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 that can improve the performance of a lithium secondary battery, and comprises a lithium composite transition metal oxide in single-particle form and a coating portion formed on the lithium composite transition metal oxide and containing an amorphous lithium compound, 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 continuously formed coating layer-like, and 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 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, and the present invention relates to a positive electrode and a lithium secondary battery containing the same.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2023-0071875 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 A1 [Overview of the project] [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 the elution of lithium ions and side reactions between lithium ions and electrolytes are reduced by forming an amorphous lithium compound on the surface of the positive electrode active material, thereby reducing lithium by-products, and suppressing gelation of the positive electrode slurry during manufacturing.

[0010] Another problem that the present invention aims to solve is to provide a positive electrode and a lithium secondary battery containing the positive electrode active material. [Means for solving the problem]

[0011] To solve the above problems, the present invention provides a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery.

[0012] (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 lithium composite transition metal oxide and containing an amorphous lithium compound, 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 continuously formed coating layer-like, and 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 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.

[0013] (2) The present invention provides a positive electrode active material having a phase gradient from an amorphous structure to a spinel structure and then to a layered structure in the direction from the surface to the center, as described in (1).

[0014] (3) In the present invention according to (1) or (2) above, the first coating portion provides a cathode active material that is dispersed and distributed on at least one of the surface of the lithium composite transition metal oxide and the surface of the second coating portion.

[0015] (4) In the present invention according to any one of (1) to (3) above, the amorphous lithium compound provides a cathode active material containing lithium borate.

[0016] (5) In the present invention according to any one of (1) to (4) above, the coating portion provides a cathode active material containing one or more compounds selected from the group consisting of lithium cobalt oxide, lithium borate, and lithium cobalt-borate.

[0017] (6) In the present invention according to any one of (1) to (5) above, the lithium composite transition metal oxide provides a cathode active material having a composition represented by the following Chemical Formula [1]. [Chemical Formula 1] Li f , e , h , g , 1 , 1 Ni b Co c Mn d M 1 e O2 In Chemical Formula [1] above, 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, 0.9 ≦ a ≦ 1.1, 0.6 ≦ b < 1, 0 < c < 0.4, 0 < d < 0.4, 0 ≦ e < 0.1.

[0018] (7) In the present invention according to any one of (1) to (6) above, the first coating portion provides a cathode active material containing a compound having a composition represented by the following Chemical Formula [2]. <00​​​​​​​​​2 i M 3 j O2 In the aforementioned chemical formula 2, M 2 is one or more elements selected from the group consisting of Ni 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. 0.9≦f≦1.1, 0.6≦g<1, 0 <h<0.3、0<i<0.4、0≦j<0.1である。

[0019] (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, 0.6≦l<1, 0 <m<0.3、0≦n<0.4、0≦o<0.3である。

[0020] (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 fCo g B h M 2 i M 3 j O2 In the aforementioned chemical formula 2, M 2 is one or more elements selected from the group consisting of Ni 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. 0.9≦f≦1.1, 0.6≦g<1, 0 <h<0.3、0<i<0.4、0≦j<0.1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, 0.6≦l<1, 0 <m<0.3、0≦n<0.4、0≦o<0.3である。

[0021] (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.

[0022] (11) The present invention provides a positive electrode comprising a positive electrode active material according to any one of (1) to (10) above.

[0023] (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]

[0024] 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 lithium composite transition metal oxide and containing an amorphous lithium compound, 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, and each of the first and second coating portions independently contains boron (B) and cobalt (Co), and selectively contains 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, thereby reducing the elution of lithium ions from the positive electrode active material by forming the amorphous lithium compound, suppressing side reactions with the electrolyte, preventing an increase in the pH of the slurry due to lithium byproducts, and suppressing gelation. [Brief explanation of the drawing]

[0025] [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](A) is an EPMA analysis image of the positive electrode active material produced in Example 1, (B) is an EPMA analysis image of the positive electrode active material produced in Example 2, and (C) is an EPMA analysis image of the positive electrode active material produced in Example 3. [Figure 7] (A) is a TEM image of the cross-section of the positive electrode active material produced in Example 1, and (B) is a TEM image of the cross-section of the positive electrode active material produced in Example 2. The graph shows the Co content as it changes with etching time, analyzed using [a specific method]. [Modes for carrying out the invention]

[0026] The present invention will be described in more detail below to facilitate understanding of it.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] positive electrode active material The positive electrode active material of the present invention will be described below.

[0033] 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 lithium composite transition metal oxide and containing an amorphous lithium compound, 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 continuously formed coating layer-like, and each of the first and second coating portions independently contains boron (B) and cobalt (Co), and selectively contains 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The present invention, by including a coating portion, has the effect of reducing side reactions between the positive electrode active material and the electrolyte, thereby reducing the NiO content in the positive electrode active material. Furthermore, by including boron (B) cobalt (Co) in the first and second coating portions, the density of the positive electrode active material is reduced, 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. 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 and second coating portions do not include boron and cobalt, there is an excess of lithium by-products, resulting in poor dispersibility of the positive electrode active material, and a problem of excessive gelation during the production of the positive electrode slurry.

[0038] According to one embodiment of the present invention, the positive electrode active material may have a phase gradient from an amorphous structure to a spinel structure and then to a layered structure in the direction from the surface to the center. Specifically, the amorphous structure may include lithium boron oxide, the spinel structure may include lithium cobalt oxide, and the layered structure may include lithium cobalt oxide, nickel cobalt manganese aluminum oxide, and so on.

[0039] According to one embodiment of the present invention, the first coating portion may be dispersed and distributed on one or more of the surfaces of the lithium composite transition metal oxide and the second coating portion. "Dispersed and distributed" means that it is formed in a manner that is scattered and dotted rather than being formed in a continuous, connected manner. In this case, the first coating portion does not act as a resistor and has the effect of improving capacitance characteristics and lifetime characteristics.

[0040] According to one embodiment of the present invention, the amorphous lithium compound may include lithium boron oxide. In this case, the density of the positive electrode active material is reduced, which has the effect of 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, the precipitation of positive electrode active material particles in the positive electrode slurry over time is reduced, and gelation, that is, the phenomenon in which aggregation occurs between particles while positive electrode active material particles settle to the bottom in the positive electrode slurry, can be reduced.

[0041] According to one embodiment of the present invention, the 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.

[0042] 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.

[0043] [Chemical formula 1] Li a Ni b Co c Mn d M 1 e O2

[0044] In the aforementioned chemical formula 1, M 1 This is one or more elements 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. 0.9 ≤ a ≤ 1.1, 0.6 ≤ b < 1, 0 <c<0.4、0<d<0.4、0≦e<0.1である。

[0045] In the aforementioned chemical formula 1, Said M 1This 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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 0.1. 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.

[0051] 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.

[0052] [Chemical formula 2] Li f Co g B h M 2 i M 3 j O2

[0053] In the aforementioned chemical formula 2, M 2 is one or more elements selected from the group consisting of Ni 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. 0.9≦f≦1.1, 0.6≦g<1, 0 <h<0.3、0<i<0.4、0≦j<0.1である。

[0054] In the above chemical formula 2, M 2 is one or more selected from the group consisting of Ni and Mn, and 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, and Hf. 3 While not a mandatory component, it can improve capacity and lifespan characteristics.

[0055] The aforementioned f may be 0.9 or greater, or 1 or greater, or 1.1 or less.

[0056] The aforementioned g may be 0.6 or greater, 0.7 or greater, 0.8 or greater, 0.9 or greater, or less than 1.

[0057] The aforementioned h may be greater than 0, 0.1 or greater, or 0.2 or greater, and may be less than 0.3.

[0058] The aforementioned i may be greater than 0, 0.1 or greater, or 0.2 or greater, and may be 0.3 or less, or less than 0.4.

[0059] The aforementioned j may be 0 or greater, 0.05 or less, or 0.1 or less.

[0060] When f, g, h, i, and j are within the specified range, the capacity characteristics, efficiency characteristics, and resistance characteristics of the manufactured battery can be improved.

[0061] According to one embodiment of the present invention, the first coating portion may include a lithium cobalt oxide coating portion, a lithium boron oxide coating portion, and a lithium cobalt-boron oxide coating portion located between the lithium cobalt oxide coating portion and the lithium boron oxide coating portion. The lithium boron oxide coating portion may contain Li2BO2, Li2B4O7, and Li x B y O z The lithium cobalt-boron oxide coating portion may include one or more selected from the group consisting of (1≦x≦2, 1≦y≦4, 2≦z≦4), and the lithium cobalt-boron oxide coating portion may include LiCoBO3 and LiMg 0.1 Co 0.9 It may include one or more species selected from the group consisting of BO3.

[0062] According to one embodiment of the present invention, the first coating portion may have a boron (B) content of 0.1 mol% or more and 1.25 mol% or less among the total metals other than lithium in the positive electrode active material. Specifically, the boron (B) content may be 0.1 mol% or more, or 0.15 mol% or more, or 1.1 mol% or less, 1.2 mol% or less, or 1.25 mol% or less. When the boron (B) content 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, an improvement in the dispersibility of the positive electrode active material, and an increase in sphericity.

[0063] 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.

[0064] [Chemical formula 3] Li k Co l B m M 4 n M 5 o O2

[0065] In the aforementioned chemical formula 3, M 4is 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, 0.6≦l<1, 0 <m<0.3、0≦n<0.4、0≦o<0.3である。

[0066] 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, Sr, Ta, and Hf. 5 While not a mandatory component, it can improve capacity and lifespan characteristics.

[0067] The aforementioned k may be 0.9 or greater, or 1 or greater, or 1.1 or less.

[0068] The value of l may be 0.6 or greater, 0.7 or greater, 0.8 or greater, 0.9 or greater, or less than 1.

[0069] The aforementioned m may be greater than 0, 0.1 or greater, or 0.2 or greater, and may be less than 0.3.

[0070] The aforementioned n may be greater than 0, 0.1 or greater, or 0.2 or greater, and may be 0.3 or less, or less than 0.4.

[0071] The aforementioned o may be 0 or greater, or it may be 0.1 or less, 0.2 or less, or 0.3 or less.

[0072] When k, l, m, n, and o are within the specified range, the capacity characteristics, efficiency characteristics, and resistance characteristics of the manufactured battery can be improved.

[0073] 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 chemical formula 3.

[0074] In this specification, the surface refers to the outermost edge of the lithium composite transition metal oxide. Alternatively, a region having a predetermined thickness extending from the outermost edge of the lithium composite transition metal oxide towards the center may 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. In contrast to the surface portion, the interior of the lithium composite transition metal oxide, excluding the surface portion, may be referred to as the core.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] The steps of the present invention will be described in detail below.

[0083] (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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] The pulverization in the step (A1) may be performed using a pin mill, ACM, jet mill, etc. On the other hand, for the pin mill, under the condition of 18,000 rpm, for ACM, using the equipment manufactured by Hosokawa, under the conditions of classification at 6,000 rpm and pulverization at 12,000 rpm, and for the jet mill, using the equipment manufactured by ZM solution, it may be performed under the conditions of a pulverization pressure of 6 bar and classification at 3,500 rpm. In this case, a positive electrode active material having a desired average particle size (D 50 ) can be easily obtained.

[0097] (2) Step Next, it includes the step (2) of firing the mixture to produce a fired product.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] (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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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 toward the center of the lithium composite transition metal oxide.

[0108] According to yet another embodiment of the present invention, a positive electrode containing the above-mentioned positive electrode active material is provided.

[0109] 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.

[0110] 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.

[0111] The positive electrode active material layer may include a conductive material and a binder, along with the positive electrode active material described above.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0122] 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. βExamples 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.

[0123] Furthermore, the binder and conductive material are as described above in the section on the positive electrode.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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).

[0132] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0133] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0134] The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical, rectangular, pouch-type, or coin-type using a can.

[0135] In addition to being usable as a battery cell for powering small devices, the lithium secondary battery according to the present invention can also be preferably used as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0136] Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0137] Manufacturing example Manufacturing Example 1 Composite transition metal hydroxide [composition: Ni 0.95 Co 0.03 Mn 0.02 (OH)2, average particle size (D 50 Mixing [3.5 μm] and LiOH so that the molar ratio of (Ni+Co+Mn):Li is 1:1.05, and then primary calcination is performed at 820°C for 6 hours under an oxygen atmosphere to produce a primary calcined product. After crushing the primary calcined product, secondary calcination is performed at 750°C for 9 hours under an oxygen atmosphere to produce a single-particle form of LiNi 0.95 Co0.03 Mn 0.02 A lithium composite transition metal oxide having a composition represented by O2 was produced.

[0138] Examples and Comparative Examples Example 1 The lithium composite transition metal oxide produced in Production Example 1 and powdered 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 97.82:2.18, and dry mixing was performed using an acoustic mixer to produce a mixture. The mixture was fired at 700 °C for 5 hours to obtain a fired product in a cake state, which was pulverized to produce a powdered fired product.

[0139] The powdered fired product and B(OH)3 were charged so that the molar ratio of the fired product to B(OH)3 was 99.55:0.45, and after dry mixing using an acoustic mixer, heat treatment was performed at 300 °C for 5 hours to obtain a positive electrode active material in a cake state, which was pulverized to produce a powdered positive electrode active material. The positive electrode active material has a coating portion containing cobalt and boron formed on a single-particle form of lithium composite transition metal oxide, with an average particle diameter (D 50 ) of 3.8 μm.

[0140] Example 2 The lithium composite transition metal oxide produced in Production Example 1, powdered Co(OH)2 (manufactured by Huayou Cobalt Co., Ltd.) and Al(OH)3 were charged into a reactor so that the molar ratio of the lithium composite transition metal oxide, Co(OH)2 and Al(OH)3 was 97.72:2.18:0.1, and dry mixing was performed using an acoustic mixer to produce a mixture. The mixture was fired at 700 °C for 5 hours to obtain a fired product in a cake state, which was pulverized to produce a powdered fired product.

[0141] The aforementioned powdered calcined product and B(OH)3 were added in a molar ratio of 99.37:0.63, dry-mixed using an acoustic mixer, and then heat-treated at 300°C for 5 hours to obtain a cake-like positive electrode active material. This cake was then pulverized to produce a powdered positive electrode active material. The positive electrode active material has a coating portion containing cobalt and boron formed on a single-particle lithium composite transition metal oxide, with an average particle size (D 50 The thickness is 3.9 μm.

[0142] Example 3 In a reactor, lithium complex transition metal oxide produced in Production Example 1, powdered Co(OH)2 (manufactured by HUAYOU Cobalt Co., Ltd.), and Al(OH)3 were added in a molar ratio of 97.4:2.5:0.1. The mixture was then dry-mixed using an acoustic mixer to produce a mixture. The mixture was baked at 720°C for 5 hours to obtain a cake-like product, which was then pulverized to produce a powdered product.

[0143] The aforementioned powdered calcined product and B(OH)3 were added in a molar ratio of 99.55:0.45, dry-mixed using an acoustic mixer, and then heat-treated at 330°C for 5 hours to obtain a cake-like positive electrode active material. This cake was then pulverized to produce a powdered positive electrode active material. The positive electrode active material has a coating portion containing cobalt and boron formed on a single-particle lithium composite transition metal oxide, with an average particle size (D 50 The thickness is 3.9 μm.

[0144] Comparative Example 1 The lithium complex transition metal oxide produced in Production Example 1 and powdered Co(OH)2 (manufactured by HUAYOU Cobalt Co., Ltd.) were added to a reactor in a molar ratio of 97.82:2.18, and the mixture was dry-mixed using an acoustic mixer to produce a mixture. The mixture was baked at 820°C for 5 hours to obtain a baked cake, which was then pulverized to produce a powdered baked product.

[0145] The aforementioned powdered calcined product and B(OH)3 were added in a molar ratio of 99.1:0.9, dry-mixed using an acoustic mixer, and then heat-treated at 300°C for 5 hours to obtain a cake-like positive electrode active material. This cake was then pulverized to produce a powdered positive electrode active material. The positive electrode active material has a coating portion containing cobalt and boron formed on a single-particle lithium composite transition metal oxide, with an average particle size (D 50 The thickness is 3.8 μm.

[0146] Comparative Example 2 The lithium complex transition metal oxide and Al(OH)3 produced in Production Example 1 were added to a reactor in a molar ratio of 98.1:1.9, and the mixture was dry-mixed using an acoustic mixer to produce a mixture. The mixture was baked at 500°C for 5 hours to obtain a cake-like product, which was then pulverized to produce a powder-like baked product.

[0147] The aforementioned powdered calcined product and B(OH)3 were added in a molar ratio of 99.37:0.63, dry-mixed using an acoustic mixer, and then heat-treated at 300°C for 5 hours to obtain a cake-like positive electrode active material. This cake was then pulverized to produce a powdered positive electrode active material. The positive electrode active material has a coating portion containing aluminum and boron formed on a single-particle lithium composite transition metal oxide, with an average particle size (D 50 The thickness is 3.9 μm.

[0148] 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 5.

[0149] Figure 1 is an SEM image of the positive electrode active material produced in Example 1.

[0150] Figure 2 is an SEM image of the positive electrode active material produced in Example 2.

[0151] Figure 3 is an SEM image of the positive electrode active material produced in Example 3.

[0152] Figure 4 is an SEM image of the positive electrode active material produced in Comparative Example 1.

[0153] Figure 5 is an SEM image of the positive electrode active material produced in Comparative Example 2.

[0154] Referring to Figures 1 to 3, it was confirmed that the positive electrode active material produced in the examples was in single-particle form.

[0155] In Figures 1-3 and 5, the uneven, bumpy areas, i.e., the irregularities, are the areas where the coating is present. Referring to Figures 1-3, it was confirmed that the positive electrode active material produced in the examples contains discontinuously formed island-like first coating areas. On the other hand, Figure 4 shows that there are no irregularities, i.e., it does not contain the first coating areas.

[0156] 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, a cross-sectional image of the positive electrode sample was observed at an acceleration voltage of 15kV and a probe current of 50nA, and is shown in Figure 6.

[0157] Figure 6(A) is an EPMA analysis image of the positive electrode active material produced in Example 1, (B) is an EPMA analysis image of the positive electrode active material produced in Example 2, and (C) is an EPMA analysis image of the positive electrode active material produced in Example 3.

[0158] In Figure 6, the green areas represent the regions where a coating layer containing Co exists. Referring to Figure 6, it was confirmed that the green areas are continuous and that the second coating portion is a continuous coating layer formed on the lithium composite transition metal oxide.

[0159] Experimental Example 3: TEM-EDS Image Analysis Using a transmission electron microscope (TEM) (FEI, Titan cubed G2 60-300), TEM images of the cross-sections of the positive electrode active materials produced in the above examples and comparative examples were acquired, and the TEM images of the cross-sections of the positive electrode active materials produced in Example 1 and Example 2 are shown in Figure 7.

[0160] Figure 7(A) is a TEM image of the cross-section of the positive electrode active material manufactured in Example 1, and (B) is a TEM image of the cross-section of the positive electrode active material manufactured in Example 2.

[0161] Referring to Figure 7, it was confirmed that the positive electrode active materials produced in Examples 1 and 2 included a coating portion containing an amorphous lithium compound.

[0162] Experimental Example 4: XPS Etching Analysis The distribution of B and Co 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, and the atomic % content of boron (B) and cobalt (Co) contained in the coating layer with a thickness of 0 to 100 nm was measured and is shown in Tables 1 and 2 below, respectively.

[0163] [Table 1]

[0164] [Table 2]

[0165] Referring to Tables 1 and 2, it was confirmed that the coating portion of the positive electrode active material produced in Examples 1 to 3 contained boron (B) and cobalt (Co).

[0166] Experimental Example 5: Viscosity Analysis of Cathode Slurry Manufacturing of positive electrode slurry The cathode active materials produced in the above examples and comparative examples, carbon black (DENKA, FX35), and binders PVdF (Kureha, KF9709) and BM740H (Zeon) 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.

[0167] Measurement of positive electrode slurry viscosity After collecting each of the manufactured cathode slurries, their viscosity was measured using a viscometer (DV2T viscometer, Brookfield Ametek) by shearing at 16 rpm for 1 minute. The change in viscosity over time was measured for up to 7 days after the manufacture of the cathode slurry, and the results are shown in Table 3 below.

[0168] Slurry viscosity (cP) = Shear stress (g / cm·s) / Shear coefficient (1 / s)

[0169] [Table 3]

[0170] Referring to Table 3, it was confirmed that the viscosity of the cathode slurries containing the cathode active material produced in Examples 1 to 3 was lower initially, after 3 days, and after 7 days compared to the cathode slurries containing the cathode active material produced in Comparative Examples 1 and 2.

[0171] Experimental Example 6: Evaluation of Lithium By-products For each of the positive electrode active materials produced in the above examples and comparative examples, the content of lithium by-products (lithium by-products (mol%)) was measured using the Warder titration method, which involves titrating the amounts of OH ions and CO3 ions, with a Mettler Toledo 888 titrando instrument, and is shown in Table 4 below.

[0172] [Table 4]

[0173] Referring to Table 4, it was confirmed that the cathode active materials produced in Examples 1 to 3 had a lower lithium by-product content compared to the cathode active materials containing the cathode active materials produced in Comparative Examples 1 and 2.

[0174] Experimental Example 7: 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.

[0175] 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%.

[0176] 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.

[0177] The lithium secondary batteries manufactured in this manner were charged in CC / CV mode at 25°C with a constant current (CC) of 0.1C until the voltage reached 4.25V (end current 0.005C). Then, after being left for 20 minutes, they were discharged in CC mode with a constant current (CC) of 0.1C until the voltage reached 2.5V. The charge capacity (mAh) and discharge capacity (mAh) were measured, and the percentage of discharge capacity to charge capacity (efficiency (%)) was calculated and is shown in Table 5 below.

[0178] Furthermore, the DC internal resistance (DCIR) (Ω) was calculated and is shown in Table 5 below. The DCIR is calculated by dividing the difference between the voltage at which 10 seconds have passed while discharging with a constant current of 0.2C during initial charging and discharging and the initial voltage by the applied current.

[0179] [Table 5]

[0180] Referring to Table 5, it was confirmed that batteries containing the positive electrode active materials produced in Examples 1 to 3 exhibited superior charge / discharge capacity, efficiency, and DCIR-related battery characteristics compared to batteries containing the positive electrode active materials produced in Comparative Examples 1 and 2.

Claims

1. Lithium composite transition metal oxides in single-particle form, The lithium composite transition metal oxide comprises a coating portion formed on the lithium composite transition metal oxide and containing an amorphous lithium compound. 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 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, as a positive electrode active material.

2. The positive electrode active material according to claim 1, having a sequential phase gradient from an amorphous structure to a spinel structure and then to a layered structure in the direction from the surface to the center.

3. 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.

4. The amorphous lithium compound comprises lithium boron oxide, as described in claim 1, for the positive electrode active material.

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

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 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. 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 Co ｇ B ｈ M ２ ｉ M ３ ｊ O ２ In the aforementioned chemical formula 2, M ２ is one or more selected from the group consisting of Ni 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. 0.9 ≤ f ≤ 1.1, 0.6 ≤ g < 1, 0 < h < 0.3, 0 < i < 0.4, 0 ≤ j < 0.

1.

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, 0.6 ≤ l < 1, 0 < m < 0.3, 0 ≤ n < 0.4, 0 ≤ o < 0.

3.

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 Co ｇ B ｈ M ２ ｉ M ３ ｊ O ２ In the aforementioned chemical formula 2, M ２ is one or more selected from the group consisting of Ni 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. 0.9 ≤ f ≤ 1.1, 0.6 ≤ g < 1, 0 < h < 0.3, 0 < i < 0.4, 0 ≤ j < 0.1, [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, 0.6 ≤ l < 1, 0 < m < 0.3, 0 ≤ n < 0.4, 0 ≤ o < 0.

3.

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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