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

Abstract

The present invention relates to a positive electrode active material capable of simultaneously solving conventional secondary particle and single particle problems, and a positive electrode and a lithium secondary battery comprising the same, in which the positive electrode active material comprises secondary particles, the present invention relates to a lithium secondary battery comprising a plurality of secondary particles including the same particles as conventional single particles as primary particles and formed by aggregating a plurality of primary particles, whereby not only can cell characteristics be improved, such as improving the lifespan of the lithium secondary battery and reducing gas generation, but also energy density can be improved due to excellent density characteristics.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2023-0056231, filed on April 28, 2023, and Korean Patent Application No. 10-2024-0057079, filed on April 29, 2024, the disclosures of which are incorporated herein by reference in their entirety. Technical Field

[0003] This invention relates to a positive electrode active material, and a positive electrode and a lithium secondary battery including the positive electrode active material. Background Technology

[0004] In recent years, with the development of technologies such as electric vehicles, the demand for high-capacity secondary batteries has been increasing. Therefore, research on high-nickel cathode active materials with excellent capacity characteristics is being actively carried out.

[0005] In high-nickel cathode active materials formed from secondary particle structures containing primary particles, structural degradation may occur during the charging and discharging process of a lithium-ion battery, and changes in the lattice structure constant may occur, meaning a relatively large change in the volume per unit lattice. This volume change can lead to cracks in the cathode active material. Furthermore, even with electrode rolling, the cathode active material may still develop cracks due to pressure.

[0006] The cracks in the high-nickel cathode active material produced in this way become more severe during the charging and discharging process of the lithium secondary battery. As a result, these cracks become voids that the electrolyte cannot reach or voids that reduce conductivity, leading to a decrease in the life characteristics of the lithium secondary battery or increasing its resistance.

[0007] As a method to minimize the occurrence of cracks in secondary particle structures, researchers have attempted to manufacture positive electrode active materials in single-particle form. However, this single-particle form suffers from uneven particle size, resulting in a larger particle size distribution after pulverization. Furthermore, single-particle positive electrode active materials have a lower specific surface area, making them more susceptible to the influence of cell resistance characteristics.

[0008] Therefore, there is a need to develop a positive electrode active material that can simultaneously solve the problems of traditional secondary particles and single particles.

[0009] Meanwhile, Korean Patent Registration No. 10-1785262 (Patent Document 1) discloses a large-diameter secondary particle comprising aggregated primary particles. The secondary particles include nickel-based lithium transition metal oxides, with the primary particles having an average particle size of 3 μm to 5 μm and the secondary particles having an average particle size of 10 μm to 20 μm. This large-diameter secondary particle, comprising primary particles with an average particle size in the micrometer range, can improve rolling density to minimize cracks caused by rolling, and the secondary particle structure can improve specific surface area, thereby improving cell characteristics.

[0010] To manufacture the aforementioned (as disclosed in Patent Document 1) cathode active material with a primary particle size in the micrometer range as a secondary particle, heat treatment must be performed at a higher temperature than that for secondary particles with a primary particle size of less than 1 μm in the submicrometer range. However, as the heat treatment temperature increases, the layered structure of the lithium transition metal composite oxide degenerates into a rock salt structure, resulting in reduced crystallinity, which in turn leads to a decrease in the performance of the cathode active material. In particular, since nickel is most likely to cause the layered structure of the lithium transition metal composite oxide to degenerate into a rock salt structure at high heat treatment temperatures, this degradation becomes more severe when the nickel content in the lithium transition metal composite oxide constituting the cathode active material increases. Therefore, conventionally, as shown in Patent Document 1, the cathode active material with a primary particle size in the micrometer range as a secondary particle can only be used for medium-nickel cathode active materials with a nickel content level of 50 mol% in the transition metal of the lithium transition metal composite oxide. For high-nickel cathode active materials that have excellent capacity characteristics due to the high nickel content in the transition metal of lithium transition metal composite oxides, it is impossible to manufacture cathode active materials in the form of secondary particles with a primary particle size in the micrometer range.

[0011] [Existing Technical Documents]

[0012] [Patent Literature]

[0013] (Patent Document 1) KR 10-1785262 B1

[0014] (Patent Document 2) KR 10-2017-0119573 A Summary of the Invention

[0015] [Technical Issues]

[0016] The purpose of this invention is to provide a positive electrode active material that can simultaneously solve the problems of conventional secondary particles and single particles in high-nickel positive electrode active materials.

[0017] In other words, the present invention was made to solve the problems of the prior art mentioned above. Its purpose is to provide a positive electrode active material, which is a high-nickel positive electrode active material with high nickel content in the transition metal of lithium transition metal composite oxide and excellent capacity characteristics. By realizing the positive electrode active material in which the primary particle size is in the form of secondary particles, it can not only improve the cell characteristics, such as improving lifespan and reducing gas generation, but also improve the energy density due to its excellent density characteristics.

[0018] Furthermore, another aspect of the present invention provides a positive electrode and a lithium secondary battery comprising the aforementioned positive electrode active material.

[0019] [Technical Solution]

[0020] To address the aforementioned problems, the present invention provides a positive electrode active material, as well as a positive electrode and a lithium secondary battery comprising the positive electrode active material.

[0021] (1) The present invention provides a positive electrode active material comprising secondary particles having aggregated a plurality of primary particles; wherein the plurality of primary particles have an average particle size of 1.5 μm or more and 5.0 μm or less as measured by SEM images, the particle size of the primary particles being based on the particle size of the major axis of the primary particles, wherein the plurality of primary particles include disc-shaped primary particles, wherein, in the primary particles observed from SEM images of the surface or cross section of the secondary particles, when an imaginary contact line with the maximum number of contact points is drawn for two boundary lines of the primary particles existing within an angle of 45° or less with reference to the major axis, and an imaginary line intersecting the two contact lines is drawn, the same-side interior angle of the disc-shaped primary particles is 150° or more and 210° or less, and wherein the area ratio of the (003) plane in the crystal plane on the surface of the primary particles is the largest.

[0022] (2) The present invention provides a positive electrode active material as described in (1) above, wherein the plurality of primary particles include three or more disc-shaped primary particles.

[0023] (3) The present invention provides a positive electrode active material as described in (1) or (2) above, wherein the positive electrode active material comprises a lithium transition metal composite oxide containing nickel, cobalt and manganese.

[0024] (4) The present invention provides a positive electrode active material as described in any one of (1) to (3) above, wherein the positive electrode active material comprises a lithium transition metal composite oxide in which nickel accounts for more than 60 mol% of the total transition metals.

[0025] (5) The present invention provides a positive electrode active material as described in any one of (1) to (4) above, wherein the positive electrode active material contains a lithium transition metal composite oxide having an average composition represented by the following Chemical Formula 1.

[0026] [Chemical Formula 1]

[0027] Li x Ni a Co b Mn c M 1 d O2

[0028] Wherein, M 1 is at least one selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, V, F, P, S, and Y; and 0.9 ≤ x ≤ 1.3, 0.6 ≤ a < 1.0, 0 < b < 0.4, 0 < c < 0.4, 0 ≤ d ≤ 0.2, and a + b + c + d = 1.

[0029] (6) The present invention provides a positive electrode active material as described in any one of (1) to (5) above, wherein the plurality of primary particles include single crystal primary particles.

[0030] (7) The present invention provides a positive electrode active material as described in any one of (1) to (6) above, wherein, according to the cumulative volume distribution measured by a laser diffraction particle size analyzer, the average particle size (D 50 ) of the secondary particles is 7.0 μm or more and 20.0 μm or less.

[0031] (8) The present invention provides a positive electrode active material as described in any one of (1) to (7) above, wherein the short diameter of the disk-shaped primary particle is 0.3 μm or more, and the aspect ratio (long diameter / short diameter) is 1.5 or more.

[0032] (9) The present invention provides a positive electrode active material as described in any one of (1) to (7) above, wherein the short diameter of the disk-shaped primary particle is 0.8 μm or more, and the aspect ratio (long diameter / short diameter) is 1.5 or more.

[0033] (10) The present invention provides a positive electrode comprising a positive electrode active material as described in any one of (1) to (9) above.

[0034] (11) The present invention provides a lithium secondary battery, which includes a positive electrode as described in (10) above; a negative electrode; and a separator and an electrolyte interposed between the positive electrode and the negative electrode.

[0035] [Advantageous Effects]

[0036] The positive electrode active material of the present invention is a positive electrode active material that can simultaneously solve the problems of traditional secondary particles and single particles in high-nickel positive electrode active materials. In this positive electrode active material, by realizing the form of secondary particles in which the primary particles have a particle size of micrometers, it can not only improve cell characteristics, such as improving lifespan and reducing gas generation, but also improve energy density due to its excellent density characteristics. Attached Figure Description

[0037] Figure 1 (A) SEM image of the positive electrode active material of Example 1, and (B) SEM image of the cross section of the positive electrode active material.

[0038] Figure 2 (A) SEM image of the positive electrode active material of Example 2, and (B) SEM image of the cross section of the positive electrode active material.

[0039] Figure 3 (A) SEM image of the positive electrode active material of Example 3, and (B) SEM image of the cross section of the positive electrode active material.

[0040] Figure 4 (A) SEM image of the positive electrode active material of Example 4, and (B) SEM image of the cross section of the positive electrode active material.

[0041] Figure 5 (A) SEM image of the positive electrode active material of Example 5, and (B) SEM image of the cross-section of the positive electrode active material.

[0042] Figure 6 (A) SEM image of the positive electrode active material of Example 6, and (B) SEM image of the cross section of the positive electrode active material.

[0043] Figure 7 (A) SEM image of the positive electrode active material of Example 7, and (B) SEM image of the cross section of the positive electrode active material.

[0044] Figure 8 (A) SEM image of the positive electrode active material of Example 8, and (B) SEM image of the cross section of the positive electrode active material.

[0045] Figure 9 (A) SEM image of the positive electrode active material of Example 9, and (B) SEM image of the cross section of the positive electrode active material.

[0046] Figure 10 (A) SEM image of the positive electrode active material of Example 10, and (B) SEM image of the cross section of the positive electrode active material.

[0047] Figure 11 (A) SEM image of the positive electrode active material of Example 11, and (B) SEM image of the cross section of the positive electrode active material.

[0048] Figure 12 (A) SEM image of the positive electrode active material of Comparative Example 1, and (B) SEM image of the cross-section of the positive electrode active material.

[0049] Figure 13 (A) SEM image of the positive electrode active material of Comparative Example 2, and (B) SEM image of the cross-section of the positive electrode active material.

[0050] Figure 14 (A) SEM image of the positive electrode active material of Comparative Example 3, and (B) SEM image of the cross-section of the positive electrode active material.

[0051] Figure 15 (A) SEM image of the positive electrode active material of Comparative Example 4, and (B) SEM image of the cross-section of the positive electrode active material.

[0052] Figure 16 (A) SEM image of the positive electrode active material of Comparative Example 5, and (B) SEM image of the cross-section of the positive electrode active material.

[0053] Figure 17 The image segmentation shows multiple lithium composite transition metal oxides segmented from the SEM image of the positive electrode active material of Example 1 after image analysis based on an artificial intelligence model.

[0054] Figure 18 The image segmentation shows multiple lithium composite transition metal oxides segmented from the SEM image of the positive electrode active material of Comparative Example 1 after image analysis based on an artificial intelligence model.

[0055] Figure 19 This is a TEM pattern image of the cross-section of the positive electrode active material of Example 1.

[0056] Figure 20 This is a TEM image of the cross-section of the positive electrode active material in Example 2.

[0057] Figure 21 This is a TEM pattern image of the cross-section of the positive electrode active material of Example 8.

[0058] Figure 22 This is an EBSD pattern image of the cross-section of the positive electrode active material of Example 1.

[0059] Figure 23This is an EBSD pattern image of the cross-section of the positive electrode active material in Example 2.

[0060] Figure 24 This is an EBSD pattern image of the cross-section of the positive electrode active material in Example 3.

[0061] Figure 25 This is an EBSD pattern image of the cross-section of the positive electrode active material in Example 4.

[0062] Figure 26 This is an EBSD pattern image of the cross-section of the positive electrode active material of Example 8.

[0063] Figure 27 This is an EBSD pattern image of the cross-section of the positive electrode active material of Example 10.

[0064] Figure 28 The image shows an EBSD pattern of the cross-section of the positive electrode active material of Example 11.

[0065] Figure 29 EBSD pattern image of the cross section of the positive electrode active material of Comparative Example 3.

[0066] Figure 30 This is an EPMA analysis image of the positive electrode active material of Example 1.

[0067] Figure 31 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 1 using a laser diffraction particle size analyzer, the x-axis represents a linear scale of particle size with x values ​​gradually increasing from left to right, and the y-axis represents a weighted distribution with y values ​​gradually increasing from bottom to top.

[0068] Figure 32 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 2 using a laser diffraction particle size analyzer, the x-axis represents a linear scale of particle size with x values ​​gradually increasing from left to right, and the y-axis represents a weighted distribution with y values ​​gradually increasing from bottom to top.

[0069] Figure 33 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 3 using a laser diffraction particle size analyzer, the x-axis represents a linear scale of particle size with x values ​​gradually increasing from left to right, and the y-axis represents a weighted distribution with y values ​​gradually increasing from bottom to top.

[0070] Figure 34 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 4 using a laser diffraction particle size analyzer, the x-axis represents a linear scale of particle size with x values ​​gradually increasing from left to right, and the y-axis represents a weighted distribution with y values ​​gradually increasing from bottom to top.

[0071] Figure 35 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 5 using a laser diffraction particle size analyzer, the x-axis represents a linear scale of particle size with x values ​​gradually increasing from left to right, and the y-axis represents a weighted distribution with y values ​​gradually increasing from bottom to top.

[0072] Figure 36 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 6 using a laser diffraction particle size analyzer, the x-axis represents a linear scale of particle size with x values ​​gradually increasing from left to right, and the y-axis represents a weighted distribution with y values ​​gradually increasing from bottom to top.

[0073] Figure 37 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 7 using a laser diffraction particle size analyzer, the x-axis represents a linear scale of particle size with x values ​​gradually increasing from left to right, and the y-axis represents a weighted distribution with y values ​​gradually increasing from bottom to top.

[0074] Figure 38 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 8 using a laser diffraction particle size analyzer, the x-axis represents a linear scale of particle size with x values ​​gradually increasing from left to right, and the y-axis represents a weighted distribution with y values ​​gradually increasing from bottom to top.

[0075] Figure 39 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 9 using a laser diffraction particle size analyzer, the x-axis represents a linear scale of particle size with x values ​​gradually increasing from left to right, and the y-axis represents a weighted distribution with y values ​​gradually increasing from bottom to top.

[0076] Figure 40 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 10 using a laser diffraction particle size analyzer, the x-axis represents a linear scale of particle size with x values ​​gradually increasing from left to right, and the y-axis represents a weighted distribution with y values ​​gradually increasing from bottom to top.

[0077] Figure 41 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 11 using a laser diffraction particle size analyzer, the x-axis represents a linear scale of particle size with x values ​​gradually increasing from left to right, and the y-axis represents a weighted distribution with y values ​​gradually increasing from bottom to top.

[0078] Figure 42To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Comparative Example 1 using a laser diffraction particle size analyzer, the x-axis represents the linear scale of particle size with x values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y values ​​gradually increasing from bottom to top.

[0079] Figure 43 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Comparative Example 3 using a laser diffraction particle size analyzer, the x-axis represents the linear scale of particle size with x-values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y-values ​​gradually increasing from bottom to top.

[0080] Figure 44 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 1 using a laser diffraction particle size analyzer, the x-axis represents the logarithmic scale of the particle size with x values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y values ​​gradually increasing from bottom to top.

[0081] Figure 45 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 2 using a laser diffraction particle size analyzer, the x-axis represents the logarithmic scale of the particle size with x values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y values ​​gradually increasing from bottom to top.

[0082] Figure 46 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 3 using a laser diffraction particle size analyzer, the x-axis represents the logarithmic scale of the particle size with x values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y values ​​gradually increasing from bottom to top.

[0083] Figure 47 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 4 using a laser diffraction particle size analyzer, the x-axis represents the logarithmic scale of the particle size with x values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y values ​​gradually increasing from bottom to top.

[0084] Figure 48 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 5 using a laser diffraction particle size analyzer, the x-axis represents the logarithmic scale of the particle size with x values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y values ​​gradually increasing from bottom to top.

[0085] Figure 49 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 6 using a laser diffraction particle size analyzer, the x-axis represents the logarithmic scale of the particle size with x values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y values ​​gradually increasing from bottom to top.

[0086] Figure 50 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 7 using a laser diffraction particle size analyzer, the x-axis represents the logarithmic scale of the particle size with x values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y values ​​gradually increasing from bottom to top.

[0087] Figure 51 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 8 using a laser diffraction particle size analyzer, the x-axis represents the logarithmic scale of the particle size with x values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y values ​​gradually increasing from bottom to top.

[0088] Figure 52 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 9 using a laser diffraction particle size analyzer, the x-axis represents the logarithmic scale of the particle size with x values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y values ​​gradually increasing from bottom to top.

[0089] Figure 53 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 10 using a laser diffraction particle size analyzer, the x-axis represents the logarithmic scale of the particle size with x values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y values ​​gradually increasing from bottom to top.

[0090] Figure 54 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Example 11 using a laser diffraction particle size analyzer, the x-axis represents the logarithmic scale of the particle size with x values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y values ​​gradually increasing from bottom to top.

[0091] Figure 55 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Comparative Example 1 using a laser diffraction particle size analyzer, the x-axis represents the logarithmic scale of the particle size with x values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y values ​​gradually increasing from bottom to top.

[0092] Figure 56 To display the frequency distribution of the cumulative volume distribution obtained by measuring the positive electrode active material of Comparative Example 3 using a laser diffraction particle size analyzer, the x-axis represents the logarithmic scale of the particle size with x values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y values ​​gradually increasing from bottom to top. Detailed Implementation

[0093] The invention will be described in more detail below to aid in understanding it.

[0094] The terms or words used in the specification and claims of this invention should not be construed as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts consistent with the technical spirit of the invention, based on the principle that the inventors can adequately define the concepts of the terms in order to best interpret their invention.

[0095] In this invention, the term "primary particle" refers to the smallest particle unit that can be identified as a single piece when the cross-section of the positive electrode active material is observed using a scanning electron microscope (SEM), and can be formed by a single crystal or multiple grains.

[0096] 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 particles can be measured using a particle size analyzer.

[0097] In this invention, the term "average particle size (D)" is used. 50 The average particle size (D) is calculated based on the particle size distribution at 50% of the cumulative volume distribution. This is achieved by dispersing the powder to be measured in a dispersion medium, then introducing the dispersion medium into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is obtained by measuring the differences in diffraction patterns caused by particle size as particles pass through a laser beam. The average particle size (D) is then calculated by calculating the particle size at 50% of the cumulative volume distribution in this analyzer. 50 ).

[0098] In this invention, the term "major diameter of a primary particle" refers to the length of the longest line segment when drawn through two points on the boundary of a primary particle, as observed from an SEM image of the surface or cross-section of a secondary particle.

[0099] In this invention, the term "minor diameter of a primary particle" refers to the length of the shortest line segment when drawn through two points on the boundary of a primary particle, as observed from an SEM image of the surface or cross-section of a secondary particle.

[0100] Positive electrode active material

[0101] This invention provides a positive electrode active material.

[0102] According to an embodiment of the present invention, the positive electrode active material may include secondary particles in which a plurality of primary particles are aggregated, wherein the plurality of primary particles may have an average particle size of 5.0 μm or more and 5.0 μm or less as measured by SEM images.

[0103] According to an embodiment of the present invention, a secondary particle is a secondary particle in which a plurality of primary particles are aggregated, and it may be a secondary particle in which at least two, for example, at least three or more primary particles are aggregated.

[0104] According to embodiments of the present invention, the average particle size of the plurality of primary particles, as measured by SEM images, can be 1.5 μm or more, 1.6 μm or more, 1.7 μm or more, 1.8 μm or more, 1.9 μm or more, 2.0 μm or more, 2.1 μm or more, 2.2 μm or more, 2.3 μm or more, 2.4 μm or more, or 2.5 μm or more, and can also be less than 5.0 μm, less than 4.9 μm, less than 4.8 μm, less than 4.7 μm, less than 4.6 μm, less than 4.5 μm, less than 4.4 μm, less than 4.3 μm, less than 4.2 μm, less than 4.1 μm, less than 4.0 μm, less than 3.9 μm, less than 3.8 μm, less than 3.7 μm, less than 3.6 μm, less than 3.5 μm, less than 3.4 μm, less than 3.3 μm, less than 3.2 μm, less than 3.1 μm, or less than 3.0 μm. Here, when measuring the average particle size of multiple primary particles from SEM images, the particle size of each primary particle can be based on its major axis. Within this range, the rolling density of the cathode active material and the lifespan of the lithium secondary battery can be further improved.

[0105] According to embodiments of the present invention, the positive electrode active material may include a lithium transition metal composite oxide containing nickel, cobalt, and manganese. As a specific example, the positive electrode active material may include a lithium transition metal composite oxide in which nickel comprises 60 mol% or more of all transition metals. The lithium transition metal composite oxide may be primary particles, secondary particles, or a positive electrode active material containing them. As a specific example, the positive electrode active material may include secondary particles in which multiple primary particles formed of the lithium transition metal composite oxide are aggregated.

[0106] According to embodiments of the present invention, the positive electrode active material may comprise a lithium transition metal composite oxide having an average composition represented by the following chemical formula 1:

[0107] [Chemical Formula 1]

[0108] Li x Ni a Co b Mn c M 1 d O2

[0109] Among them, M 1is selected from at least one of the group consisting of aluminum Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, V, F, P, S, and Y; and 0.9 ≤ x ≤ 1.3, 0.6 ≤ a < 1.0, 0 < b < 0.4, 0 < c < 0.4, 0 ≤ d ≤ 0.2 and a + b + c + d = 1.

[0110] According to an embodiment of the present invention, in Chemical Formula 1 above, x is the molar ratio of lithium to transition metal in the lithium transition metal composite oxide, which may be 0.9 or more, 0.95 or more, or 1.0 or more, and may also be 1.1 or less, 1.07 or less, 1.05 or less, or 1.03 or less.

[0111] According to an embodiment of the present invention, in Chemical Formula 1, a, b, c, and d may be the molar fractions of nickel (Ni), cobalt (Co), manganese (Mn), and doping element (M 1 ) in the transition metal, respectively. As a specific example, a is the molar fraction of nickel (Ni) in the transition metal, and may be 0.6 or more, 0.7 or more, 0.8 or more, 0.85 or more, 0.88 or more, 0.90 or more, 0.91 or more, 0.92 or more, 0.93 or more, 0.94 or more, 0.95 or more, or 0.96 or more, and may also be less than 1.0, 0.99 or less, 0.98 or less, 0.97 or less, or 0.96 or less. In addition, b is the molar fraction of cobalt (Co) in the transition metal, and may be greater than 0, 0.01 or more, 0.02 or more, or 0.03 or more, and may also be less than 0.4, 0.3 or less, 0.2 or less, 0.1 or less, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, or 0.05 or less. c may be the molar fraction of manganese (Mn) in the transition metal, and may be greater than 0, 0.01 or more, or 0.05 or more, and may also be less than 0.4, 0.3 or less, 0.2 or less, 0.1 or less, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, or 0.05 or less. d is the doping element (M 1The mole fraction of a substance in a transition metal, and may be 0, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, 0.10 or more, 0.11 or more, 0.12 or more, 0.13 or more, 0.14 or more, 0.15 or more, 0.16 or more, 0.17 or more, 0.18 or more, or 0. The concentration can be 19 or higher, or less than 0.20, 0.19, 0.18, 0.17, 0.16, 0.15, 0.14, 0.13, 0.12, 0.11, 0.10, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, or 0.01. When the composition of the lithium transition metal composite oxide is adjusted as described above, the capacity can be further improved.

[0112] According to embodiments of the present invention, a plurality of primary particles may include single-crystal primary particles, in which case the rolling density of the positive electrode active material can be further increased. A single-crystal primary particle refers to a primary particle formed from a single crystal.

[0113] According to an embodiment of the present invention, based on the cumulative volume distribution measured using a laser diffraction particle size analyzer, the average particle size (D) of the secondary particles is... 50 The particle size can be greater than 7.0 μm and less than 20.0 μm. As a specific example, the average particle size (D) of the secondary particles... 50The micrometer size can be 7.0 μm or larger, 7.1 μm or larger, 7.2 μm or larger, 7.3 μm or larger, 7.4 μm or larger, 7.5 μm or larger, 7.6 μm or larger, 7.7 μm or larger, 7.8 μm or larger, 7.9 μm or larger, 8.0 μm or larger, 8.1 μm or larger, 8.2 μm or larger, 8.3 μm or larger, 8.4 μm or larger, 8.5 μm or larger, 8.6 μm or larger, 8.7 μm or larger, 8.8 μm or larger, 8.9 μm or larger, or 9.0 μm or larger. It can also be below 20.0 μm, below 19.9 μm, below 19.8 μm, below 19.7 μm, below 19.6 μm, below 19.5 μm, below 19.4 μm, below 19.3 μm, below 19.2 μm, below 19.1 μm, below 19.0 μm, or below 18.9 μm. Below 18.8 μm, below 18.7 μm, below 18.6 μm, below 18.5 μm, below 18.4 μm, below 18.3 μm, below 18.2 μm, below 18.1 μm, below 18.0 μm, below 17.9 μm, below 17.8 μm, below 17.7 μm, below 17.6 μm, below 17.5 μm, below 17.4 μm, below 17.3 μm, below 17.2 μm, below 17.1 μm, below 17.0 μm, below 16.9 μm, below 16.8 μm, below 16.7 μm, below 16.6 μm, below 16.5 μm, below 16.4 μm, below 16.3 μm, below 16.2 μm, below 16.1 μm, below 16.0 μm, 15.9 The micrometer diameters are below 15.0 μm, 15.8 μm, 15.7 μm, 15.6 μm, 15.5 μm, 15.4 μm, 15.3 μm, 15.2 μm, 15.1 μm, or 15.0 μm. Within this range, the rolling density and lifetime of the positive electrode active material can be further improved.

[0114] As a specific example, the positive electrode active material can be a high-nickel positive electrode active material containing lithium transition metal composite oxides with a nickel content of more than 60 mol% in the total transition metals, and can include an average particle size (D). 50The secondary particles are large-diameter particles with a diameter greater than 7.0 μm and less than 20.0 μm. These large-diameter secondary particles are formed by the aggregation of multiple primary particles with the same diameter as traditional single particles as measured by SEM images, ranging from 0.5 μm to 5.0 μm, specifically from 1.0 μm to the micrometer scale, and more specifically from 2.0 μm to 3.5 μm in average particle size. In the sense that large particles are formed by the aggregation of primary particles in the form of single particles, these particles can be represented as large single-particle clusters.

[0115] As described in the background section of this invention, in order to manufacture cathode active materials in the form of secondary particles with primary particle sizes in the micrometer range, heat treatment must be performed at a higher temperature than that for secondary particles with primary particle sizes less than 1 μm in the submicrometer range. However, as the heat treatment temperature increases, the layered structure of lithium transition metal composite oxides degenerates into a rock salt structure, resulting in reduced crystallinity, which in turn leads to a decrease in the performance of the cathode active material. In particular, at high heat treatment temperatures, nickel is most likely to cause the layered structure of lithium transition metal composite oxides to degenerate into a rock salt structure. Therefore, this degradation becomes more severe when the nickel content in the lithium transition metal composite oxide constituting the cathode active material increases. Therefore, conventionally, cathode active materials in the form of secondary particles with primary particle sizes in the micrometer range are only suitable for medium-nickel cathode active materials where the nickel content in the transition metal of the lithium transition metal composite oxide is 50 mol%. For high-nickel cathode active materials, which have excellent capacity characteristics due to the high nickel content in the transition metal of the lithium transition metal composite oxide, it is not possible to manufacture cathode active materials in the form of secondary particles with primary particle sizes in the micrometer range.

[0116] However, in the cathode active material of the present invention, even if the nickel content in the transition metal of the lithium transition metal composite oxide is high and thus the layered structure of the lithium transition metal composite oxide degenerates into a rock salt structure at high heat treatment temperatures, the rock salt structure can be restored to a layered structure to solve the aforementioned problems. Specifically, unlike conventional nickel cathode active materials, the cathode active material of the present invention is a high-nickel cathode active material containing a lithium transition metal composite oxide with a nickel content of 60 mol% or more in the total transition metal, and includes secondary particles with a primary particle size in the micrometer range. However, by restoring the rock salt structure formed by high-temperature heat treatment to a layered structure, the lithium transition metal composite oxide exhibits excellent crystallinity, thus simultaneously solving the problems of conventional secondary particles and single particles. The cathode active material of the present invention can be manufactured by restoring the rock salt structure formed by high heat treatment temperatures to a layered structure as described above, and the method of restoring the rock salt structure to a layered structure is not limited, but according to an embodiment of the present invention, this method can be a method of applying a cobalt (Co) coating to a lithium transition metal composite oxide including a rock salt structure formed by high heat treatment temperatures.

[0117] According to embodiments of the present invention, multiple primary particles may include disc-shaped primary particles. As a specific example, three or more disc-shaped primary particles are used, in which case the cell life and energy density are excellent.

[0118] According to an embodiment of the present invention, a disc-shaped primary particle can refer to a particle with an interior angle on the same side of 150° or more and 210° or less, a minor diameter of 0.3 μm or more, and an aspect ratio (major diameter / minor diameter) of 1.5 or more. Specifically, when observing a SEM image of the surface or cross-section of a secondary particle, the interior angle on the same side is generated when an imaginary contact line with the most contact points is drawn from two boundary lines existing within an angle of 45° or less, with the major diameter direction of the primary particle as a reference, and an imaginary line intersecting these two contact lines is drawn. As a specific example, the minor diameter of the disc-shaped primary particle can be 0.3 μm or more, 0.4 μm or more, 0.5 μm or more, 0.6 μm or more, 0.7 μm or more, 0.8 μm or more, 0.9 μm or more, or 1.0 μm or more. Here, when the minor diameter of the disk-shaped primary particle is 0.3 μm or more and the aspect ratio (major diameter / minor diameter) is 1.5 or more, the area ratio of the (003) plane in the crystal plane on the surface of the primary particle can be maximized.

[0119] According to an embodiment of the present invention, a disk-shaped primary particle can refer to a particle with an interior angle on the same side of 150° or more and 210° or less, and the area ratio of the (003) facet among the crystal planes on the surface of the primary particle is the largest. The same-side interior angle is generated when, from an SEM image of the surface or cross-section of a secondary particle, an imaginary contact line with the most contact points is drawn from two boundary lines existing within an angle of 45° or less with the major axis direction of the primary particle as a reference, and an imaginary line intersecting these two contact lines is drawn. Here, when the area ratio of the (003) facet among the crystal planes on the surface of the disk-shaped primary particle is the largest, the minor axis of the primary particle can be 0.3 μm or more, and the aspect ratio (major axis / minor axis) is 1.5 or more. In other words, the fact that the area ratio of the (003) facet among the crystal planes on the surface of the primary particle is the largest can be confirmed by the fact that the minor axis of the primary particle is 0.3 μm or more and the aspect ratio (major axis / minor axis) is 1.5 or more.

[0120] As a specific example, the positive electrode active material may include secondary particles in which a plurality of primary particles are aggregated; wherein the plurality of primary particles have an average particle size of more than 1.5 μm and less than 5.0 μm as measured by SEM images, and the particle size of the primary particles is based on the particle size of the major axis of the primary particles; wherein the plurality of primary particles include disc-shaped primary particles, wherein, in the primary particles observed from SEM images of the surface or cross section of the secondary particles, when an imaginary contact line with the maximum number of contact points is drawn for the two boundary lines of the primary particles existing within an angle of less than 45° based on the major axis direction, and an imaginary line intersecting the two contact lines is drawn, the same-side interior angle of the disc-shaped primary particles is more than 150° and less than 210°, and wherein the area ratio of the (003) plane in the crystal planes on the surface of the primary particles is the largest.

[0121] According to an embodiment of the present invention, in a frequency distribution plot showing the cumulative volume distribution of a positive electrode active material measured using a laser diffraction particle size analyzer, where the x-axis represents the logarithmic scale of particle size with x-values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y-values ​​gradually increasing from bottom to top, when a triangle is drawn with the peak point at the top of the y-axis where the peak appears at the mode, and the two contact points of the frequency distribution curve that contact at the full width at half maximum (FWHM) of the mode, the interior angle (θ) of the left contact point among the two contact points of the frequency distribution curve of the positive electrode active material is... L ) and the interior angle (θ R The difference (θ) between L -θ R The angle (θ) can be greater than 6 and less than 20. As a specific example, the interior angle (θ) at the left contact point... L The interior angle (θ) at the right contact point R The difference (θ) between L -θR The value can be 6 or higher, 7 or higher, 8 or higher, 9 or higher, 10 or higher, 11 or higher, 12 or higher, 13 or higher, or 14 or higher, or it can be less than 20, less than 19, less than 18, less than 17, less than 16, or less than 15. The ratio of the interior angle of the left contact point to the interior angle of the right contact point (θL / θR) of the positive electrode active material can be 1.100 or higher and less than 2.000. As a specific example, the ratio of the interior angle at the left contact point to the interior angle at the right contact point (θL / θR) is... L / θ R The values ​​can be 1.100 or higher, 1.110 or higher, 1.120 or higher, 1.130 or higher, 1.140 or higher, 1.150 or higher, 1.160 or higher, 1.170 or higher, 1.180 or higher, 1.190 or higher, 1.200 or higher, 1.210 or higher, 1.220 or higher, 1.230 or higher, 1.240 or higher, 1.250 or higher, 1.260 or higher, 1.270 or higher, 1.280 or higher, 1.290 or higher, 1.300 or higher, 1.310 or higher, 1.320 or higher, 1.330 or higher, 1.340 or higher, or 1.350 or higher. The values ​​can be above 1.360, 1.370, 1.380, 1.390, 1.400, 1.410, 1.420, 1.430, or 1.440, and can also be below 1.450, below 1.460, below 1.470, below 1.480, below 1.490, below 1.500, below 1.550, below 1.600, below 1.650, below 1.700, below 1.750, below 1.800, below 1.850, below 1.900, below 1.950, or below 2.000. Here, the frequency distribution plot can be a single-peaked distribution plot.

[0122] According to an embodiment of the present invention, in the frequency distribution plot showing the cumulative volume distribution of the positive electrode active material obtained by measuring the positive electrode active material using a laser diffraction particle size analyzer, the positive electrode active material can exhibit a positively skewed state, where the x-axis represents a linear scale of particle size with x-values ​​gradually increasing from left to right, and the y-axis represents a weighted distribution with y-values ​​gradually increasing from bottom to top. Here, the frequency distribution plot can be a unimodal distribution plot.

[0123] According to an embodiment of the present invention, the skewness value (S) of the positive electrode active material is compared with the y-value (P) of the peak point at the y-axis apex of the peak appearing in the mode of the cumulative volume distribution. 众数 The ratio of S / P 众数 The value can be above 0.037 and below 0.150. As a specific example, in positive electrode active materials, the skewness value (S) of the peak at the y-axis apex of the mode peak of the cumulative volume distribution differs from the y-value (P). 众数The ratio of S / P 众数 The possible values ​​are 0.037 or higher, 0.038 or higher, 0.039 or higher, 0.040 or higher, 0.041 or higher, 0.042 or higher, 0.043 or higher, 0.044 or higher, 0.045 or higher, 0.046 or higher, 0.047 or higher, 0.048 or higher, 0.049 or higher, 0.050 or higher, 0.051 or higher, 0.052 or higher, 0.053 or higher, and 0. 054 and above, 0.055 and above, 0.056 and above, 0.057 and above, 0.058 and above, 0.059 and above, 0.060 and above, 0.061 and above, 0.062 and above, 0 .063 and above, 0.064 and above, 0.065 and above, 0.066 and above, 0.067 and above, 0.068 and above, 0.069 and above, 0.070 and above, 0.071 and above, 0 .072 and above, 0.073 and above, 0.074 and above, 0.075 and above, 0.076 and above, 0.077 and above, 0.078 and above, 0.079 and above, 0.080 and above, 0.081 and above, 0.082 and above, 0.083 and above, 0.083 and above, 0.084 and above, 0.085 and above, 0.086 and above, 0.087 and above, 0.088 and above, The skewness value (S) can be 0.089 or higher, 0.090 or higher, 0.091 or higher, 0.092 or higher, 0.093 or higher, 0.094 or higher, 0.095 or higher, 0.096 or higher, 0.097 or higher, 0.098 or higher, 0.099 or higher, or 0.100 or higher, and can also be below 0.150, below 0.140, below 0.130, below 0.120, or below 0.110. Here, the skewness value (S) can be calculated according to Equation 3 below.

[0124] [Equation 3]

[0125] Skewness value (S) = 3 X {(volume average particle size - (D)} 50 )} / (Standard deviation of particle size of positive electrode active material)

[0126] According to one embodiment of the present invention, the positive electrode active material may have a surface area of ​​0.20 m², as measured by nitrogen adsorption BET specific surface area analysis. 2 / g or more and 0.35 m 2 The BET specific surface area is below / g. As a specific example, in positive electrode active materials, the BET specific surface area measured by nitrogen adsorption BET specific surface area analysis can be as low as 0.20 m². 2 / g or more, 0.21m 2 / g or more, 0.22 m 2 / g or more, 0.23 m 2 / g or more, 0.24 m2 / g or more, 0.25 m 2 / g or more, 0.26 m 2 / g or more, 0.27 m 2 / g or more, 0.28 m 2 / g or more, 0.29 m 2 / g or more, 0.30 m 2 / g or more, or 0.31 m 2 / g or more, and can also be 0.35 m 2 / g or less, or 0.34 m 2 / g or less. Within this range, DC resistance can be reduced and rolling density improved.

[0127] According to one embodiment of the present invention, in the positive electrode active material, based on the cumulative volume distribution of secondary particles measured using a laser diffraction particle size analyzer, the average particle size (D) is... 50 The size can be greater than 7.0 μm and less than 20.0 μm; and, based on SEM images of the secondary particle cross-section, the size is within the range of the average particle size (D) of the secondary particles. 50 Within the range of the secondary particle cross-section, the number of primary particle cross-sections identified within a unit area of ​​5 μm width × 5 μm length in the secondary particle cross-section can be more than 1 and less than 100.

[0128] According to one embodiment of the present invention, based on SEM images of secondary particle cross-sections, for particles with sizes within the average particle size (D... 50 For the secondary particle cross-section within the range of ), the number of primary particle cross-sections identified within a 5 μm wide × 5 μm long unit area of ​​the secondary particle cross-section refers to the total number of primary particle cross-sections identified within that unit area. This includes not only primary particles whose entire cross-section is contained within that unit area, but also primary particles whose at least a portion of their cross-section is contained within that unit area. Furthermore, the 5 μm wide × 5 μm long unit area within the secondary particle cross-section is the unit area at any point on the secondary particle cross-section, and its location is unrestricted as long as it is on the secondary particle cross-section.

[0129] According to one embodiment of the present invention, the size observed in the SEM image of the cross-section of the secondary particles is within the average particle size (D) of the secondary particles. 50Regarding the cross-section of secondary particles within the range of ), the number of primary particle cross-sections identified within a unit area of ​​5 μm width × 5 μm length in the cross-section of secondary particles can be 1 or more and 100 or less. Specifically, this can be 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, or 10 or more, and can also be less than 100, less than 95, less than 90, less than 85, less than 80, less than 75, less than 70, less than 65, less than 60, less than 55, less than 50, less than 45, less than 40, less than 35, less than 30, or less than 25. When this range is met, the positive electrode active material can include an average particle size (D). 50 The secondary particles are large-diameter secondary particles with a diameter of 7.0 μm or more and 20.0 μm or less. These large-diameter secondary particles are formed by the aggregation of multiple primary particles with the same particle size as conventional single particles as measured by SEM images, ranging from 0.5 μm to 5.0 μm (specifically, micrometer-level size of 1.0 μm or more, and more specifically, average particle size of 2.0 μm or more and 3.5 μm or less).

[0130] According to one embodiment of the present invention, in the positive electrode active material, based on the cumulative volume distribution of secondary particles measured using a laser diffraction particle size analyzer, the average particle size (D) is... 50 The size can be greater than 7.0 μm and less than 20.0 μm; and, for the electron backscatter diffraction (EBSD) pattern of the SEM image of the secondary particle cross-section (measured under the following conditions: accelerating voltage 20 kV, WD 16 mm, measurement magnification 5,000x (16 μm width × 16 μm height), step size 0.025 μm), the size observed in the secondary particle's average particle size (D) is within the range of the secondary particle's average particle size. 50 For secondary particle cross sections within the range of ), the number of grain cross sections identified within a unit area of ​​5 μm width × 5 μm length in the secondary particle cross section can be more than 1 and less than 150.

[0131] According to one embodiment of the present invention, the size observed in the electron backscatter diffraction (EBSD) pattern of the SEM image of the secondary particle cross-section (measured under the following conditions: accelerating voltage 20 kV, WD 16 mm, measurement magnification 5,000x (16 μm width × 16 μm height), step size 0.025 μm) is in the average particle size (D) of the secondary particles. 50For the cross-section of secondary particles within the range of ), the number of grain cross-sections identified within a 5 μm wide × 5 μm long unit area of ​​the secondary particle cross-section refers to the number of cross-sections of all grains identified within that unit area. This includes not only grains whose entire cross-section is contained within that unit area, but also grains whose cross-section is at least partially contained within that unit area. Furthermore, the 5 μm wide × 5 μm long unit area within the cross-section of the secondary particle is the unit area at any point on the cross-section of the secondary particle, and its location is unrestricted as long as it is on the cross-section of the secondary particle.

[0132] According to one embodiment of the present invention, in a positive electrode active material, the size observed in the electron backscatter diffraction (EBSD) pattern of a SEM image of a secondary particle cross-section (measured under the following conditions: accelerating voltage 20 kV, WD 16 mm, measurement magnification 5,000x (16 μm width × 16 μm height), step size 0.025 μm) is relative to the average particle size (D) of the secondary particles. 50 For the secondary particle cross-section within the range of ), the number of grains identified in the cross-section of the secondary particle within a unit area of ​​5 μm width × 5 μm length can be more than 1 and less than 150. As specific examples, it can be more than 1, more than 2, more than 3, more than 4, more than 5, more than 6, more than 7, more than 8, more than 9, and it can also be less than 150, less than 145, less than 140, less than 135, less than 130, less than 125, less than 120, less than 115, less than 110, less than 105, less than 100, less than 95, less than 90, less than 85, less than 80, less than 75, less than 70, less than 65, less than 60, less than 55, less than 50, less than 45, less than 40, less than 35, less than 30, less than 25, or less than 20. When this range is met, the positive electrode active material may include an average particle size (D). 50 The secondary particles are large-diameter secondary particles with a diameter of 7.0 μm or more and 20.0 μm or less. These large-diameter secondary particles are formed by the aggregation of multiple primary particles with the same diameter as conventional single particles as measured by SEM images, ranging from 0.5 μm to 5.0 μm (specifically, micrometer-level size of 1.0 μm or more, and more specifically, average particle size of 2.0 μm or more and 3.5 μm or less).

[0133] According to one embodiment of the present invention, the single crystallinity of the positive electrode active material can be 0.15 μm. 3 The above is calculated using the following equation 1.

[0134] [Equation 1]

[0135]

[0136] Among them, the size observed in the electron backscatter diffraction (EBSD) pattern of the SEM image of the secondary particle cross-section (measured under the following conditions: accelerating voltage 20 kV, WD 16 mm, measurement magnification 5000x (16 μm width × 16 μm height), step size 0.025 μm) is the average particle size of the secondary particles (D). 50 Among all grains identified in the cross-section of secondary particles within the range of ) , for a cross-sectional area of ​​0.196 μm 2 The cross-section of the above grains, the radius (grain) is the radius of the grain cross-section assuming the grain cross-section is circular; and n is the number of grains.

[0137] According to one embodiment of the present invention, the single crystallinity of the positive electrode active material can be calculated to be 0.15 μm using Equation 1 above. 3 Above and 12.70 μm 3 Below, as a specific example, the single crystallinity of the positive electrode active material calculated by Equation 1 above can be 0.15 μm. 3 Above, 0.20 μm 3 Above, 0.25 μm 3 Above, 0.30 μm 3 Above, 0.35 μm 3 Above, 0.40μm 3 Above, 0.45 μm 3 Above, 0.50 μm 3 Above, 0.55 μm 3 Above, 0.60 μm 3 Above, 0.65 μm 3 Above, 0.70 μm 3 Above, 0.75 μm 3 Above, 0.80 μm 3 Above, 0.85 μm 3 Above, 0.90 μm 3 Above, 0.95 μm 3 Above, 1.00 μm 3 Above, or 1.05 μm 3 The above can also be 20.00 μm 3 Below, 19.00 μm 3 Below, 18.00 μm 3 Below, 17.00 μm 3 Below, 16.00 μm 3 Below, 15.00 μm 3Below, 14.00 μm 3 Below, 13.00 μm 3 Below, or 12.70 μm 3 The following limits apply, but there is no specific upper limit.

[0138] According to one embodiment of the present invention, the positive electrode active material may include a lithium transition metal composite oxide containing aluminum (Al), yttrium (Y), and zirconium (Zr). As a specific example, the positive electrode active material may include aluminum (Al), yttrium (Y), and zirconium (Zr) as doping elements.

[0139] According to one embodiment of the present invention, the aluminum (Al) content can be from 500 ppm to 3,000 ppm based on the total weight of the lithium transition metal complex oxide. As a specific example, the aluminum (Al) content can be more than 500 ppm, more than 1,000 ppm, or more than 1,500 ppm based on the total weight of the lithium transition metal complex oxide, and can also be less than 3,000 ppm, less than 2,500 ppm, or less than 2,000 ppm.

[0140] According to one embodiment of the present invention, the yttrium (Y) content can be from 100 ppm to 2,000 ppm based on the total weight of the lithium transition metal complex oxide. As a specific example, the yttrium (Y) content can be 100 ppm or more, 200 ppm or more, 300 ppm or more, 400 ppm or more, or 500 ppm or more, and can also be less than 2,000 ppm, less than 1,900 ppm, less than 1,800 ppm, less than 1,700 ppm, less than 1,600 ppm, or less than 1,500 ppm.

[0141] According to one embodiment of the present invention, the zirconium (Zr) content can be from 500 ppm to 5,000 ppm based on the total weight of the lithium transition metal complex oxide. As a specific example, the zirconium (Zr) content can be more than 500 ppm, more than 1,000 ppm, or more than 1,500 ppm based on the total weight of the lithium transition metal complex oxide, and can also be less than 5,000 ppm, less than 4,500 ppm, less than 4,000 ppm, less than 3,500 ppm, or less than 3,000 ppm.

[0142] According to one embodiment of the present invention, the positive electrode active material may include a lithium transition metal composite oxide with an average composition represented by the following chemical formula 2.

[0143] [Chemical Formula 2]

[0144] Li x [Ni a Co b Mn c Al e Y f Zr g M 2 d O 2-y A y

[0145] In Equation 2, M 2 The x is selected from one or more of B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, V, F, P, and S; and A is selected from one or more of F, Cl, Br, I, and S; and 0.9 ≤ x ≤ 1.3, 0.6 ≤ a < 1.0, 0 <b<0.4、0<c<0.4、0≤d≤0.2、0<e≤0.01、0<f≤0.0006、0<g≤0.0005、a+b+c+d+e+f+g=1、0≤y≤0.2。

[0146] According to an embodiment of the present invention, in the above chemical formula 2, x is the molar ratio of lithium to transition metal in the lithium transition metal composite oxide, and can be 0.9 or more, 0.95 or more, or 1.0 or more, or 1.1 or less, 1.07 or less, 1.05 or less, or 1.03 or less.

[0147] According to an embodiment of the present invention, in chemical formula 2, a, b, c, d, e, f, and g can be nickel (Ni), cobalt (Co), manganese (Mn), and a dopant element (Mn), respectively, among transition metals. 2The mole fractions of nickel (Ni), aluminum (Al), yttrium (Y), and zirconium (Zr) in the transition metal are denoted as a. As a specific example, a represents the mole fraction of nickel (Ni) in the transition metal, and can be 0.6 or more, 0.7 or more, 0.8 or more, 0.85 or more, 0.88 or more, 0.90 or more, 0.91 or more, 0.92 or more, 0.93 or more, 0.94 or more, 0.95 or more, or 0.96 or more, and can also be less than 1.0, less than 0.99, less than 0.98, less than 0.97, or less than 0.96. Furthermore, b represents the mole fraction of cobalt (Co) in the transition metal, and can be greater than 0, 0.01 or more, 0.02 or more, or 0.03 or more, and can also be less than 0.4, less than 0.3, less than 0.2, less than 0.1, less than 0.09, less than 0.08, less than 0.07, less than 0.06, or less than 0.05. c represents the mole fraction of manganese (Mn) in the transition metal, and can be greater than 0, 0.01, or 0.05, or less than 0.4, 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, or 0.05. d represents the dopant element (Mn). 2 The mole fraction of a substance in a transition metal, and may be 0, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, 0.10 or more, 0.11 or more, 0.12 or more, 0.13 or more, 0.14 or more, 0.15 or more, 0.16 or more, 0.17 or more, 0.18 or more, or 0. The value can be greater than 19, or less than 0.20, 0.19, 0.18, 0.17, 0.16, 0.15, 0.14, 0.13, 0.12, 0.11, 0.10, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, or 0.01. e represents the mole fraction of aluminum (Al) in the transition metal, and can be greater than 0, greater than 0.001, greater than 0.002, greater than 0.003, greater than 0.004, or greater than 0.005, or less than 0.01, less than 0.009, or less than 0.008. f represents the mole fraction of yttrium (Y) in the transition metal, and can be greater than 0, greater than 0.0001, greater than 0.0002, or greater than 0.0003, or less than 0.0006, less than 0.0005, or less than 0.0004. g represents the mole fraction of zirconium (Zr) in the transition metal, and can be greater than 0, greater than 0.0001, or greater than 0.0002, or less than 0.0005, or less than 0.0004.

[0148] According to an embodiment of the present invention, in chemical formula 2, y is the molar ratio of element A that replaces oxygen in the lithium transition metal composite oxide, and can be greater than 0, more than 0.01, more than 0.02, or more than 0.03, or less than 0.2, less than 0.15, or less than 0.1.

[0149] According to embodiments of the present invention, the positive electrode active material may include aluminum (Al), zirconium (Zr), and M. 3 Transition metal composite oxides. As specific examples, positive electrode active materials may include aluminum (Al), zirconium (Zr), and Mn. 3 As a dopant element.

[0150] According to an embodiment of the present invention, M 3 It can be a metallic element with an oxidation state of +4 or higher. For example, M 3 It can be at least one selected from titanium (Ti), tantalum (Ta), tungsten (W), vanadium (V), molybdenum (Mo), and niobium (Nb).

[0151] According to embodiments of the present invention, the total weight of the lithium transition metal complex oxide may contain 500 ppm to 3,000 ppm of aluminum (Al). As a specific example, the aluminum (Al) content may be 500 ppm or more, 1,000 ppm or more, or 1,500 ppm or more, and may also be 3,000 ppm or less, 2,500 ppm or less, or 2,000 ppm or less.

[0152] According to embodiments of the present invention, the total weight of the lithium transition metal complex oxide may contain 500 ppm to 3,000 ppm of zirconium (Zr). As a specific example, the zirconium (Zr) content may be 500 ppm or more, 1,000 ppm or more, or 1,500 ppm or more, and may also be less than 3,000 ppm, less than 2,500 ppm, or less than 2,000 ppm.

[0153] According to embodiments of the present invention, based on the total weight of the lithium transition metal composite oxide, it may contain 100 ppm to 2,000 ppm of M. 3 As a specific example, based on the total weight of lithium transition metal composite oxides, M 3The content can be above 100 ppm, above 200 ppm, above 300 ppm, above 400 ppm, or above 500 ppm, and can also be below 2,000 ppm, below 1,900 ppm, below 1,800 ppm, below 1,700 ppm, below 1,600 ppm, or below 1,500 ppm.

[0154] According to an embodiment of the present invention, the positive electrode active material includes a coating portion formed on at least one of the surface of primary particles, the interface of primary particles, and the surface of secondary particles, wherein the coating portion may include at least one coating element selected from the group consisting of cobalt (Co) and boron (B).

[0155] According to an embodiment of the present invention, the coating portion may be an island-shaped coating portion formed on at least one of the surface of the primary particle, the interface of the primary particle, and the surface of the secondary particle.

[0156] According to an embodiment of the present invention, the coating portion may be a coating layer formed around at least one of the surface of the primary particle, the interface of the primary particle, and the surface of the secondary particle.

[0157] According to embodiments of the present invention, the coating portion may include at least one of the following: a coating portion containing cobalt (Co), a coating portion containing cobalt (Co) and boron (B), and a coating portion containing boron (B).

[0158] According to an embodiment of the present invention, the coating portion may include a coating portion containing cobalt (Co), a coating portion containing cobalt (Co) and boron (B), and a coating portion containing boron (B) formed sequentially.

[0159] According to one embodiment of the present invention, the coated portion may include cobalt boron oxide.

[0160] According to one embodiment of the present invention, when positive electrode active material is placed in a cylindrical mold with a diameter of 13 mm and a force is applied using an automatic pelletizing machine until a force equivalent to 9,000 kgf is reached to form pellets, the positive electrode active material can have a particle size of 3.60 g / cm³, calculated by the following Equation 2. 3 The above rolling density.

[0161] [Equation 2]

[0162] Rolled density (g / cm³) 3 = Weight of positive electrode active material (g) / Volume of aggregate (cm³) 3 )

[0163] According to an embodiment of the present invention, the positive electrode active material may have a concentration of 3.60 g / cm³, calculated using Equation 2 above. 3 The rolling density mentioned above, as a specific example, can be 3.61 g / cm³. 3 Above, 3.62 g / cm 3 Above, 3.63 g / cm 3 Above, 3.64 g / cm 3 Above, 3.65 g / cm 3 Above, 3.66 g / cm 3 Above, 3.67 g / cm 3 Above, 3.68 g / cm 3 Above, 3.69 g / cm 3 Above, 3.70 g / cm 3 Above, or 3.71 g / cm 3 The above can also be 10.0 g / cm³. 3 The following limits apply, but there is no specific upper limit.

[0164] According to an embodiment of the present invention, for a lithium secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode, a separator disposed between the positive and negative electrodes, and an electrolyte, when the lithium secondary battery is charged with a current of 0.5 C and then discharged with a current of 1.0 C, the discharge capacity of the positive electrode active material can be more than 92.0% of the discharge capacity when charged with a current of 0.5 C and then discharged with a current of 0.1 C. Here, the lithium secondary battery is used to test the discharge capacity based on the output characteristics of the positive electrode active material, wherein there are no particular restrictions on the components other than the positive electrode active material as long as they can be used in the lithium secondary battery. As a specific example, the discharge capacity of the positive electrode active material when charging the lithium secondary battery with a current of 0.5 C and then discharging it with a current of 1.0 C can be more than 92.0%, 92.1%, 92.2%, 92.3%, 92.4%, 92.5%, 92.6%, 92.7%, 92.8%, 92.9%, 93.0%, or 93.1% of the discharge capacity when charging the lithium secondary battery with a current of 0.5 C and then discharging it with a current of 0.1 C, or it can be less than 100%, but there is no particular upper limit.

[0165] According to an embodiment of the present invention, for a lithium secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode, a separator disposed between the positive and negative electrodes, and an electrolyte, when the lithium secondary battery is charged with a current of 0.5 C and then discharged with a current of 2.0 C, the discharge capacity can be more than 89.0% of the discharge capacity when charged with a current of 0.5 C and then discharged with a current of 0.1 C. Here, the lithium secondary battery is used to test the discharge capacity based on the output characteristics of the positive electrode active material, wherein there are no particular restrictions on the components other than the positive electrode active material as long as they can be used in the lithium secondary battery. As a specific example, the discharge capacity of the positive electrode active material when charging the lithium secondary battery with a current of 0.5 C and then discharging it with a current of 2.0 C can be more than 89.0%, 89.1%, 89.2%, 89.3%, 89.4%, 89.5%, 89.6%, 89.7%, 89.8%, 89.9%, 90.0%, 90.1%, 90.2%, 90.3%, or 90.4% of the discharge capacity when charging the lithium secondary battery with a current of 0.5 C and then discharging it with a current of 0.1 C, or it can be less than 100%, but there is no particular upper limit.

[0166] According to an embodiment of the present invention, when the volume value is calculated for each primary particle observed in a SEM image (measurement magnification of 3,000x) of the secondary particle surface based on the following Equation 5, the positive electrode active material can have a single particle formation degree (Dv) of 1.2 μm or more and 3.8 μm or less. 50 ), which corresponds to the diameter of the volume at 50% of the cumulative volume distribution of particles.

[0167] [Equation 5]

[0168]

[0169] In equation 5 above:

[0170] The radius is the radius of the surface of the primary particle, assuming it is circular, as observed from the SEM image (measured at 3,000x magnification) of the secondary particle surface.

[0171] As a specific example, the single-particle formation degree (Dv) of positive electrode active materials 50The micrometer can be 1.2 μm or larger, 1.3 μm or larger, 1.4 μm or larger, 1.5 μm or larger, 1.6 μm or larger, or 1.65 μm or larger, or it can be 3.8 μm or smaller, 3.7 μm or smaller, 3.6 μm or smaller, 3.59 μm or smaller, 3.58 μm or smaller, 3.57 μm or smaller, 3.56 μm or smaller, or 3.55 μm or smaller.

[0172] Method for manufacturing positive electrode active materials

[0173] This invention provides a method for manufacturing a positive electrode active material.

[0174] According to an embodiment of the present invention, the method for manufacturing the positive electrode active material can be the above-described method for preparing the positive electrode active material.

[0175] According to an embodiment of the present invention, a method for manufacturing a positive electrode active material may include the step of preparing a sintered product by mixing a positive electrode active material precursor containing nickel, cobalt and manganese with a lithium raw material and sintering the mixture.

[0176] According to an embodiment of the present invention, step (S10) can be performed by the following methods: a method of sintering in one sintering step by dividing the temperature range (one-step method), a method of sintering by dividing the sintering into two sintering steps (two-step method), a method of pre-sintering and then dividing the temperature range in one sintering step (pre-sintering method), etc.

[0177] According to an embodiment of the present invention, the one-step method is a method of continuously sintering at two temperature ranges in a single sintering step. In this method, a mixture of positive electrode active material precursor and lithium raw material can be sintered in the first stage, and then a second stage of sintering can be performed immediately by changing the temperature range. In this case, the second stage of sintering can be performed at a lower temperature than the first stage of sintering, and each sintering temperature can be adjusted according to the nickel content. Through this temperature adjustment, the shape and size of the primary particles and the average particle size of the secondary particles can be controlled.

[0178] According to an embodiment of the present invention, the two-step method involves sintering in two stages: primary sintering and secondary sintering. The primary sintering can be performed on a mixture of a cathode active material precursor and a lithium raw material. The product obtained from the primary sintering can be pulverized, and then the pulverized product can be subjected to secondary sintering. In this case, the secondary sintering can be performed at a lower temperature than the primary sintering, and the sintering temperature can be adjusted according to the nickel content. This temperature adjustment allows control over the shape and size of the primary particles and the average particle size of the secondary particles.

[0179] According to an embodiment of the present invention, the pre-sintering method is a method of pre-sintering before one-step sintering, wherein a mixture of positive electrode active material precursor and lithium raw material can be pre-sintered, and the pre-sintered product can be processed in one step. In this case, pre-sintering can be carried out at a lower temperature than one-step sintering, and each sintering temperature can be adjusted according to the nickel content. Through this temperature adjustment, the shape and size of the primary particles and the average particle size of the secondary particles can be controlled.

[0180] According to one embodiment of the present invention, the positive electrode active material precursor may contain nickel at a content of 60 mol% or more in the transition metal. As a specific example, the positive electrode active material precursor may be a transition metal hydroxide containing nickel, cobalt, and manganese, wherein the nickel content in the transition metal is 60 mol% or more. As a specific example, the transition metal hydroxide may have an average composition represented by the following formula 3:

[0181] [Chemical Formula 3]

[0182] Ni a' Co b' Mn c'( OH)2

[0183] Where 0.6≤a'<1.0, 0 <b'<0.4, 0<c'<0.4, a'+b'+c’=1。

[0184] According to an embodiment of the present invention, in chemical formula 3, a', b', and c' can be the mole fractions of nickel (Ni), cobalt (Co), and manganese (Mn) in the transition metal, respectively. As a specific example, a' is the mole fraction of nickel (Ni) in the transition metal, and can be 0.6 or more, 0.7 or more, 0.8 or more, 0.85 or more, 0.88 or more, 0.90 or more, 0.91 or more, 0.92 or more, 0.93 or more, 0.94 or more, 0.95 or more, or 0.96 or more, and can also be less than 1.0, less than 0.99, less than 0.98, less than 0.97, or less than 0.96. Furthermore, b' represents the mole fraction of cobalt (Co) in the transition metal, and can be greater than 0, greater than 0.01, greater than 0.02, or greater than 0.03, or less than 0.4, less than 0.3, less than 0.2, less than 0.1, less than 0.09, less than 0.08, less than 0.07, less than 0.06, or less than 0.05. c' can represent the mole fraction of manganese (Mn) in the transition metal, and can be greater than 0, greater than 0.01, or greater than 0.05, or less than 0.4, less than 0.3, less than 0.2, less than 0.1, less than 0.09, less than 0.08, less than 0.07, less than 0.06, or less than 0.05.

[0185] According to embodiments of the present invention, the lithium raw material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or hydroxy oxide, such as Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7 or mixtures thereof.

[0186] According to an embodiment of the present invention, step (S10) can be performed by further including at least one doping material selected from the group consisting of: Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S, and Y. The doping material can be acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or hydroxyoxide containing the above elements, for example, Al2O3, Al(OH)3, Al(NO3)3·9H2O, Al2(SO4)3, Y2O3, ZrO2, etc.

[0187] According to embodiments of the present invention, the doping material may include Al, Y, and Zr. Additionally, the doping material may include Al, Zr, and a metal element with an oxidation state of +4 or higher (M). 3 ).

[0188] According to one embodiment of the present invention, when the positive electrode active material precursor and the lithium raw material are mixed in step (S10), the molar ratio (Li / M) of lithium (Li) in the lithium raw material to the transition metal (M) in the positive electrode active material precursor can be 0.9 or more and 1.3 or less. As a specific example, Li / M can be 0.9 or more, 0.95 or more, or 1.0 or more, or 1.1 or less, 1.07 or less, 1.05 or less, or 1.04 or less, and the Li / M can be adjusted according to the nickel content in the transition metal.

[0189] According to one embodiment of the present invention, the method for preparing the positive electrode active material may further include a step (S20) of coating the positive electrode active material prepared in step (S10). As a specific example, step (S20) may be performed by comprising at least one coating material selected from the group consisting of Co and B. Furthermore, step (S20) may be performed by further comprising an Al coating material.

[0190] According to an embodiment of the present invention, the coating in step (S20) can be performed by coating each coating material simultaneously, or by coating each coating material separately and sequentially. As a specific example, the coating in step (S20) may include: a step (S21) of mixing the positive electrode active material with Co coating material and Al coating material and performing heat treatment, and a step (S22) of mixing B coating material with the coating product prepared in step (S21) and performing heat treatment.

[0191] According to embodiments of the present invention, the Co coating material can be a cobalt hydroxide, such as Co(OH)2, the Al coating material can be an aluminum hydroxide, such as Al(OH)3, and the B coating material can be H3BO3.

[0192] According to an embodiment of the present invention, when performing steps (S10) and (S20), the method for preparing the positive electrode active material may include a step of pulverizing the sintered product as needed after sintering, wherein the pulverization can be performed using any pulverizing device capable of pulverizing the positive electrode active material without particular limitation.

[0193] According to embodiments of the present invention, doping raw materials and coating raw materials can be added and adjusted to meet the doping element content and coating element content of the above-mentioned positive electrode active material.

[0194] positive electrode

[0195] This invention provides a positive electrode comprising a positive electrode active material.

[0196] According to an embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer may include a positive electrode active material.

[0197] According to embodiments of the present invention, the positive electrode current collector may include a highly conductive metal, and there are no particular limitations, as long as the positive electrode active material layer is easily adhered thereto and it is not reactive within the voltage range of the battery. The positive electrode current collector may be, for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. Furthermore, the positive electrode current collector can typically have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0198] According to embodiments of the present invention, in addition to the positive electrode active material, the positive electrode active material layer may also include conductive materials and binders as needed. In this case, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be from 80% to 99% by weight, more specifically, from 85% to 98.5% by weight, and excellent capacity characteristics can be exhibited within this range.

[0199] According to embodiments of the present invention, a conductive material is used to impart conductivity to the electrode, and any material can be used without particular limitation, as long as it is conductive in the battery to be constructed without causing a chemical change. Specific examples may include graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, and carbon fibers; metal powders or metal fibers, such as copper, nickel, aluminum, silver, etc.; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more thereof may be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material can be from 0.1% by weight to 15% by weight.

[0200] According to embodiments of the present invention, the adhesive improves the adhesion between particles of the positive electrode active material and the adhesion between the positive electrode active material and the current collector. Specific examples may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid and polymers in which hydrogen is substituted by Li, Na or Ca, or various copolymers thereof, and any one or a mixture of two or more thereof may be used. Based on the total weight of the positive electrode active material layer, the adhesive content may be from 0.1% by weight to 15% by weight.

[0201] According to embodiments of the present invention, in addition to using the aforementioned positive electrode active material, the positive electrode can be manufactured using conventional methods for manufacturing positive electrodes. Specifically, the aforementioned positive electrode active material, along with a binder, conductive material, and dispersant as needed, can be dissolved or dispersed in a solvent to prepare a composition for forming a positive electrode active material layer. This composition can be coated onto a positive electrode current collector, and then dried and calendered to produce a positive electrode. Alternatively, the positive electrode can be manufactured by casting the composition for forming the positive electrode active material layer onto a separate support, peeling the film from the support, and then pressing the film layer onto the positive electrode current collector.

[0202] According to embodiments of the present invention, the solvent can be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, water, etc., and any one or a mixture of two or more thereof can be used. Considering the coating thickness and manufacturing yield of the slurry, the amount of solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, and allows the slurry to have a certain viscosity, which can exhibit excellent thickness uniformity in the subsequent positive electrode preparation coating process.

[0203] Lithium secondary batteries

[0204] The present invention provides a lithium secondary battery including the above-described positive electrode.

[0205] According to one embodiment of the present invention, the lithium secondary battery may include: a positive electrode; a negative electrode; and a separator and an electrolyte between the positive electrode and the negative electrode. Furthermore, the lithium secondary battery may optionally further include: a battery container for housing an electrode assembly formed by the positive electrode, the negative electrode, and the separator, and a seal for sealing the battery container.

[0206] According to one embodiment of the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0207] According to one embodiment of the present invention, the negative electrode current collector is not particularly limited, as long as it has high conductivity and does not cause chemical changes in the battery. For example, it can be copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys, etc. Furthermore, the negative electrode current collector can typically have a thickness of 3 μm to 500 μm, and similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to increase the adhesion of the negative electrode active material. For example, it can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0208] According to one embodiment of the present invention, in addition to the negative electrode active material, the negative electrode active material layer may optionally include an adhesive and a conductive material.

[0209] According to one embodiment of the present invention, compounds capable of reversibly inserting and deintercalating lithium can be used as negative electrode active materials. Specific examples may include carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metal compounds that can be alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and metal oxides that can be doped or undoped with lithium, such as SiO₂. β(0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing metal compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more thereof can be used. Furthermore, lithium metal films can be used as anode active materials. In addition, low-crystallinity carbon, high-crystallinity carbon, etc., can all be used as carbon materials. Representative examples of low-crystallinity carbon can be soft carbon and hard carbon, while representative examples of high-crystallinity carbon can include amorphous, plate-like, sheet-like, spherical, or fibrous natural or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and high-temperature sintered carbon, such as coke derived from petroleum or coal tar pitch. Based on the total weight of the anode active material layer, the content of the anode active material can be from 80% to 99% by weight.

[0210] According to one embodiment of the invention, the adhesive for the negative electrode active material layer is a component that facilitates adhesion between the conductive material, the active material, and the current collector, and is typically added in an amount from 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such adhesives include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0211] According to one embodiment of the present invention, the conductive material of the negative electrode active material layer is a component used to further improve the conductivity of the negative electrode active material, wherein the amount added, based on the total weight of the negative electrode active material layer, can be less than 10% by weight, preferably less than 5% by weight. There are no particular limitations on the conductive material, as long as it is conductive and does not cause chemical changes in the battery. For example, it can be graphite such as natural or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking black; conductive fibers such as carbon fiber or metal fiber; fluorocarbons; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0212] According to one embodiment of the invention, a composition for forming a negative electrode active material layer can be prepared by dissolving or dispersing a negative electrode active material, an optional binder, and a conductive material in a solvent. This composition can be applied to a negative electrode current collector and dried to produce a negative electrode. Alternatively, the negative electrode can be manufactured by casting the composition for forming the negative electrode active material layer onto a separate support, peeling the film off the support, and then pressing the film layer onto the negative electrode current collector.

[0213] Meanwhile, according to one embodiment of the invention, the separator is used to separate the negative electrode and the positive electrode to provide a path for lithium ion movement. Any separator can be used without particular limitation, as long as it is commonly used as a separator in lithium secondary batteries. In particular, separators with excellent water retention capacity for the electrolyte and low resistance to electrolyte ion transfer are preferred. Specifically, porous polymer membranes can be used, for example, porous polymer membranes made of polyolefin polymers, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures having two or more layers thereof. Alternatively, conventional porous nonwoven fabrics can also be used, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, to ensure heat resistance or mechanical strength, coated separators comprising ceramic components or polymer materials can be used, and can optionally be used in single-layer or multi-layer structures.

[0214] According to one embodiment of the present invention, the electrolyte may be an organic liquid electrolyte, inorganic liquid electrolyte, solid polymer electrolyte, gel polymer electrolyte, solid inorganic electrolyte, or molten inorganic electrolyte, etc., which can be used to prepare lithium secondary batteries, but is not limited thereto. As a specific example, the electrolyte may contain an organic solvent and a lithium salt.

[0215] According to one embodiment of the present invention, any solvent can be used as the organic solvent without particular limitation, as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent can be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether solvent such as butyl ether or tetrahydrofuran; a ketone solvent such as cyclohexanone; an aromatic hydrocarbon solvent such as benzene or fluorobenzene; a carbonate solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (PC); an alcohol solvent such as ethanol or isopropanol; a nitrile solvent such as R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include double bonds, aromatic rings, or ether bonds); an amide solvent such as dimethylformamide; a dioxolane solvent such as 1,3-dioxolane; or sulfolane. Among them, carbonate solvents are preferred, and mixtures of cyclic carbonates (such as ethylene carbonate, propylene carbonate, etc.) with high ionic conductivity and high dielectric constant and low viscosity linear carbonate compounds (such as ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) that can improve the charge and discharge performance of the battery are more preferred.

[0216] According to one embodiment of the present invention, the lithium salt can be any compound without particular limitation, as long as it can provide lithium ions for use in lithium secondary batteries. Specifically, the anion of the lithium salt can be at least one selected from the group consisting of: F- Cl - ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - 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, LiB(C2O4)2, etc. The lithium salt is preferably used in a concentration range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, excellent electrolyte performance can be exhibited due to the appropriate conductivity and viscosity of the electrolyte, and lithium ions can move efficiently.

[0217] According to one embodiment of the present invention, in order to improve the battery's lifespan characteristics, suppress battery capacity reduction, and increase the battery's discharge capacity, in addition to the electrolyte components described above, the electrolyte may further contain one or more additives, such as alkylene carbonate halocarbonates, like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexaphosphotriamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinanes, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, based on the total weight of the electrolyte, the content of the additives may be from 0.1% by weight to 5% by weight.

[0218] Because lithium secondary batteries containing the positive electrode active material of this invention stably exhibit excellent capacity, output, and lifespan characteristics, they are very useful in portable devices such as mobile phones, laptops, and digital cameras, as well as in electric vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0219] The shape of the lithium secondary battery of the present invention is not particularly limited, and it can be cylindrical, prismatic, pouch-shaped or coin-shaped.

[0220] The lithium secondary battery according to the present invention can be used not only in battery cells used as power sources for small devices, but also preferably as unit cells in medium and large battery modules comprising multiple battery cells.

[0221] Therefore, according to one embodiment of the present invention, a battery module including a lithium secondary battery as a unit cell and a battery pack including the battery module are provided.

[0222] According to embodiments of the present invention, the battery module or battery pack can be used as a power source for any one or more of the following groups: large and medium-sized power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or energy storage systems.

[0223] The embodiments of the present invention will now be described in detail to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein.

[0224] Examples and Comparative Examples

[0225] Example 1

[0226] The secondary particles, formed by the aggregation of tens to hundreds of primary particles, are expressed as Ni. 0.89 Co 0.03 Mn 0.08 (OH)2 transition metal complex hydroxide (D 50 Li(Li) was mixed with LiOH to achieve a molar ratio (Li / (Ni+Co+Mn)) of 1.04 for the transition metal (Ni+Co+Mn). Based on the total weight of the transition metal complex hydroxide, 1,470 ppm of Al(OH)3, 1,000 ppm of Y2O3, and 1,500 ppm of ZrO2 were further added and mixed to prepare a mixture.

[0227] The mixture was sintered at 850°C for 6 hours in an oxygen atmosphere, followed by sintering at 800°C for 9 hours to obtain the sintered product. The sintered product was then pulverized at room temperature to prepare lithium transition metal oxides with an average particle size (D).50 The thickness is 9.8 μm, and the composition is expressed as LiNi. 0.8833 Co 0.0298 Mn 0.0794 Al 0.0050 Y 0.0010 Zr 0.0015 O2, and in the form of secondary particles in which primary particles are aggregated.

[0228] Co(OH)₂ was added to the lithium transition metal oxide in the secondary particulate form prepared above, such that the molar ratio of cobalt (Co) to metals other than lithium (Ni+Co+Mn+Al+Y+Zr) (Co / (Ni+Co+Mn+Al+Y+Zr)) was 0.02, and based on the total weight of the lithium transition metal oxide, 500 ppm of Al(OH)₃ was added, and the mixture was uniformly mixed to prepare a mixture. The mixture was heat-treated at 740°C for 3 hours in an oxygen atmosphere, followed by heat-treated at 500°C for 3 hours to obtain a first coated product. The first coated product was pulverized at room temperature to achieve an average particle size (D). 50 A cathode active material with a particle size of 10.2 μm was prepared, in which a coating containing Co and Al was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.8641 Co 0.0491 Mn 0.0777 Al 0.006 6Y 0.0010 Zr 0.0015 O2.

[0229] Based on the total weight of the pulverized first coating product, H3BO3 was added at a rate of 500 ppm and mixed to prepare a mixture. The mixture was heat-treated at 330°C for 5 hours in atmospheric atmosphere to obtain a second coating product. The second coating product was pulverized at room temperature to achieve an average particle size (D... 50 A cathode active material with a particle size of 10.2 μm was prepared, in which a coating containing Co, Al, and B was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.8602 Co 0.048 9Mn 0.0773 Al 0.0066 Y 0.0010 Zr 0.0015 B 0.0045 O2.

[0230] Example 2

[0231] The secondary particles, formed by the aggregation of tens to hundreds of primary particles, are expressed as Ni. 0.89 Co 0.03 Mn 0.08 (OH)2 transition metal complex hydroxide (D 50 Lithium (Li) was mixed with LiOH to achieve a molar ratio (Li / (Ni+Co+Mn)) of 1.00 to that of the transition metal (Ni+Co+Mn). Based on the total weight of the transition metal complex hydroxide, 1,470 ppm of Al(OH)3, 1,000 ppm of Y2O3, and 1,500 ppm of ZrO2 were further added and mixed to prepare a mixture.

[0232] The mixture was sintered at 850°C for 6 hours in an oxygen atmosphere to obtain a first sintered product. The first sintered product was then pulverized at room temperature to achieve an average particle size (D...). 50 The thickness is 9.8 μm.

[0233] The pulverized first sintered product was mixed with LiOH to achieve a lithium (Li) to transition metal (Ni+Co+Mn) molar ratio (Li / (Ni+Co+Mn)) of 0.04, and then subjected to a second sintering at 800°C for 9 hours in an oxygen atmosphere to obtain a second sintered product. The second sintered product was pulverized at room temperature to prepare lithium transition metal oxide with an average particle size (D). 50 The thickness is 9.8 μm, and the composition is expressed as LiNi. 0.8833 Co 0.0298 Mn 0.0794 Al 0.0050 Y 0.0010 Zr 0.0015 O2, and in the form of secondary particles aggregated with primary particles.

[0234] Co(OH)₂ was added to the lithium transition metal oxide in the secondary particulate form prepared above, such that the molar ratio of cobalt (Co) to the metal other than lithium (Ni+Co+Mn+Al+Y+Zr) (Co / (Ni+Co+Mn+Al+Y+Zr)) was 0.02, and based on the total weight of the lithium transition metal oxide, 500 ppm of Al(OH)₃ was added, and the mixture was uniformly mixed to prepare a mixture. The mixture was heat-treated at 740°C for 3 hours in an oxygen atmosphere, followed by heat-treated at 500°C for 3 hours to obtain a first coating. The first coated product was pulverized at room temperature to achieve an average particle size (D). 50A cathode active material with a particle size of 10.2 μm was prepared, in which a coating containing Co and Al was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.8641 Co 0.0491 Mn 0.0777 Al 0.0066 Y 0.0010 Zr 0.0015 O2.

[0235] Based on the total weight of the pulverized first coating product, H3BO3 was added at a rate of 500 ppm and mixed to prepare a mixture. The mixture was heat-treated at 330°C for 5 hours in atmospheric atmosphere to obtain a second coating product. The second coating product was pulverized at room temperature to achieve an average particle size (D... 50 A cathode active material with a particle size of 10.2 μm was prepared, in which a coating containing Co, Al, and B was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.8602 Co 0.048 9Mn 0.0773 Al 0.0066 Y 0.0010 Zr 0.0015 B 0.0045 O2.

[0236] Example 3

[0237] The secondary particles, formed by the aggregation of tens to hundreds of primary particles, are expressed as Ni. 0.89 Co 0.03 Mn 0.08 (OH)2 transition metal complex hydroxide (D 50 Li(Li) was mixed with LiOH to achieve a molar ratio (Li / (Ni+Co+Mn)) of 1.04 for the transition metal (Ni+Co+Mn). Based on the total weight of the transition metal complex hydroxide, 1,470 ppm of Al(OH)3, 1,000 ppm of Y2O3, and 1,500 ppm of ZrO2 were further added and mixed to prepare a mixture.

[0238] The mixture was pre-sintered at 550°C for 5 hours in an oxygen atmosphere to obtain a pre-sintered product. Then, the pre-sintered product was pulverized at room temperature to achieve an average particle size (D...). 50 The thickness is 9.8 μm.

[0239] The pulverized pre-sintered product was sintered at 850°C for 6 hours in an oxygen atmosphere, followed by sintering at 800°C for 9 hours to obtain the sintered product. The sintered product was then pulverized at room temperature to prepare lithium transition metal oxides with an average particle size (D). 50 The thickness is 9.8 μm, and the composition is expressed as LiNi. 0.8833 Co 0.0298 Mn 0.0794 Al 0.0050 Y 0.0010 Zr 0.0015 O2, and in the form of secondary particles in which primary particles are aggregated.

[0240] Co(OH)₂ was added to the lithium transition metal oxide in the secondary particulate form prepared above, such that the molar ratio of cobalt (Co) to metals other than lithium (Ni+Co+Mn+Al+Y+Zr) (Co / (Ni+Co+Mn+Al+Y+Zr)) was 0.02, and based on the total weight of the lithium transition metal oxide, 500 ppm of Al(OH)₃ was added, and the mixture was uniformly mixed to prepare a mixture. The mixture was heat-treated at 740°C for 3 hours in an oxygen atmosphere, followed by heat-treated at 500°C for 3 hours to obtain a first coated product. The first coated product was pulverized at room temperature to achieve an average particle size (D). 50 A cathode active material with a particle size of 10.2 μm was prepared, in which a coating containing Co and Al was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.8641 Co 0.0491 Mn 0.0777 Al 0.006 6Y 0.0010 Zr 0.0015 O2.

[0241] Based on the total weight of the pulverized first coating product, H3BO3 was added at a rate of 500 ppm and mixed to prepare a mixture. The mixture was heat-treated at 330°C for 5 hours in atmospheric atmosphere to obtain a second coating product. The second coating product was pulverized at room temperature to achieve an average particle size (D... 50 A cathode active material with a particle size of 10.2 μm was prepared, in which a coating containing Co, Al, and B was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.8602 Co 0.048 9Mn 0.0773 Al 0.0066 Y 0.0010 Zr 0.0015 B 0.0045 O2.

[0242] Example 4

[0243] The secondary particles, formed by the aggregation of tens to hundreds of primary particles, are expressed as Ni. 0.89 Co 0.03 Mn 0.08 (OH)2 transition metal complex hydroxide (D 50 Li(Li) was mixed with LiOH to achieve a molar ratio (Li / (Ni+Co+Mn)) of 1.04 for the transition metal (Ni+Co+Mn). Based on the total weight of the transition metal complex hydroxide, 1,470 ppm of Al(OH)3, 1,000 ppm of Y2O3, and 1,500 ppm of ZrO2 were further added and mixed to prepare a mixture.

[0244] The mixture was sintered at 880°C for 6 hours in an oxygen atmosphere, followed by sintering at 800°C for 9 hours to obtain the sintered product. The sintered product was then pulverized at room temperature to prepare lithium transition metal oxides with an average particle size (D). 50 The thickness is 9.8 μm, and the composition is expressed as LiNi. 0.8833 Co 0.0298 Mn 0.0794 Al 0.0050 Y 0.0010 Zr 0.0015 O2, and in the form of secondary particles in which primary particles are aggregated.

[0245] Co(OH)₂ was added to the lithium transition metal oxide in the secondary particulate form prepared above, such that the molar ratio of cobalt (Co) to metals other than lithium (Ni+Co+Mn+Al+Y+Zr) (Co / (Ni+Co+Mn+Al+Y+Zr)) was 0.02, and based on the total weight of the lithium transition metal oxide, 500 ppm of Al(OH)₃ was added, and the mixture was uniformly mixed to prepare a mixture. The mixture was heat-treated at 740°C for 3 hours in an oxygen atmosphere, followed by heat-treated at 500°C for 3 hours to obtain a first coated product. The first coated product was pulverized at room temperature to achieve an average particle size (D). 50 A cathode active material with a particle size of 10.2 μm was prepared, in which a coating containing Co and Al was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.8641 Co 0.0491 Mn 0.0777 Al 0.006 6Y 0.0010 Zr 0.0015 O2.

[0246] Based on the total weight of the pulverized first coating product, H3BO3 was added at a rate of 500 ppm and mixed to prepare a mixture. The mixture was heat-treated at 330°C for 5 hours in atmospheric atmosphere to obtain a second coating product. The second coating product was pulverized at room temperature to achieve an average particle size (D... 50 A cathode active material with a particle size of 10.2 μm was prepared, in which a coating containing Co, Al, and B was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.8602 Co 0.048 9Mn 0.0773 Al 0.0066 Y 0.0010 Zr 0.0015 B 0.0045 O2.

[0247] Example 5

[0248] The secondary particles, formed by the aggregation of tens to hundreds of primary particles, are expressed as Ni. 0.89 Co 0.03 Mn 0.08 (OH)2 transition metal complex hydroxide (D 50 Li(Li) was mixed with LiOH to achieve a molar ratio (Li / (Ni+Co+Mn)) of 1.04 for the transition metal (Ni+Co+Mn). Based on the total weight of the transition metal complex hydroxide, 1,470 ppm of Al(OH)3, 2,000 ppm of Y2O3, and 1,500 ppm of ZrO2 were further added and mixed to prepare a mixture.

[0249] The mixture was sintered at 850°C for 6 hours in an oxygen atmosphere, followed by sintering at 800°C for 9 hours to obtain the sintered product. The sintered product was then pulverized at room temperature to prepare lithium transition metal oxides with an average particle size (D). 50 The thickness is 9.8 μm, and the composition is expressed as LiNi. 0.8824 Co 0.0297 Mn 0.0793 Al 0.0050 Y 0.0021 Zr 0.0015 O2, and in the form of secondary particles in which primary particles are aggregated.

[0250] Co(OH)₂ was added to the lithium transition metal oxide in the secondary particulate form prepared above, such that the molar ratio of cobalt (Co) to metals other than lithium (Ni+Co+Mn+Al+Y+Zr) (Co / (Ni+Co+Mn+Al+Y+Zr)) was 0.02, and based on the total weight of the lithium transition metal oxide, 500 ppm of Al(OH)₃ was added, and the mixture was uniformly mixed to prepare a mixture. The mixture was heat-treated at 740°C for 3 hours in an oxygen atmosphere, followed by heat-treated at 500°C for 3 hours to obtain a first coated product. The first coated product was pulverized at room temperature to achieve an average particle size (D). 50 A cathode active material with a particle size of 10.2 μm was prepared, in which a coating containing Co and Al was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.8632 Co 0.0491 Mn 0.0776 Al 0.006 6Y 0.0020 Zr 0.0015 O2.

[0251] Based on the total weight of the pulverized first coating product, H3BO3 was added at a rate of 500 ppm and mixed to prepare a mixture. The mixture was heat-treated at 330°C for 5 hours in atmospheric atmosphere to obtain a second coating product. The second coating product was pulverized at room temperature to achieve an average particle size (D... 50 A cathode active material with a particle size of 10.2 μm was prepared, in which a coating containing Co, Al, and B was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.8593 Co 0.048 9Mn 0.0772 Al 0.0066 Y 0.0020 Zr 0.0015 B 0.0045 O2.

[0252] Example 6

[0253] The secondary particles, formed by the aggregation of tens to hundreds of primary particles, are expressed as Ni. 0.89 Co 0.03 Mn 0.08 (OH)2 transition metal complex hydroxide (D 50Li(Li) was mixed with LiOH to achieve a molar ratio (Li / (Ni+Co+Mn)) of 1.04 for lithium (Li) to transition metal (Ni+Co+Mn). Based on the total weight of the transition metal complex hydroxide, 2,940 ppm of Al(OH)3, 1,000 ppm of Y2O3, and 1,500 ppm of ZrO2 were further added and mixed to prepare a mixture.

[0254] The mixture was sintered at 850°C for 6 hours in an oxygen atmosphere, followed by sintering at 800°C for 9 hours to obtain the sintered product. The sintered product was then pulverized at room temperature to prepare lithium transition metal oxides with an average particle size (D). 50 The thickness is 9.8 μm, and the composition is expressed as LiNi. 0.8789 Co 0.0296 Mn 0.0790 Al 0.0100 Y 0.0010 Zr 0.0015 O2, and in the form of secondary particles in which primary particles are aggregated.

[0255] Co(OH)₂ was added to the lithium transition metal oxide in the secondary particulate form prepared above, such that the molar ratio of cobalt (Co) to metals other than lithium (Ni+Co+Mn+Al+Y+Zr) (Co / (Ni+Co+Mn+Al+Y+Zr)) was 0.02, and based on the total weight of the lithium transition metal oxide in the secondary particulate form above, 500 ppm of Al(OH)₃ was added, and the mixture was uniformly mixed to prepare a mixture. The mixture was heat-treated at 740°C for 3 hours in an oxygen atmosphere, and then heat-treated at 500°C for 3 hours to obtain a first coated product. The first coated product was pulverized at room temperature to achieve an average particle size (D). 50 A cathode active material with a particle size of 10.2 μm was prepared, in which a coating containing Co and Al was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.8597 Co 0.0490 Mn 0.0773 Al 0.0115 Y 0.0010 Zr 0.0015 O2.

[0256] Based on the total weight of the pulverized first coating product, H3BO3 was added at a rate of 500 ppm and mixed to prepare a mixture. The mixture was heat-treated at 330°C for 5 hours in atmospheric atmosphere to obtain a second coating product. The second coating product was pulverized at room temperature to achieve an average particle size (D... 50A cathode active material with a particle size of 10.2 μm was prepared, in which a coating containing Co, Al, and B was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.8559 Co 0.048 8Mn 0.0769 Al 0.0115 Y 0.0010 Zr 0.0014 B 0.0045 O2.

[0257] Example 7

[0258] The secondary particles, formed by the aggregation of tens to hundreds of primary particles, are expressed as Ni. 0.89 Co 0.03 Mn 0.08 (OH)2 transition metal complex hydroxide (D 50 Li(Li) was mixed with LiOH to achieve a molar ratio (Li / (Ni+Co+Mn)) of 1.04 for lithium (Li) to transition metal (Ni+Co+Mn). Based on the total weight of the transition metal complex hydroxide, 1,470 ppm of Al(OH)3, 1,000 ppm of Y2O3, and 3,500 ppm of ZrO2 were further added and mixed to prepare a mixture.

[0259] The mixture was sintered at 850°C for 6 hours in an oxygen atmosphere, followed by sintering at 800°C for 9 hours to obtain the sintered product. The sintered product was then pulverized at room temperature to prepare lithium transition metal oxides with an average particle size (D). 50 The thickness is 9.8 μm, and the composition is expressed as LiNi. 0.8815 Co 0.0297 Mn 0.0793 Al 0.0050 Y 0.0010 Zr 0.0035 O2, and in the form of secondary particles in which primary particles are aggregated.

[0260] Co(OH)₂ was added to the lithium transition metal oxide in the secondary particulate form prepared above, such that the molar ratio of cobalt (Co) to metals other than lithium (Ni+Co+Mn+Al+Y+Zr) (Co / (Ni+Co+Mn+Al+Y+Zr)) was 0.02, and based on the total weight of the lithium transition metal oxide, 500 ppm of Al(OH)₃ was added, and the mixture was uniformly mixed to prepare a mixture. The mixture was heat-treated at 740°C for 3 hours in an oxygen atmosphere, followed by heat-treated at 500°C for 3 hours to obtain a first coated product. The first coated product was pulverized at room temperature to achieve an average particle size (D). 50A cathode active material with a particle size of 10.2 μm was prepared, in which a coating containing Co and Al was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.8623 Co 0.0491 Mn 0.0775 Al 0.006 6Y 0.0010 Zr 0.0035 O2.

[0261] Based on the total weight of the pulverized first coating product, H3BO3 was added at a rate of 500 ppm and mixed to prepare a mixture. The mixture was heat-treated at 330°C for 5 hours in atmospheric atmosphere to obtain a second coating product. The second coating product was pulverized at room temperature to achieve an average particle size (D... 50 A cathode active material with a particle size of 10.2 μm was prepared, in which a coating containing Co, Al, and B was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.8584 Co 0.048 9Mn 0.0772 Al 0.0066 Y 0.0010 Zr 0.0034 B 0.0045 O2.

[0262] Example 8

[0263] The secondary particles, formed by the aggregation of tens to hundreds of primary particles, are expressed as Ni. 0.96 Co 0.03 Mn 0.01 (OH)2 transition metal complex hydroxide (D 50 Li(Li) was mixed with LiOH to achieve a molar ratio (Li / (Ni+Co+Mn)) of 1.02 for lithium (Li) to transition metal (Ni+Co+Mn). Based on the total weight of the transition metal complex hydroxide, 1,470 ppm of Al(OH)3, 1,000 ppm of Y2O3, and 1,500 ppm of ZrO2 were further added and mixed to prepare a mixture.

[0264] The mixture was sintered at 800°C for 6 hours in an oxygen atmosphere, followed by sintering at 760°C for 9 hours to obtain the sintered product. The sintered product was then pulverized at room temperature to prepare lithium transition metal oxides with an average particle size (D). 50 The thickness is 14.2 μm, and the composition is expressed as LiNi. 0.9528 Co 0.0298 Mn0.0099 Al 0.0050 Y 0.0010 Zr 0.0015 O2, and in the form of secondary particles in which primary particles are aggregated.

[0265] Co(OH)₂ was added to the lithium transition metal oxide in the secondary particulate form prepared above, such that the molar ratio of cobalt (Co) to the metal other than lithium (Ni+Co+Mn+Al+Y+Zr) (Co / (Ni+Co+Mn+Al+Y+Zr)) was 0.02, and based on the total weight of the lithium transition metal oxide, 500 ppm of Al(OH)₃ was added, and the mixture was uniformly mixed to prepare a mixture. The mixture was heat-treated at 700°C for 3 hours in an oxygen atmosphere, followed by heat-treated at 500°C for 3 hours to obtain a first coated product. The first coated product was pulverized at room temperature to achieve an average particle size (D). 50 A cathode active material with a particle size of 14.5 μm was prepared, in which a coating containing Co and Al was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.9320 Co 0.0491 Mn 0.0097 Al 0.006 7Y 0.0010 Zr 0.0015 O2.

[0266] Based on the total weight of the pulverized first coating product, H3BO3 was added at a rate of 500 ppm and mixed to prepare a mixture. The mixture was heat-treated at 330°C for 5 hours in atmospheric atmosphere to obtain a second coating product. The second coating product was pulverized at room temperature to achieve an average particle size (D... 50 A cathode active material with a particle size of 14.2 μm was prepared, in which a coating containing Co, Al, and B was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.9278 Co 0.048 9Mn 0.0097 Al 0.0066 Y 0.0010 Zr 0.0015 B 0.0045 O2.

[0267] Example 9

[0268] The secondary particles, formed by the aggregation of tens to hundreds of primary particles, are expressed as Ni. 0.96 Co 0.03 Mn 0.01(OH)2 transition metal complex hydroxide (D 50 Li(Li) was mixed with LiOH to achieve a molar ratio (Li / (Ni+Co+Mn)) of 0.98 for lithium (Li) to transition metal (Ni+Co+Mn). Based on the total weight of the transition metal complex hydroxide, 1,470 ppm of Al(OH)3, 1,000 ppm of Y2O3, and 1,500 ppm of ZrO2 were further added and mixed to prepare a mixture.

[0269] The mixture was sintered once at 800°C for 6 hours in an oxygen atmosphere to obtain a first sintered product. The first sintered product was then pulverized at room temperature to achieve an average particle size (D...). 50 The value is 14.2 μm.

[0270] The pulverized first sintered product was mixed with LiOH to achieve a lithium (Li) to transition metal (Ni+Co+Mn) molar ratio (Li / (Ni+Co+Mn)) of 0.04, and then subjected to a second sintering at 760°C for 9 hours in an oxygen atmosphere to obtain a second sintered product. The second sintered product was pulverized at room temperature to prepare lithium transition metal oxide with an average particle size (D). 50 The thickness is 14.2 μm, and the composition is expressed as LiNi. 0.9528 Co 0.0298 Mn 0.0099 Al 0.0050 Y 0.0010 Zr 0.0015 O2, and in the form of secondary particles in which primary particles are aggregated.

[0271] Co(OH)₂ was added to the lithium transition metal oxide in the secondary particulate form prepared above, such that the molar ratio of cobalt (Co) to the metal other than lithium (Ni+Co+Mn+Al+Y+Zr) (Co / (Ni+Co+Mn+Al+Y+Zr)) was 0.02, and based on the total weight of the lithium transition metal oxide, 500 ppm of Al(OH)₃ was added, and the mixture was uniformly mixed to prepare a mixture. The mixture was heat-treated at 700°C for 3 hours in an oxygen atmosphere, followed by heat-treated at 500°C for 3 hours to obtain a first coated product. The first coated product was pulverized at room temperature to achieve an average particle size (D). 50 A cathode active material with a particle size of 14.5 μm was prepared, in which a coating containing Co and Al was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.9320 Co 0.0491 Mn 0.0097 Al 0.006 7Y0.0010 Zr 0.0015 O2.

[0272] Based on the total weight of the pulverized first coating product, H3BO3 was added at a rate of 500 ppm and mixed to prepare a mixture. The mixture was heat-treated at 330°C for 5 hours in atmospheric atmosphere to obtain a second coating product. The second coating product was pulverized at room temperature to achieve an average particle size (D... 50) A cathode active material with a particle size of 14.2 μm was prepared, in which a coating containing Co, Al, and B was formed on a secondary particle form of lithium transition metal oxide aggregated from primary particles. The overall composition of the cathode active material, including the coating, is LiNi. 0.9278 Co 0.048 9Mn 0.0097 Al 0.0066 Y 0.0010 Zr 0.0015 B 0.0045 O2.

[0273] Example 10

[0274] The secondary particles, formed by the aggregation of tens to hundreds of primary particles, are expressed as Ni. 0.96 Co 0.03 Mn 0.01 (OH)2 transition metal complex hydroxide (D 50 Li(Li) was mixed with LiOH to achieve a molar ratio (Li / (Ni+Co+Mn)) of 1.02 for lithium (Li) to transition metal (Ni+Co+Mn). Based on the total weight of the transition metal complex hydroxide, 1,470 ppm of Al(OH)3, 1,000 ppm of Y2O3, and 1,500 ppm of ZrO2 were further added and mixed to prepare a mixture.

[0275] The mixture was pre-sintered at 550°C for 5 hours in an oxygen atmosphere to obtain a pre-sintered product. Then, the pre-sintered product was pulverized at room temperature to achieve an average particle size (D...). 50 The value is 14.2 μm.

[0276] The pulverized pre-sintered product was sintered at 800℃ for 6 hours in an oxygen atmosphere, followed by sintering at 760℃ for 9 hours to obtain the sintered product. The sintered product was then pulverized at room temperature to prepare lithium transition metal oxides with an average particle size (D). 50 The thickness is 14.2 μm, and the composition is expressed as LiNi. 0.9528 Co 0.0298 Mn 0.0099 Al 0.0050 Y 0.0010Zr 0.0015 O2, and in the form of secondary particles in which primary particles are aggregated.

[0277] Co(OH)₂ was added to the lithium transition metal oxide in the secondary particulate form prepared above, such that the molar ratio of cobalt (Co) to the metal other than lithium (Ni+Co+Mn+Al+Y+Zr) (Co / (Ni+Co+Mn+Al+Y+Zr)) was 0.02, and based on the total weight of the lithium transition metal oxide, 500 ppm of Al(OH)₃ was added, and the mixture was uniformly mixed to prepare a mixture. The mixture was heat-treated at 700°C for 3 hours in an oxygen atmosphere, followed by heat-treated at 500°C for 3 hours to obtain a first coated product. The first coated product was pulverized at room temperature to achieve an average particle size (D). 50 A cathode active material with a particle size of 14.5 μm was prepared, in which a coating containing Co and Al was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.9320 Co 0.0491 Mn 0.0097 Al 0.006 7Y 0.0010 Zr 0.0015 O2.

[0278] Based on the total weight of the pulverized first coating product, H3BO3 was added at a rate of 500 ppm and mixed to prepare a mixture. The mixture was heat-treated at 330°C for 5 hours in atmospheric atmosphere to obtain a second coating product. The second coating product was pulverized at room temperature to achieve an average particle size (D... 50 A cathode active material with a particle size of 14.2 μm was prepared, in which a coating containing Co, Al, and B was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.9278 Co 0.048 9Mn 0.0097 Al 0.0066 Y 0.0010 Zr 0.0015 B 0.0045 O2.

[0279] Example 11

[0280] The secondary particles, formed by the aggregation of tens to hundreds of primary particles, are expressed as Ni. 0.96 Co 0.03 Mn 0.01 (OH)2 transition metal complex hydroxide (D 50Li(Li) was mixed with LiOH to achieve a molar ratio (Li / (Ni+Co+Mn)) of 1.02 for lithium (Li) to transition metal (Ni+Co+Mn). Based on the total weight of the transition metal complex hydroxide, 1,470 ppm of Al(OH)3, 1,000 ppm of Y2O3, and 1,500 ppm of ZrO2 were further added and mixed to prepare a mixture.

[0281] The mixture was sintered at 830°C for 6 hours in an oxygen atmosphere, followed by sintering at 760°C for 9 hours to obtain the sintered product. The sintered product was then pulverized at room temperature to prepare lithium transition metal oxides with an average particle size (D). 50 The thickness is 14.2 μm, and the composition is expressed as LiNi. 0.9528 Co 0.0298 Mn 0.0099 Al 0.0050 Y 0.0010 Zr 0.0015 O2, and in the form of secondary particles in which primary particles are aggregated.

[0282] Co(OH)₂ was added to the lithium transition metal oxide in the secondary particulate form prepared above, such that the molar ratio of cobalt (Co) to the metal other than lithium (Ni+Co+Mn+Al+Y+Zr) (Co / (Ni+Co+Mn+Al+Y+Zr)) was 0.02, and based on the total weight of the lithium transition metal oxide, 500 ppm of Al(OH)₃ was added, and the mixture was uniformly mixed to prepare a mixture. The mixture was heat-treated at 700°C for 3 hours in an oxygen atmosphere, followed by heat-treated at 500°C for 3 hours to obtain a first coated product. The first coated product was pulverized at room temperature to achieve an average particle size (D). 50 A cathode active material with a particle size of 14.5 μm was prepared, in which a coating containing Co and Al was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.9320 Co 0.0491 Mn 0.0097 Al 0.006 7Y 0.0010 Zr 0.0015 O2.

[0283] Based on the total weight of the pulverized first coating product, H3BO3 was added at a rate of 500 ppm and mixed to prepare a mixture. The mixture was heat-treated at 330°C for 5 hours in atmospheric atmosphere to obtain a second coating product. The second coating product was pulverized at room temperature to achieve an average particle size (D... 50A cathode active material with a particle size of 14.2 μm was prepared, in which a coating containing Co, Al, and B was formed on a secondary particle form of lithium transition metal oxide in the form of primary particle aggregation. The overall composition of the cathode active material including the coating is LiNi. 0.9278 Co 0.048 9Mn 0.0097 Al 0.0066 Y 0.0010 Zr 0.0015 B 0.0045 O2.

[0284] Comparative Example 1

[0285] The secondary particles, formed by the aggregation of tens to hundreds of primary particles, are expressed as Ni. 0.87 Co 0.05 Mn 0.08 (OH)2 transition metal complex hydroxide (D 50 Li(Li) was mixed with LiOH to achieve a molar ratio (Li / (Ni+Co+Mn)) of 1.05 for lithium (Li) to transition metal (Ni+Co+Mn). Based on the total weight of the transition metal complex hydroxide, 1,470 ppm of Al(OH)3, 1,000 ppm of Y2O3, and 1,500 ppm of ZrO2 were further added and mixed to prepare a mixture.

[0286] The mixture was sintered at 780°C for 5 hours in an oxygen atmosphere to obtain a sintered product. The sintered product was then pulverized at room temperature to prepare lithium transition metal oxides with an average particle size (D). 50 The thickness is 9.8 μm, and the composition is expressed as LiNi. 0.8635 Co 0.0496 Mn 0.0794 Al 0.0050 Y 0.0010 Zr 0.0015 O2, and in the form of secondary particles in which primary particles are aggregated. Subsequently, 100 parts by weight of the prepared secondary particle form of lithium transition metal oxide and 100 parts by weight of water were stirred for 5 minutes, and then washed with water using a filter press. The washed product was dried at 130°C for 4 hours to prepare a dried product.

[0287] Based on the total weight of lithium transition metal oxides, H3BO3 was added to the prepared dried product at a rate of 1,000 ppm, and they were mixed to prepare a mixture. The mixture was heat-treated at 300°C for 5 hours in atmospheric atmosphere to obtain the coated product. The coated product was pulverized at room temperature to achieve an average particle size (D... 50A cathode active material with a particle size of 10.2 μm was prepared, in which a boron-containing coating portion was formed on a lithium transition metal oxide in the form of secondary particles aggregated from primary particles. The overall composition of the cathode active material including the coating portion is LiNi. 0.8558 Co 0.0492 Mn 0.0787 Al 0.004 9Y 0.0010 Zr 0.0015 B 0.0089 O2.

[0288] Comparative Example 2

[0289] The secondary particles, formed by the aggregation of tens to hundreds of primary particles, are expressed as Ni. 0.87 Co 0.05 Mn 0.08 (OH)2 transition metal complex hydroxide (D 50 Li(Li) was mixed with LiOH to achieve a molar ratio (Li / (Ni+Co+Mn)) of 1.05 for lithium (Li) to transition metal (Ni+Co+Mn). Based on the total weight of the transition metal complex hydroxide, 1,470 ppm of Al(OH)3, 1,000 ppm of Y2O3, and 1,500 ppm of ZrO2 were further added and mixed to prepare a mixture.

[0290] The mixture was sintered at 780°C for 5 hours in an oxygen atmosphere to obtain a sintered product. The sintered product was then pulverized at room temperature to prepare lithium transition metal oxides with an average particle size (D). 50 The thickness is 11.8 μm, and the composition is expressed as LiNi. 0.8635 Co 0.0496 Mn 0.0794 Al 0.0050 Y 0.0010 Zr 0.0015 O2, and in the form of secondary particles in which primary particles are aggregated. Subsequently, 100 parts by weight of the prepared secondary particle form of lithium transition metal oxide and 100 parts by weight of water were stirred for 5 minutes, and then washed with water using a filter press. The washed product was dried at 130°C for 4 hours to prepare a dried product.

[0291] Based on the total weight of lithium transition metal oxides, H3BO3 was added to the prepared dried product at a rate of 1,000 ppm, and they were mixed to prepare a mixture. The mixture was heat-treated at 300°C for 5 hours in atmospheric atmosphere to obtain the coated product. The coated product was pulverized at room temperature to achieve an average particle size (D... 50A cathode active material with a particle size of 12.2 μm was prepared, in which a boron-containing coating portion was formed on a lithium transition metal oxide in the form of secondary particles aggregated from primary particles. The overall composition of the cathode active material, including the coating portion, is LiNi. 0.8558 Co 0.0492 Mn 0.0787 Al 0.004 9Y 0.0010 Zr 0.0015 B 0.0089 O2.

[0292] Comparative Example 3

[0293] The secondary particles, formed by the aggregation of tens to hundreds of primary particles, are expressed as Ni. 0.94 Co 0.05 Mn 0.01 (OH)2 transition metal complex hydroxide (D 50 Li(Li) was mixed with LiOH to achieve a molar ratio (Li / (Ni+Co+Mn)) of 1.02 for lithium (Li) to transition metal (Ni+Co+Mn). Based on the total weight of the transition metal complex hydroxide, 1,470 ppm of Al(OH)3, 1,000 ppm of Y2O3, and 1,500 ppm of ZrO2 were further added and mixed to prepare a mixture.

[0294] The mixture was sintered at 730°C for 5 hours in an oxygen atmosphere to obtain a sintered product. The sintered product was then pulverized at room temperature to prepare lithium transition metal oxides with an average particle size (D). 50 The thickness is 14.2 μm, and the composition is expressed as LiNi. 0.9330 Co 0.0496 Mn 0.0099 Al 0.0050 Y 0.0010 Zr 0.0015 O2, and in the form of secondary particles in which primary particles are aggregated. Subsequently, 100 parts by weight of the prepared secondary particle form of lithium transition metal oxide and 100 parts by weight of water were stirred for 5 minutes, and then washed with water using a filter press. The washed product was dried at 130°C for 4 hours to prepare a dried product.

[0295] Based on the total weight of lithium transition metal oxides, H3BO3 was added to the prepared dried product at a rate of 1,000 ppm, and they were mixed to prepare a mixture. The mixture was heat-treated at 300°C for 5 hours in atmospheric atmosphere to obtain the coated product. The coated product was pulverized at room temperature to achieve an average particle size (D... 50A cathode active material with a particle size of 14.2 μm was prepared, in which a boron-containing coating portion was formed on a lithium transition metal oxide in the form of secondary particles aggregated from primary particles. The overall composition of the cathode active material, including the coating portion, is LiNi. 0.9246 Co 0.0492 Mn 0.0098 Al 0.005 0Y 0.0010 Zr 0.0015 B 0.0089 O2.

[0296] Comparative Example 4

[0297] The secondary particles, formed by the aggregation of tens to hundreds of primary particles, are expressed as Ni. 0.94 Co 0.05 Mn 0.01 (OH)2 transition metal complex hydroxide (D 50 Li(Li) was mixed with LiOH to achieve a molar ratio (Li / (Ni+Co+Mn)) of 1.02 for the transition metal (Ni+Co+Mn). Based on the total weight of the transition metal complex hydroxide, 1,470 ppm of Al(OH)3, 1,000 ppm of Y2O3, and 1,500 ppm of ZrO2 were further added and mixed to prepare a mixture.

[0298] The mixture was sintered at 730°C for 5 hours in an oxygen atmosphere to obtain a sintered product. The sintered product was then pulverized at room temperature to prepare lithium transition metal oxides with an average particle size (D). 50 The thickness is 9.8 μm, and the composition is expressed as LiNi. 0.9330 Co 0.0496 Mn 0.0099 Al 0.0050 Y 0.0010 Zr 0.0015 O2, and in the form of secondary particles in which primary particles are aggregated. Subsequently, 100 parts by weight of the prepared secondary particle form of lithium transition metal oxide and 100 parts by weight of water were stirred for 5 minutes, and then washed with water using a filter press. The washed product was dried at 130°C for 4 hours to prepare a dried product.

[0299] Based on the total weight of lithium transition metal oxides, H3BO3 was added to the prepared dried product at a rate of 1,000 ppm, and they were mixed to prepare a mixture. The mixture was heat-treated at 300°C for 5 hours in atmospheric atmosphere to obtain the coated product. The coated product was pulverized at room temperature to achieve an average particle size (D... 50A cathode active material with a particle size of 10.2 μm was prepared, in which a boron-containing coating portion was formed on a lithium transition metal oxide in the form of secondary particles aggregated from primary particles. The overall composition of the cathode active material including the coating portion is LiNi. 0.9246 Co 0.0492 Mn 0.0098 Al 0.005 0Y 0.0010 Zr 0.0015 B 0.0089 O2.

[0300] Comparative Example 5

[0301] The secondary particles, formed by the aggregation of tens to hundreds of primary particles, are expressed as Ni. 0.89 Co 0.03 Mn 0.08 (OH)2 transition metal complex hydroxide (D 50 A mixture of lithium (Li) and transition metal (Ni+Co+Mn) (4.2 μm) was prepared with LiOH to achieve a molar ratio (Li / (Ni+Co+Mn)) of 1.04. Based on the total weight of the transition metal complex hydroxide, 1,470 ppm of Al(OH)3, 1,000 ppm of Y2O3, and 1,500 ppm of ZrO2 were further added and mixed to prepare a mixture.

[0302] The mixture was sintered at 930°C for 6 hours in an oxygen atmosphere, followed by sintering at 830°C for 9 hours to obtain the sintered product. The sintered product was then pulverized at room temperature to prepare lithium transition metal oxides with an average particle size (D). 50 The thickness is 3.8 μm, and the composition is expressed as LiNi. 0.8833 Co 0.0298 Mn 0.0794 Al 0.0050 Y 0.0010 Zr 0.0015 O2, and in single-particle form.

[0303] Co(OH)₂ was added to the prepared single-particle lithium transition metal oxide to achieve a molar ratio (Co / (Ni+Co+Mn+Al+Y+Zr)) of 0.02 for cobalt (Co) to metals other than lithium (Ni+Co+Mn+Al+Y+Zr). Based on the total weight of the lithium transition metal oxide, 500 ppm of Al(OH)₃ was added, and the mixture was homogeneously mixed to prepare a mixture. The mixture was heat-treated at 740°C for 3 hours in an oxygen atmosphere, followed by heat-treatment at 500°C for 3 hours to obtain a coated product. The coated product was then pulverized at room temperature to achieve an average particle size (D). 50The cathode active material was prepared by using a particle size of 3.8 μm, in which a coating containing Co and Al was formed on a single-particle lithium transition metal oxide. The overall composition of the cathode active material, including the coating, is LiNi. 0.8641 Co 0.0491 Mn 0.0777 Al 0.0066 Y 0.0010 Zr 0.0015 O2.

[0304] Experimental Example

[0305] Experimental Example 1: Particle Analysis 1

[0306] The positive electrode active materials prepared in Examples 1 to 11 and Comparative Examples 1 to 5 were photographed using a scanning electron microscope (FEI quanta 250 FEG). The SEM images of Examples 1 to 11 are shown in the figure below. Figure 1 (A) to Figure 11 As shown in (A), the SEM images of Comparative Examples 1 to 5 are shown in the following figures respectively. Figure 12 (A) to Figure 16 As shown in (A). The average particle size of the primary particles present in each embodiment and comparative example was measured from the SEM images and is shown in Table 1 below.

[0307] In addition, the positive electrode active materials prepared in Examples 1 to 11 and Comparative Examples 1 to 5 were subjected to ion milling and then photographed using a scanning electron microscope. The SEM images of Examples 1 to 11 are shown in the figure below. Figure 1 (B) to Figure 11 As shown in (B), the SEM images of Comparative Examples 1 to 5 are respectively as follows: Figure 12 (B) to Figure 16 As shown in (B). Figure 1 (B) to Figure 15 The white squares in (B) represent the secondary particles observed in SEM images of the cross-section of the positive electrode active material, taken from the cross-section of the material. For particles with a size within the average particle size (D... 50 For SEM images of secondary particle cross sections within the range of ), a unit area of ​​5 μm wide × 5 μm long is set in the secondary particle cross section. The number of primary particle cross sections identified within the above unit area is shown in Table 1 below.

[0308] Furthermore, based on an artificial intelligence model, image analysis was performed on the SEM image of Embodiment 1 of the present invention, displaying the segmented images of the multiple lithium composite transition metal oxides as shown below. Figure 17 As shown, the segmented image of Comparative Example 1 is as follows: Figure 18 As shown.

[0309] [Table 1]

[0310]

[0311] Experimental Example 2: Particle Analysis 2

[0312] The positive electrode active materials prepared in Examples 1, 2, and 8 were subjected to ion milling and then photographed using a transmission electron microscope (FEI Titan cubed G2 60-300). The TEM images of the cross-sections of the primary particles of the positive electrode active materials in Examples 1, 2, and 8 are shown below. Figures 19 to 21 As shown.

[0313] refer to Figures 1 to 11 As shown in Table 1, it can be confirmed that the positive electrode active materials of Examples 1 to 11 comprise secondary particles in which a plurality of primary particles are aggregated, wherein the plurality of primary particles have an average particle size of 1.5 μm or more and 5.0 μm or less as measured by SEM images. Furthermore, it can be confirmed that the plurality of primary particles includes three or more disc-shaped primary particles. In this case, among the primary particles observed from SEM images of the surface or cross-section of the secondary particles, when an imaginary contact line with the maximum number of contact points is drawn for two primary particle boundary lines existing within an angle of 45° or less relative to the major axis, and an imaginary line intersecting these two contact lines is drawn, the disc-shaped primary particle refers to a primary particle with an interior angle of 150° or more and 210° or less on the same side. For reference, in Figure 1 (B) to Figure 11 In (B), when drawing a yellow imaginary contact line with the most contact points on the two boundary lines of a primary particle existing within an angle of 45° or less, with the red major axis as the reference, an imaginary line (not shown) intersecting these two yellow contact lines satisfies an interior angle on the same side of 150° or more and 210° or less. A primary particle in this case is defined as a disc-shaped primary particle. Furthermore, it can be confirmed that the minor axis of a disc-shaped primary particle is 0.3 μm or more, and the aspect ratio (major axis / minor axis) is 1.5 or more. Furthermore, it can be confirmed that the number of cross-sections of a primary particle per unit area is 1 or more and 100 or less. Specifically, it can be confirmed that the number of cross-sections of a primary particle per unit area is 8 or more and 24 or less.

[0314] Additionally, refer to Figures 1 to 11 and Figures 19 to 21 As can be seen, in the case of the positive electrode active material according to the embodiment of the present invention, the area ratio of the (003) plane in the crystal plane on the surface of the primary particle is the largest.

[0315] Meanwhile, it can be confirmed that, in the case of the positive electrode active materials of Comparative Examples 1 to 4, the average particle size of the primary particles measured from the SEM images is small, less than 500 nm. Furthermore, it can be confirmed that the positive electrode active material of Comparative Example 5 does not include disc-shaped primary particles.

[0316] In addition, refer to Figure 17 and Figure 18 It can be confirmed that the positive electrode active material according to the embodiments of the present invention includes single-crystal primary particles.

[0317] Experimental Example 3: Particle Analysis 3

[0318] The positive electrode active materials prepared in Examples 1 to 11 and Comparative Examples 1 to 5 were photographed using a scanning electron microscope (FEI quanta 250 FEG) equipped with EBSD.

[0319] Among them, the EBSD patterns of SEM images of the secondary particle cross-sections of the positive electrode active materials from Examples 1 to 4, 8, 10 and 11 and Comparative Example 3 (measured under the following conditions: accelerating voltage 20 kV, WD 16 mm, measurement magnification 5000x (16 μm width × 16 μm height), step size 0.025 μm) were observed. For particles with a size within the average particle size (D... 50 Electron backscattering diffraction (EBSD) patterns of the cross-section of secondary particles within a certain range were obtained. Unit areas of 5 μm width × 5 μm length were defined in the central and outer regions of the secondary particle cross-section, and these patterns were presented in [the following text is incomplete and requires further context]. Figure 22 (Example 1) Figure 23 (Example 2) Figure 24 (Example 3) Figure 25 (Example 4) Figure 26 (Example 8) Figure 27 (Example 10) Figure 28 (Example 11) and Figure 29 (Comparative Example 3). Furthermore, the number of grain sections identified per unit area and the monocrystalline degree calculated according to Equation 1 below are shown in Table 2 below.

[0320] [Equation 1]

[0321]

[0322] [Table 2]

[0323]

[0324] Referring to Table 2, it can be confirmed that, in the case of the positive electrode active materials of Examples 1 to 11, the number of grain cross-sectional areas per unit area is 1 or more and 150 or less. Specifically, it can be confirmed that the number of grain cross-sectional areas per unit area is 3 or more and 19 or less. Furthermore, it can be confirmed that the single crystallinity is 0.15 μm. 3 That's all. Furthermore, the monocrystalline density can be confirmed to be 0.86 μm. 3 Above and 1.57 μm 3 the following.

[0325] Experimental Example 4: Particle Analysis 4

[0326] From the SEM images of the positive electrode active material obtained in Experimental Example 1, the single particle formation degree (Dv) corresponding to the volume diameter at which the cumulative volume distribution of primary particles in each embodiment and comparative example reached 50% was measured. 50 ), and display them in Table 3 below.

[0327] Specifically, the SEM images of the secondary particle surfaces taken from the positive electrode active materials of Examples 1 to 11 and Comparative Examples 1 to 5 were projected onto a two-dimensional plane to obtain images. The area of ​​each primary particle was determined by the number of pixels corresponding to each of the n primary particles observed in the image. Subsequently, assuming the surface of each primary particle is circular, that is, using the radius of a circle with the same area as the surface area of ​​each primary particle, the radius of the surface of the primary particle was derived. Using this radius, the volume value was calculated according to Equation 5 below, and the degree of single particle formation (Dv) corresponding to the volume diameter at 50% of the cumulative volume distribution of the primary particles was calculated. 50 ), and display them in Table 3 below.

[0328] [Equation 5]

[0329]

[0330] [Table 3]

[0331]

[0332] Referring to Table 3, it can be confirmed that, in the case of the positive electrode active materials of Examples 1 to 11, the single particle formation degree is 1.2 μm or more and 3.8 μm or less. Specifically, it can be confirmed that the single crystal formation degree is 1.65 μm or more and 3.55 μm or less.

[0333] Experimental Example 5: Particle Analysis 5

[0334] For the positive electrode active materials prepared in Examples 1 to 11 and Comparative Examples 1 to 4, electron energy dispersive spectroscopy (ESCA) was performed using a K-alpha XPS instrument from Thermo Fisher to analyze the elemental distribution in the Co and B coatings present on their surfaces. For depth profiling, etching was performed using an Ar ion source at a rate of 0.3 nm / 10 s, and the content (atomic %) of B and Co in the coatings was measured in thicknesses from 0 nm to 100 nm. The results are shown in Table 4 (B coating) and Table 5 (Co coating), respectively.

[0335] EPMA cross-sectional analysis was performed on the positive electrode active material of Example 1 to confirm the surface coating characteristics. First, a positive electrode slurry was prepared by mixing the positive electrode active material of Example 1, carbon black conductive agent, and PVDF binder in an N-methylpyrrolidone (NMP) solvent at a weight ratio of 95:2:3. The prepared positive electrode slurry was coated onto one surface of an aluminum current collector, dried at 130°C, and calendered to achieve an electrode porosity of 20%, thereby preparing the positive electrode. To produce a flat surface for EPMA cross-sectional analysis, the positive electrode was Ar-ion milled using a HITACHI IM-5000 device at an accelerating voltage of 6 kV to obtain the cross-section of the positive electrode sample. Then, the cross-sectional image of the positive electrode sample was observed using a JEOL JXA-iHP200F device under conditions of an accelerating voltage of 15 kV and a probe current of 50 nA. Figure 30 As shown.

[0336] [Table 4]

[0337]

[0338] [Table 5]

[0339]

[0340] Refer to the above Figures 1 to 11 Based on the SEM images in Tables 4 and 5 and 30, it can be confirmed that, in the case of the positive electrode active materials of Examples 1 to 11, coating portions containing Co and / or B are formed on the surface of the primary particles, the interface of the primary particles, and / or the surface of the secondary particles. Furthermore, it can be seen that the coating portions are either island-shaped, formed on a portion of the surface of the primary particles, the interface of the primary particles, and / or the surface of the secondary particles, or coating-shaped, formed around the surface of the primary particles, the interface of the primary particles, and / or the surface of the secondary particles.

[0341] Experiment Example 6: Cumulative Volume Distribution Analysis

[0342] For the positive electrode active materials prepared in Examples 1 to 11 and Comparative Examples 1 to 5, the D particle size was measured using a particle size analyzer (PSD, Malvern, Martersizer 3500). min D 50 D max Based on the mode of the cumulative volume distribution of particle size, and based on the y-value of the peak point at the y-axis of the peak appearing in the mode of the cumulative volume distribution (P) 众数 ), θ L and θ R And calculate θ L -θ R , and are shown in Table 6 below.

[0343] Additionally, the skewness value (S) is calculated using Equation 3 below, and the y-value (P) of the skewness value (S) is calculated in relation to the peak value at the y-axis apex of the peak appearing in the mode of the cumulative volume distribution. 众数 The ratio of S / P 众数 ), and is shown in Table 6 below.

[0344] [Equation 3]

[0345] Skewness value (S) = 3 × {(volume average particle size - (D50)} / (standard deviation of particle size of positive electrode active material)

[0346] In addition, frequency distribution diagrams of the cumulative volume distribution of the positive electrode active materials of Examples 1 to 11 and Comparative Examples 1 and 3, measured using a laser diffraction particle size analyzer (where the x-axis represents a linear scale of particle size with x-values ​​gradually increasing from left to right, and the y-axis represents a weighted distribution with y-values ​​gradually increasing from bottom to top) are shown below. Figure 31 (Example 1) Figure 32 (Example 2) Figure 33 (Example 3) Figure 34 (Example 4) Figure 35 (Example 5) Figure 36 (Example 6) Figure 37 (Example 7) Figure 38 (Example 8) Figure 39 (Example 9) Figure 40 (Example 10) Figure 41 (Example 11) Figure 42 (Comparative Example 1) and Figure 43 (Comparative Example 3)

[0347] In addition, frequency distribution diagrams of the cumulative volume distribution of the positive electrode active materials of Examples 1 to 11 and Comparative Examples 1 and 3, measured using a laser diffraction particle size analyzer, are shown below (where the x-axis represents the logarithmic scale of particle size with x-values ​​gradually increasing from left to right, and the y-axis represents the weighted distribution with y-values ​​gradually increasing from bottom to top). Figure 44 (Example 1) Figure 45 (Example 2) Figure 46 (Example 3) Figure 47 (Example 4) Figure 48 (Example 5) Figure 49 (Example 6) Figure 50 (Example 7) Figure 51 (Example 8) Figure 52 (Example 9) Figure 53 (Example 10) Figure 54 (Example 11) Figure 55 (Comparative Example 1) and Figure 56 (Comparative Example 3)

[0348] [Table 6]

[0349]

[0350] Referring to Table 6, it can be confirmed that, in the case of the positive electrode active materials of Examples 1 to 11, D 50 The thickness is above 7.0 μm and below 20.0 μm. Furthermore, it can be confirmed that (θ) L - θ R The value is 6 or higher and 20 or lower. Furthermore, it can be seen that the frequency distribution plot showing the cumulative volume distribution of the positive electrode active material measured using a laser diffraction particle size analyzer exhibits a positive skewness, where the x-axis represents a linear scale of particle size with x-values ​​gradually increasing from left to right, and the y-axis represents a weighted distribution with y-values ​​gradually increasing from bottom to top.

[0351] Experiment Example 7: Measurement of Rolling Density

[0352] Using an automatic pelletizer (Carver, 3887.4), the thickness zero point of a circular pellet holder with a diameter of 13 mm was adjusted using a cylindrical die. Subsequently, 3 g of each of the positive electrode active material prepared in Examples 1 and 11 and Comparative Examples 1 to 5 were placed into the circular pellet holder, and a force was applied up to 9,000 kgf to form pellets. The thickness of the pellets was then measured. The pellet volume and rolling density were then calculated using Equations 4 and 2 below, and are shown in Table 7 below.

[0353] [Equation 4]

[0354] Aggregate volume (cm) 3 =π (radius of the circular granule container) 2 × Granule thickness

[0355] [Equation 2]

[0356] Rolled density (g / cm³) 3 = Weight of positive electrode active material (g) / Volume of aggregate (cm³) 3 )

[0357] [Table 7]

[0358]

[0359] Referring to Table 7, it can be confirmed that, in the case of the positive electrode active materials of Examples 1 to 11, the rolling density is 3.60 g / cm³. 3 That's all. Specifically, the rolling density can be confirmed as 3.66 g / cm³. 3 above.

[0360] Experiment Example 8: BET Specific Surface Area Measurement

[0361] Specific surface area was measured using nitrogen adsorption and desorption methods. Specifically, after measuring the weight of the empty electrode, 3 g of each of the positive electrode active material prepared in Examples 1 to 11 and Comparative Examples 1 to 5 were taken and pretreated at 130°C for 3 hours. After measuring the weight of the electrode after the pretreatment process, a Dewar container filled with liquid nitrogen was prepared and the electrode was fixed in place. Under a nitrogen atmosphere, the BET specific surface area was measured based on the amount of nitrogen adsorbed using a gas adsorption analyzer (Micromeritics TriStarr II), and the results are shown in Table 8 below.

[0362] [Table 8]

[0363]

[0364] Referring to Table 8, it can be confirmed that, in the case of the positive electrode active materials of Examples 1 to 11, the BET specific surface area is 0.20 m². 2 / g or more and 0.35 m 2 Below / g. Specifically, it can be confirmed that the specific surface area of ​​BET is 0.240 m². 2 / g or more and 0.338 m 2 / g or less.

[0365] Experiment Example 9: Manufacturing and Charge / Discharge Evaluation of Button-Type Semi-Cells

[0366] A positive electrode slurry was prepared by mixing 95 parts by weight of each positive electrode active material prepared in Examples 1 to 11 and Comparative Examples 1 to 5, 2 parts by weight of a conductive agent (Denka, FX35), and 3 parts by weight of a binder (KUREHA, KF9709) in an N-methylpyrrolidone (NMP) solvent. The prepared positive electrode slurry was coated onto one surface of a 20 μm thick aluminum current collector and rolled to achieve a porosity of 24% by volume for the positive electrode active material layer, thereby preparing a positive electrode.

[0367] A lithium metal electrode is used as the negative electrode, and an electrode assembly is manufactured by inserting a porous polyethylene separator between the negative and positive electrodes. The electrode assembly is placed in a battery case and an electrolyte is injected to manufacture a lithium secondary battery. In this case, the electrolyte is prepared by dissolving 1 M LiPF6 in an organic solvent in which ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) are mixed in a volume ratio of 3:3:4.

[0368] For the lithium secondary batteries prepared above, including the positive electrode active materials of Examples 1 to 11 and Comparative Examples 1 to 5, they were charged at 25°C in CC / CV mode with a constant current of 0.1 C to 4.25 V (termination current 0.05 C), and then discharged in CC mode to 2.5 V. The charging capacity and discharging capacity were measured and are shown in Table 9 below. Here, 1 C = 200 mA / g is set.

[0369] In addition, the lithium secondary battery prepared above was repeated for 50 charge-discharge cycles, wherein one cycle consisted of charging to 4.25 V at a constant current of 0.5 C in CC / CV mode at 45°C (with a termination current of 0.05 C), and then discharging to 2.5 V at a constant current of 1.0 C in CC mode. The percentage of the discharge capacity of the 50th cycle relative to the discharge capacity of the 1st cycle was set as the capacity retention rate, and is shown in Table 9 below.

[0370] [Table 9]

[0371]

[0372] Experimental Example 10: Evaluation of High-Rate Discharge Capacity

[0373] For the lithium secondary battery prepared in Example 9, the discharge capacity was measured by charging at 25°C with a constant current of 0.5 C in CC / CV mode to 4.25 V (with a termination current of 0.05 C), and then discharging at a constant current of 0.1 C in CC mode to 2.5 V. Additionally, the discharge capacity was measured by charging at 25°C with a constant current of 0.5 C in CC / CV mode to 4.25 V (with a termination current of 0.05 C), and then discharging at a constant current of 1.0 C in CC mode to 2.5 V. The percentages compared to the discharge capacity when charging at 0.5 C and then discharging at 0.1 C are shown in Table 10 below.

[0374] [Table 10]

[0375]

[0376] Referring to Tables 9 and 10, it can be confirmed that the batteries containing the positive electrode active materials of Examples 1 to 11 have large discharge capacity, high efficiency and high-temperature capacity retention, low DC resistance, and excellent rate performance. In contrast, it can be confirmed that the batteries containing the positive electrode active materials of Comparative Examples 1 to 4 have poor rate characteristics, and the battery containing the positive electrode active material of Comparative Example 5 has small discharge capacity, low efficiency, and poor rate characteristics.

[0377] These results confirm that the positive electrode active material of the present invention is a positive electrode active material that can simultaneously solve the problems of traditional secondary particles and single particles in high-nickel positive electrode active materials. In particular, by realizing the form of secondary particles in which the primary particles have a particle size of micrometers, the positive electrode active material can not only improve cell characteristics, such as improving lifespan and reducing gas generation, but also improve energy density due to its excellent density characteristics.

Claims

1. A positive electrode active material, comprising: Secondary particles in which a plurality of primary particles are aggregated, in, The plurality of primary particles have an average particle diameter of 1.5 μm or more and 5.0 μm or less as measured by SEM images, and the particle diameter of the primary particles is the particle diameter based on the major axis of the primary particles, Among them, the plurality of primary particles include disk-shaped primary particles, Among them, in the primary particles observed from the SEM image of the surface or cross-section of the secondary particles, when a hypothetical contact line having the maximum number of contact points is drawn for two boundary lines whose included angle with the major axis direction of the primary particles is 45° or less, and a hypothetical line intersecting these two contact lines is drawn, the same-side interior angle of the disk-shaped primary particles is 150° or more and 210° or less, and Among them, the area ratio of the (003) plane in the crystal planes on the surface of the primary particles is the largest.

2. The positive electrode active material as described in claim 1, wherein, The plurality of primary particles include three or more disk-shaped primary particles.

3. The positive electrode active material according to claim 1, comprising: a lithium transition metal composite oxide containing nickel, cobalt, and manganese.

4. The positive electrode active material according to claim 1, comprising: a lithium transition metal composite oxide in which the content of nickel in all transition metals is 60 mol% or more.

5. The positive electrode active material according to claim 1, comprising: a lithium transition metal composite oxide having an average composition represented by the following Chemical Formula 1: [Chemical Formula 1] Li x Ni a Co b Mr c M 1 d O2 Where: M 1 It is selected from at least one of the following groups: Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, V, F, P, S, and Y; and 0.9 ≤ x ≤ 1.3, 0.6 ≤ a < 1.0, 0 < b < 0.4, 0 < c < 0.4, 0 ≤ d ≤ 0.2 and a + b + c + d = 1.

6. The positive electrode active material as described in claim 1, wherein, The plurality of primary particles include single crystal primary particles.

7. The positive electrode active material as described in claim 1, wherein, According to the cumulative volume distribution measured by a laser diffraction particle size analyzer, the average particle diameter D50 of the secondary particles is 7.0 μm or more and 20.0 μm or less.

8. The positive electrode active material as described in claim 1, wherein, The minor axis of the disk-shaped primary particles is 0.3 μm or more, and the aspect ratio obtained as the major axis / minor axis is 1.5 or more.

9. The positive electrode active material as described in claim 1, wherein, The minor axis of the disk-shaped primary particles is 0.8 μm or more, and the aspect ratio obtained as the major axis / minor axis is 1.5 or more.

10. A positive electrode, comprising the positive electrode active material according to any one of claims 1 to 9.

11. A lithium secondary battery, comprising: The positive electrode according to claim 10; A negative electrode; And A separator and an electrolyte interposed between the positive electrode and the negative electrode.

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