Positive electrode active material, and positive electrode and lithium secondary battery containing the same

Abstract

The present invention relates to a positive electrode active material comprising a lithium composite transition metal oxide in single-particle form and a coating portion formed on the surface of the lithium composite transition metal oxide, wherein the coating portion comprises a first coating portion and a second coating portion, the first coating portion being discontinuously formed in the form of islands, and the second coating portion being continuously formed in the form of a coating layer, the first coating portion having a concentration gradient in which the boron (B) content decreases and the cobalt (Co) content increases from the surface toward the center of the positive electrode active material particles, and the boron (B) content of the total metals other than lithium in the positive electrode active material being 0.1 mol% or more and 1.25 mol% or less, and a positive electrode and a lithium secondary battery containing the same.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2023-0071874 dated June 2, 2023, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material, and a positive electrode and lithium secondary battery containing the same. [Background technology]

[0003] Recently, with the advancement of technologies such as electric vehicles, the demand for high-capacity secondary batteries has increased, and consequently, research on cathodes using high-nickel (High Ni) cathode active materials with excellent capacity characteristics is being actively conducted.

[0004] High-nickel cathode active materials are manufactured using a co-precipitation method, resulting in a secondary particle form formed by the aggregation of primary particles. However, active materials with a secondary particle form have disadvantages: fine cracks can develop in the secondary particles during long-term charge-discharge processes, causing side reactions; and if the electrode density is increased to improve energy density, the secondary particles undergo structural breakdown, leading to a decrease in energy density and reduced lifetime characteristics due to a reduction in active material and electrolyte.

[0005] To address the problems associated with secondary particle-type high-nickel cathode active materials, single-particle nickel-based cathode active materials have recently been developed. Single-particle nickel-based cathode active materials have the advantage of not causing particle breakdown even when increasing electrode density due to their high energy density. However, because single-particle nickel-based cathode active materials require relatively high firing temperatures to manufacture, the R-3m layered structure is not properly maintained, lithium detaches from the crystal structure, and a phase change occurs to an Fm-3m rock-salt structure like NiO. This reduces the crystallinity of the cathode active material, increasing the proportion of NiO on the surface of the manufactured single-particle particles. As NiO increases, resistance increases, leading to problems such as a decrease in energy density and power output.

[0006] Furthermore, in order to manufacture a positive electrode using a positive electrode active material, it is essential to mix the positive electrode active material with a conductive material, binder, additives, and solvent to form a slurry. During this process, Li by-products located on the surface base the solvent, and the based solvent mixes with the binder to gel the slurry. Using such a gelled slurry makes it difficult to uniformly coat the slurry for the manufacture of the positive electrode.

[0007] Therefore, there is a need to develop a method for manufacturing positive electrode active materials that involves introducing an additional process to suppress the reaction of Li by-products present on the surface of the positive electrode active material with external substances, thereby preventing performance degradation of the positive electrode active material and gelation of the slurry. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] KR2019-0094529 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The problem that this invention aims to solve is to provide a positive electrode active material in which gelation of the positive electrode slurry is suppressed during manufacturing, reaction of lithium by-products on the surface with external substances is suppressed, long-term capacity retention is excellent, and resistance increase rate is suppressed. [Means for solving the problem]

[0010] To solve the above problems, the present invention provides a positive electrode active material, a method for producing the same, and a positive electrode and a lithium secondary battery containing the same.

[0011] (1) The present invention provides a positive electrode active material comprising a lithium composite transition metal oxide in single-particle form and a coating portion formed on the surface of the lithium composite transition metal oxide, wherein the coating portion comprises a first coating portion and a second coating portion, the first coating portion being discontinuously formed in the form of islands, the second coating portion being continuously formed in the form of a coating layer, the first coating portion having a concentration gradient in which the boron (B) content decreases and the cobalt (Co) content increases from the surface toward the center of the positive electrode active material particles, and the boron (B) content of the total metals other than lithium in the positive electrode active material is 0.1 mol% or more and 1.25 mol% or less.

[0012] (2) In the present invention, the first coating portion provides a positive electrode active material that is dispersed and distributed on one or more of the surfaces of the lithium composite transition metal oxide and the second coating portion.

[0013] (3) In the present invention, the first coating portion comprises one or more compounds selected from the group consisting of lithium cobalt oxide, lithium boron oxide, and lithium cobalt-boron oxide, which constitute a positive electrode active material.

[0014] (4) The present invention provides a positive electrode active material in any one of the above (1) to (3), wherein the content of boron (B) among all the metals other than lithium in the positive electrode active material is 0.13 mol% or more and 1.1 mol% or less.

[0015] (5) The present invention provides a positive electrode active material in any one of the above (1) to (4), wherein the first coating part and the second coating part each independently contain boron (B) and cobalt (Co), and optionally contain one or more coating elements selected from the group consisting of Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf.

[0016] (6) The present invention provides a positive electrode active material in any one of the above (1) to (5), wherein the lithium composite transition metal oxide has a composition represented by the following Chemical Formula 1. [Chemical Formula 1] Li a Ni b Co c Mn d M 1 e O2 In the above Chemical Formula 1, M 1 is one or more selected from the group consisting of B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf, 0.9 ≦ a ≦ 1.1, 0.6 ≦ b < 1, 0 < c < 0.4, 0 < d < 0.4, 0 ≦ e < 0.1.

[0017] (7) The present invention provides a positive electrode active material in any one of the above (1) to (6), wherein the first coating part contains a compound having a composition represented by the following Chemical Formula 2. [Chemical Formula 2] Li f B g M 2 h M 3 i O j In the aforementioned chemical formula 2, M 2 is one or more elements selected from the group consisting of Ni, Co, and Mn. M 3 This is one or more elements selected from the group consisting of Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf. 0 <f≦4、1≦g≦4、0≦h≦1、0≦i≦1、1≦j≦8である。

[0018] (8) In any one of (1) to (7) above, the present invention provides a positive electrode active material in which the second coating portion comprises a compound having a composition represented by the following chemical formula 3. [Chemical formula 3] Li k Co l B m M 4 n M 5 o O2 In the aforementioned chemical formula 3, M 4 is one or more elements selected from the group consisting of Ni and Mn. M 5 This is one or more elements selected from the group consisting of Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf. 0.9 ≤ k ≤ 1.1, 0 <l<1、0<m≦1、0≦n<0.4、0≦o<0.4である。

[0019] (9) The present invention provides a positive electrode active material in any one of (1) to (8) above, wherein the first coating portion comprises a compound having a composition represented by the following chemical formula 2, and the second coating portion comprises a compound having a composition represented by the following chemical formula 3. [Chemical formula 2] Li f B g M 2 h M 3 iO j In the aforementioned chemical formula 2, M 2 is one or more elements selected from the group consisting of Ni, Co, and Mn. M 3 This is one or more elements selected from the group consisting of Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf. 0 <f≦4、1≦g≦4、0≦h≦1、0≦i≦1、1≦j≦8であり、 [Chemical formula 3] Li k Co l B m M 4 n M 5 o O2 In the aforementioned chemical formula 3, M 4 is one or more elements selected from the group consisting of Ni and Mn. M 5 This is one or more elements selected from the group consisting of Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf. 0.9 ≤ k ≤ 1.1, 0 <l<1、0<m≦1、0≦n<0.4、0≦o<0.4である。

[0020] (10) The present invention provides a positive electrode active material in any one of (1) to (9) above, wherein the total area of ​​the coating portion is 10% or more and 100% or less of the total surface area of ​​the lithium composite transition metal oxide.

[0021] (11) The present invention provides a positive electrode comprising a positive electrode active material according to any one of (1) to (10) above.

[0022] (12) The present invention provides a lithium secondary battery comprising a positive electrode according to (11), a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. [Effects of the Invention]

[0023] The positive electrode active material of the present invention comprises a lithium composite transition metal oxide in single-particle form and a coating portion formed on the surface of the lithium composite transition metal oxide, wherein the coating portion comprises a first coating portion and a second coating portion, the first coating portion being discontinuously formed island-like, and the second coating portion being a continuously formed coating layer, the first coating portion having a concentration gradient in which the boron (B) content decreases and the cobalt (Co) content increases from the surface toward the center of the positive electrode active material particles, and the boron (B) content of the total metals other than lithium in the positive electrode active material is 0.1 mol% or more and 1.25 mol% or less, thereby reducing gelation during slurry production, and the battery containing the positive electrode active material has the effect of improving capacity characteristics, resistance characteristics and life characteristics. [Brief explanation of the drawing]

[0024] [Figure 1] This is an SEM image of the positive electrode active material produced in Example 1. [Figure 2] This is an SEM image of the positive electrode active material produced in Example 2. [Figure 3] This is an SEM image of the positive electrode active material produced in Example 3. [Figure 4] This is an SEM image of the positive electrode active material produced in Comparative Example 1. [Figure 5] This is an SEM image of the positive electrode active material produced in Comparative Example 2. [Figure 6] This is an SEM image of the positive electrode active material produced in Comparative Example 3. [Figure 7] This is an SEM image of the positive electrode active material produced in Comparative Example 4. [Figure 8] This is an SEM image of the positive electrode active material produced in Comparative Example 5. [Figure 9] This is an EPMA analysis image of the positive electrode active material produced in Example 1. [Figure 10] This is an EPMA analysis image of the positive electrode active material produced in Example 2. [Figure 11]This is an EPMA analysis image of the positive electrode active material produced in Example 3. [Figure 12] This is an EPMA analysis image of the positive electrode active material produced in Comparative Example 4. [Figure 13] This graph shows the content of B as a percentage of etching time, analyzed using ESCA for the positive electrode active materials of Examples 1-3 and Comparative Examples 1-5. [Figure 14] This graph shows the Co content of the positive electrode active materials of Examples 1-3 and Comparative Examples 1-3 as analyzed by ESCA based on etching time. [Modes for carrying out the invention]

[0025] The present invention will be described in more detail below to facilitate understanding of it.

[0026] The terms and words used in the description and claims of this invention should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​this invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0027] In the present invention, the term "primary particle" refers to the smallest particle unit that can be distinguished as a single mass when a cross-section of the positive electrode active material is observed using a scanning electron microscope (SEM), and can consist of one crystal grain or multiple crystal grains.

[0028] In this invention, the term "secondary particle" refers to a secondary structure formed by the aggregation of multiple primary particles. The average particle size of the secondary particle can be measured using a particle size analyzer.

[0029] In this specification, "single particle form" is a concept contrasted with the form of spherical secondary particles formed by the aggregation of tens to hundreds of primary particles manufactured by conventional methods, and refers to a form consisting of 50 or fewer primary particles. Specifically, in the present invention, the single particle form may be a single particle consisting of one primary particle, or it may be a form of secondary particles formed by the aggregation of 2 or more, 3 or more, 4 or more, 5 or more, 10 or more, and 30 or fewer, 35 or fewer, 40 or fewer, 45 or fewer, or 50 or fewer primary particles.

[0030] In this specification, the term "average particle size (D)" is used. 50 )" refers to the particle size at the 50% point of the cumulative volume distribution by particle size. The average particle size is calculated by dispersing the powder to be measured in a dispersion medium, introducing it into a commercially available laser diffraction particle size analyzer (for example, Microtrac's S3500), measuring the difference in diffraction patterns due to particle size as the particles pass through the laser beam to calculate the particle size distribution, and then calculating the particle size at the point where the cumulative volume distribution by particle size in the measuring device reaches 50%. 50 It can be measured.

[0031] positive electrode active material The positive electrode active material of the present invention will be described below.

[0032] The positive electrode active material of the present invention comprises a lithium composite transition metal oxide in single-particle form and a coating portion formed on the surface of the lithium composite transition metal oxide, wherein the coating portion comprises a first coating portion and a second coating portion, the first coating portion being discontinuously formed island-like, and the second coating portion being a continuously formed coating layer, the first coating portion having a concentration gradient in which the boron (B) content decreases and the cobalt (Co) content increases from the surface toward the center of the positive electrode active material particles, and the boron (B) content of the total metals other than lithium in the positive electrode active material is 0.1 mol% or more and 1.25 mol% or less.

[0033] The lithium composite transition metal oxide is in the form of a single particle consisting of 50 or fewer primary particles. That is, the lithium composite transition metal oxide is in the form of a single particle or a single particle formed by the aggregation of 2 to 50 particles. Specifically, it may be in the form of 2 to 40, 2 to 30, 2 to 20, or 2 to 10 primary particles, and preferably 2 to 10. The single particle form is distinguished from secondary particles formed by the aggregation of more than 50 primary particles.

[0034] When the lithium composite transition metal oxide is in the form of a single particle, it exhibits excellent stability, and even when the positive electrode active material containing it is rolled, the positive electrode active material either cracks or develops fewer cracks, thus reducing side reactions between the positive electrode active material and the electrolyte. This improves the battery's resistance to volume changes during charging and discharging, and thus improves its lifespan. On the other hand, lithium composite transition metal oxides, which are secondary particles, are prone to particle cracking during the electrode rolling process. This increases the surface area of ​​the positive electrode active material, leading to a significant decrease in storage performance at high temperatures and a reduced lifespan. In particular, lithium composite transition metal oxides containing a high nickel content are susceptible to particle cracking during rolling for the manufacture of the positive electrode. In this case, side reactions between the lithium composite transition metal oxide and the electrolyte may increase, potentially resulting in inferior battery properties.

[0035] The lithium composite transition metal oxide may have a layered (R-3m) structure and may have a high NiO content before the coating is formed on the lithium composite transition metal oxide. Since the formation of NiO is induced by the high firing temperature required during the manufacture of the lithium composite transition metal oxide, the lithium composite transition metal oxide may have a high NiO content on its surface, and this NiO has the problem of lowering the energy density of the battery and degrading its resistance and output characteristics.

[0036] The present invention, by including a coating portion, reduces side reactions between the positive electrode active material and the electrolyte, and has the effect of reducing the NiO content in the positive electrode active material. Furthermore, the first coating portion contains boron (B) and cobalt (Co), and the first coating portion has a concentration gradient in which the boron (B) content decreases and the cobalt (Co) content increases from the surface toward the center of the positive electrode active material particles. This reduces the density of the positive electrode active material, improving the dispersibility of the positive electrode active material during the production of the positive electrode slurry. During storage of the produced positive electrode slurry, this reduces the precipitation of positive electrode active material particles in the slurry over time, and reduces gelation, that is, the phenomenon in which positive electrode active material particles settle to the bottom in the positive electrode slurry while aggregation occurs between particles. In addition, the sphericity of the positive electrode active material can be increased, and consequently, it is possible to reduce collisions between particles and friction between the agitator and particles during the production of the positive electrode slurry. On the other hand, if the lithium composite transition metal oxide does not include a coating portion, there is a problem of poor lifetime characteristics due to side reactions between the positive electrode active material and the electrolyte; if the first coating portion does not contain boron, the dispersibility of the positive electrode active material is poor, and there is a problem of excessive gelation occurring during the production of the positive electrode slurry; and if the first coating portion does not have a concentration gradient, there is a problem of poor lifetime characteristics.

[0037] Furthermore, according to the present invention, the content of boron (B) among the total metals other than lithium in the positive electrode active material is 0.1 mol% or more and 1.25 mol% or less. Specifically, the content of boron (B) may be 0.1 mol% or more, or 0.2 mol% or more, or 1.1 mol% or less, 1.2 mol% or less, or 1.25 mol% or less. When the content of boron (B) is within the above range, there is an effect of reducing gelation of the positive electrode slurry due to a decrease in the density of the positive electrode active material, improvement in the dispersibility of the positive electrode active material, and an increase in sphericity. In particular, when the content of boron (B) is 0.13 mol% or more and 1.1 mol% or less, there is an effect of improving the capacity characteristics. On the other hand, when the content of boron (B) is less than 0.1 mol%, there is a problem that it is difficult to increase the dispersibility of the positive electrode active material or improve the sphericity, and when it is greater than 1.25 mol%, there is a problem that the resistance characteristics are inferior.

[0038] According to one embodiment of the present invention, the first coating portion may be dispersed on one or more of the surfaces of the lithium composite transition metal oxide and the second coating portion. "Dispersed distribution" means that the coating portions are not formed in a continuous, connected manner, but rather dispersed as dots. In this case, the first coating portion does not act as a resistor and has the effect of improving capacitance characteristics and lifetime characteristics.

[0039] According to one embodiment of the present invention, the first coating portion may contain one or more compounds selected from the group consisting of lithium cobalt oxide, lithium boron oxide, and lithium cobalt-boron oxide. In this case, lithium by-products on the surface of the positive electrode active material are reduced, the dispersibility of the positive electrode active material is improved, and gelation is suppressed during the production of the positive electrode slurry.

[0040] According to one embodiment of the present invention, the first coating portion and the second coating portion each independently contain boron (B) and cobalt (Co), and may selectively contain one or more coating elements selected from the group consisting of Co, Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf. In this case, lithium by-products on the surface of the positive electrode active material are reduced, the dispersibility of the positive electrode active material is improved, and gelation is suppressed during the production of the positive electrode slurry.

[0041] According to one embodiment of the present invention, the lithium composite transition metal oxide may have a composition represented by the following chemical formula 1.

[0042] [Chemical formula 1] Li a Ni b Co c Mn d M 1 e O2

[0043] In the aforementioned chemical formula 1, M 1 is one or more elements selected from the group consisting of B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf. 0.9 ≤ a ≤ 1.1, 0.6 ≤ b < 1, 0 <c<0.4、0<d<0.4、0≦e<0.1である。

[0044] In the aforementioned chemical formula 1, Said M 1 This is a doping element, specifically, the aforementioned M 1 is one or more selected from the group consisting of Al, B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf. 1 While not a mandatory component, it can improve capacity and lifespan characteristics.

[0045] The value of a may be 0.9 or greater, or 1.0 or greater, or 1.1 or less. When a satisfies the above range, high safety and high energy density per unit volume can be achieved.

[0046] The above b is the molar ratio of nickel (Ni) among the total metals other than lithium in the lithium composite transition metal compound, and may be 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more, and may be 0.96 or less, 0.97 or less, 0.98 or less, 0.99 or less, or less than 1. When b satisfies the above range, high energy characteristics can be achieved.

[0047] The aforementioned c is the molar ratio of cobalt (Co) among all metals other than lithium in the lithium composite transition metal compound, and may be greater than 0, 0.01 or more, or 0.02 or more, and may be 0.03 or less, 0.04 or less, 0.05 or less, 0.06 or less, 0.07 or less, 0.08 or less, 0.09 or less, 0.1 or less, 0.11 or less, 0.12 or less, 0.13 or less, 0.14 or less, 0.15 or less, 0.16 or less, It may be 0.17 or less, 0.18 or less, 0.19 or less, 0.2 or less, 0.21 or less, 0.22 or less, 0.23 or less, 0.24 or less, 0.25 or less, 0.26 or less, 0.27 or less, 0.28 or less, 0.29 or less, 0.3 or less, 0.31 or less, 0.32 or less, 0.33 or less, 0.34 or less, 0.35 or less, 0.36 or less, 0.37 or less, 0.38 or less, 0.39 or less, or less than 0.4. When c satisfies the above range, stability during the charge-discharge process can be improved and rate characteristics can be enhanced.

[0048] The above d is the molar ratio of manganese (Mn) among the total metals other than lithium in the lithium composite transition metal compound, and may be greater than 0, 0.01 or more, or 0.02 or more, and may be 0.03 or less, 0.04 or less, 0.05 or less, 0.06 or less, 0.07 or less, 0.08 or less, 0.09 or less, 0.1 or less, 0.11 or less, 0.12 or less, 0.13 or less, 0.14 or less, 0.15 or less, 0.16 or less, It may be 0.17 or less, 0.18 or less, 0.19 or less, 0.2 or less, 0.21 or less, 0.22 or less, 0.23 or less, 0.24 or less, 0.25 or less, 0.26 or less, 0.27 or less, 0.28 or less, 0.29 or less, 0.3 or less, 0.31 or less, 0.32 or less, 0.33 or less, 0.34 or less, 0.35 or less, 0.36 or less, 0.37 or less, 0.38 or less, 0.39 or less, or less than 0.4. When d satisfies the above range, high-temperature stability can be increased and side reactions with the electrolyte can be relatively reduced.

[0049] The aforementioned e is M, which is the total amount of metals other than lithium in the lithium composite transition metal compound. 5 The molar ratio of e is such that e may be 0 or greater, 0.01 or greater, 0.02 or greater, 0.03 or greater, 0.04 or greater, or 0.05 or greater, and may be 0.06 or less, 0.07 or less, 0.08 or less, 0.09 or less, or less than 1. When e satisfies the above range, the stability of the positive electrode active material crystal structure is improved and the grain shape can be improved.

[0050] According to one embodiment of the present invention, the first coating portion may contain a compound having a composition represented by the following chemical formula 2.

[0051] [Chemical formula 2] Li f B g M 2 h M 3 i O j

[0052] In the aforementioned chemical formula 2, M 2 is one or more elements selected from the group consisting of Ni, Co, and Mn. M 3 This is one or more elements selected from the group consisting of Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf. 0 <f≦4、1≦g≦4、0≦h≦1、0≦i≦1、1≦j≦8である。

[0053] In the above chemical formula 2, M 2 is one or more elements selected from the group consisting of Ni, Co, and Mn, and M 3 This is one or more elements selected from the group consisting of Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf.

[0054] The aforementioned f may be 0 or greater, and may be 1 or less, 2 or less, 3 or less, or 4 or less.

[0055] The aforementioned g may be 1 or more, or it may be 2 or less, 3 or less, or 4 or less.

[0056] The aforementioned h may be 0 or greater, 0.5 or less, or 1 or less.

[0057] The aforementioned i may be 0 or greater, 0.5 or less, or 1 or less.

[0058] The aforementioned j may be 1 or more, 2 or more, or 3 or more, and may be 4 or less, 5 or less, 6 or less, 7 or less, or 8 or less.

[0059] If f, g, h, i, and j are within the specified range, the capacity characteristics and lifespan characteristics of the manufactured battery can be improved.

[0060] According to one embodiment of the present invention, the second coating portion may contain a compound having a composition represented by the following chemical formula 3.

[0061] [Chemical formula 3] Li k Co l B m M 4 n M 5 o O2

[0062] In the aforementioned chemical formula 3, M 4 is one or more elements selected from the group consisting of Ni and Mn. M 5 This is one or more elements selected from the group consisting of Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf. 0.9 ≤ k ≤ 1.1, 0 <l<1、0<m≦1、0≦n<0.4、0≦o<0.4である。

[0063] In the above chemical formula 3, M 4 is one or more selected from the group consisting of Ni and Mn, and M 5 is one or more selected from the group consisting of Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, and Hf. 5 While not a mandatory component, it can improve capacity and lifespan characteristics.

[0064] The aforementioned k may be 0.9 or greater, or 1 or greater, or 1.1 or less.

[0065] The aforementioned l may be greater than 0, 0.5 or less, or less than 1.

[0066] The aforementioned m may be greater than 0, 0.5 or less, or 1 or less.

[0067] The aforementioned n may be 0 or greater, 0.2 or less, or 0.4 or less.

[0068] The aforementioned o may be 0 or greater, 0.2 or less, or less than 0.4.

[0069] When k, l, m, n, and o are within the specified range, the capacity characteristics and lifespan characteristics of the manufactured battery can be improved.

[0070] According to one embodiment of the present invention, the first coating portion may contain a compound having the composition represented by the chemical formula 2, and the second coating portion may contain a compound having the composition represented by the following chemical formula 3.

[0071] In this specification, the surface of a lithium composite transition metal oxide refers to the outermost edge of the lithium composite transition metal oxide. Furthermore, a region having a predetermined thickness extending from the outermost edge of the lithium composite transition metal oxide towards the center of the positive electrode active material particles can be referred to as the surface portion. This surface portion may be a region with a depth of 1 nm to 50 nm, specifically 5 nm to 30 nm, extending from the outermost edge of the lithium composite transition metal oxide towards the center of the positive electrode active material particles. In contrast to the surface portion, the interior of the lithium composite transition metal oxide, excluding the surface portion, can be referred to as the core.

[0072] The surface portion of the lithium composite transition metal oxide may be doped with cobalt, boron, or cobalt and boron diffused from the coating portion.

[0073] The coating portion may be formed on the outermost surface of the lithium composite transition metal oxide, and the coating portion may be formed on part or all of the outer edge of the surface.

[0074] According to one embodiment of the present invention, the total area of ​​the coating portion may be 10% or more and 100% or less of the total surface area of ​​the lithium composite transition metal oxide. Specifically, the total area of ​​the coating portion may be 10% or more, 15% or more, 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, 45% or more, or 50% or more of the total surface area of ​​the lithium composite transition metal oxide, and may be 55% or less, 60% or less, 65% or less, 70% or less, 75% or less, 80% or less, 90% or less, 95% or less, or 100% or less. When the total area of ​​the coating portion is within the above range, it does not act as a resistor and prevents side reactions between the positive electrode active material and the electrolyte, thereby improving the battery's lifespan and capacity characteristics.

[0075] According to one embodiment of the present invention, the first coating portion and the second coating portion may have the same or different compositions. The content may be a comparison of the content of the first coating portion and the content of the second coating portion located in a region twice the diameter of the first coating portion, centered on the first coating portion. If the compositions differ, the content of coating elements other than B and Co may differ, and the content of coating elements other than B and Co in the first coating portion may be higher than the content of coating elements other than B and Co in the second coating portion.

[0076] According to one embodiment of the present invention, the average particle size (D 50 The average particle size (D) may be 3 μm or more and 20 μm or less. Specifically, the average particle size (D) 50 The particle size may be 3 μm or larger, or 3.5 μm or larger, and may be 5 μm or smaller, 6 μm or smaller, 7 μm or smaller, 8 μm or smaller, 9 μm or smaller, 10 μm or smaller, 11 μm or smaller, 12 μm or smaller, 13 μm or smaller, 14 μm or smaller, 15 μm or smaller, 16 μm or smaller, 17 μm or smaller, 18 μm or smaller, 19 μm or smaller, or 20 μm or smaller. When the average particle size is within the above range, excellent electrode density can be achieved and capacitance characteristics can be improved.

[0077] Method for manufacturing positive electrode active material Next, the method for producing the positive electrode active material of the present invention will be described. The method for producing the positive electrode active material of the present invention is the method for producing the positive electrode active material according to the present invention.

[0078] The positive electrode active material according to the present invention comprises the steps of (1) mixing a lithium composite transition metal oxide in single-particle form with a cobalt-containing raw material, selectively mixing with a coating element-containing raw material to produce a mixture; (2) firing the mixture to produce a fired product; and (3) mixing the fired product with a boron-containing raw material and heat-treating it to form a coating portion containing cobalt (Co) and boron (B) on the lithium composite transition metal oxide, wherein the coating element is one or more selected from the group consisting of Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf, and the firing may be carried out at a temperature of 600°C to 800°C.

[0079] The positive electrode active material according to the present invention described above can be manufactured by appropriately adjusting the type of raw material, the mixing ratio of the raw material, the heat treatment step, the heat treatment temperature, the heat treatment heating rate, the heat treatment atmosphere, and so on.

[0080] The steps of the present invention will be described in detail below.

[0081] (1) Step The present invention comprises the step of (1) mixing a lithium composite transition metal oxide in single-particle form with a cobalt-containing raw material and selectively mixing with a coating element-containing raw material to produce a mixture.

[0082] The mixture of the present invention, specifically the lithium composite transition metal oxide, is mixed using a dry mixing method with a solid-phase raw material mixture. This dry mixing method has the advantage of enabling mass production through a relatively simple synthesis process.

[0083] According to one embodiment of the present invention, the cobalt-containing raw material can be mixed with the lithium composite transition metal oxide in an amount of 0.1 mol% to 10 mol%, specifically 0.5 mol% to 5 mol%, and more specifically 1 mol% to 3 mol%. When the cobalt raw material is mixed within this range, no unreacted cobalt compound remains on the surface of the particles, and a cobalt-containing coating can be sufficiently formed on the lithium composite transition metal oxide.

[0084] The cobalt-containing raw material may be an oxide, hydroxide, oxyhydroxide, carbonate, sulfate, halide, sulfide, acetate, nitrate, carboxylate, or combination thereof, and examples include Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, or Co(SO4)2·7H2O, and one or more of these can be used, and specifically, Co(OH)2 can be used.

[0085] The coating element is one or more selected from the group consisting of Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf. The raw material containing the coating element may be, for example, an oxide, hydroxide, oxyhydroxide, carbonate, sulfate, halide, sulfide, acetate, nitrate, carboxylate, or a combination thereof, specifically Co(OH)2, ZrO2, Zr(OH)4, ZnO, TiO2, WO3, Al2O3, Al(OH)3, Al2(SO4)3, ·xH2O, AlCl3, C2H5O4Al, Al-isopropoxide, Al(NO3)3, AlF, Li3WO4, (NH4) 10 W 12 O 41 Examples include, but are not limited to, 5H2O or NH4H2PO4.

[0086] According to one embodiment of the present invention, the coating element-containing raw material can be used in an amount such that the coating element is 0.001 mol% to 10 mol%, specifically 0.005 mol% to 5 mol%, based on the total number of metal moles of the lithium composite transition metal oxide. When the amount of the coating element-containing raw material is within this range, it can be expected that side reactions with the electrolyte will be effectively suppressed, and the electrochemical properties can be further improved.

[0087] According to one embodiment of the present invention, the lithium composite transition metal oxide in single-particle form may be manufactured by a method comprising the steps of (A) mixing a composite transition metal hydroxide containing nickel, cobalt, and manganese with a first lithium-containing raw material and performing primary calcination at a temperature of 800°C to 950°C to produce a primary calcined product, and (B) performing secondary calcination of the primary calcined product at a temperature of 680°C to 850°C to produce a secondary calcined product.

[0088] Specifically, the primary firing may be performed at temperatures of 800°C or higher, or 820°C or higher, and 850°C or lower, 900°C or lower, or 950°C or lower, and the secondary firing may be performed at temperatures of 680°C or higher, 700°C or higher, or 720°C or higher, and 750°C or lower, 760°C or lower, 770°C or lower, 780°C or lower, 790°C or lower, 800°C or lower, 810°C or lower, 820°C or lower, 830°C or lower, 840°C or lower, or 850°C or lower. When the primary firing is performed within the above temperature range, sufficient energy necessary for the formation of single particles can be supplied, and when the secondary firing is performed within the above range, the crystallinity of the lithium composite transition metal oxide can be improved.

[0089] The aforementioned primary calcination may be carried out under an oxygen atmosphere in order to prevent the lithium composite transition metal oxide from degenerating into a rock salt structure.

[0090] The aforementioned primary firing may be carried out for 3 hours or more, 4 hours or more, 5 hours or more, or 6 hours or more, and 9 hours or less, 10 hours or less, 11 hours or less, or 12 hours or less, in order to aggregate the primary particles and improve the crystallinity of the primary fired product.

[0091] The aforementioned secondary calcination may be carried out under an oxygen atmosphere in order to prevent the lithium composite transition metal oxide from degenerating into a rock salt structure.

[0092] The aforementioned secondary firing may be performed for 3 hours or more, and for 9 hours or less, 10 hours or less, 11 hours or less, or 12 hours or less, in order to increase the degree of crystallinity of the internal crystal structure of the positive electrode active material.

[0093] According to one embodiment of the present invention, immediately after step (A), a step (A1) of grinding the primary calcined product may be further included. In this case, the particle size can be adjusted to improve process efficiency and the quality of the positive electrode active material. In terms of preventing high initial resistance, the primary calcined product may be given an average particle size (D 50 The particles may be ground to a size of 3 μm to 20 μm.

[0094] The grinding in step (A1) above may be carried out using a pin mill, ACM, jet mill, etc. Alternatively, the pin mill may be used at 18,000 rpm, the ACM may be used with Hosokawa equipment at 6,000 rpm for classification and 12,000 rpm for grinding, and the jet mill may be used with ZM Solution equipment at a grinding pressure of 6 bar and 3,500 rpm for classification. In this case, the desired average particle size (D 50 A positive electrode active material having ) can be easily obtained.

[0095] (2) Step Next, the process includes step (2) of firing the mixture to produce a fired product.

[0096] The firing is carried out at a temperature of 500°C or higher and 800°C or lower. Specifically, the firing is carried out at a temperature of 500°C or higher, 550°C or higher, 600°C or higher, 650°C or higher, or 700°C or higher, and 750°C or lower, or below 800°C. When the firing temperature is within the above range, during the heating process for firing, the cobalt-containing coating portion on the lithium composite transition metal oxide, specifically the cobalt that was formed as a discontinuous island-like structure on the surface of the lithium composite transition metal oxide and existed as a LiCoO2 phase, penetrates into the interior of the lithium composite transition metal oxide to an appropriate depth, and the degenerated NiO layer can be appropriately transformed into a nickel-cobalt-manganese (NCM) oxide layered structure. As a result, the surface portion of the lithium composite transition metal oxide has a layered (R-3m) structure, and the surface portion includes an oxidation number gradient layer in which the oxidation number of nickel increases towards the outermost edge, thereby exhibiting excellent effects in cell performance such as charge / discharge capacity, initial efficiency, and initial resistance. On the other hand, if the firing temperature is less than 500°C, the thickness of the coating portion becomes thicker, and an excessive amount of the coating portion is formed, making it difficult to realize the benefits of forming the coating portion as described above. If the firing temperature is 800°C or higher, the cobalt is deeply doped into the lithium composite transition metal oxide, and there is a possibility that the coating portion will not be properly formed on the surface, and island-like coating portions may not be formed.

[0097] The firing can be carried out for a period of 2 hours or more, and 6 hours or less, 9 hours or less, or 12 hours or less. When the firing is carried out within the above time range, excellent productivity can be achieved and uniform firing can be ensured.

[0098] According to one embodiment of the present invention, by performing step (2), a coating portion containing Co can be formed on a lithium composite transition metal oxide, specifically, a second coating portion represented by chemical formula 1 or 2 as described herein can be formed.

[0099] (3) Step The process includes (3) mixing the calcined product with a boron-containing raw material and heat-treating it to form a coating portion containing cobalt (Co) and boron (B) on the lithium composite transition metal oxide.

[0100] The boron-containing raw material may be an oxide, hydroxide, oxyhydroxide, carbonate, sulfate, halide, sulfide, acetate, nitrate, carboxylate, or combination thereof, and examples include, but are not limited to, B(OH)3, H2BO3, HBO2, H3BO3, H2B4O7, B2O3, C6H5B(OH)2, (C6H5O)3B, [(CH3(CH2)3O)3B, C3H9B3O6, (C3H7O3)B, etc.

[0101] According to one embodiment of the present invention, the boron-containing raw material can be mixed with the calcined product in an amount of 0.15 mol% to 1.25 mol%, specifically 0.20 mol% to 1.10 mol%, and more specifically 0.25 to 1.05 mol%. When the amount of the boron-containing raw material mixed is within the above range, the boron content of the formed coating can satisfy the appropriate range.

[0102] According to one embodiment of the present invention, the heat treatment may be performed at temperatures of 200°C or higher, 250°C or higher, or 300°C or higher, and 350°C or lower, 400°C or lower, 420°C or lower, 440°C or lower, 460°C or lower, 480°C or lower, or 500°C or lower. When the heat treatment temperature is within the above range, the boron-containing raw material can appropriately form an amorphous boron coating instead of boron oxide. If the heat treatment temperature is too high, boron oxide may be formed on the surface of the lithium composite transition metal oxide, potentially hindering its properties as a positive electrode active material, and if the heat treatment temperature is too low, the coating may not be properly formed.

[0103] The heat treatment may be carried out for 2 hours or more, or 3 hours or more, and for 6 hours or less, 7 hours or less, 8 hours or less, 9 hours or less, 10 hours or less, 11 hours or less, or 12 hours or less. When the heat treatment is carried out within the above time range, excellent productivity can be achieved and uniform firing can be ensured.

[0104] According to one embodiment of the present invention, by performing step (3), a coating portion containing B can be formed on a lithium composite transition metal oxide, specifically, a first coating portion represented by chemical formula 2 or a second coating portion represented by chemical formula 3 as described herein can be formed.

[0105] According to one embodiment of the present invention, in steps (1) to (3), a coating portion may be formed by the diffusion of cobalt, boron, or cobalt and boron from the surface of the lithium composite transition metal oxide toward the center of the positive electrode active material particles. As a result, the first coating portion may have a concentration gradient in which the boron (B) content decreases and the cobalt (Co) content increases toward the center of the positive electrode active material particles from the surface.

[0106] According to yet another embodiment of the present invention, a positive electrode containing the above-mentioned positive electrode active material is provided.

[0107] 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 containing the positive electrode active material described above.

[0108] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector can usually have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0109] The positive electrode active material layer may include a conductive material and a binder, along with the positive electrode active material described above.

[0110] Here, the conductive material is used to impart conductivity to the electrodes and can be used without particular limitations as long as it does not cause chemical changes and has electronic conductivity in the battery it is used in. Specific examples 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; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Of these, one or more can be used. The conductive material can usually be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0111] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (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, of which one or more can be used. The binder can be contained in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0112] The positive electrode can be manufactured according to a conventional method for manufacturing a positive electrode, except that the positive electrode active material described above is used. Specifically, it can be manufactured by coating a positive electrode active material layer-forming composition, prepared by dissolving or dispersing the positive electrode active material and, selectively, a binder and a conductive material in a solvent, onto a positive electrode current collector, followed by drying and rolling. Here, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0113] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these can be used individually or in mixtures of two or more. The amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode.

[0114] Alternatively, the positive electrode may be manufactured by casting the positive electrode active material layer forming composition onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0115] According to yet another example of the present invention, an electrochemical element including the positive electrode is provided. Specifically, the electrochemical element may be a battery, a capacitor, and more specifically, a lithium secondary battery.

[0116] The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and electrolyte interposed between the positive and negative electrodes, the positive electrode being as previously described. The lithium secondary battery may also selectively further include a battery container housing the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0117] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0118] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. The negative electrode current collector can usually have a thickness of 3 to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0119] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0120] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include metallic oxides that can be doped and dedoped with lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites; and any one or more mixtures thereof can be used. A metallic lithium thin film can also be used as the negative electrode active material. Furthermore, both low-crystallinity carbon and high-crystallinity carbon can be used as the carbon material. Examples of low-crystalline carbon include soft carbon and hard carbon, while examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0121] Furthermore, the binder and conductive material are as described above in the section on the positive electrode.

[0122] The negative electrode active material layer may be manufactured, for example, by coating a negative electrode forming composition, which is prepared by dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and drying it, or by casting the negative electrode forming composition onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0123] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations, but those with low resistance to ion movement of the electrolyte and excellent electrolyte impregnation ability are particularly preferred. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof, can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used as single-layer or multi-layer structures.

[0124] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0125] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0126] The organic solvent can be used without particular limitations, as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Suitable solvents include carbonate-based solvents such as carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a C2-C20 linear, branched, or cyclic hydrocarbon group, which can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can improve the charge-discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the cyclic carbonate and linear carbonate can be mixed in a volume ratio of about 1:1 to about 1:9 to produce an electrolyte with excellent performance.

[0127] The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, without any particular limitations. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0128] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. These additives may include, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. Here, the additives may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0129] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and capacity retention rate stably, making it useful in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0130] 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.

[0131] The battery module or battery pack can be used as a power source for one or more medium and large-sized devices, such as a power tool; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0132] The outer shape of the lithium secondary battery of the present invention is not particularly limited, and may be, for example, a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0133] In addition to being usable as a battery cell for a small device power source, the lithium secondary battery according to the present invention is also preferably usable as a unit battery in a medium and large-sized battery module including a large number of battery cells.

[0134] Hereinafter, embodiments of the present invention will be described in detail so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement it. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0135] Manufacturing example Production Example 1 Composite transition metal hydroxide [composition: Ni 0.95 Co 0.03 Mn 0.02 (OH)2, average particle size (D 50 ) 3.5 μm] and LiOH were mixed so that the molar ratio of (Ni + Co + Mn): Li was 1: 1.05, and after primary firing at 850 ° C for 6 hours in an oxygen atmosphere to produce a primary fired product, the primary fired product was crushed and then secondary fired at 750 ° C for 9 hours in an oxygen atmosphere to obtain a single particle form, LiNi 0.95 Co0.03 Mn 0.02 A lithium-compound transition metal oxide having a composition represented by O2 was fabricated.

[0136] The lithium complex transition metal oxide and powdered Co(OH)2 (manufactured by HUAYOU Cobalt Co., Ltd.) were added to a reactor in a molar ratio of 98:2. Al(OH)3 was then added at a concentration of 500 ppm relative to the total weight of the lithium complex transition metal oxide, and the mixture was dry-mixed using an acoustic mixer to produce a mixture. The mixture was baked at 700°C for 5 hours to obtain a cake-like product, which was then pulverized to produce a powder-like baked product.

[0137] Example 1 In Manufacturing Example 1, the calcined product and B(OH)3 were dry-mixed so that the molar ratio of the calcined product to B(OH)3 was 99.75:0.25. The mixture was then heat-treated at 330°C for 5 hours to obtain a cake-like positive electrode active material, which was then pulverized to produce a powder-like positive electrode active material. The positive electrode active material has a coating portion containing cobalt and boron formed on a lithium composite transition metal oxide, with an average particle size (D 50 The thickness is 3.8 μm.

[0138] Example 2 The positive electrode active material was manufactured in the same manner as in Example 1, except that the calcined product manufactured in Manufacturing Example 1 and B(OH)3 were dry-mixed so that the molar ratio of the calcined product to B(OH)3 was 99.5:0.5.

[0139] Example 3 The positive electrode active material was produced in the same manner as in Example 1, except that the calcined product produced in Production Example 1 and B(OH)3 were dry-mixed so that the molar ratio of the calcined product to B(OH)3 was 99.0:1.0.

[0140] Comparative Example 1 The powdered calcined product produced in Manufacturing Example 1 was used as the positive electrode active material in Comparative Example 1.

[0141] Comparative Example 2 A positive electrode active material was produced in the same manner as in Example 1, except that the fired product produced in Production Example 1 and B(OH)3 were dry-mixed so that the molar ratio of the fired product to B(OH)3 was 99.9:0.1.

[0142] Comparative Example 3 A positive electrode active material was produced in the same manner as in Example 1, except that the fired product produced in Production Example 1 and B(OH)3 were dry-mixed so that the molar ratio of the fired product to B(OH)3 was 98.5:1.5.

[0143] Comparative Example 4 Lithium composite transition metal oxide produced in Production Example 1 and powdery Co(OH)2 (manufactured by HUAYOU Cobalt Co., Ltd.) were charged into a reactor so that the molar ratio of the lithium composite transition metal oxide to Co(OH)2 was 98:2, and Al(OH)3 was charged so that the content was 500 ppm based on the total weight of the lithium composite transition metal oxide. Then, dry mixing was performed using an acoustic mixer to produce a mixture. The mixture was fired at 800 °C for 3 hours to obtain a fired product in a cake state, which was pulverized to produce a powdery fired product. A positive electrode active material was produced in the same manner as in Example 1, except that the fired product produced in Production Example 1 and B(OH)3 were dry-mixed so that the molar ratio of the fired product to B(OH)3 was 99.5:0.5.

[0144] Comparative Example 5 Composite transition metal hydroxide [composition: Ni 0.95 Co 0.03 Mn 0.02 (OH)2, average particle size (D 50 ) 3.5 μm] and LiOH were mixed so that the molar ratio of (Ni + Co + Mn) to Li was 1:1.05, and primary firing was performed at 650 °C for 3 hours in an oxygen atmosphere to produce a primary fired product. After the primary fired product was crushed, secondary firing was performed at 690 °C for 4 hours in an oxygen atmosphere, and it was in the form of secondary particles, LiNi 0.95 Co 0.03 Mn 0.02The positive electrode active material was produced in the same manner as in Example 2, except that a lithium composite transition metal oxide having a composition represented by O2 was produced.

[0145] [Table 1]

[0146] Experimental example Experimental Example 1: SEM Image Analysis Scanning electron microscope (JEOL, JSM-7610F) was used to capture SEM images of the cathode active materials produced in the examples and comparative examples, which are shown in Figures 1 to 8.

[0147] Figure 1 is an SEM image of the positive electrode active material produced in Example 1.

[0148] Figure 2 is an SEM image of the positive electrode active material produced in Example 2.

[0149] Figure 3 is an SEM image of the positive electrode active material produced in Example 3.

[0150] Figure 4 is an SEM image of the positive electrode active material produced in Comparative Example 1.

[0151] Figure 5 is an SEM image of the positive electrode active material produced in Comparative Example 2.

[0152] Figure 6 is an SEM image of the positive electrode active material produced in Comparative Example 3.

[0153] Figure 7 is an SEM image of the cathode active material produced in Comparative Example 4.

[0154] Figure 8 is an SEM image of the cathode active material produced in Comparative Example 5.

[0155] Referring to Figures 1 to 3, it was confirmed that the positive electrode active material produced in the examples was in the form of single particles.

[0156] In Figures 1 to 6, the uneven, bumpy areas, i.e., the irregularities, are the areas where the first coating is present. Referring to Figures 1 to 3, it was confirmed that the positive electrode active material manufactured in the examples has discontinuously formed island-like first coating areas. On the other hand, Figure 7 confirms that there are no irregularities, i.e., that the first coating area is not included.

[0157] Experimental Example 2: EPMA Image Analysis EPMA cross-sectional analysis was performed on the positive electrode active materials manufactured in the examples to confirm their surface coating properties. First, the positive electrode active materials, carbon black conductive material, and PVDF binder manufactured in Examples 1-3 were mixed in N-methylpyrrolidone (NMP) solvent in a weight ratio of 95:2:3 to produce positive electrode slurries. The produced positive electrode slurry was applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to an electrode porosity of 20% to produce a positive electrode. To obtain a flat surface for EPMA cross-sectional analysis, the positive electrode was subjected to Ar-ion milling at an acceleration voltage of 6kV using a HITACHI Ar Blade 5000 instrument to obtain a cross-section of the positive electrode sample. Then, using a JEOL JXA-iHP200F instrument, the cross-sectional images of the positive electrode sample were observed at an acceleration voltage of 15kV and a probe current of 50nA, and are shown in Figures 9-12.

[0158] Figure 9 shows the EPMA analysis image of the positive electrode active material produced in Example 1, Figure 10 shows the EPMA analysis image of the positive electrode active material produced in Example 2, Figure 11 shows the EPMA analysis image of the positive electrode active material produced in Example 3, and Figure 12 shows the EPMA analysis image of the positive electrode active material produced in Comparative Example 4.

[0159] In Figures 9 to 12, the green and red areas represent the parts where the Co-containing coating is present. Referring to Figures 9 to 11, it was confirmed that the positive electrode active material produced in the example has continuous green areas and partial red areas, and that it includes discontinuously formed island-like first coating areas and continuously formed coating layer-like second coating areas on the lithium composite transition metal oxide.

[0160] On the other hand, referring to Figure 12, it was confirmed that in the positive electrode active material produced in Comparative Example 4, cobalt was deeply doped into the lithium composite transition metal oxide, and the Co-containing coating portion was not properly formed.

[0161] Experimental Example 3: Analysis of XPS etching The distribution of Co and B in the coating area on the surface of each positive electrode active material produced in the above examples and comparative examples was analyzed using ESCA (K-Alpha, Thermo Fisher Scientific Inc.). Depth profiling conditions involved etching at a rate of 0.3 nm / 10 s using an Ar ion source. The atomic %) content of boron (B) and cobalt (Co) in the region from 0 to 100 nm from the surface of the positive electrode active material toward the center of the positive electrode active material particles was measured. The boron (B) content (%) is shown in Table 2, and the ratio of boron content to cobalt content was calculated and is shown in Table 3 below. For reference, the range of 0.1 mol% or less corresponds to the error range during XPS etching analysis.

[0162] Furthermore, Figure 13 shows a graph of boron content as a result of etching time, and Figure 14 shows a graph of cobalt content as a result of etching time.

[0163] Figure 13 is a graph showing the content of B as a function of etching time, analyzed using ESCA, for the positive electrode active materials of Examples 1-3 and Comparative Examples 1-5. Specifically, A* represents data for Example 1, B* for Example 2, C* for Example 3, D* for Comparative Example 1, E* for Comparative Example 2, F* for Comparative Example 3, G* for Comparative Example 4, and H* for Comparative Example 5.

[0164] Figure 14 is a graph showing the Co content of the positive electrode active materials of Examples 1-3 and Comparative Examples 1-3 as determined by etching time, analyzed using ESCA. Specifically, A* represents data for Example 1, B* for Example 2, C* for Example 3, D* for Comparative Example 1, E* for Comparative Example 2, F* for Comparative Example 3, G* for Comparative Example 4, and H* for Comparative Example 5.

[0165] Referring to Figure 13, it was confirmed that the boron content decreases in the region from 0 nm to 90 nm from the surface of the positive electrode active material toward the center of the positive electrode active material particles. Furthermore, it was confirmed that the thickness of the boron-containing coating increases as the amount of B(OH)3 mixed increases.

[0166] Referring to Figure 14, it was confirmed that the cobalt content increases in the region from 0 nm to 7.5 nm in the direction from the surface of the positive electrode active material toward the center of the positive electrode active material particles.

[0167] [Table 2]

[0168] Referring to Table 2, it was confirmed that the content of boron (B) among the total metals other than lithium in the positive electrode active material produced in the examples was between 0.1 mol% and 1.25 mol%.

[0169] [Table 3]

[0170] Referring to Table 3, it was confirmed that for the positive electrode active material produced in the examples, the B / Co ratio decreased with time up to 200 s. In the region measured from 500 s onward, it was confirmed that the material contained both B and Co, and that the B / Co ratio did not exhibit a specific trend.

[0171] This allows us to predict that the region measured between 0 s and 200 s will include island-like first coating portions that are discontinuously formed, and that the first coating portions will have a concentration gradient in which the boron (B) content decreases and the cobalt (Co) content increases from the surface toward the center of the positive electrode active material particles.

[0172] Furthermore, in the examples and comparative examples, it was confirmed that as the amount of B(OH)3 mixed increased, the B content present on the surface was higher.

[0173] Experimental Example 4: Evaluation of Electrochemical Properties Each of the cathode active materials produced in the above examples and comparative examples, along with carbon black (DENKA, FX35), and PVdF (Kureha, KF9709) and BM740H (Zeon) as binders, were added to a solvent (N-methylpyrrolidone (NMP)) in a weight ratio of 95:2:2.8:0.2. The mixture was then stirred at 1,500 rpm for 95 minutes using a homogenizing disper model 2.5 (Primix) to produce a cathode slurry.

[0174] The positive electrode slurry produced as described above was coated onto one surface of an aluminum foil current collector, dried at 130°C for 3 hours, and then rolled using a roll persing method to produce a positive electrode with a positive electrode layer porosity of 20%.

[0175] After manufacturing an electrode assembly by interposing a separator between the positive electrode and the lithium metal disk negative electrode manufactured as described above, this assembly was placed inside a battery case, and then an electrolyte solution of 1M LiPF6 dissolved in an EC / EME / DMC (3:3:4, volume ratio) organic solvent was injected to manufacture a lithium secondary battery.

[0176] The lithium secondary battery manufactured as described above was charged in CC / CV mode at 25°C with a constant current (CC) of 0.2C until it reached 4.25V (end current 0.005C). Then, after being left for 20 minutes, it was discharged in CC mode with a constant current (CC) of 0.2C until it reached 2.5V. The charge capacity was measured, and the percentage of discharge capacity to charge capacity (efficiency (%)) was calculated and is shown in Table 4 below. Here, 1C = 200mA / g was set.

[0177] On the other hand, the lithium secondary battery was charged in CC / CV mode at 45°C with a constant current (CC) of 0.5C until it reached 4.25V (termination current 0.005C), and then, after being left for 20 minutes, it was discharged in CC mode with a constant current (CC) of 1.0C until it reached 2.5V. Each of these charge and discharge cycles was considered one cycle, and a total of 50 charge and discharge cycles were repeated. The discharge capacity (mAh / g) and DC internal resistance (DCIR) were measured for the first and 50th cycles. The percentage of the discharge capacity in the 50th cycle relative to the discharge capacity in the first cycle (capacity retention rate (%)) and the percentage of the DC internal resistance in the 50th cycle relative to the DC internal resistance (initial resistance (Ω)) in the first cycle (resistance increase rate (%)) were calculated and are shown in Table 4 below.

[0178] [Table 4]

[0179] Referring to Table 4 above, it was confirmed that for batteries containing the positive electrode active material manufactured in Examples 1 to 3, the charge / discharge efficiency was 87% or higher, the DCIR was 26Ω or less, the capacity retention rate at high temperatures was 95% or higher, the initial resistance was 15Ω or less, and the resistance increase rate was 170% or less. On the other hand, for batteries containing the positive electrode active material manufactured in Comparative Examples 1 and 2, it was confirmed that the charge / discharge efficiency was less than 87%, for the battery containing the positive electrode active material manufactured in Comparative Example 3, the DCIR was greater than 26Ω, the initial resistance at high temperatures was greater than 15Ω, and the resistance increase rate was greater than 170%, for the battery containing the positive electrode active material manufactured in Comparative Example 5, the capacity retention rate was less than 95%, and the resistance increase rate was greater than 170%, and for the battery containing the positive electrode active material manufactured in Comparative Example 4, it was confirmed that the charge / discharge efficiency was less than 87%, the DCIR was greater than 26Ω, the capacity retention rate at high temperatures was less than 95%, the initial resistance was greater than 15Ω, and the resistance increase rate was greater than 170%.

Claims

1. Lithium composite transition metal oxides in single-particle form, The lithium composite transition metal oxide includes a coating portion formed on the surface of the lithium composite transition metal oxide, The coating portion includes a first coating portion and a second coating portion. The first coating portion is formed discontinuously in the form of islands, and the second coating portion is formed continuously in the form of a coating layer. The first coating portion has a concentration gradient in which the boron (B) content decreases and the cobalt (Co) content increases from the surface of the first coating portion toward the center of the positive electrode active material particles. A positive electrode active material in which the content of boron (B) among all metals other than lithium is 0.1 mol% or more and 1.25 mol% or less.

2. The positive electrode active material according to claim 1, wherein the first coating portion is dispersed and distributed on one or more of the surfaces of the lithium composite transition metal oxide and the second coating portion.

3. The positive electrode active material according to claim 1, wherein the first coating portion comprises one or more compounds selected from the group consisting of lithium cobalt oxide, lithium boron oxide, and lithium cobalt-boron oxide.

4. The positive electrode active material according to claim 1, wherein the content of boron (B) among the total metals other than lithium in the positive electrode active material is 0.13 mol% or more and 1.1 mol% or less.

5. The positive electrode active material according to claim 1, wherein the first coating portion and the second coating portion each independently contain boron (B) and cobalt (Co), and selectively contain one or more coating elements selected from the group consisting of Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf.

6. The positive electrode active material according to claim 1, wherein the lithium composite transition metal oxide has a composition represented by the following chemical formula 1. [Chemical formula 1] Li ａ Ni ｂ Co ｃ Mn ｄ M １ ｅ O ２ In the aforementioned chemical formula 1, M １ is one or more selected from the group consisting of B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf. 0.9 ≤ a ≤ 1.1, 0.6 ≤ b < 1, 0 < c < 0.4, 0 < d < 0.4, 0 ≤ e < 0.

1.

7. The positive electrode active material according to claim 1, wherein the first coating portion comprises a compound having a composition represented by the following chemical formula 2. [Chemical formula 2] Li ｆ B ｇ M ２ ｈ M ３ ｉ O ｊ In the aforementioned chemical formula 2, M ２ is one or more elements selected from the group consisting of Ni, Co, and Mn. M ３ is one or more selected from the group consisting of Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf. 0 < f ≤ 4, 1 ≤ g ≤ 4, 0 ≤ h ≤ 1, 0 ≤ i ≤ 1, 1 ≤ j ≤ 8.

8. The positive electrode active material according to claim 1, wherein the second coating portion comprises a compound having a composition represented by the following chemical formula 3. [Chemical formula 3] Li ｋ Co ｌ B ｍ M ４ ｎ M ５ ｏ O ２ In the aforementioned chemical formula 3, M ４ is one or more selected from the group consisting of Ni and Mn, M ５ is one or more selected from the group consisting of Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf. 0.9 ≤ k ≤ 1.1, 0 < l < 1, 0 < m ≤ 1, 0 ≤ n < 0.4, 0 ≤ o < 0.

4.

9. The positive electrode active material according to claim 1, wherein the first coating portion contains a compound having a composition represented by the following chemical formula 2, and the second coating portion contains a compound having a composition represented by the following chemical formula 3. [Chemical formula 2] Li ｆ B ｇ M ２ ｈ M ３ ｉ O ｊ In the aforementioned chemical formula 2, M ２ is one or more elements selected from the group consisting of Ni, Co, and Mn. M ３ is one or more selected from the group consisting of Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf. 0 < f ≤ 4, 1 ≤ g ≤ 4, 0 ≤ h ≤ 1, 0 ≤ i ≤ 1, 1 ≤ j ≤ 8, [Chemical formula 3] Li ｋ Co ｌ B ｍ M ４ ｎ M ５ ｏ O ２ In the aforementioned chemical formula 3, M ４ is one or more selected from the group consisting of Ni and Mn, M ５ is one or more selected from the group consisting of Al, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf. 0.9 ≤ k ≤ 1.1, 0 < l < 1, 0 < m ≤ 1, 0 ≤ n < 0.4, 0 ≤ o < 0.

4.

10. The positive electrode active material according to claim 1, wherein the total area of ​​the coating portion is 10% or more and 100% or less of the total surface area of ​​the lithium composite transition metal oxide.

11. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 10.

12. The positive electrode according to claim 11, The negative electrode and, A separator interposed between the positive electrode and the negative electrode, A lithium secondary battery containing an electrolyte.

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