Positive electrode active material, positive electrode comprising same, and lithium secondary battery

Abstract

The present invention relates to a positive electrode active material comprising a large-particle-size lithium nickel-based transition metal oxide and a small-particle-size lithium nickel-based transition metal oxide, in which the large-particle-size lithium nickel-based transition metal oxide is in the form of secondary particles which are aggregates of primary particles; the small-particle-size lithium nickel-based transition metal oxide is in the form of at least one of a single particle and a quasi-single particle, the single particle is formed by a particle node, and the quasi-single particle is a compound of 30 or less particle nodes; the large-particle-size lithium nickel-based transition metal oxide has a D50 of 5 [mu] m to 30 [mu] m and a Y value defined by a particle size distribution characteristic factor of 2.2 or less. The present invention also provides a lithium secondary battery in which the positive electrode active material is applied to a positive electrode, suppressing breakage of particles of the positive electrode active material, thereby improving lifespan and output characteristics and reducing gas production.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Korean Patent Application No. 10-2022-0184962, filed on December 26, 2022, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to a positive electrode active material for a lithium secondary battery, and a positive electrode and a lithium secondary battery comprising the positive electrode active material. Background Art

[0004] Lithium secondary batteries are generally composed of a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode and the negative electrode include active materials capable of intercalating and deintercalating lithium ions.

[0005] As positive electrode active materials for lithium secondary batteries, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2, LiMnO4, etc.), lithium iron phosphate compounds (LiFePO4), etc. have been used. Among them, lithium cobalt oxide has the advantages of high operating voltage and excellent capacity characteristics, but the price of cobalt as a raw material is high, and its supply is unstable, making it difficult to commercially apply it to large-capacity batteries. The structural stability of lithium nickel oxide is poor, making it difficult to obtain sufficient life characteristics. At the same time, lithium manganese oxide has excellent stability, but has the problem of poor capacity characteristics. Therefore, in order to compensate for the problems of lithium transition metal oxides containing Ni, Co or Mn alone, lithium nickel-based transition metal oxides containing two or more transition metals have been developed, and in particular, lithium nickel cobalt manganese composite oxides containing Ni, Co and Mn are widely used in the field of electric vehicle batteries.

[0006] Conventional lithium nickel cobalt manganese oxide is usually in the form of spherical secondary particles in which tens to hundreds of primary particles are aggregated. However, for lithium nickel cobalt manganese oxide in the form of secondary particles in which a large number of primary particles are aggregated, there is a problem that particle rupture may occur during the rolling process when manufacturing the positive electrode, causing the primary particles to fall off, and cracks to appear inside the particles during charging and discharging. When the particles of the positive electrode active material are broken or cracked, the contact area with the electrolyte increases, which increases the gas generation and active material degradation caused by the side reaction with the electrolyte, thereby reducing the life characteristics. Summary of the invention

[0007] [Technical issues]

[0008] The present invention aims to solve the above problems and to provide a positive electrode active material capable of suppressing particle breakage and cracking during electrode manufacturing and charge / discharge processes and having excellent rolling density.

[0009] Furthermore, the present invention provides a positive electrode and a lithium secondary battery including the above positive electrode active material, thereby having a low crack rate and thus reducing a side reaction with an electrolyte, which leads to improved high temperature lifespan, output, and high temperature storage characteristics.

[0010] [Technical solution]

[0011] In order to solve the above problems, according to one aspect of the present invention, there is provided a positive electrode active material, comprising: a large-particle lithium nickel-based transition metal oxide and a small-particle lithium nickel-based transition metal oxide, wherein the large-particle lithium nickel-based transition metal oxide is in the form of secondary particles, the secondary particles are aggregates of primary particles, and the small-particle lithium nickel-based transition metal oxide is in the form of at least one of a single particle and a quasi-single particle, the single particle is formed by one nodule, the quasi-single particle is a composite of 30 or less nodule nodes, and wherein the D of the large-particle lithium nickel-based transition metal oxide is 50 is 5 μm to 30 μm, and the Y value defined by the following equation 1 is 2.2 or less:

[0012] [Equation 1]

[0013] Y=I D max / (D FWHM ×R L )

[0014] Among them, I D max and D FWHM is the value obtained from the volume cumulative particle size distribution diagram obtained from the particle size analysis (PSD) of large-particle lithium nickel-based transition metal oxides, where D FWHM is the full width at half maximum (FWHM) of the peak, I D max is the maximum value of the peak, R L refers to the weight ratio of large-particle lithium nickel-based transition metal oxide in the total positive electrode active material and is a rational number greater than 0 and less than 1, where I D max , D FWHM and R L It is a dimensionless number without units.

[0015] In order to solve the above problems, according to another aspect of the present invention, a positive electrode including the positive electrode active material of the present invention is provided.

[0016] In order to solve the above problems, according to another aspect of the present invention, a lithium secondary battery including the positive electrode of the present invention is provided.

[0017] [Beneficial Effects]

[0018] The positive electrode active material for lithium secondary batteries of the present invention includes lithium nickel-based transition metal oxides in the form of single particles and / or quasi-single particles with excellent particle strength, and lithium nickel-based transition metal oxides in the form of secondary particles, wherein the secondary particles are aggregates of primary particles that meet specific particle size and roundness characteristics, thereby reducing the occurrence of particle breakage or cracks caused by rolling when manufacturing electrodes, and achieving excellent rolling density levels.

[0019] In addition, in the positive electrode active material for lithium secondary battery of the present invention, particle crushing can be minimized, thereby reducing the side reaction with the electrolyte and thus reducing the gas production. In addition, during the charging and discharging process, the change of the crystal structure can be minimized, thereby suppressing the degradation of the positive electrode active material and thus improving the high temperature life characteristics and high temperature storage characteristics. In addition, due to the low resistance increase rate, the output characteristics can be excellent. DETAILED DESCRIPTION

[0020] The terms or words used in the specification and claims of this application should not be construed as limited to their ordinary or dictionary meanings, but should be construed as meanings and concepts consistent with the technical spirit of the present invention based on the principle that the inventor can fully define the concepts of the terms to best describe his invention.

[0021] It should be understood that terms such as "include", "comprising" and "having" used herein are intended to indicate the existence of implemented features, numbers, steps, components or a combination thereof, but do not exclude the possibility of the existence or addition of one or more other features, numbers, steps, components or a combination thereof.

[0022] In the present disclosure, a "single particle" is a particle formed by a single nodule. In the present disclosure, a "nodule" refers to a particle unit, which can be a single crystal without crystal grain boundaries, or a polycrystal without obvious grain boundaries when observed using a scanning electron microscope (SEM) at a field of view of 5000 to 20000 times. In the present disclosure, a "quasi-single particle" refers to a particle that is a composite formed by 30 or less nodules.

[0023] In the present disclosure, "secondary particles" refer to particles formed by agglomeration of tens to hundreds of primary particles. More specifically, secondary particles are agglomerates of 50 or more primary particles.

[0024] The term "particle" used in the present disclosure may include any one or all of a single particle, a quasi-single particle, a primary particle, a particle segment, and a secondary particle.

[0025] In this disclosure, “D 50” refers to the particle size of 50% in the volume cumulative particle size distribution of the positive electrode active material powder. The average particle size (or median particle size) D 50 It can be measured using a laser diffraction method. For example, the positive electrode active material powder is dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and irradiated with an ultrasonic wave of about 28 kHz with an output of 60 W. Thereafter, the average particle size can be determined by obtaining a volume cumulative particle size distribution diagram and then obtaining a particle size corresponding to 50% of the volume cumulative amount.

[0026] In the present invention, “aspect ratio” and “roundness” are obtained by using a scanning electron microscope (SEM) to obtain a two-dimensional image of the positive electrode active material particles and using an image analysis program to analyze the particles from the minimum particle size (D min , short diameter), maximum particle size (D max In the present invention, these values ​​refer to the average values ​​of tens to hundreds of particles, preferably 300 particles, and are specifically calculated by the following equations A and B:

[0027] [Equation A]

[0028] Aspect ratio = D min / D max

[0029] [Equation B]

[0030] Roundness = (4 × area) / (π × (D max ) 2 )

[0031] In addition, since the roundness in this specification is a value obtained from a scanning electron microscope image, it is not substantially different from the meaning of "circularity". However, considering the fact that the positive electrode active material particles are three-dimensional particles, the value analyzed as circularity in the image analysis is expressed as circularity.

[0032] Hereinafter, the present invention will be described in more detail.

[0033] Positive electrode active material

[0034] The positive electrode active material of the first embodiment of the present invention comprises: a large-particle lithium nickel-based transition metal oxide and a small-particle lithium nickel-based transition metal oxide, wherein the large-particle lithium nickel-based transition metal oxide is in the form of secondary particles, the secondary particles are aggregates of primary particles, and the small-particle lithium nickel-based transition metal oxide is in the form of at least one of a single particle and a quasi-single particle, the single particle is formed by one particle segment, the quasi-single particle is a composite of 30 or less particle segments, and wherein the D of the large-particle lithium nickel-based transition metal oxide is 50 is 5 μm to 30 μm, and the Y value defined by the following equation 1 is 2.2 or less:

[0035] [Equation 1]

[0036] Y=I D max / (D FWHM ×R L )

[0037] Among them, I D max and D FWHM is the value obtained from the volume cumulative particle size distribution diagram obtained from the particle size analysis (PSD) of large-particle lithium nickel-based transition metal oxides, where D FWHM is the full width at half maximum (FWHM) of the peak, I D max is the maximum value of the peak, R L refers to the weight ratio of large-particle lithium nickel-based transition metal oxide in the total positive electrode active material and is a rational number greater than 0 and less than 1, where I D max , D FWHM and R L It is a dimensionless number without units.

[0038] The present inventors have proposed that by mixing large-particle lithium nickel-based transition metal oxides in the form of secondary particles having advantages in energy density and small-particle lithium nickel-based transition metal oxides in the form of single particles and / or quasi-single particles having reduced particle breakage, the particle characteristics can have advantages in both active material particle breakage and energy density.

[0039] According to one embodiment, in the large-particle lithium nickel-based transition metal oxide, D 50 The maximum value (I D max ) and the peak half-maximum width (D FWHM ) ratio (I D max / DFWHM ) is below 2.20.

[0040] The volume cumulative particle size distribution diagram can be measured using a laser diffraction method. For example, the volume cumulative particle size distribution diagram can be obtained by dispersing a lithium nickel-based transition metal oxide powder in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and irradiating ultrasonic waves of about 28 kHz at an output of 60 W. Through this diagram, D can be measured by obtaining a particle size corresponding to 50% of the volume cumulative amount. 50 , and the maximum value of the peak value (I D max ), full width at half maximum (D FWHM ) and their ratios.

[0041] D of large particle size lithium nickel-based transition metal oxides 50 It may be preferably 7 μm or more, 8 μm or more, 10 μm or more, or 11 μm or more, and may be 27 μm or less, 25 μm or less, 23 μm or less, 21 μm or less, or 20 μm or less. 50 When the above range is satisfied, the possibility of side reactions and gas generation due to particle breakage, as well as capacity and output characteristics problems due to increased energy density and resistance can be prevented.

[0042] In general, the energy density of the positive electrode can be determined by how the positive electrode active material particles are arranged in the positive electrode active material layer according to their particle size characteristics, and therefore, can be determined by how high the rolling density can be increased without damaging the particles when subjected to high rolling pressure. In order to prevent particle rupture and minimize porosity even under high rolling pressure, the strength of the particles must be high, and the good degree to which the small diameter particles are arranged between the large diameter particles is also important. Depending on the ratio of large and small particle sizes, whether the particle size distribution of each particle is wide or narrow, and in which particle size the particles are most distributed (even if the average particle size is the same), the arrangement of the particles can vary, and their ability to withstand high rolling pressures can be correspondingly different.

[0043] In view of this relationship, the Y value in the present invention is defined taking into account the following situation: in the positive electrode active material with a bimodal distribution, large-particle lithium nickel-based transition metal oxides, especially particles in the form of secondary particles, have a particle size characteristic that greatly affects the particle arrangement, and are weaker in strength than small-particle lithium nickel-based transition metal oxides in the form of single particles or quasi-single particles, so particle breakage is prone to occur.

[0044] According to one example, the Y value can be obtained from the following values: the half-height full width and maximum value of the peak obtained from the volume cumulative particle size distribution diagram of the large-particle lithium nickel-based transition metal oxide, and the weight ratio of the large-particle lithium nickel-based transition metal oxide in the total positive electrode active material. The smaller the Y value, the better the energy density of the positive electrode; the smaller the maximum value compared to the half-maximum full width of the peak, the better the energy density; and the smaller the proportion of large-particle particles, the more favorable it can be. In other words, when the particle size distribution of large-particle particles is wider and the proportion of particles corresponding to the average particle size is smaller, it can be considered to be a particle size characteristic that can achieve better performance. However, when the ratio of the maximum value of the peak to the half-maximum full width is too small or the proportion of large-particle particles is too small, a bimodal distribution cannot be displayed. As a result, the rolling density can be determined based on the particle size distribution of small-particle particles, so the Y value needs to be controlled accordingly.

[0045] For example, the Y value may be 2.2 or less, preferably 0.5 to 2.2. More preferably, the lower limit may be 0.7 or more, 0.8 or more, or 1.0 or more, and the upper limit may be 2.1 or less, 2.0 or less, 1.9 or less, 1.8 or less, or 1.7 or less.

[0046] As described above, the Y value can reflect the influence of the ratio of the maximum value of the peak to the full width at half maximum on the particle size characteristics of large diameter particles in the mixed active material. If the Y value is less than 0.5, the width of the peak is relatively wide and the maximum value is small, so that even in large particle size particles, the ratio of large particles with large particle size to small particles with small particle size is also high, which may lead to electrode durability problems. In addition, this can be combined with the particle size distribution of small diameter lithium nickel-based transition metal oxides, resulting in a particle size distribution shift from a bimodal distribution to a unimodal distribution. In this case, the movement path of lithium may be adversely affected, and particle crushing may occur during rolling because the proportion of large diameter particles may be relatively high. When the Y value is greater than 2.2, the width of the peak is relatively narrow and the maximum value is large, so the proportion of large diameter particles is relatively small, and the arrangement structure of the particles is poor, so the porosity may increase, thereby reducing the energy density. Therefore, in order to suppress problems such as energy density and gas generation, it is necessary to control the particle size characteristics to meet the above range.

[0047] According to one embodiment, R L It may be 0.4 to 0.9, and the Y value may be meaningful when the proportion of large-size particles contained is about 40 wt % to 90 wt %, preferably 45 wt % or more, 50 wt % or more, or 55 wt % or more.

[0048] According to one embodiment, I D max / D FWHMIt may be 0.5 to 3.0. Preferably, the ratio of the maximum value to the full width at half maximum is small, but in order to achieve a high rolling pressure in a positive electrode active material having a bimodal particle size distribution, it should be greater than 0.5, and may preferably be less than 3.0. More preferably, it may be 0.6 or more, 0.7 or more, 2.5 or less, 2.0 or less, 1.5 or less, or 1.3 or less.

[0049] The positive electrode active material of the second embodiment of the present invention comprises: a large-particle lithium nickel-based transition metal oxide and a small-particle lithium nickel-based transition metal oxide, wherein the large-particle lithium nickel-based transition metal oxide is in the form of secondary particles, the secondary particles are aggregates of primary particles, and the small-particle lithium nickel-based transition metal oxide is in the form of at least one of a single particle and a quasi-single particle, the single particle is formed by one particle segment, the quasi-single particle is a composite of 30 or less particle segments, and wherein the D of the large-particle lithium nickel-based transition metal oxide is 50 is 5 μm to 30 μm, the Z value defined by the following Equation 2 is 1.0 to 9.0, and the negative skewness factor (NSF) defined by the following Equation 3 is 0.1 to 0.9.

[0050] [Equation 2]

[0051] Z=F R max / S R

[0052] Among them, F R max and S R- The value obtained by dividing the circularity into units of 0.05 and plotting a histogram with the number of particles as the frequency in the circularity dispersion diagram of the large-particle lithium nickel-based transition metal oxide obtained by scanning electron microscopy (SEM) and image analysis program, where F R max is the maximum frequency circularity ratio (modal circularity ratio), which is the value obtained by dividing the number of particles of the category (circularity) with the highest frequency (number of particles) by the total number of particles analyzed, and S R is the standard deviation of roundness.

[0053] [Equation 3]

[0054] NSF=(R 50 -R 10 ) / F R max

[0055] Among them, F R max , R 50 and R 10The value obtained by dividing the circularity into units of 0.05 and plotting a histogram with the number of particles as the frequency in the circularity dispersion diagram of the large-particle lithium nickel-based transition metal oxide obtained by scanning electron microscopy (SEM) and image analysis program, where F R max is the maximum frequency circularity ratio (modal circularity ratio), which is the value obtained by dividing the number of particles of the category (circularity) with the highest frequency (number of particles) by the total number of particles analyzed, R 50 is the circularity at the point where the cumulative frequency is 50%, R 10 is the circularity at the point where the cumulative frequency is 10%.

[0056] At the same time, the roundness of the positive electrode active material particles affects the ease of particle crushing and can also affect the particle filling capacity because the particle arrangement structure can change according to the roundness. Generally, when the roundness increases, that is, when the particles are closer to spherical, the damage to the particles can be reduced, but the closer to spherical particles may be more disadvantageous in terms of the filling capacity of the particles.

[0057] Therefore, the present invention proposes a roundness characteristic of particles that can improve electrode performance due to small particle breakage while improving energy density without damaging the particles even at high rolling density.

[0058] According to one embodiment, for large-particle lithium nickel-based transition metal oxides, a histogram of roundness dispersion is obtained, and the Z value and NSF value can be defined by the values ​​obtained from the distribution. Specifically, the Z value is defined as the ratio of the "maximum frequency roundness ratio" to the standard deviation of the roundness, and the "maximum frequency roundness ratio" is a value representing the ratio of the most distributed roundness to the overall roundness value. This value can mean: the smaller the value, the more likely it is to show favorable performance. Specifically, the larger the standard deviation and the smaller the maximum frequency roundness ratio, the more the particle breakage can be reduced even at high rolling density. However, even in this case, if the standard deviation is too small or the maximum frequency roundness ratio is too large, the filling of the particles cannot be dense, and there may be a problem of reduced energy density, so they need to be controlled at appropriate values.

[0059] According to one embodiment, the Z value on the roundness distribution histogram of the large particle size lithium nickel-based transition metal oxide may be 1.0 to 9.0, preferably 1.5 to 8.5. More preferably, the lower limit may be 1.7 or more, 2.0 or more, or 2.5 or more, and the upper limit may be 8.0 or less, 7.5 or less, or 7.0 or less. When the Z value satisfies the above range, the particle shape can be optimized, and thus the particle breakage is reduced to reduce the possibility of side reactions, thereby preventing a reduction in life or output.

[0060] In addition, the negative skewness factor (NSF) of the large particle size lithium nickel-based transition metal oxide defined by the above Equation 3 may be 0.1 to 0.9.

[0061] The negative skewness coefficient of roundness is intended to take into account that performance cannot be achieved simply by satisfying the values ​​of the standard deviation and the maximum frequency roundness ratio on the roundness distribution histogram, and if there are many particles with too low roundness, particle breakage is more likely to occur. This means that it can be considered desirable that the graph shows a tendency to shift to the right. In other words, when the peak migrates to the right at an appropriate level, the volume fraction increases on the side with higher roundness, resulting in the effect of obtaining stable performance in terms of particle strength and the amount of fine powder produced. Therefore, preferably, the negative skewness coefficient may be 0.15 or more, 0.2 or more, or 0.25 or more, and may be 0.8 or less, 0.7 or less, or 0.6 or less.

[0062] Furthermore, according to one embodiment, the standard deviation of roundness (S R ) can be 0.05 to 0.2, preferably 0.06 or more, and can also be 0.15 or less, 0.13 or less, or 0.1 or less. In addition, the maximum frequency roundness ratio (F r max ) can be 0.1 to 0.5, preferably 0.15 or more, 0.20 or more, or 0.22 or more, and can also be 0.45 or less, 0.40 or less, or 0.35 or less.

[0063] According to the first and second embodiments of the present invention, the positive electrode active material including the large particle size lithium nickel-based transition metal oxide and the small particle size lithium nickel-based transition metal oxide may have an aspect ratio of 0.60 to 0.99 and a circularity of 0.60 to 0.99. Here, the aspect ratio and the circularity may be values ​​obtained by using an image analysis program on an image obtained by photographing the positive electrode active material particles with a scanning electron microscope, and may be an average value of about 300 or more particles.

[0064] The aspect ratio of the positive electrode active material may be 0.65 or more, 0.70 or more, 0.75 or more, 0.78 or more, or 0.80 or more, and may be 0.98 or less. In addition, the roundness may be 0.65 or more, 0.70 or more, 0.75 or more, 0.78 or more, or 0.80 or more, and may be 0.98 or less. When the aspect ratio and roundness of the positive electrode active material satisfy the above ranges, the particle characteristics of the mixed active material may be more easily controlled, thereby improving performance.

[0065] According to the first and second embodiments of the present invention, the mixing weight ratio of the large particle size lithium nickel-based transition metal oxide to the small particle size lithium nickel-based transition metal oxide can be from 90:10 to 30:70. Preferably, it can be 85:15 or less, or 80:20 or less, and can be 35:75 or more, 40:60 or more, 50:50 or more, or 60:40 or more. If this mixing range is satisfied, particle breakage can be reduced, and the roll pressing density can be increased.

[0066] Meanwhile, the positive electrode active materials of the first and second embodiments of the present invention may include large particle size and small particle size lithium nickel-based transition metal oxides, and each of them may independently include a lithium nickel-based transition metal oxide having a composition shown in Chemical Formula 1 below:

[0067] [Chemical Formula 1]

[0068] Li 1+x Ni a Co b M 1 c M 2 d O 2-e X e

[0069] Wherein, M 1 includes one or more selected from Mn and Al; M 2 includes one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb; X includes one or more selected from the group consisting of N, P, S, F, and Cl; -0.1 ≤ x ≤ 0.5, 0.5 ≤ a < 1, 0 < b ≤ 0.4, 0 < c ≤ 0.4, 0 ≤ d ≤ 0.05, and 0 ≤ e ≤ 0.05.

[0070] In the above Formula 1, M 1 is Mn, Al, or a combination thereof, preferably Mn or a combination of Mn and Al; M 2 can be at least one selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, and is preferably at least one selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. The M 2 element is not necessarily included, but when included in an appropriate amount, it can play a role in promoting grain growth or improving crystal structure stability during calcination. In addition, X is an anion substituting for the oxygen site and can include N, P, S, F, or Cl.

[0071] 1 + x represents the molar ratio of lithium in the lithium nickel-based transition metal oxide, and can be -0.10 ≤ x ≤ 0.30, -0.10 ≤ x ≤ 0.20 or -0.10 ≤ x ≤ 0.15.

[0072] a represents the molar ratio of nickel among all metals other than lithium in the lithium nickel-based transition metal oxide, and can be 0.60 ≤ a < 1.00, 0.70 ≤ a < 1.00, 0.75 ≤ a ≤ 0.99, 0.80 ≤ a ≤ 0.99, 0.82 ≤ a ≤ 0.99, 0.84 ≤ a ≤ 0.99 or 0.86 ≤ a ≤ 0.99. Here, the value of a, i.e., the content of nickel in the transition metal, can be 60 mol% or more, preferably 70 mol% or more, or 75 mol% or more. The higher the nickel content and the lower the cobalt content, the more problematic the amount of gas generated and the capacity retention rate may be. However, when the roundness characteristics and / or particle size characteristics are satisfied, particle breakage can be reduced and the roll pressing density can be increased, resulting in slightly more synergistic effects, because the positive electrode active material with a high nickel content has high capacity and high output characteristics, but the disadvantages can be offset.

[0073] b represents the molar ratio of cobalt among all metals other than lithium in the lithium nickel-based transition metal oxide, and can be 0 < b < 0.30, 0.001 ≤ b < 0.25, 0.001 ≤ b < 0.20 or 0.001 ≤ b ≤ 0.15.

[0074] c represents the molar ratio of M 1 among all metals other than lithium in the lithium nickel-based transition metal oxide, and can be 0 < c < 0.30, 0.01 ≤ c < 0.25, 0.01 ≤ c < 0.20 or 0.01 ≤ c ≤ 0.15.

[0075] d represents the molar ratio of the M 2 element among all metals other than lithium in the lithium nickel-based transition metal oxide, and can be 0 ≤ d ≤ 0.05, 0 ≤ d ≤ 0.02 or 0 ≤ d ≤ 0.01.

[0076] e represents the molar ratio of element X among all non-metals other than oxygen in the lithium nickel-based transition metal oxide, and can be 0 ≤ e ≤ 0.05, 0 ≤ e ≤ 0.02 or 0 ≤ e ≤ 0.01.

[0077] Meanwhile, the lithium nickel-based transition metal oxide may also include a coating on the particle surface, and the coating contains one or more coating elements selected from Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si and S.

[0078] When the coating layer is present on the surface of the lithium nickel-based transition metal oxide particles, contact between the electrolyte and the lithium nickel-based transition metal oxide can be suppressed by the coating layer, thereby having the effect of reducing transition metal elution or gas generation caused by a side reaction with the electrolyte.

[0079] Preferably, the coating layer may include Co as a coating element. When the coating layer containing Co is formed on the surface of lithium nickel-based transition metal oxide particles in the form of single particles and / or quasi-single particles, the effect of improving output and the effect of suppressing side reactions with electrolytes may be obtained.

[0080] The cathode active material of the third embodiment of the present invention is characterized by including the characteristics of both the cathode active material of the first embodiment and the cathode active material of the second embodiment.

[0081] In this case, in the positive electrode active material in which large and small particle sizes having bimodal particle size characteristics are mixed, only particles having precisely controlled particle size and roundness characteristics can be applied, so that the rolling density can be increased by withstanding high rolling pressure without particle breakage. As a result, a high energy density positive electrode can be realized in which the resistance increase rate can be minimized by reducing the generation of fine powder and the life can be improved.

[0082] Method for producing positive electrode active material

[0083] Next, a method for producing the cathode active material of the present invention will be described.

[0084] The method for manufacturing the positive electrode active material of the present invention comprises the following steps: (S1) adding a 1 A transition metal solution containing cations of the present invention, an alkaline aqueous solution and an ammonium solution are mixed and coprecipitated to prepare a positive electrode active material precursor; and (S2) the positive electrode active material precursor and a lithium raw material are mixed and heat-treated to prepare a positive electrode active material.

[0085] In addition, by the conditions of the coprecipitation reaction and the firing conditions (such as the firing temperature and time of the lithium raw material and the precursor), the manufactured positive electrode active material can be in the form of a single particle (formed by one grain segment) or a quasi-single particle (a composite of 30 or less grain segments), or in the form of a secondary particle (an aggregate of primary particles). The positive electrode active material of the present invention can be obtained by separately preparing a large-particle lithium nickel-based transition metal oxide and a small-particle lithium nickel-based transition metal oxide and then mixing them, or by firing each of them and then mixing them for coating.

[0086] Hereinafter, each step of the method of manufacturing the positive electrode active material will be described in detail.

[0087] First, a material containing nickel (Ni), cobalt (Co) and M is prepared. 1 For example, the transition metal solution may include a nickel-containing raw material, a cobalt-containing raw material, and a M-containing raw material. 1 Raw materials, including M 1 The raw material may be a manganese-containing raw material and / or an aluminum-containing raw material.

[0088] Thereafter, a positive electrode active material precursor may be prepared by adding a complex forming agent containing ammonium cations and an alkaline aqueous solution to the transition metal solution and performing a coprecipitation reaction.

[0089] The nickel-containing raw material can be, for example, nickel-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, hydroxy oxides, etc., in particular, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, fatty acid nickel, nickel halides or combinations thereof, but are not limited thereto.

[0090] The cobalt-containing raw material can be a cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxyl, etc., especially Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, Co(SO4)2·7H2O or a combination thereof, but is not limited thereto.

[0091] The manganese-containing raw material can be, for example, manganese-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, oxyhydroxides or combinations thereof, specifically manganese oxides, such as Mn2O3, MnO2, Mn3O4, etc.; manganese salts, such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, dicarboxylic acid manganese salts, manganese citrate, fatty acid manganese salts; manganese oxyhydroxides, manganese chloride, or combinations thereof, but are not limited thereto.

[0092] The aluminum-containing raw material can be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3, aluminum halides, or combinations thereof.

[0093] The transition metal solution can be prepared by mixing a nickel-containing raw material, a cobalt-containing raw material and a M-containing raw material. 1 The raw materials are added to a solvent for preparation, wherein the solvent is particularly water, or a mixed solvent of water and an organic solvent (such as alcohol) that can be uniformly mixed with water, or an aqueous solution containing a nickel raw material, an aqueous solution containing a cobalt raw material and an aqueous solution containing M 1 Raw materials to prepare.

[0094] The complex forming agent containing ammonium cations can be, for example, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, (NH4)2CO3 or a combination thereof, but is not limited thereto. Meanwhile, the complex forming agent containing ammonium cations can be used in the form of an aqueous solution, wherein the solvent can be water, or a mixture of water and an organic solvent (specifically, alcohol, etc.) uniformly miscible with water.

[0095] The basic compound can be an alkali metal or alkaline earth metal hydroxide, such as NaOH, KOH or Ca (OH) 2, a hydrate thereof, or a combination thereof. The basic compound can also be used in the form of an aqueous solution, wherein the solvent can be water, or a mixture of water and an organic solvent (particularly, alcohol, etc.) uniformly miscible with water.

[0096] The basic compound is added to adjust the pH of the reaction solution, and the amount thereof added may be such that the pH of the metal solution is 8 to 12.

[0097] The coprecipitation reaction can be carried out at a temperature of 35°C to 80°C under an inert atmosphere such as nitrogen or argon.

[0098] Thus, it is possible to prepare a 1 A positive electrode active material precursor of a cation.

[0099] By the above method, nickel-cobalt-M 1 The hydroxide positive electrode active material precursor particles are precipitated in the reaction solution. By controlling the nickel-containing raw material, the cobalt-containing raw material and the M-containing raw material 1 The concentration of the raw materials can be such that the positive electrode active material precursor has a nickel (Ni) content of 70 mol % or more, 75 mol % or more, preferably 80 mol % or more, and more preferably 82 mol % or more in the total metal content. The precipitated positive electrode active material precursor particles can be separated and dried according to conventional methods to produce a positive electrode active material precursor.

[0100] Thereafter, the positive electrode active material precursor and the lithium raw material are mixed and heat-treated.

[0101] The lithium raw material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide, but is not particularly limited as long as it is soluble in water. Specifically, the lithium raw material may be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi or Li3C6H5O7, and any one or a mixture of two or more thereof may be used.

[0102] The positive electrode active material precursor and the lithium raw material may be mixed in a molar ratio of 1:1 to 1:1.30. The positive electrode active material precursor and the lithium raw material may be mixed in a molar ratio of, for example, about 1:1, about 1:1.05, about 1:1.07, about 1:1.10, about 1:1.5, about 1:1.20, or about 1:1.30, but is not limited thereto.

[0103] In the case of a high Ni-type NCM-based lithium composite transition metal oxide having a nickel (Ni) content of 70 mol % or more, the heat treatment may be performed at a temperature of 630° C. to 1000° C. The heat treatment may be preferably performed, for example, at a temperature of 630° C. to 925° C., and more preferably at a temperature of 630° C. to 910° C. The formation of the positive electrode active material powder in the form of a single particle and / or a quasi-single particle is affected by the heat treatment temperature conditions.

[0104] Therefore, the manufactured positive electrode active material can have reduced particle breakage and crystal structure strain during a roll-pressing process or during charging and discharging of a lithium secondary battery including the same, and can have improved initial resistance characteristics.

[0105] Heat treatment can be carried out in air or oxygen atmosphere for example 4 to 12 hours. Specifically, heat treatment can be carried out for example more than 4 hours, more than 6 hours, more than 8 hours, more than 10 hours, can be carried out for less than 12 hours, less than 10 hours, less than 8 hours, and less than 6 hours.

[0106] At the same time, when preparing 2 When a lithium nickel-based transition metal oxide containing a metal or a lithium nickel-based transition metal oxide containing a non-metal (e.g., X) for anion substitution at an oxygen site is to be prepared, a catalyst containing M may be additionally mixed during the coprecipitation reaction or in the firing step. 2 Metal raw materials and / or raw materials containing element X. In this case, the raw materials containing M 2 The raw material of metal can be M 2 The raw material containing the element X can be a lithium salt of X or an acid containing X.

[0107] On the other hand, when it is necessary to form a coating on the surface of the lithium nickel-based transition metal oxide, after the above-mentioned heat treatment, the following steps may be further performed: the lithium nickel-based transition metal oxide prepared by the heat treatment is mixed with the coating raw material, and then the two are heat-treated. In this case, the mixing may be performed by solid phase mixing or liquid phase mixing, and the heat treatment may be performed at an appropriate temperature according to the coating raw material. For example, the heat treatment of the coating process may be performed at a temperature of 200°C to 700°C or 300°C to 600°C, but is not limited thereto.

[0108] In addition, when the positive active material powder of the present invention is manufactured, it is preferred that no water washing treatment is performed after the heat treatment. Conventionally, when a high nickel (Ni) type NCM-based lithium composite transition metal oxide is manufactured, a water washing process is generally performed after the heat treatment to reduce the content of lithium by-products. However, according to the research of the present inventors, it has been found that when a water washing process is performed in the production of lithium nickel-based transition metal oxides in the form of single particles and / or quasi-single particles, the surface properties of the lithium nickel-based transition metal oxide deteriorate during water washing, and thus the resistance increases. Therefore, when the positive active material powder of the present invention is manufactured, it is preferred not to perform water washing, but to consume the remaining lithium on the surface of the lithium nickel-based transition metal oxide by a coating formation process. In this way, when the positive active material is manufactured without cleaning the lithium nickel-based transition metal oxide, the increase in resistance caused by surface defects can be suppressed.

[0109] The positive electrode active materials of the first to third embodiments of the present invention can be manufactured according to the above-mentioned manufacturing method. During the production process, the particle size distribution or circularity distribution can be adjusted by controlling the conditions in the coprecipitation reaction or the firing reaction. After the reaction is completed, these distributions can be controlled by a pulverization process and / or a classification process.

[0110] positive electrode

[0111] The positive electrode of the present invention comprises the positive electrode active material of the present invention as described above. Specifically, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material powder of the present invention. Since the positive electrode active material powder has been described above, its detailed description will be omitted, and only the remaining components will be described in detail below.

[0112] The positive electrode current collector may include a highly conductive metal, and there is no particular limitation, as long as the positive electrode active material layer can be easily adhered thereto and is not reactive within the voltage range of the battery. The positive electrode current collector may be, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium or silver. Moreover, the positive electrode current collector may generally have a thickness of 3 μm to 500 μm, and microscopic irregularities may be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. The positive electrode current collector may be used, for example, in various shapes, such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabrics.

[0113] If necessary, the positive electrode active material layer may optionally include a conductive material and a binder in addition to the positive electrode active material powder.

[0114] In this case, the positive electrode active material powder may be contained in an amount of 80 wt % to 99 wt %, more specifically 85 wt % to 98.5 wt %, based on the total weight of the positive electrode active material layer, and when included within the above content range, excellent capacity characteristics may be exhibited.

[0115] The conductive material is used to provide conductivity to the electrode, and any conductive material can be used without particular limitation, as long as it has electronic conductivity and does not cause chemical changes in the battery. Specific examples of conductive materials may include: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one thereof or a mixture of two or more thereof may be used. The content of the conductive material may be 0.1 wt % to 15 wt % based on the total weight of the positive electrode active material layer.

[0116] Binder is used to improve the adhesion between positive active material particles and the adhesion between positive active material and current collector. Specific examples of binders may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, hydrogen is replaced by Li, Na or Ca these polymers or its various copolymers, and one or more mixtures thereof can be used. Based on the gross weight of the positive active material layer, the content of the binder may be 0.1 wt % to 15 wt %.

[0117] In addition to using the above-mentioned positive electrode active material powder, the positive electrode can be prepared according to a conventional positive electrode preparation method. Specifically, the above-mentioned positive electrode active material powder and, if necessary, a binder, a conductive material and a dispersant can be dissolved or dispersed in a solvent to prepare a positive electrode slurry composition, which can be coated on a positive electrode current collector, and then dried and rolled to prepare a positive electrode.

[0118] The solvent may be any solvent commonly used in the art, for example, any one or a mixture of two or more of dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone or water may be used. The amount of the solvent may be sufficient to dissolve or disperse the positive electrode active material, conductive material, binder and dispersant (considering the coating thickness and manufacturing yield of the slurry), and the viscosity of the slurry is allowed to exhibit excellent thickness uniformity in the subsequent coating process of preparing the positive electrode.

[0119] Alternatively, the positive electrode may be prepared by casting the positive electrode slurry composition on a separate support and then laminating a film peeled off from the support on a positive electrode current collector.

[0120] Electrochemical Devices

[0121] Next, the electrochemical device of the present invention will be described. The electrochemical device of the present invention includes the above-mentioned positive electrode of the present invention. Specifically, the electrochemical device may be a battery, a capacitor, etc., and more specifically, may be a lithium secondary battery.

[0122] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode disposed opposite to the positive electrode, and a separator and an electrolyte disposed between the positive electrode and the negative electrode. Since the positive electrode is the same as above, its detailed description is omitted, and only the remaining components will be described in detail below.

[0123] In addition, the lithium secondary battery may optionally further include a battery container that accommodates an electrode assembly formed of a positive electrode, a negative electrode, and a separator, and a sealing member that seals the battery container.

[0124] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0125] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surface-treated with carbon, nickel, titanium or silver, or aluminum-cadmium alloy can be used. In addition, the negative electrode current collector can generally have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, microscopic irregularities can be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. The negative electrode current collector can be used in various shapes, such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabrics.

[0126] The negative electrode active material layer may optionally include a binder and a conductive material in addition to the negative electrode active material.

[0127] As the negative electrode active material, a compound capable of reversibly inserting and deinserting lithium can be used. Specific examples thereof may be: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal substances capable of alloying with lithium, such as silicon 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), SnO2, vanadium oxide and lithium vanadium oxide; or a composite comprising the metal substance and a carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one thereof or a mixture of two or more thereof can be used. In addition, a metallic lithium film can be used as a negative electrode active material. In addition, low-crystalline carbon and high-crystalline carbon, etc. can be used as carbonaceous materials. Common examples of low-crystalline carbon can be soft carbon and hard carbon, and common examples of high-crystalline carbon can be irregular, planar, flaky, spherical or fibrous natural graphite or artificial graphite, floating (Kish) graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch and high-temperature sintered carbon, such as coke derived from petroleum or coal tar pitch.

[0128] The negative electrode active material may be contained in an amount of 80 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0129] The binder is a component that helps to bind the conductive material, the active material and the current collector, wherein the binder is generally added in an amount of 0.1 wt % to 10 wt % based on the total weight of the negative electrode active material layer. Examples of binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber and various copolymers thereof.

[0130] The conductive material is a component for further improving the conductivity of the negative electrode active material, wherein the amount of the conductive material added may be 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery, and may be, for example: graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers, such as carbon fibers and metal fibers; carbon fluoride; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive materials such as polyphenylene derivatives.

[0131] The negative electrode active material layer can be prepared by dissolving or dispersing the negative electrode active material and optional binder and conductive material in a solvent to form a negative electrode slurry composition, coating the slurry composition on the negative electrode collector and drying. Alternatively, the negative electrode active material layer can be prepared by casting the negative electrode slurry composition on a separate support, and then laminating the film peeled off from the support on the negative electrode collector.

[0132] Meanwhile, in lithium secondary batteries, the separator separates the negative electrode from the positive electrode and provides a path for the movement of lithium ions, and any separator can be used without particular limitation, as long as it is generally used as a separator in lithium secondary batteries. In particular, it is preferred to use a separator having excellent moisture retention ability to the electrolyte and low resistance to the transmission of electrolyte ions. Specifically, a porous polymer film can be used, for example, a porous polymer film made of a polyolefin polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer), or a laminated structure having more than two layers of the above-mentioned polymer can be used. Moreover, common porous nonwoven fabrics can be used, for example, nonwoven fabrics formed of high melting point glass fiber or polyethylene terephthalate fiber. In addition, a coated separator including a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a separator having a monolayer or multilayer structure can be selectively used.

[0133] In addition, the electrolyte used in the present invention may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte or a molten inorganic electrolyte that can be used to prepare a lithium secondary battery, but the present invention is not limited thereto.

[0134] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0135] Any solvent can be used as an organic solvent without particular limitation, as long as it can be used as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, the organic solvent can be: an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone and ε-caprolactone; an ether solvent such as dibutyl ether or tetrahydrofuran; a ketone solvent such as cyclohexanone; an aromatic hydrocarbon solvent such as benzene and fluorobenzene; or a carbonate solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) and propylene carbonate (PC); an alcohol solvent such as ethanol and isopropanol; a nitrile such as R-CN (wherein R is a linear, branched or cyclic C2 to C20 hydrocarbon group, and may include a double bond aromatic ring or an ether bond); an amide such as dimethylformamide; a dioxolane such as 1,3-dioxolane; or a sulfolane. Among these solvents, carbonate solvents are preferred, and a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) having high ion conductivity and high dielectric constant and low viscosity chain carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) which can improve the charge / discharge performance of the battery is more preferably used.

[0136] The lithium salt may be any compound without particular limitation as long as it can provide lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt may be selected from F - , Cl - Br - ,I - 、NO3 - 、N(CN)2 - 、BF4 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N -At least one of the group consisting of, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, LiB(C2O4)2, etc. The lithium salt is preferably used in a concentration of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, thereby excellent electrolyte performance can be exhibited, and lithium ions can be efficiently moved.

[0137] In order to improve the life characteristics of the battery, suppress the reduction of the battery capacity and increase the discharge capacity of the battery, in addition to the above-mentioned electrolyte components, the electrolyte may also include at least one additive, for example, halogenated alkylene carbonate compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidinones, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol or aluminum chloride. In this case, based on the total weight of the electrolyte, the content of the additive may be 0.1 wt % to 5 wt %.

[0138] Example

[0139] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in various forms and is not limited to the embodiments described herein.

[0140] Example 1

[0141] Preparation of large-particle lithium nickel-based transition metal oxide, the Ni:Co:Mn molar ratio of which is 8:1:1, is a secondary particle powder, which is an aggregate of primary particles, with an average particle size of D 50 is 14.8μm, and I D max and D FWHM The values ​​are shown in Table 1. Preparation of small-particle lithium nickel-based transition metal oxide, the Ni:Co:Mn molar ratio of which is 8:1:1, is a single particle and quasi-single particle powder, and the average particle size D 50 The large-particle size and small-particle size lithium nickel-based transition metal oxides were mixed in a weight ratio of 5:5 to prepare a positive electrode active material having a bimodal particle size distribution.

[0142] Example 2

[0143] A positive electrode active material was prepared in the same manner as in Example 1, except that it had a particle size characteristic as shown in Table 1 below, and the large particle size lithium nickel-based transition metal oxide and the small particle size lithium nickel-based transition metal oxide were mixed in a weight ratio of 8:2.

[0144] Example 3

[0145] The positive electrode active material was prepared in the same manner as in Example 1, except that it had the particle size characteristics shown in Table 1 below, and the average particle size D of the large-particle lithium nickel-based transition metal oxide was 50 It is 11.9μm.

[0146] Example 4

[0147] The positive electrode active material was prepared in the same manner as in Example 3, except that it had a particle size characteristic as shown in Table 1 below, and the large particle size lithium nickel-based transition metal oxide and the small particle size lithium nickel-based transition metal oxide were mixed in a weight ratio of 6:4.

[0148] Comparative Example 1

[0149] The positive electrode active material was prepared in the same manner as in Example 3, except that it had a particle size characteristic as shown in Table 1 below, and the large particle size lithium nickel-based transition metal oxide and the small particle size lithium nickel-based transition metal oxide were mixed in a weight ratio of 8:2.

[0150] Comparative Example 2

[0151] A positive electrode active material was prepared in the same manner as in Example 3, except that it had a particle size characteristic as shown in Table 1 below, and only a large particle size lithium nickel-based transition metal oxide was used without using a small particle size lithium nickel-based transition metal oxide.

[0152] Experimental Example 1: Particle size characteristics of positive electrode active materials

[0153] For the positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 and 2, the active material powder was dispersed in a dispersion medium using a laser diffraction method, and then introduced into a laser diffraction particle size measuring device (Microtrac MT 3000), and irradiated with ultrasonic waves of about 28 kHz with an output of 60 W. Thereafter, a volume cumulative particle size distribution diagram was obtained to give the values ​​shown in Table 1 below.

[0154] [Table 1]

[0155]

[0156] Experimental Example 2: Evaluation of positive electrode performance

[0157] The rolling density (g / cm2) of each positive electrode active material prepared in Examples 1 to 4 and Comparative Examples 1 to 2 was measured using a densitometer (Caver Pellet Press). 3 Specifically, 3 g of each positive electrode active material prepared in the above-mentioned embodiments and comparative examples was subdivided and densely packed into a cylindrical support with a diameter of 13 mm, and then a pressure of 9 tons was applied to measure the rolling density (g / cm 3 ). The results are shown in Table 2 below.

[0158] In addition, for an area of ​​1 μm or less, a pressure of 6 tons was applied to the positive electrode active material using a caver pellet press, and then the amount of fine powder generated (volume %) was calculated using the value obtained from the particle size analysis (PSD).

[0159] [Table 2]

[0160] <![CDATA[Rolled density (g / cm 3 )]]> Amount of fine powder produced (volume %) Example 1 3.53 0 Example 2 3.44 2.37 Example 3 3.43 0 Example 4 3.42 0 Comparative Example 1 3.37 4.93 Comparative Example 2 3.19 7.82

[0161] Referring to Table 2, it can be seen that the rolling density of the embodiment satisfying the Y value is better than the rolling density of Comparative Examples 1 and 2, and the amount of fine powder generated is also significantly higher. The above evaluation is not performed on the actually manufactured positive electrode, but is performed by providing the same environment as the actual environment for manufacturing the positive electrode, and can therefore be basically regarded as the positive electrode performance.

[0162] Experimental Example 3: Evaluation of high temperature performance

[0163] A single cell including a positive electrode and a negative electrode was manufactured. In the case of the positive electrode, 95 wt % of each positive electrode active material prepared in Examples 1 to 4 and Comparative Examples 1 and 2, 3 wt % of PVDF and 2 wt % of carbon black were mixed in a solvent to prepare a slurry, which was applied to a current collector and dried to prepare a positive electrode. Natural graphite and artificial graphite were mixed in a ratio of 5:5 as negative electrode active materials, and a negative electrode was prepared using a mixture of 95.8 wt % of negative electrode active materials, 0.5 wt % of carbon black and 3.7 wt % of CMC and SBR. The loading amount of the negative electrode was 10.7 mg / cm 2 , the N / P ratio of the negative and positive electrodes was fixed at 1.08.

[0164] The capacity retention rate (%) of the single cell including the positive electrode active material powder of Examples 1a to 4a and Comparative Examples 1a to 2a was measured after 30 cycles at a temperature of 45°C. When the life was evaluated under the above method and conditions, the voltage and current during discharge were used to calculate the resistance ((V0-V1) / I, where V0 is the discharge start voltage, V1 is the voltage after 60 seconds of discharge, and I is the applied current), and the resistance increase rate was calculated using the resistance after the cycle compared to the initial resistance. The results are shown in Table 3 below.

[0165] [Table 3]

[0166] Capacity retention rate at 45°C (%) Resistance increase rate at 45°C (%) Example 1 94.4 90.3 Example 2 93.6 93.7 Example 3 94.8 97.5 Example 4 93.4 98.7 Comparative Example 1 91.6 128.8 Comparative Example 2 90.2 143.5

[0167] Referring to Table 3 above, it can be seen that the life characteristics are also affected by whether the Y value is satisfied, but the resistance characteristics are greatly affected by it. In addition, considering that although the battery life of 30 cycles is relatively early, the increase in resistance is already significant, it can be expected that there will be a significant difference in the effect when considering the entire long-term performance.

Claims

1. A positive electrode active material comprising: Large particle size lithium nickel-based transition metal oxides and small particle size lithium nickel-based transition metal oxides, in, The large-particle-size lithium nickel-based transition metal oxide is in the form of secondary particles, which are aggregates of primary particles. The small-particle lithium nickel-based transition metal oxide is in the form of at least one of a single particle and a quasi-single particle, wherein the single particle is formed by one particle segment, and the quasi-single particle is a composite of 30 or less particle segments, and Wherein, the D of the large-particle lithium nickel-based transition metal oxide 50 is 5 μm to 30 μm, and the Y value defined by the following equation 1 is 2.2 or less: [Equation 1] Y=I D max / (D FWHM ×R L ) Among them, I D max and D FWHM is the value obtained from the volume cumulative particle size distribution diagram obtained from the particle size analysis (PSD) of large-particle lithium nickel-based transition metal oxides, where D FWHM is the full width at half maximum (FWHM) of the peak, I D max is the maximum value of the peak, R L refers to the weight ratio of large-particle lithium nickel-based transition metal oxide in the total positive electrode active material and is a rational number greater than 0 and less than 1, where I D max , D FWHM and R L It is a dimensionless number without units. 2 . The positive electrode active material as claimed in claim 1 , wherein the value of Y is 0.7 to 2.

0.

3. The positive electrode active material according to claim 1, wherein R L It is 0.4 to 0.

9.

4. The positive electrode active material according to claim 1, wherein D max / D FWHM 0.5 to 3.

0.

5. The positive electrode active material according to claim 1, wherein The mixing weight ratio of the large-particle lithium nickel-based transition metal oxide to the small-particle lithium nickel-based transition metal oxide is 9:1 to 3:

7.

6. The positive electrode active material according to claim 1, wherein The positive electrode active material has an aspect ratio of 0.60 to 0.99 and a circularity of 0.60 to 0.

99.

7. The positive electrode active material according to claim 1, wherein The large-particle lithium nickel-based transition metal oxide and the small-particle lithium nickel-based transition metal oxide are each independently represented by the following Chemical Formula 1: [Chemical formula 1] Li 1+x Ni a Co b M 1 c M 2 d O 2-e X e Among them, M 1 includes one or more selected from Mn and Al; M 2 includes one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, V, Mg, Ta, and Nb; X includes one or more selected from the group consisting of N, P, S, F, and Cl; 0 ≤ x ≤ 0.5, 0.5 ≤ a < 1, 0 < b ≤ 0.4, 0 < c ≤ 0.4, 0 ≤ d ≤ 0.05, and 0 ≤ e ≤ 0.

05.

8. The positive electrode active material according to claim 1, wherein The nickel content in the transition metal of the large-particle lithium nickel-based transition metal oxide and the small-particle lithium nickel-based transition metal oxide is independently 70 mol % or more. 9 . A positive electrode comprising the positive electrode active material according to claim 1 . 10 . A lithium secondary battery comprising the positive electrode according to claim 9 .

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