KR20190093454A - Positive electrode active material for secondary battery, method for preparing the same and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a positive electrode active material for a secondary battery, which comprises a first positive electrode active material and a second positive electrode active material. The first positive electrode active material and the second positive electrode active material are lithium composite transition metal oxides including at least two transition metals selected from a group consisting of nickel (Ni), cobalt (Co), and manganese (Mn). An average particle diameter (D50) of the first positive electrode active material is 1.5 times or more of an average particle diameter (D50) of the second positive electrode active material. In the first positive electrode active material, at least one of nickel (Ni), cobalt (Co), and manganese (Mn) contained in the lithium composite transition metal oxide has a concentration gradient difference of 5 mol% at the center and a surface of the lithium composite transition metal oxide particle. The second positive electrode active material has a crystallite size of 200 nm or more.

Description

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

The present invention relates to a cathode active material for a secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same.

Recently, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, the demand for small, lightweight, and relatively high capacity secondary batteries is rapidly increasing. In particular, the lithium secondary battery has attracted attention as a driving power source for portable devices because of its light weight and high energy density. Accordingly, research and development efforts for improving the performance of lithium secondary batteries have been actively conducted.

The lithium secondary battery is oxidized when lithium ions are inserted / desorbed from the positive electrode and the negative electrode in a state in which an organic electrolyte or a polymer electrolyte is charged between a positive electrode and a negative electrode made of an active material capable of intercalations and deintercalation of lithium ions. Electrical energy is produced by the reduction reaction.

Lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMnO ₂ or LiMn ₂ O _4, etc.), lithium iron phosphate compound (LiFePO ₄ ), and the like were used as a cathode active material of a lithium secondary battery. . In addition, as a method for improving low thermal stability while maintaining excellent reversible capacity of LiNiO ₂ , a lithium composite metal oxide in which a part of nickel (Ni) is replaced with cobalt (Co) or manganese (Mn) / aluminum (Al) ( Hereinafter, simply referred to as 'NCM-based lithium composite transition metal oxide' or 'NCA-based lithium composite transition metal oxide'.

In order to increase the capacity per unit volume of the lithium composite transition metal oxide and to improve stability, studies have been made such as forming a concentration gradient of the metal composition or increasing the content of nickel. In addition, studies have been made to increase the rolling density by blending alleles and small particles in order to increase the capacity per unit volume of the electrode to produce a cathode active material layer by bimodal. However, there is still a need for the development of a cathode active material that satisfies both high capacity and excellent thermal stability at the same time.

Korean Patent Registration No. 10-1510940

The present invention is to provide a positive electrode active material for secondary batteries with improved energy density, high capacity and thermal stability using the positive electrode active material of the large particles and small particles.

In addition, the present invention is to provide a cathode active material for secondary batteries with improved stability, such as preventing the crack (crack) and cracking of the positive electrode active material by rolling, improve the high temperature life characteristics, lower the amount of gas generated during high temperature storage will be.

The present invention includes a first positive electrode active material and a second positive electrode active material, wherein the first positive electrode active material and the second positive electrode active material are at least two or more transitions selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn) a lithium composite transition metal oxide comprising a metal, wherein the average particle diameter (D ₅₀₎ of the first cathode active material is 1.5 and the fold, the first cathode active material having an average particle size (D ₅₀₎ of the second cathode active material, lithium At least one of nickel (Ni), cobalt (Co) and manganese (Mn) contained in the composite transition metal oxide has a concentration gradient having a concentration difference of 5 mol% or more at the center and the surface of the lithium composite transition metal oxide particle. 2 positive electrode active material provides a positive electrode active material for secondary batteries having a crystal size of 200nm or more.

In addition, the present invention after preparing a first positive electrode active material and a second positive electrode active material of a lithium composite transition metal oxide containing at least two or more transition metals selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn) And mixing the first positive electrode active material and the second positive electrode active material, wherein the average particle diameter (D ₅₀ ) of the first positive electrode active material is 1.5 times or more of the average particle diameter (D ₅₀ ) of the second positive electrode active material, In the first positive electrode active material, at least one of nickel (Ni), cobalt (Co), and manganese (Mn) contained in the lithium composite transition metal oxide has a concentration difference of 5 mol% at the center and the surface of the lithium composite transition metal oxide particle. It has a concentration gradient that is above, the second positive electrode active material provides a method for producing a positive electrode active material for secondary batteries prepared by over-firing so that the crystal size (Crystalite size) is 200nm or more.

In addition, the present invention provides a cathode and a lithium secondary battery including the cathode active material.

According to the present invention, the energy density can be improved by blending alleles and small particles to produce a bimodal positive electrode active material, wherein the alleles having a concentration gradient and oversintering the crystal size ( By using small particles with a crystal size of 200 nm or more, thermal stability can be improved while achieving high capacity. In addition, it is possible to prevent cracking and cracking of the positive electrode active material due to rolling, and to improve stability, such as improving the high temperature life characteristics and reducing the amount of gas generated during high temperature storage.

1 is a graph showing the rolling density of a positive electrode active material according to Examples and Comparative Examples.
FIG. 2 is a graph showing thermal stability by differential scanning calorimetry (DSC) of positive electrode active materials according to Examples and Comparative Examples. FIG.
3 is a graph showing the amount of gas generated during high temperature storage of the positive electrode active material according to Examples and Comparative Examples.

Hereinafter, the present invention will be described in more detail to aid in understanding the present invention. At this time, the terms or words used in the present specification and claims should not be construed as being limited to the ordinary or dictionary meanings, and the inventors appropriately define the concept of terms in order to explain their invention in the best way. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that it can.

<Anode active material>

The positive electrode active material for a secondary battery of the present invention includes a first positive electrode active material and a second positive electrode active material, and the first positive electrode active material and the second positive electrode active material are selected from the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn). A lithium composite transition metal oxide including at least two transition metals selected, wherein the average particle diameter (D ₅₀ ) of the first positive electrode active material is 1.5 times or more than the average particle diameter (D ₅₀ ) of the second positive electrode active material, and the first The positive electrode active material has a concentration gradient in which at least one of nickel (Ni), cobalt (Co), and manganese (Mn) contained in the lithium composite transition metal oxide has a concentration difference of 5 mol% or more at the center and the surface of the lithium composite transition metal oxide particle. The second positive electrode active material has a crystal size of 200 nm or more.

The positive electrode active material for secondary batteries of the present invention includes a first positive electrode active material which is an allele and a second positive electrode active material which is a small particle.

In order to improve the capacity per volume of the secondary battery positive electrode, it is necessary to increase the density of the positive electrode active material layer.A method of increasing the density of the positive electrode active material layer increases the rolling density (or electrode density) by reducing the voids between the positive electrode active material particles. This is used. In the case of the bimodal positive electrode active material in which the positive active material of the large particles and the small particles are mixed as in the present invention, since the empty space between the particles of the large particle positive active material can be filled with the small particle positive electrode active material, more compact filling is achieved. It is possible to increase the energy density of the anode.

The average particle diameter (D ₅₀ ) of the first positive electrode active material is 1.5 times or more of the average particle diameter (D ₅₀ ) of the second positive electrode active material.

In the present invention, the average particle diameter (D ₅₀ ) may be defined as a particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. The average particle diameter D ₅₀ may be measured using, for example, a laser diffraction method. For example, the measuring method of the average particle diameter (D ₅₀ ) of the positive electrode active material is dispersed in the dispersion medium particles in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring apparatus (for example, Microtrac MT 3000) to After irradiating an ultrasonic wave of 28 kHz with an output of 60 W, the average particle diameter D ₅₀ corresponding to 50% of the volume accumulation amount in the measuring device can be calculated.

More specifically, the average particle diameter (D ₅₀ ) of the first positive electrode active material and the second positive electrode active material may be 2: 1 to 5: 1, and more preferably, the average particle diameter of the first positive electrode active material and the second positive electrode active material. (D ₅₀ ) may be from 2: 1 to 3.5: 1. The average particle diameter (D ₅₀ ) ratio of the first positive electrode active material and the second positive electrode active material satisfies the above range, thereby effectively reducing the voids between the positive electrode active material particles, increasing the packing density, and improving the positive electrode density to increase the capacity per positive electrode volume. Can be effectively improved.

Specifically, the average particle diameter (D ₅₀ ) of the first positive electrode active material may be 10 to 30㎛, more preferably 13 to 25㎛, more preferably 15 to 22㎛.

The average particle diameter (D ₅₀ ) of the second positive electrode active material may be 9 μm or less, more preferably 1 to 8 μm, still more preferably 2 to 6 μm.

The first positive electrode active material and the second positive electrode active material of the present invention are lithium composite transition metal oxides including at least two or more transition metals selected from the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn). In this case, the first positive electrode active material, which is an allele, is a lithium composite transition metal oxide having a concentration gradient, and the second positive electrode active material, which is a small particle, does not have a concentration gradient, and is excessively calcined and has a lithium composite transition having a crystal size of 200 nm or more. Metal oxides. In this way, by using a mixture of alleles having a concentration gradient and no concentration gradient, undersintered small particles, a higher capacity and thermal stability can be ensured, and high temperature life characteristics and high temperature storage stability can be improved.

The relatively positive first positive electrode active material is a lithium composite transition metal oxide having a concentration gradient of a metal composition, and at least one of nickel (Ni), cobalt (Co), and manganese (Mn) contained in the lithium composite transition metal oxide The difference in concentration between the center and the surface of the lithium composite transition metal oxide particles is 5 mol% or more. More preferably, the nickel (Ni) contained in the lithium composite transition metal oxide may have a concentration difference of 8 mol% or more, more preferably 10 mol% or more at the center and the surface of the lithium composite transition metal oxide particles.

In the present invention, the concentration gradient composition and concentration of the transition metal in the positive electrode active material particles may be determined by using an Electron Probe Micro Analyzer (EPMA), Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-). AES), Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS), or X-ray photoelectron spectroscopy (XPS). The atomic ratio of each metal may be measured while moving from the center of the cathode active material to the surface, or the atomic ratio of each metal may be measured while etching from the surface of the cathode active material to the center through XPS.

In one embodiment of the present invention, the first positive electrode active material is composed of a core portion and a shell portion surrounding the core portion, wherein the core portion has a constant transition metal concentration, and the shell portion is nickel (Ni), cobalt ( At least one of Co) and manganese (Mn) may exhibit a concentration gradient that gradually increases or decreases. More preferably, the shell portion of the first positive electrode active material may exhibit a concentration gradient in which the concentration of nickel (Ni) gradually decreases toward the particle surface side. Since the concentration of nickel (Ni) is maintained at the particle center side of the shell portion and the concentration of nickel (Ni) decreases toward the particle surface side of the shell portion, it is possible to prevent a decrease in capacity while showing thermal stability.

On the other hand, the shell portion, at least one of the manganese (Mn) and cobalt (Co) may have a concentration gradient gradually increases toward the particle surface side. In this case, since the concentration of manganese (Mn) is maintained at the particle center side of the shell portion and the concentration of manganese (Mn) increases toward the particle surface side of the shell portion, excellent thermal stability can be obtained, and at the particle center side of the shell portion Cobalt (Co) maintains a low concentration, and by increasing the concentration of cobalt (Co) toward the particle surface side of the shell portion, it is possible to prevent a decrease in capacity while reducing the amount of cobalt (Co) used.

The shell portion of the cathode active material decreases with a concentration gradient of nickel (Ni) contained in the shell portion toward the particle surface side, and at least one of manganese (Mn) and cobalt (Co) toward the particle surface side. It can increase with a concentration gradient that is complementary to the concentration gradient of nickel (Ni).

In the present invention, "representing a concentration gradient in which the concentration of the transition metal gradually changes (increases or decreases)" means that the concentration of the transition metal exists in a concentration distribution that gradually changes. Specifically, the concentration distribution is 0.1 to 5 mol%, more specifically 0.1 to 3 mol, based on the total number of moles of the metal included in the positive electrode active material, the change in the transition metal concentration per 1 μm in the particles %, More specifically, may be a difference of 1 to 2 mol%.

In another embodiment of the present invention, the first positive electrode active material, at least one of nickel (Ni), cobalt (Co) and manganese (Mn) contained in the lithium composite transition metal oxide from the center of the lithium composite transition metal oxide particles It may have a concentration gradient that gradually changes (increases or decreases) to the surface.

More preferably, the first cathode active material may have a concentration gradient in which nickel (Ni) gradually decreases from the center of the lithium composite transition metal oxide particle to the surface. Since the concentration of nickel (Ni) is maintained at the center of the particle of the first positive electrode active material, and the concentration of nickel (Ni) decreases toward the surface, it is possible to prevent a decrease in capacity while showing thermal stability.

Alternatively, at least one of manganese (Mn) and cobalt (Co) may have a concentration gradient that gradually increases from the center of the lithium composite transition metal oxide particle to the surface. In this case, since the concentration of manganese (Mn) is maintained at the center of the particle of the first positive electrode active material and the concentration of manganese (Mn) increases toward the particle surface, it is possible to obtain excellent thermal stability without reducing the capacity. The concentration of cobalt (Co) at the center of the particle of the positive electrode active material maintains a low concentration, and by increasing the concentration of cobalt (Co) toward the particle surface, it is possible to prevent a decrease in capacity while reducing the amount of cobalt (Co) used.

In the first positive electrode active material according to an embodiment of the present invention, the concentration of nickel (Ni) contained in the first positive electrode active material decreases with a continuous concentration gradient from the center of the particle to the particle surface layer, and manganese (Mn) And at least one of cobalt (Co) may increase with a concentration gradient complementary to that of the nickel (Ni) from the center of the particle to the particle surface. As such, the concentration of nickel (Ni) gradually decreases from the center of the particle to the particle surface in the first positive electrode active material, and the concentration of manganese (Mn) and / or cobalt (Co) gradually increases. By having a gradient, thermal stability can be exhibited while maintaining capacity characteristics.

In another embodiment of the present invention, the first positive electrode active material includes a core portion, a concentration gradient portion formed surrounding the core portion, and a surface portion formed surrounding the concentration gradient portion, and the core portion and the surface portion independently of each other. The concentration of the transition metal is constant, and the concentration gradient may have a concentration gradient in which at least one of nickel (Ni), cobalt (Co), and manganese (Mn) gradually changes from the core portion composition to the surface portion composition. . More preferably, the core portion has a higher concentration of nickel (Ni) than the surface portion, and the concentration gradient portion of the first positive electrode active material decreases gradually as the concentration of nickel (Ni) increases from the core portion side to the surface portion side. The concentration gradient can be indicated. In the core portion of the concentration gradient portion, the concentration of nickel (Ni) is maintained at a high concentration, and the concentration of nickel (Ni) decreases toward the surface portion, thereby exhibiting thermal stability and preventing a decrease in capacity.

On the other hand, the concentration gradient, the manganese (Mn) and cobalt (Co) may have a concentration gradient that gradually increases toward the surface portion. In this case, since the concentration of manganese (Mn) is maintained at the core side of the concentration gradient portion, and the concentration of manganese (Mn) increases toward the surface portion side of the concentration gradient portion, excellent thermal stability can be obtained. The concentration of cobalt (Co) is kept low at the core side of the gradient, and the concentration of cobalt (Co) increases toward the surface side of the gradient, thereby reducing the amount of cobalt (Co) while preventing a decrease in capacity. Can be.

The concentration gradient of the cathode active material decreases as the concentration of nickel (Ni) included in the concentration gradient increases toward the surface portion and has a continuous concentration gradient, and at least one of manganese (Mn) and cobalt (Co) is a surface portion. Towards the side may increase with a concentration gradient complementary to the concentration gradient of the nickel (Ni).

As described above, the first positive electrode active material, which is an allele, has a concentration gradient by varying the concentration of the transition metal element according to the position in the particle, thereby easily utilizing the characteristics of the transition metal to further improve the battery performance improvement effect of the positive electrode active material. Can be.

The second active material, which is relatively small particles, is over-fired and has a crystal size of 200 nm or more. When the crystal size of the second cathode active material is less than 200 nm, high temperature life characteristics and stability at high temperatures may be deteriorated, and cracking and cracking of the cathode active material may occur by rolling. The method of overfiring the second positive electrode active material is not particularly limited as long as it can increase the crystal size to 200 nm or more. May overcalcin with increased temperature. More preferably, the second cathode active material may have a crystal size of 200 to 500 nm, and more preferably 220 to 400 nm.

In the present invention, the 'particle' refers to a grain of micro units, and when magnified, it can be classified into a 'grain' having a crystal form of several tens of nano units. Further magnification can identify the distinct regions of the form of atoms in a lattice structure in a certain direction, which is called 'crystallite', and the size of the particles observed in the XRD is defined as the size of the crystallite. . The crystallite size can be measured using the peak broadening of the XRD data to determine the crystallite size. This can be calculated quantitatively using the scherrer equation.

The first positive electrode active material and the second positive electrode active material may be secondary particles formed by aggregation of primary particles. In this case, the second cathode active material, which is relatively small particles, may be over-fired so that an average particle diameter (D ₅₀ ) of the primary particles may be 1 μm or more. When the average particle diameter (D ₅₀ ) of the primary particles of the second positive electrode active material is less than 1 μm, stability may be deteriorated, such as high temperature life characteristics and an increase in gas generation during high temperature storage, and cracking of the positive electrode active material by rolling. ) And cracking may occur. More specifically, the second positive electrode active material may have an average particle diameter (D ₅₀ ) of the primary particles of 1 to 8 μm, and more specifically, the second positive electrode active material may have an average particle diameter (D ₅₀ ) of the primary particles. 1 to 6 μm. By reducing the specific surface area of the second cathode active material, which is a relatively small particle, it is possible to exhibit an effect of reducing side reactions with the electrolyte, thereby improving thermal stability and reducing gas generation. Meanwhile, the average particle diameter (D ₅₀ ) of the primary particles of the first positive electrode active material, which are relatively alleles, may be 100 nm to 2 μm.

According to one embodiment of the present invention, at least one of the first positive electrode active material and the second positive electrode active material may be an NCM-based positive electrode active material including nickel (Ni), cobalt (Co) and manganese (Mn), or It may be an NCA-based positive electrode active material including nickel (Ni), cobalt (Co), and aluminum (Al), and requires four components of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). It may be a four-component positive electrode active material comprising.

In addition, at least one of the first positive electrode active material and the second positive electrode active material according to an embodiment of the present invention has a high content of nickel (Ni) of at least 60 mol% of all metal elements contained in the lithium composite transition metal oxide. It may be a cathode active material of nickel (High-Ni). More preferably, the content of nickel (Ni) in the total metal elements may be 80 mol% or more. As described in the present invention, the use of the first positive electrode active material and the second positive electrode active material of high content nickel (High-Ni) having a content of nickel (Ni) in the total metal element of 60 mol% or more may enable higher capacity. The first positive electrode active material having a concentration gradient may be a high-nickel positive electrode active material having a content of nickel (Ni) of 60 mol% or more, more preferably 80 mol% or more in the average concentration of the whole particle. have.

Meanwhile, the first positive electrode active material and the second positive electrode active material may be lithium composite transition metal oxides having the same composition or lithium composite transition metal oxides having different compositions.

More specifically, the first positive electrode active material and the second positive electrode active material may be a lithium composite transition metal oxide represented by Formula 1 below. In the case of the first positive electrode active material having a concentration gradient, the average composition of the whole particle may satisfy the following Formula 1.

[Formula 1]

Li _p Ni _{1- (x1 + y1 + z1)} Co _x1 M ^a _y1 M ^b _z1 M ^c _q1 O ₂

In the above formula, M ^a is at least one element selected from the group consisting of Mn and Al, M ^b is at least one element selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo, M ^c is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, 0.9≤p≤1.5, 0 <x1≤0.4, 0 <y1≤0.4, 0≤z1 ≤ 0.1, 0 ≤ q1 ≤ 0.1, and 0 <x1 + y1 + z1 ≤ 0.4.

In the lithium composite transition metal oxide of Chemical Formula 1, Li may be included in an amount corresponding to p, that is, 0.9 ≦ p ≦ 1.5. If p is less than 0.9, the capacity may be lowered. If it is more than 1.5, the particles may be sintered in the firing process, and the production of the positive electrode active material may be difficult. Considering the remarkable effect of improving the capacity characteristics of the positive electrode active material according to the control of the Li content and the balance of the sintering property at the time of manufacturing the active material, the Li may be more preferably included in a content of 1.0≤p≤1.15.

In the lithium composite transition metal oxide of Formula 1, Ni may be included as an amount corresponding to 1- (x1 + y1 + z1), for example, 0.6 ≦ 1- (x1 + y1 + z1) <1. When the Ni content in the lithium composite transition metal oxide of Formula 1 is 0.6 or more, the amount of Ni sufficient to contribute to charging and discharging may be secured, thereby achieving high capacity. More preferably, Ni may be included as 0.8 ≦ 1- (x1 + y1 + z1) ≦ 0.99.

In the lithium composite transition metal oxide of Chemical Formula 1, Co may be included in an amount corresponding to x1, that is, 0 <x1 ≦ 0.4. When the content of Co in the lithium composite transition metal oxide of Formula 1 exceeds 0.4, there is a fear of increase in cost. Considering the remarkable effect of improving the capacity characteristics according to the inclusion of Co, Co may be included in a content of 0.05≤x1≤0.2 more specifically.

In the lithium composite transition metal oxide of Chemical Formula 1, M ^a may be Mn or Al, or Mn and Al, and these metal elements may improve the stability of the active material, and as a result, may improve the stability of the battery. In consideration of the improvement of lifespan characteristics, M ^a may be included in an amount corresponding to y1, that is, 0 <y1 ≦ 0.4. When y1 in the lithium composite transition metal oxide of Formula 1 exceeds 0.4, the output characteristics and capacity characteristics of the battery may be deteriorated, and M ^a may be included in an amount of 0.05 ≦ y1 ≦ 0.2.

In the lithium composite transition metal oxide of Chemical Formula 1, M ^b may be a doping element included in the crystal structure of the lithium composite transition metal oxide, and M ^b may be included in an amount corresponding to z1, that is, 0 ≦ z1 ≦ 0.1. have.

In the lithium composite transition metal oxide of the above formula 1, M ^c of the metal element is a lithium composite transition may not be contained in the metal oxide structure, when mixing the precursor and a lithium source and baking M ^c is mixed with a source firing or After forming the lithium composite transition metal oxide, a lithium composite transition metal oxide may be prepared in which the M ^c is doped onto the surface of the lithium composite transition metal oxide by adding and firing an M ^c source separately. The M ^c may be included in an amount corresponding to q1, that is, a content which does not deteriorate the characteristics of the positive electrode active material within a range of 0 ≦ q1 ≦ 0.1.

According to an embodiment of the present invention, the first positive electrode active material and the second positive electrode active material may be mixed in a weight ratio of 9: 1 to 1: 9, more preferably in a weight ratio of 8: 2 to 3: 7, most preferably May be mixed in a weight ratio of 8: 2 to 5: 5. By mixing and using the first positive electrode active material having an allele and a concentration gradient and the second positive electrode active material having a small particle and the crystal size of 200 nm or more within the above range, the energy density of the positive electrode can be increased, and high capacity and excellent thermal stability can be secured. It is possible to suppress side reactions with the electrolyte. Accordingly, the lithium secondary battery manufactured using the cathode active material as described above may implement high capacity, reduce gas generation, and improve battery characteristics such as high temperature life characteristics.

<Method of Manufacturing Anode Active Material>

Next, the manufacturing method of the positive electrode active material of this invention is demonstrated.

The cathode active material of the present invention includes a first cathode active material and a second cathode active material of a lithium composite transition metal oxide including at least two or more transition metals selected from the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn). Thereafter, the step of mixing the first positive electrode active material and the second positive electrode active material, the average particle diameter (D ₅₀ ) of the first positive electrode active material is at least 1.5 times the average particle diameter (D ₅₀ ) of the second positive electrode active material In the first positive electrode active material, at least one of nickel (Ni), cobalt (Co), and manganese (Mn) contained in the lithium composite transition metal oxide has a concentration difference of 5 mol between the center and the surface of the lithium composite transition metal oxide particle. It has a concentration gradient that is greater than or equal to%, and the second cathode active material is manufactured by underfiring such that a crystal size is 200 nm or more.

The first positive electrode active material may use an allele having an average particle diameter (D ₅₀ ) of 10 to 30 μm, more preferably 13 to 25 μm, and more preferably 15 to 22 μm.

The second cathode active material may use small particles having an average particle diameter (D ₅₀ ) of 9 μm or less, more preferably 1 to 8 μm, and more preferably 2 to 6 μm.

At this time, the relatively positive allele of the first positive electrode active material uses a lithium composite transition metal oxide having a concentration gradient by varying the concentration of the transition metal element according to the position in the particle. The transition metal concentration gradient composition of the first positive electrode active material is omitted because it overlaps with the description of the positive electrode active material.

In this case, the second cathode active material, which is relatively small particles, is manufactured by underfiring, and has a crystal size of 200 nm or more. The overfiring method is not particularly limited, but may be overfired at a temperature increased by about 50 to 150 ° C., for example, from about 800 to 1000 ° C., which is a firing temperature of a general cathode active material. More preferably, the second cathode active material may be manufactured by underfiring such that the crystal size is 200 to 500 nm, more preferably 220 to 400 nm.

In addition, the second cathode active material, which is relatively small particles, may be manufactured by underfiring such that the average particle diameter (D ₅₀ ) of the primary particles is 1 μm or more. More specifically, the second positive electrode active material has an average particle diameter (D ₅₀ ) of the primary particles of 1 to 8 μm, and more specifically, the second positive electrode active material has an average particle diameter (D ₅₀ ) of the primary particles of 1 to 6 μm. It may be prepared by overfiring to a thickness. On the other hand, the average particle diameter (D ₅₀ ) of the primary particles of the first positive electrode active material that is a relatively large particle may be 100nm to 3㎛.

In addition, since the composition and the mixing ratio of the first positive electrode active material and the second positive electrode active material are overlapped with the description of the positive electrode active material, it will be omitted.

<Anode and Secondary Battery>

According to another embodiment of the present invention provides a lithium secondary battery positive electrode and a lithium secondary battery comprising the positive electrode 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 including the positive electrode active material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive without causing chemical change in the battery. For example, the positive electrode current collector is made of stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. Surface treated with nickel, titanium, silver, or the like may 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 positive electrode current collector to increase the 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, summer 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, and the like, or a mixture of two or more kinds 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 positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode 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, and the like, and one or a mixture of two or more thereof may be used. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the cathode 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 composition for forming a cathode active material layer including the cathode active material and optionally, a binder and a conductive material may be coated on a cathode 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 manufactured 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 or a capacitor, and more specifically, may be a lithium secondary battery.

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 about 3 to 500 μm, and like 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 may be coated with a negative electrode active material and a negative electrode active material, and optionally a composition for forming a negative electrode including a binder and a conductive material and dried, or the negative electrode active material may be cast 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 _β (0 <β <2), SnO ₂ , vanadium oxide, and 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 and petroleum or coal tar pitch High-temperature calcined carbon such as 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 for ion transfer 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 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can 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 0.1 to 5% by weight based on the total weight of the electrolyte.

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

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

The battery module or 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.

Example 1

As the first positive electrode active material, the average particle diameter (D ₅₀ ) is 11 µm, the particle center is LiNi _0.83 Co _0.07 Mn _0.08 Al _0.02 O ₂ , and the particle surface is LiNi _{0 . 74} Co _{0 . 13} Mn _{0 .} A lithium composite transition metal oxide having ₁₃ O ₂ and gradually changing concentrations of nickel (Ni), cobalt (Co), and manganese (Mn) from the particle center to the surface was prepared. LiNi ₀ as the second positive electrode active material _{. 70} Co _{0 . 15} Mn _{0 . 15} O ₂ particles (D ₅₀ = 6 μm) were prepared. At this time, the second positive electrode active material was over-baked, and the crystal size was 230 nm, and the average particle diameter (D ₅₀ ) of the primary particles was 2 μm. The first positive electrode active material and the second positive electrode active material were mixed at a weight ratio of 7: 3 to prepare a positive electrode active material.

Example  2

As the first positive electrode active material, the average particle diameter (D ₅₀ ) is 11㎛, and the core portion _{LiNi 0.83 Co 0.07 Mn 0.08 Al 0.02} O 2 concentration of the transition metal, and a constant, the shell portion of the particle core side _{LiNi 0.83 Co 0.07 Mn 0.08 Al 0.02} O 2 LiNi 0 from the side of the particle _{surface. 71} Co _{0 . 13} Mn _{0 . 15} Al _{0 .} A lithium composite transition metal oxide having a gradual concentration gradient up to ₀₁ O ₂ was used, and LiNi _{0 . 70} Co _{0 . 15} Mn _{0 .} Example 1 except that ₁₅ O ₂ particles (D ₅₀ = 6 μm), which were over-baked to have a crystal size of 230 nm and an average particle diameter (D ₅₀ ) of the primary particles of 2 μm. In the same manner to prepare a positive electrode active material.

Comparative example  One

LiNi ₀ as the first positive electrode active material _{. 80} Co _{0 . 10} Mn _{0 . 08} Al _{0 . 02} O ₂ particles (D ₅₀ = 11 μm), LiNi _0. As the second positive electrode active material _{. 70} Co _{0 . 15} Mn _{0 . 15} O ₂ particles (D ₅₀ = 4 μm) were prepared. In this case, the first positive electrode active material does not have a concentration gradient, and the second positive electrode active material is implemented except that the crystal size is 117 nm and the average particle diameter (D ₅₀ ) of the primary particles is 0.8 μm. A positive electrode active material was prepared in the same manner as in Example 1.

Comparative example  2

The first positive electrode active material uses the same lithium composite transition metal oxide as in Example 1, except that the crystallite size is 117 nm and the average particle diameter (D ₅₀ ) of the primary particles is 0.8 μm. Except that was carried out in the same manner as in Example 1 to prepare a positive electrode active material.

Comparative example  3

LiNi ₀ as a positive electrode active material _{. 80} Co _{0 . 10} Mn _{0 . 08} Al _{0 . A} cathode active material was prepared using monomodal, which is a particle of 02O ₂ (D ₅₀ = 12 μm).

[ Experimental Example  1: rolling density evaluation]

Rolling densities of the positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were evaluated, and the results are shown in Table 1 and FIG. 1.

The rolling density was divided into 5 g of the positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 to 3 to fill the cylindrical holders tightly, and then increased from 400 kgf to 400 kgf to apply a pressure of up to 2000 kgf. The density of was measured.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Rolling density (g / cc) (@ 400kgf) 2.84 3.0 2.68 2.69 2.6 Rolling density (g / cc) (@ 2000kgf) 3.30 3.37 3.06 3.12 2.94

Referring to Table 1 and FIG. 1, the rolling density of the cathode active materials of Examples 1 to 2 was improved as compared with Comparative Examples 1 to 3. Specifically, compared to Comparative Example 3 using a monomodal positive electrode active material, the rolling density of the positive electrode active materials of Examples 1 and 2 was remarkably improved, and the small particle having a crystal size of less than 200 nm was bimodal but not under plastic. It can be confirmed that the rolling density of the positive electrode active material of Examples 1 to 2 is improved as compared with Comparative Examples 1 to 2 using.

[ Experimental Example  2: thermal stability evaluation]

Each positive electrode active material, carbon black conductive material, and PVdF binder prepared in Examples 1 to 2 and Comparative Examples 1 to 3 were mixed in an N-methylpyrrolidone solvent at a weight ratio of 96.5: 1.5: 2 to mix the positive electrode. (Viscosity: 5000 mPa · s) was prepared, which was applied to one surface of an aluminum current collector, dried at 130 ° C., and rolled to prepare a positive electrode.

The negative electrode used lithium metal.

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.

Each lithium secondary battery half cell manufactured by using the respective positive electrode active materials prepared by Examples 1 to 2 and Comparative Examples 1 to 3 was charged with a current of 0.2 C, and a state of charge of 100% SOC. The thermal stability was measured by differential scanning calorimetry (DSC) while dissolving at, and adding a positive electrode and a new electrolyte solution to the DSC measuring cell and raising the temperature from 400 ° C. to 10 ° C. per minute. As a result, the temperature at which the maximum heat peak (Main peak) appears is shown in Table 2 and FIG.

DSC Main peak (℃) Example 1 235.7 Example 2 240.5 Comparative Example 1 227.6 Comparative Example 2 228.3 Comparative Example 3 223.5

Referring to Table 2 and FIG. 2, in Examples 1 and 2, a maximum heat flow peak was observed at a high temperature of 235 ° C. or higher during DSC measurement. On the other hand, in Comparative Examples 1 to 3, the maximum heat flow peak (Main peak) was found at less than 230 ° C. Through this, it can be seen that the positive electrode active material of Examples 1 to 2 is significantly improved thermal stability compared to the positive electrode active material of Comparative Examples 1 to 3.

[ Experimental Example  3: high temperature life characteristics evaluation]

For each lithium secondary battery half cell prepared as in Example 2 using the respective positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 to 3, 1.0 in CCCV mode at 45 ° C. Evaluation of high temperature life characteristics by measuring the capacity retention rate during 100 charge / discharge experiments by charging until C, 4.25V (end current 1 / 20C), and discharge until 2.5V with a constant current of 1.0C. Proceeded. The results are shown in Table 3.

Initial discharge capacity (mAh / g) Capacity maintenance rate (%)
(@ 100 cycles) Example 1 189 88 Example 2 190 90 Comparative Example 1 185 80 Comparative Example 2 186 82 Comparative Example 3 182 71

Referring to Table 3, it can be seen that in Examples 1 and 2, the high temperature life characteristics were significantly improved as compared with Comparative Example 1, which uses a large particle having no concentration gradient and a small particle having a crystal size of less than 200 nm. . In addition, in Examples 1 to 2, the high temperature life characteristics were improved compared to Comparative Example 2 using an allele having a concentration gradient and a small particle having a crystalite size of less than 200 nm, and a monomodal cathode active material was used. Compared with the comparative example 3 used, the high temperature life characteristic and the initial capacity were remarkably increased.

[ Experimental Example  4: high temperature storage characteristics evaluation]

For each lithium secondary battery half cell prepared in the same manner as in Experiment 2 using the respective positive electrode active materials prepared in Examples 1 to 2 and Comparative Examples 1 to 3, 1.0C / 1.0 at 45 ° C. After 100 cycles under C conditions, the gas generation amount was measured using a gas chromatograph-mass spectrometer (GC-MS) for the discharge cells, and the results are shown in Table 4 and FIG. 3.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 H ₂ (μl) 0.1 0.1 0.1 0.1 0.1 CO (μl) 12.9 10.3 11.1 29.2 11.4 CO ₂ (μl) 29.2 19.6 60.8 43.8 77.8 CH ₄ (μl) 2.4 2.6 3.2 2.1 4.1 C ₂ H ₂ (μl) 0.1 0.1 0.1 0.1 0.1 C ₂ H ₄ (μl) 3.6 7.6 8.4 4.0 9.5 C ₂ H ₆ (μl) 0.6 1.0 1.2 0.1 2.0 C ₃ H ₆ (Μl) 0.1 0.1 0.1 1.6 0.1 C ₃ H ₈ (μl) 0.6 0.1 0.1 0.1 0.1 Total gas generation amount (μl) 49.6 41.5 85.1 81.1 105.2

Referring to Tables 4 and 3 above, in Examples 1 and 2, the amount of gas generated during high temperature storage was significantly higher than that of Comparative Example 1 using an allele having no concentration gradient and a small particle having a crystalite size of less than 200 nm. It can be seen that the decrease. In addition, in Examples 1 and 2, high-temperature storage was also compared with Comparative Example 2 using a particle having a concentration gradient and small particles having a crystalite size of less than 200 nm and Comparative Example 2 using a monomodal cathode active material. The amount of gas produced was reduced.

Claims (22)

A first positive electrode active material and a second positive electrode active material,
The first positive electrode active material and the second positive electrode active material are lithium composite transition metal oxides including at least two or more transition metals selected from the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn),
The average particle diameter (D ₅₀ ) of the first positive electrode active material is 1.5 times or more of the average particle diameter (D ₅₀ ) of the second positive electrode active material,
In the first positive electrode active material, at least one of nickel (Ni), cobalt (Co), and manganese (Mn) contained in the lithium composite transition metal oxide has a concentration difference of 5 mol% at the center and the surface of the lithium composite transition metal oxide particle. Have a concentration gradient that is greater than
The second cathode active material is a cathode active material for secondary batteries having a crystal size of 200 nm or more.
The method of claim 1,
The second positive electrode active material is secondary particles formed by agglomeration of primary particles, and the primary particle average particle diameter (D ₅₀ ) of the second positive electrode active material is a secondary battery positive electrode active material.
The method of claim 1,
The average particle diameter (D ₅₀ ) of the second positive electrode active material is a secondary battery positive electrode active material.
The method of claim 1,
The average particle diameter (D ₅₀ ) of the first positive electrode active material is a secondary battery positive electrode active material.
The method of claim 1,
The first positive electrode active material is composed of a core portion and a shell portion surrounding the core portion,
The core part has a constant transition metal concentration, and the shell part has a concentration gradient in which at least one of nickel (Ni), cobalt (Co), and manganese (Mn) gradually increases or decreases.
The method of claim 5,
The shell portion of the first positive electrode active material, the secondary battery positive electrode active material having a concentration gradient gradually decreases as the concentration of nickel (Ni) toward the particle surface side.
The method of claim 1,
The first positive electrode active material has a concentration gradient in which at least one of nickel (Ni), cobalt (Co), and manganese (Mn) gradually increases or decreases from the center of the particle to the surface thereof.
The method of claim 7, wherein
The first cathode active material has a concentration gradient in which nickel (Ni) gradually decreases from the center of the particles to the surface thereof.
The method of claim 1,
The first positive electrode active material includes a core portion, a concentration gradient portion formed to surround the core portion, and a surface portion formed to surround the concentration gradient portion.
The core portion and the surface portion have a constant concentration of transition metal independently of each other,
The concentration gradient unit has a concentration gradient in which at least one of nickel (Ni), cobalt (Co), and manganese (Mn) gradually changes from the core portion composition to the surface portion composition.
The method of claim 1,
At least one of the first positive electrode active material and the second positive electrode active material has a mean content of nickel (Ni) in the total metal elements contained in the lithium composite transition metal oxide, the positive electrode active material for secondary batteries.
The method of claim 1,
At least one of the first positive electrode active material and the second positive electrode active material is a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al).
The method of claim 1,
The first positive electrode active material and the second positive electrode active material are positive electrode active materials for secondary batteries represented by the following Chemical Formula 1.
[Formula 1]
Li _p Ni _{1- (x1 + y1 + z1)} Co _x1 M ^a _y1 M ^b _z1 M ^c _q1 O ₂
In the above formula, M ^a is at least one element selected from the group consisting of Mn and Al, M ^b is at least one element selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo, M ^c is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, 0.9≤p≤1.5, 0 <x1≤0.4, 0 <y1≤0.4, 0≤z1 ≤ 0.1, 0 ≤ q1 ≤ 0.1, and 0 <x1 + y1 + z1 ≤ 0.4.
The method of claim 1,
The first positive electrode active material and the second positive electrode active material are positive electrode active materials for secondary batteries mixed in a weight ratio of 9: 1 to 1: 9.
After preparing a first positive electrode active material and a second positive electrode active material of a lithium composite transition metal oxide containing at least two or more transition metals selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn), the first positive electrode Mixing the active material and the second positive electrode active material,
Wherein the average particle diameter (D ₅₀₎ of the first cathode active material is at least 1.5 times the average particle diameter (D ₅₀₎ of the second positive electrode active material, the first cathode active material is a lithium composite transition of nickel contained in the metal oxide (Ni) , At least one of cobalt (Co) and manganese (Mn) has a concentration gradient having a concentration difference of 5 mol% or more at the center and the surface of the lithium composite transition metal oxide particle, and the second cathode active material has a crystal size. Method of producing a positive electrode active material for secondary batteries prepared by oversintering to 200 nm or more.
The method of claim 14,
The second positive electrode active material is a secondary particle formed by agglomeration of primary particles, and the primary particle average particle diameter (D ₅₀ ) of the second positive electrode active material is a method of manufacturing a positive electrode active material for secondary batteries.
The method of claim 14,
The average particle diameter (D ₅₀ ) of the second positive electrode active material is a method for producing a positive electrode active material for secondary batteries.
The method of claim 14,
The average particle diameter (D ₅₀ ) of the first positive electrode active material is a method for producing a positive electrode active material for secondary batteries.
The method of claim 14,
The first positive electrode active material is composed of a core portion and a shell portion surrounding the core portion,
The core part has a constant transition metal concentration, and the shell part has a concentration gradient in which at least one of nickel (Ni), cobalt (Co), and manganese (Mn) gradually increases or decreases.
The method of claim 14,
The first cathode active material has a concentration gradient in which at least one of nickel (Ni), cobalt (Co) and manganese (Mn) gradually increases or decreases from the center of the particle to the surface thereof.
The method of claim 14,
The first positive electrode active material and the second positive electrode active material is a method of manufacturing a positive electrode active material for secondary batteries which is mixed in a weight ratio of 9: 1 to 1: 9.
A secondary battery positive electrode comprising the positive electrode active material according to any one of claims 1 to 13.
A lithium secondary battery comprising the positive electrode according to claim 21.

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