KR102410662B1 - 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 includes a first positive active material and a second positive active material, wherein the first positive active material and the second positive active material have at least two transitions selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn). It is a lithium composite transition metal oxide containing a metal, and 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, and the first positive electrode active material is lithium At least one of nickel (Ni), cobalt (Co) and manganese (Mn) contained in the composite transition metal oxide has a concentration gradient of 5 mol% or more, wherein the difference in concentration between the center and the surface of the lithium composite transition metal oxide particle is 5 mol% or more, 2 The cathode active material relates to a cathode active material for a secondary battery having a crystal size of 200 nm or more.

Description

Cathode active material for secondary battery, manufacturing method thereof, and lithium secondary battery comprising 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, a lithium secondary battery has been in the spotlight as a driving power source for a portable device because it is lightweight and has a high energy density. Accordingly, research and development efforts for improving the performance of lithium secondary batteries are being actively conducted.

In a lithium secondary battery, an organic electrolyte or polymer electrolyte is charged between a positive electrode and a negative electrode made of an active material capable of intercalation and deintercalation of lithium ions, and lithium ions are inserted/deintercalated from the positive and negative electrodes. Electric energy is produced by a reduction reaction with

As a cathode active material for a lithium secondary battery, 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 ), etc. were used. . In addition, as a method for improving low thermal stability while maintaining the excellent reversible capacity of LiNiO ₂ , a lithium composite metal oxide in which a part of nickel (Ni) is substituted 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') has been developed.

In order to increase the capacity per unit volume of the lithium composite transition metal oxide and improve stability, research has been conducted on forming a concentration gradient of a metal composition or increasing the content of nickel. In addition, in order to increase the capacity per unit volume of the electrode, a study of increasing the rolling density by blending large and small particles to prepare a positive active material layer in a bimodal manner is being conducted. However, there is still a need for development of a positive active material having a high capacity and satisfying thermal stability at the same time.

Korean Patent Registration No. 10-1510940

An object of the present invention is to provide a positive electrode active material for a secondary battery that uses positive electrode active materials of large and small particles to improve energy density and improve thermal stability while having a high capacity.

In addition, the present invention is to provide a positive electrode active material for secondary batteries with improved stability, such as preventing cracks and cracking of the positive electrode active material by rolling, improving high-temperature lifespan characteristics, and reducing the amount of gas generated during high-temperature storage. will be.

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

In addition, the present invention provides a first positive electrode active material and a second positive electrode active material of a lithium composite transition metal oxide containing at least two transition metals selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn). , mixing the first positive active material and the second positive active material, wherein the average particle diameter of the first positive active material (D ₅₀ ) is 1.5 times or more of the average particle diameter (D ₅₀ ) of the second positive active material, In the first positive 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 between the center and the surface of the lithium composite transition metal oxide particle of 5 mol% It has a concentration gradient equal to or greater than, and the second positive electrode active material provides a method of manufacturing a positive electrode active material for a secondary battery manufactured by under-calcining such that the crystal size is 200 nm or more.

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

According to the present invention, energy density can be improved by blending large and small particles to prepare a bimodal positive active material, and at this time, the large and small particles having a concentration gradient, and the crystal size ( By using small particles with a crystallite size of 200 nm or more, high capacity can be realized and thermal stability can be improved. In addition, it is possible to prevent cracking and breakage of the positive electrode active material due to rolling, and improve stability, such as improving high-temperature lifespan characteristics, and reducing the amount of gas generated during high-temperature storage.

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

Hereinafter, the present invention will be described in more detail to help the understanding of 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 conventional or dictionary meanings, and the inventor appropriately defines the concept of the term in order to describe his invention in the best way. Based on the principle that it can be done, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

<Anode active material>

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

The positive electrode active material for a secondary battery of the present invention includes a first positive electrode active material as opposites and a second positive active material as small particles.

In order to improve the capacity per volume of the positive electrode for secondary batteries, it is necessary to increase the density of the positive electrode active material layer. A method of increasing the density of the positive active material layer is to increase the rolling density (or electrode density) by reducing the voids between the positive active material particles. this is used In the case of a bimodal positive electrode active material in which the positive active material of opposite and small particles is mixed as in the present invention, since the empty space between the particles of the opposite positive electrode active material can be filled with the small particle positive active material, more dense filling is possible It is possible, and 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 diameter 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, in the method for measuring the average particle diameter (D ₅₀ ) of the positive active material, the particles of the positive active material are dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (eg, Microtrac MT 3000). After irradiating the ultrasonic wave of 28 kHz with the output 60W, the average particle diameter D50 corresponding to ₅₀ % of the volume accumulation amount in a measuring apparatus can be computed.

More specifically, the average particle diameter (D ₅₀ ) of the first positive active material and the second positive active material may be 2:1 to 5:1, more preferably, the average particle diameter of the first positive active material and the second positive active material (D ₅₀ ) may be 2:1 to 3.5:1. By satisfying the average particle diameter (D ₅₀ ) ratio of the first positive active material and the second positive active material within the above range, the voids between the positive active material particles are more effectively reduced, the filling density is increased, and the positive electrode density is improved 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 μm, more preferably 13 to 25 μm, and still more preferably 15 to 22 μm.

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

The first positive active material and the second positive active material of the present invention are lithium composite transition metal oxides containing at least two or more transition metals selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn). In this case, the opposite first positive active material is a lithium composite transition metal oxide having a concentration gradient, and the second positive active material, which is a small particle, does not have a concentration gradient, and is under-calcined to have a lithium composite transition having a crystal size of 200 nm or more. It is a metal oxide. In this way, by using a mixture of small particles that are under-calcined without having a concentration gradient with a large particle having a concentration gradient, a higher capacity and thermal stability can be ensured, and high-temperature lifespan characteristics and high-temperature storage stability can be improved.

The relatively opposite first positive 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 is 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 difference in the concentration of nickel (Ni) contained in the lithium composite transition metal oxide between the center and the surface of the lithium composite transition metal oxide particles may be 8 mol% or more, more preferably 10 mol% or more.

In the present invention, the concentration gradient composition and concentration of the transition metal in the positive active material particles is determined by an electron probe micro analyzer (Electron Probe Micro Analyzer, EPMA), inductively coupled plasma-atomic emission spectroscopy (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 positive electrode active material to the surface, or the atomic ratio of each metal may be measured while etching from the surface of the positive electrode active material to the center through XPS.

In an embodiment of the present invention, the first positive active material includes a core part and a shell part formed to surround the core part, the core part having a constant concentration of transition metal, and the shell part being 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. Since the concentration of nickel (Ni) is maintained at a high concentration at the particle center side of the shell part and the concentration of nickel (Ni) decreases toward the particle surface side of the shell part, it is possible to prevent a decrease in capacity while exhibiting thermal stability.

Meanwhile, in the shell part, at least one of manganese (Mn) and cobalt (Co) may have a concentration gradient that gradually increases toward the particle surface. In this case, excellent thermal stability can be obtained because the concentration of manganese (Mn) is maintained at a low concentration on the particle center side of the shell part, and the concentration of manganese (Mn) increases toward the particle surface side of the shell part, and at the particle center side of the shell part By maintaining the low concentration of cobalt (Co) and increasing the concentration of cobalt (Co) toward the particle surface side of the shell part, it is possible to reduce the amount of cobalt (Co) used while preventing the decrease in capacity.

In the shell portion of the positive electrode active material, the concentration of nickel (Ni) contained in the shell portion decreases with a continuous concentration gradient toward the particle surface, and at least one of manganese (Mn) and cobalt (Co) increases toward the particle surface. It may increase while having a continuous concentration gradient complementary to the concentration gradient of nickel (Ni).

In the present invention, "shows a concentration gradient in which the concentration of the transition metal is gradually changed (increased or decreased)" means that the concentration of the transition metal exists in a concentration distribution in which the concentration is gradually changed. Specifically, the concentration distribution indicates that the change in the transition metal concentration per 1 μm in the particle is 0.1 to 5 mol%, more specifically 0.1 to 3 mol, respectively, based on the total number of moles of the corresponding metal included in the positive active material. %, more specifically, may be a difference of 1 to 2 mol%.

In another embodiment of the present invention, 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 is formed from the center of the lithium composite transition metal oxide particle. It can have a gradient (increasing or decreasing) that gradually changes (increasing or decreasing) to the surface.

More preferably, the first positive active material may have a concentration gradient in which nickel (Ni) gradually decreases from the center of the lithium composite transition metal oxide particles to the surface. Since the concentration of nickel (Ni) is maintained at a high concentration at the particle center 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 exhibiting 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 a low concentration at the particle center of the first positive electrode active material and the concentration of manganese (Mn) increases toward the particle surface, excellent thermal stability can be obtained without reducing the capacity, and the first By maintaining a low concentration of cobalt (Co) at the particle center of the positive electrode active material and increasing the concentration of cobalt (Co) toward the particle surface, it is possible to reduce the amount of cobalt (Co) and prevent a decrease in capacity.

In the first positive active material according to an embodiment of the present invention, the concentration of nickel (Ni) contained in the first positive 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 while having a continuous concentration gradient complementary to the concentration gradient of nickel (Ni) from the center of the particle toward 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) is a combination of progressively increasing concentrations. By having the gradient, it is possible to exhibit thermal stability while maintaining capacity characteristics.

In another embodiment of the present invention, the first positive electrode active material includes a core part, a concentration gradient part formed to surround the core part, and a surface part formed to surround the concentration gradient part, and the core part and the surface part are independent of each other. The concentration of the transition metal is constant, and the concentration gradient part may have a concentration gradient in which at least one of nickel (Ni), cobalt (Co) and manganese (Mn) is gradually changed from the composition of the core part to the composition of the surface part. . More preferably, the concentration of nickel (Ni) in the core portion is higher than that of the surface portion, and in the concentration gradient portion of the first positive electrode active material, the concentration of nickel (Ni) gradually decreases from the core portion to the surface portion. Concentration gradients can be shown. Since the concentration of nickel (Ni) is maintained at a high concentration on the core part side of the concentration gradient part and the concentration of nickel (Ni) decreases toward the surface part side, it is possible to prevent a decrease in capacity while exhibiting thermal stability.

Meanwhile, the concentration gradient portion may have a concentration gradient in which at least one of manganese (Mn) and cobalt (Co) gradually increases toward the surface portion. In this case, excellent thermal stability can be obtained because the concentration of manganese (Mn) is maintained at a low concentration on the core part side of the concentration gradient part, and the concentration of manganese (Mn) increases toward the surface part side of the concentration gradient part. In the core part of the gradient part, the concentration of cobalt (Co) is maintained at a low concentration, and by increasing the concentration of cobalt (Co) toward the surface part of the concentration gradient part, the amount of cobalt (Co) is reduced while preventing a decrease in capacity. can

In the concentration gradient portion of the positive electrode active material, the concentration of nickel (Ni) contained in the concentration gradient portion decreases while having a continuous concentration gradient toward the surface portion, and at least one of manganese (Mn) and cobalt (Co) is a surface portion It may increase while having a continuous concentration gradient complementary to the concentration gradient of nickel (Ni) toward the side.

As described above, the opposite first positive active material has a concentration gradient by varying the concentration of the transition metal element according to the position in the particle, so that the characteristics of the transition metal can be easily utilized to further improve the battery performance improvement effect of the positive electrode active material. can

The second active material, which is a relatively small particle, has a crystal size of 200 nm or more due to under-baking. When the crystal size of the second positive active material is less than 200 nm, high temperature lifespan characteristics and stability during high temperature storage may be deteriorated, and cracks and cracks may occur in the positive electrode active material by rolling. The method of under-calcining the second cathode active material is not particularly limited as long as it is a method capable of increasing the crystal size to 200 nm or more. For example, in the process of sintering, about 50 ° C. An increased temperature can lead to underfiring. More preferably, the second cathode active material may have a crystal size of 200 to 500 nm, more preferably 220 to 400 nm.

In the present invention, 'particles' refer to grains of micro-units, and when they are enlarged and observed, they can be divided into 'grains' having a crystal form of several tens of nano units. If you enlarge it further, you can see a divided region in the form of atoms forming a lattice structure in a certain direction, which is called 'crystallite', and the size of the particle observed in XRD is defined as the size of the crystallite. . The method to measure the crystal size is to estimate the crystallite size by using the peak broadening of XRD data. It can be quantitatively calculated through the Scherrer equation.

The first positive active material and the second positive active material may be secondary particles formed by agglomeration of primary particles. In this case, the second positive active material having relatively small particles may be over-baked, so that the 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 reduced, such as high temperature life characteristics and an increase in gas generation during high temperature storage, and cracks in the positive electrode active material by rolling ) and cracking may occur. More specifically, in the second positive active material, the average particle diameter (D ₅₀ ) of the primary particles may be 1 to 8 μm, and more specifically, the second positive active material has the average particle diameter (D ₅₀ ) of the primary particles. It may be 1 to 6 μm. By reducing the specific surface area of the second positive electrode active material, which is a relatively small particle, the effect of reducing side reactions with the electrolyte can be exhibited, and through this, the effect of improving thermal stability and reducing gas generation can be exhibited. Meanwhile, the average particle diameter (D ₅₀ ) of the primary particles of the first positive electrode active material, which is relatively opposite, may be 100 nm to 2 μm.

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

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

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

More specifically, the first positive active material and the second positive active material may be a lithium composite transition metal oxide represented by the following formula (1). In the case of the first positive electrode active material having a concentration gradient, the average composition of the entire particle may satisfy 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 or more elements selected from the group consisting of Mn and Al, M ^b is at least one or more elements selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo, and M ^c is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, and 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 Formula 1, Li may be included in a content corresponding to p, that is, 0.9≤p≤1.5. If p is less than 0.9, there is a fear that the capacity may decrease, and if it exceeds 1.5, the particles are sintered in the sintering process, so it may be difficult to manufacture the positive electrode active material. 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 sinterability during the preparation of the active material, Li may be more preferably included in an amount of 1.0≤p≤1.15.

In the lithium composite transition metal oxide of Formula 1, Ni may be included in a content corresponding to 1-(x1+y1+z1), for example, 0.6≤1-(x1+y1+z1)<1. When the content of Ni in the lithium composite transition metal oxide of Chemical Formula 1 is 0.6 or more, the amount of Ni sufficient to contribute to charging and discharging is 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 Formula 1, Co may be included in a content 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 risk of cost increase. Considering the significant effect of improving 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 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. Considering the effect of improving the lifespan characteristics, the Ma may be included in ^a content corresponding to y1, that is, a content of 0<y1≤0.4. When y1 in the lithium composite transition metal oxide of Formula 1 exceeds 0.4, there is a risk that the output characteristics and capacity characteristics of the battery are rather deteriorated, and the Ma may be included in ^a content of 0.05≤y1≤0.2 more specifically.

In the lithium composite transition metal oxide of 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 a content corresponding to z1, that is, 0≤z1≤0.1. have.

In the lithium composite transition metal oxide of Formula 1, the metal element of M ^c may not be included in the structure of the lithium composite transition metal oxide, and when the precursor and the lithium source are mixed and fired, the M ^c source is mixed and fired or , it is possible to prepare a lithium composite transition metal oxide in which M ^c is doped on the surface of the lithium composite transition metal oxide by separately adding a source of M ^c and sintering after forming the lithium composite transition metal oxide. The M ^c may be included in an amount corresponding to q1, that is, a content that does not deteriorate the characteristics of the positive electrode active material within the range of 0≤q1≤0.1.

In one embodiment of the present invention, the first positive active material and the second positive active material may be mixed in a weight ratio of 9:1 to 1:9, more preferably 8:2 to 3:7, most preferably may be mixed in a weight ratio of 8:2 to 5:5. The energy density of the positive electrode is increased by mixing and using the first positive electrode active material, which is opposite and has a concentration gradient, and the second positive electrode active material, which is small particles and has a crystal size of 200 nm or more, within the above range, to ensure high capacity and excellent thermal stability. And it is possible to suppress the side reaction with the electrolyte. Accordingly, the lithium secondary battery manufactured using the positive electrode active material as described above may realize high capacity, reduce gas generation, and improve battery characteristics such as high temperature lifespan characteristics.

<Method for producing positive electrode active material>

Next, a method for manufacturing the positive electrode active material of the present invention will be described.

The positive electrode active material of the present invention is a lithium composite transition metal oxide containing at least two transition metals selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn). A first positive active material and a second positive active material are prepared. and then mixing the first positive active material and the second positive active material, wherein the average particle diameter (D _{50 ) of the first positive active material is 1.5 times or more of the average particle diameter (D 50 )} of the second positive active material and , In the first positive 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 between the center and the surface of the lithium composite transition metal oxide particle by 5 mol % or more, and the second cathode active material is manufactured by under-firing so that the crystal size is 200 nm or more.

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

The second positive 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 still more preferably 2 to 6 μm.

In this case, the relatively opposite first positive 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 composition of the transition metal concentration gradient of the first positive electrode active material is omitted because it overlaps with the description of the positive electrode active material above.

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

In addition, the second positive electrode active material having relatively small particles may be manufactured by under-baking such that the average particle diameter (D ₅₀ ) of the primary particles is 1 μm or more. More specifically, the second positive active material has an average particle diameter (D ₅₀ ) of primary particles of 1 to 8 μm, and more specifically, the second positive active material has an average particle diameter (D ₅₀ ) of primary particles of 1 to 6 It can be manufactured by over-firing to become ㎛. Meanwhile, the average particle diameter (D ₅₀ ) of the primary particles of the first positive electrode active material, which is relatively opposite, may be 100 nm to 3 μm.

In addition, the composition and mixing ratio of the first positive active material and the second positive active material overlap with the previous description of the positive active material, and thus will be omitted.

<Anode and secondary battery>

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

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

In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface of the positive electrode current collector. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven body.

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

In this case, the conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it has electronic conductivity without causing chemical change. Specific examples 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 powders 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, and one or a mixture of two or more thereof may be used. The conductive material may be included in an amount of 1 to 30 wt% based on the total weight of the positive active material layer.

In addition, the binder serves to improve adhesion between the positive electrode active material particles and the adhesive force 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, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them 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 active material layer.

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

The solvent may be a solvent generally used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone) or water, and the like, and any one of them or a mixture of two or more thereof may be used. The amount of the solvent used is enough to dissolve or disperse the positive electrode active material, the conductive material and the binder in consideration of the application thickness of the slurry and the production yield, and to have a viscosity capable of exhibiting excellent thickness uniformity when applied for the production of the positive electrode thereafter. 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 a film obtained by peeling it from the support on the positive electrode current collector.

According to another embodiment of the present invention, an electrochemical device including the positive electrode is provided. The electrochemical device may specifically be 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. In addition, the lithium secondary battery may optionally 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, and for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel surface. Carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of typically 3 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 strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

The anode active material layer optionally includes a binder and a conductive material together with the anode active material. The anode active material layer may be formed by applying a composition for forming an anode including an anode active material, and optionally a binder and a conductive material on an anode current collector and drying, or casting the composition for forming a cathode on a separate support, and then , may be produced by laminating a film obtained by peeling from this support onto a negative electrode current collector.

As the anode 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 fiber, and amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium, such as SiO _β (0 < β < 2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; Alternatively, a composite including the metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite may be used, 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 negative electrode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are representative, and as high crystalline carbon, natural or artificial graphite of amorphous, plate-like, scale-like, spherical or fibrous shape, and Kish graphite graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitches (Mesophase pitches), and petroleum and coal tar pitch (petroleum or coal tar pitch) High-temperature calcined carbon such as derived cokes) is a representative example.

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

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for the movement of lithium ions, and can be used without particular limitation as long as it is usually used as a separator in a lithium secondary battery, especially for the movement of ions in the electrolyte It is preferable to have a low resistance to respect and an excellent electrolyte moisture content. 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 these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. 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 optionally be used in a single-layer or multi-layer structure.

In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, and the like, which can be used in the manufacture of lithium secondary batteries, and are limited to these. it's not going to be

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

The organic solvent may be used without any 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, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, carbonate-based 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 sulfolane may be used. Among them, a carbonate-based solvent is preferable, and a cyclic carbonate (eg, ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of increasing the charge/discharge performance of the battery, and a low-viscosity linear carbonate-based compound ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, 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 , etc. may 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 appropriate conductivity and viscosity, excellent electrolyte performance may be exhibited, and lithium ions may move effectively.

In the electrolyte, in addition to the electrolyte components, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as jolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

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

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

The battery module or battery pack is a power tool (Power Tool); electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for any one or more medium-to-large devices in a system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein.

Example 1

As the first positive 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 . 13} O ₂ A lithium composite transition metal oxide in which the concentrations of nickel (Ni), cobalt (Co), and manganese (Mn) are gradually changed from the particle center to the surface was prepared. LiNi ₀ as the second positive active material _{. 70} Co _{0 . 15} Mn _{0 . 15} O ₂ Particles (D ₅₀ = 6㎛) were prepared. In this case, the second positive electrode active material was over-baked, so that the crystal size was 230 nm, and the average particle diameter (D ₅₀ ) of the primary particles was 2 μm. A positive active material was prepared by mixing the first positive active material and the second positive active material in a weight ratio of 7:3.

Example 2

As the first positive active material, the average particle diameter (D ₅₀ ) is 11㎛, the core portion is LiNi _0.83 Co _0.07 Mn _0.08 Al _0.02 O ₂ The transition metal concentration is constant, the shell portion LiNi _0.83 Co _0.07 Mn _0.08 Al _0.02 O ₂ at the particle surface side LiNi _{0 . 71} Co _{0 . 13} Mn _{0 . 15} Al _{0 .} LiNi ₀ as a second positive electrode active material using a lithium composite transition metal oxide having a gradual concentration gradient to ₀₁ O _{2 . 70} Co _{0 . 15} Mn _{0 . 15} O ₂ Particles (D ₅₀ = 6㎛), under-baked, the crystal size (Crystalite size) is 230nm, the average particle diameter of the primary particles (D ₅₀ ) Example 1 and except for using the thing of 2㎛ A positive electrode active material was prepared in the same manner.

comparative example One

LiNi ₀ as the first positive 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 active material _{. 70} Co _{0 . 15} Mn _{0 . 15} O ₂ Particles (D ₅₀ = 4㎛) were prepared. At this time, the first positive active material does not have a concentration gradient, and the second positive active material has a crystal size of 117 nm and an average particle diameter (D ₅₀ ) of primary particles of 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 used the same lithium composite transition metal oxide as in Example 1, but the second positive electrode active material had a crystal size of 117 nm and an average particle diameter of primary particles (D ₅₀ ) of 0.8 μm. A positive electrode active material was prepared in the same manner as in Example 1, except that.

comparative example 3

LiNi ₀ as a positive electrode active material _{. 80} Co _{0 . 10} Mn _{0 . 08} Al _{0 . 02} O ₂ Particles (D ₅₀ = 12㎛) of monomodal (monomodal) was used to prepare a positive electrode active material.

[ Experimental example 1: Rolling density evaluation]

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

The rolling density was obtained by subdividing 5 g of each of the positive active materials prepared in Examples 1 to 2 and Comparative Examples 1 to 3, filling the cylindrical holder without gaps, and increasing the pressure by 400 kgf to 400 kgf to 2000 kgf powder when applied. 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 positive active materials of Examples 1 and 2 have improved rolling density compared to Comparative Examples 1 and 3. Specifically, the rolling density of the positive active materials of Examples 1 and 2 was significantly improved compared to Comparative Example 3 using a monomodal positive active material, and small particles having a crystal size of less than 200 nm because they were bimodal but not oversintered. It can be seen that the rolling density of the positive electrode active material of Examples 1 and 2 is improved compared to Comparative Examples 1 and 2 using

[ Experimental example 2: Thermal stability evaluation]

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

As the negative electrode, lithium metal was used.

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

For each lithium secondary battery half cell prepared by using each positive active material prepared in Examples 1 to 2 and Comparative Examples 1 to 3, charged with a current of 0.2C to have an SOC of 100% was disassembled, and the anode and a new electrolyte were put into the DSC measurement cell, and the temperature was increased from room temperature to 400°C at a rate of 10°C per minute to measure thermal stability by differential scanning calorimetry (DSC). As a result, the temperature at which the maximum peak (Main peak) of the maximum amount of heat flow appears is shown in Table 2 and FIG. 2 below.

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 the case of Examples 1 and 2, the maximum peak of heat flow (Main peak) during DSC measurement was shown at a high temperature of 235° C. or higher. On the other hand, in the case of Comparative Examples 1 to 3, the maximum heat flow peak (Main peak) appeared at less than 230 ℃. Through this, it can be confirmed that the positive active materials of Examples 1 and 2 have significantly improved thermal stability compared to the positive active materials of Comparative Examples 1 and 3.

[ Experimental example 3: Evaluation of high temperature life characteristics]

For each lithium secondary battery half cell prepared as in Experimental Example 2 using each positive active material prepared in Examples 1 to 2 and Comparative Examples 1 to 3, 1.0 in CCCV mode at 45° C. C, charge (termination current 1/20C) until it reaches 4.25V, discharge it at a constant current of 1.0C until it becomes 2.5V, and measure the capacity retention rate when 100 times of charging/discharging experiments are performed to evaluate the high-temperature lifespan characteristics proceeded. The results are shown in Table 3.

Initial discharge capacity (mAh/g) Capacity retention 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, in the case of Examples 1 and 2, it can be seen that the high-temperature lifespan characteristics are significantly improved compared to Comparative Example 1 using large particles having no concentration gradient and small particles having a crystal size of less than 200 nm. . In addition, in the case of Examples 1 and 2, the high temperature lifespan characteristics were improved compared to Comparative Example 2 using large particles having a concentration gradient and small particles having a crystal size of less than 200 nm, and a monomodal positive electrode active material was used. Compared to Comparative Example 3 used, high-temperature lifespan characteristics and initial capacity were significantly increased.

[ Experimental example 4: Evaluation of high temperature storage characteristics]

For each lithium secondary battery half cell prepared as in Experimental Example 2 using each positive active material prepared in Examples 1 to 2 and Comparative Examples 1 to 3, 1.0C/1.0 at 45°C After 100 cycles under C condition, the gas generation amount was measured for the discharge cell using a gas chromatograph-mass spectrometer (GC-MS), 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 (μl) 49.6 41.5 85.1 81.1 105.2

Referring to Table 4 and FIG. 3, in the case of Examples 1 and 2, the amount of gas generated during storage at high temperature is significantly higher than Comparative Example 1 using large particles having no concentration gradient and small particles having a crystal size of less than 200 nm. decrease can be seen. In addition, in the case of Examples 1 and 2, Comparative Example 2 using small particles having a concentration gradient and small particles having a crystal size of less than 200 nm and Comparative Example 2 using a positive active material of monomodal High temperature storage The amount of gas generated was reduced.

Claims (22)

It includes a first positive active material and a second positive active material,
The first positive active material and the second positive active material are lithium composite transition metal oxides containing at least two or more transition metals selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn),
The ratio of the average particle diameter (D50) of the first positive active material and the second positive active material is 2:1 to 3.5:1,
In the first positive 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 between the center and the surface of the lithium composite transition metal oxide particle of 5 mol% has a concentration gradient greater than or equal to
The second positive active material is secondary particles formed by aggregation of primary particles, and the average primary particle diameter (D ₅₀ ) of the second positive active material is 1 μm or more,
The second positive active material is a positive active material for a secondary battery having a crystal size of 200 nm or more.
delete According to claim 1,
The second positive electrode active material has an average particle diameter (D ₅₀ ) of 9 μm or less.
According to claim 1,
The average particle diameter (D ₅₀ ) of the first positive electrode active material is a positive electrode active material for a secondary battery of 10 to 30㎛.
According to claim 1,
The first positive electrode active material consists of a core portion and a shell portion formed to surround the core portion,
The core part has a constant concentration of the transition metal, and the shell part exhibits a concentration gradient in which at least one of nickel (Ni), cobalt (Co) and manganese (Mn) is gradually increased or decreased.
6. The method of claim 5,
The shell portion of the first positive electrode active material, the positive electrode active material for a secondary battery exhibits a concentration gradient in which the concentration of nickel (Ni) gradually decreases toward the particle surface.
According to claim 1,
The first positive active material is a positive active material for a secondary battery having 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.
8. The method of claim 7,
The first positive active material is a positive active material for a secondary battery having a concentration gradient in which nickel (Ni) gradually decreases from the center of the particle to the surface.
According to claim 1,
The first positive electrode active material includes a core portion, a concentration gradient formed to surround the core portion, and a surface portion formed to surround the concentration gradient portion,
The core part and the surface part have a constant concentration of transition metal independently of each other,
The concentration gradient portion has a concentration gradient in which at least one of nickel (Ni), cobalt (Co) and manganese (Mn) is gradually changed from the composition of the core portion to the composition of the surface portion.
According to claim 1,
At least one of the first positive active material and the second positive active material is a positive active material for a secondary battery having an average content of nickel (Ni) among all metal elements contained in the lithium composite transition metal oxide of 80 mol% or more.
According to claim 1,
At least one of the first positive active material and the second positive active material is a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al), a positive active material for a secondary battery.
According to claim 1,
The first positive active material and the second positive active material are a positive active material for a secondary battery represented by 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 or more elements selected from the group consisting of Mn and Al, M ^b is at least one or more elements selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo, and M ^c is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo and Cr, and 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.
According to claim 1,
The first positive active material and the second positive active material are mixed in a weight ratio of 9:1 to 1:9 for a secondary battery positive active material.
After preparing a first positive active material and a second positive active material of a lithium composite transition metal oxide containing at least two 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 active material,
The ratio of the average particle diameter (D50) of the first positive active material and the second positive active material is 2:1 to 3.5:1,
In the first positive 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 between the center and the surface of the lithium composite transition metal oxide particle of 5 mol% has a concentration gradient greater than or equal to
The second positive active material is secondary particles formed by aggregation of primary particles, and the average primary particle diameter (D ₅₀ ) of the second positive active material is 1 μm or more,
The method of manufacturing a cathode active material for a secondary battery, wherein the second cathode active material is manufactured by over-calcining so that the crystal size is 200 nm or more.
delete 15. The method of claim 14,
The second positive electrode active material has an average particle diameter (D ₅₀ ) of 9 μm or less.
15. The method of claim 14,
An average particle diameter (D ₅₀ ) of the first positive electrode active material is 10 to 30 μm.
15. The method of claim 14,
The first positive electrode active material consists of a core portion and a shell portion formed to surround the core portion,
The core part has a constant concentration of the transition metal, and the shell part exhibits a concentration gradient in which at least one of nickel (Ni), cobalt (Co) and manganese (Mn) is gradually increased or decreased.
15. The method of claim 14,
The method of manufacturing a cathode active material for a secondary battery, wherein 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.
15. The method of claim 14,
The method of manufacturing a positive electrode active material for a secondary battery, wherein the first positive active material and the second positive active material are mixed in a weight ratio of 9:1 to 1:9.
A positive electrode for a secondary battery 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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