Comparative Example 2-4) was evaluated for battery characteristics in the following manner.

In detail, the lithium secondary battery was charged / discharged 300 times at a temperature of 25 ° C. under a condition of 1 C / 2 C within a driving voltage range of 2.8 V to 4.15 V.

In addition, in order to evaluate the output characteristics, a battery charged and discharged at room temperature (25 ° C.) was charged based on SOC 50%, and resistance was measured. At high temperature (60 ° C.), the voltage dropped when current was applied based on 50% SOC. The width to be measured was measured.

As a result, the cycle capacity maintenance ratio (CAPACITY RETENTION RATE), which is the ratio of the discharge capacity at the 300th cycle with respect to the resistance at room temperature (25 ° C.) and high temperature (60 ° C.) and the initial capacity after 300 charge / discharge cycles at room temperature. %)) Were measured and shown in Table 5 below.

division	Room temperature (25 ℃) resistance (mohm)	High Temperature (60 ℃) Voltage Drop (V)	300 cycle capacity retention rate at room temperature (25 ℃)
Example 2-1	1.21	0.028	98.1
Example 2-2	1.14	0.021	97.4
Example 2-3	1.24	0.033	98.3
Comparative Example 2-1	1.42	0.038	96.4
Comparative Example 2-2	1.38	0.039	94.8
Comparative Example 2-3	1.65	0.051	92.6
Comparative Example 2-4	1.53	0.045	94.3

The lithium secondary batteries (Examples 2-1 to 2-3) each containing the positive electrode active materials in Examples 1-1 to 1-3, respectively include the positive electrode active materials in Comparative Examples 1-1 to 1-4. Compared to the lithium secondary batteries (Comparative Examples 2-1 to 2-4) showed a significantly reduced battery resistance and excellent life characteristics at room temperature. In addition, in terms of output characteristics at high temperatures, lithium secondary batteries (Examples 2-1 to 2-3) each containing the positive electrode active materials in Examples 1-1 to 1-3 are Comparative Examples 2-1 to 2-. Compared to 4, the voltage drop is significantly reduced, indicating that the output characteristics are better.

Claims (15)

1. A cathode active material for a secondary battery comprising lithium composite metal oxide particles represented by Formula 1 below.

   [Formula 1]

   Li _a Ni _{1 -x- y} Co _x M1 _y M2 _z M3 _w O ₂

   In Chemical Formula 1,

   M1 is a metal element whose surface energy (ΔE _surf ) calculated by the following Equation 1 is -0.5 eV or more,

   M2 is a metal element whose surface energy (ΔE _surf ) calculated by Equation 1 is -1.5 eV or more and less than -0.5 eV,

   M3 is a metal element whose surface energy (ΔE _surf ) calculated by Equation 1 below is less than -1.5 eV.

   1.0 ≦ a ≦ 1.5, 0 <x ≦ 0.5, 0 <y ≦ 0.5, 0.002 ≦ w ≦ 0.1, 0 <z ≦ 0.05, 0 <x + y ≦ 0.7.

   [Equation 1]

   △ E _surf = E _surf2 -E _surf1

   = (E _slab2 -E _bulk )-(E _slab1 -E _bulk )

   In Equation 1,

   E _surf2 indicates the degree to which the metal element is directed to the outermost surface in the lithium composite metal oxide particles.

   E _surf1 indicates the degree to which the metal element is directed toward the center of the lithium composite metal oxide particle.

   E _slab1 is the energy of the slab model of lithium composite metal oxide particles when the metal element is in the center of the lithium composite metal oxide particles.

   E _slab2 is the energy of the slab model of lithium composite metal oxide when the metal element is on the outermost surface of the lithium composite metal oxide.

   E _bulk is the energy of the bulk model corresponding to each slab model.
2. The method of claim 1,

   The M1 is distributed such that the average slope of the concentration profile from the surface of the lithium composite metal oxide particle to the center section is zero or positive (+),

   Wherein M2 and M3 are each independently distributed so that the average slope of the concentration profile from the surface of the lithium composite metal oxide particles to the center section is negative (-).
3. The method of claim 1,

   Wherein M1 is Al, Mg, Y, Zn, In and Mn, any one or two selected from the group consisting of a positive electrode active material for a secondary battery.
4. The method of claim 1,

   M2 is a positive electrode active material for a secondary battery including any one or two selected from the group consisting of Zr, Ti, Ta, Hf, Sn, Cr, Sb, Ru, Gd and Os.
5. The method of claim 1,

   Wherein M3 is W, V, Nb, Nd, and Mo including any one or two selected from the group consisting of a positive electrode active material for a secondary battery.
6. The method of claim 1,

   The lithium composite metal oxide particles are core; And a core-shell structure comprising a shell located on the surface of the core,

   The M1 is included so that the average slope of the concentration profile from the surface of the lithium composite metal oxide particle to the center section is zero,

   The M 2 is contained in the core at a concentration of 1 to 25 mol%, 75 to 99 mol% in the shell,

   Wherein M3 is contained in a concentration of 1 to 10 mol% in the core, 90 to 99 mol% in the shell positive electrode active material for secondary batteries.
7. The method of claim 6,

   The core and the shell is a positive electrode active material for secondary batteries that are included in a volume ratio of 50:50 to 80:20.
8. The method of claim 1,

   At least one metal element of nickel and cobalt in the general formula (1), the positive electrode active material for a secondary battery that exhibits a concentration gradient in the lithium composite metal oxide particles.
9. The method of claim 1,

   In Chemical Formula 1, nickel and cobalt each independently represent a concentration gradient varying throughout the lithium composite metal oxide particles.

   The concentration of nickel decreases with a concentration gradient from the center of the lithium composite metal oxide particles to the surface direction, and

   The concentration of the cobalt increases with a concentration gradient from the center of the lithium composite metal oxide particles to the surface direction of the positive electrode active material for secondary batteries.
10. The method of claim 1,

    At least one metal element selected from the group consisting of M2 and M3 on the surface of the cathode active material particle; Or a cathode active material for a secondary battery further comprising a coating layer comprising a lithium oxide containing at least one metal element.
11. The method of claim 1,

    The cathode active material is a cathode active material for secondary batteries having an average particle diameter (D ₅₀ ) of 4㎛ to 20㎛.
12. The method of claim 1,

    The positive electrode active material has a BET specific surface area of 0.3m ² / g to 1.9m ² / g of secondary battery positive electrode active material.
13. The method of claim 1,

    The cathode active material is a cathode active material for a secondary battery having a tap density of 1.7g / cc to 2.8g / cc.
14. A secondary battery positive electrode comprising the positive electrode active material according to any one of claims 1 to 13.
15. A lithium secondary battery comprising the positive electrode according to claim 14.