Positive active material for lithium secondary battery, method for preparing the same, and lithium secondary battery comprising the same

Abstract

According to an embodiment, there is provided a positive electrode active material for a lithium secondary battery, the positive electrode active material including a nickel-based composite metal oxide including secondary particles in which a plurality of primary particles are aggregated, wherein the secondary particle includes a central portion and a surface portion, the surface portion includes the nickel-based composite metal oxide doped with manganese, and an amount of manganese present at grain boundaries of the plurality of primary particles in the surface portion is greater than an amount of manganese present inside the primary particles.

Description

Technical Field

[0001] A positive electrode active material for lithium secondary batteries, its preparation method, and a lithium secondary battery including the active material are disclosed. Background Technology

[0002] To meet the demands for miniaturization and high performance in various devices, lithium-ion batteries have become increasingly important in terms of high energy density, miniaturization, and weight reduction. Furthermore, the high capacity, high-temperature stability, and safety at high voltages of lithium-ion batteries are becoming crucial for applications such as electric vehicles.

[0003] Various cathode materials have been studied to enable the application of lithium secondary batteries in the aforementioned applications.

[0004] Compared to traditional LiCoO2, nickel-based lithium transition metal oxides, which simultaneously include Ni, Co, Mn, etc., offer high discharge capacity per unit weight, but suffer from relatively low capacity per unit volume and discharge capacity due to their low fill density. Furthermore, the safety of nickel-based lithium transition metal oxides may deteriorate when driven at high voltages.

[0005] Therefore, methods are needed to improve the structural stability and cycle life of nickel-based lithium transition metal oxides. Summary of the Invention

[0006] The embodiments provide positive electrode active materials with improved structural stability and effectively improved cycle life of lithium secondary batteries.

[0007] Another embodiment provides a method for preparing a positive electrode active material.

[0008] Another embodiment provides a lithium secondary battery with improved charge / discharge efficiency and cycle life characteristics by employing a positive electrode that includes a positive electrode active material.

[0009] The embodiment provides a positive electrode active material comprising: a nickel-based composite metal oxide including secondary particles in which a plurality of primary particles are aggregated, wherein the secondary particles include a central portion and a surface portion, the surface portion comprising a nickel-based composite metal oxide doped with manganese, and the amount of manganese present at the grain boundaries of the plurality of primary particles in the surface portion is greater than the amount of manganese present inside the primary particles.

[0010] Based on the total amount of metal (mol%) in nickel-based composite metal oxides, manganese-doped nickel-based composite metal oxides may include 0.1 mol% to 5 mol% of manganese.

[0011] The central portion of the secondary particles may not include nickel-based composite metal oxides doped with manganese.

[0012] The positive electrode active material may have a concentration gradient in which the concentration of manganese continuously decreases from the surface portion of the secondary particle to the central portion of the secondary particle.

[0013] The surface portion of the secondary particle may be located within 50% by length in the direction from the outermost surface to the center of the total distance from the center of the secondary particle to the outermost surface.

[0014] The manganese-doped nickel-based composite metal oxide may be represented by Chemical Formula 1:

[0015] [Chemical Formula 1]

[0016] LiNi 1-x-y-z Co x Mn y M z O2

[0017] In Chemical Formula 1,

[0018] 0 < x ≤ 0.05, 0.001 ≤ y ≤ 0.05 and 0 ≤ z ≤ 0.02, and M is at least one metal element selected from the group consisting of Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, B, Ta, Pr, Si, Ba and Ce.

[0019] The manganese-doped nickel-based composite metal oxide may include a layered structure oxide, a spinel structure oxide, a rock salt structure oxide, or a combination thereof.

[0020] The surface portion of the secondary particle may further include a lithium manganese oxide.

[0021] The lithium manganese oxide may be LiMnO2, Li2Mn2O3, LiMn2O4, or a combination thereof.

[0022] Through X-ray diffraction analysis, the FWHM of the positive electrode active material (003) may range from 0.1° to 0.2° (degrees).

[0023] The c-axis length (d-spacing) value of the primary particles present in the surface portion of the secondary particles of the positive electrode active material may be greater than or equal to

[0024] The size of the primary particles of the positive electrode active material may be 100 nm to 800 nm.

[0025] Another embodiment provides a method for preparing a positive electrode active material for a lithium secondary battery, the method comprising:

[0026] Preparing a dispersion, wherein in the dispersion, a nickel-based composite metal compound including secondary particles formed by aggregation of a plurality of primary particles is dispersed in a solvent (wherein the secondary particles have a central portion and a surface portion); adding an aqueous solution of a manganese salt and a precipitant to the dispersion in an atmosphere with reduced oxygen content to prepare a manganese salt-coated nickel-based composite metal compound (wherein the manganese salt is coated on the primary particles in the surface portion); and drying the manganese salt-coated nickel-based composite metal compound, mixing the manganese salt-coated nickel-based composite metal compound with a lithium source, and then performing heat treatment.

[0027] The nickel-based composite metal compound can be represented by Chemical Formula 2 or Chemical Formula 3:

[0028] [Chemical Formula 2]

[0029] Ni 1-x-y-z Co x M y (OH)2Mn w O q

[0030] In Chemical Formula 2,

[0031] 0 < x ≤ 0.05, 0 ≤ y ≤ 0.02, 0 < w ≤ 3, 0 < q ≤ 4, and M is at least one metal element selected from the group consisting of Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La and Ce,

[0032] [Chemical Formula 3]

[0033] Ni 1-x-y-z Co x M y O2Mn w O q

[0034] In Chemical Formula 3,

[0035] 0 < x ≤ 0.05, 0 ≤ y ≤ 0.02, 0 < w ≤ 3, 0 < q ≤ 4, and M is at least one metal element selected from the group consisting of Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La and Ce.

[0036] The manganese salt can be selected from manganese sulfate, manganese nitrate, manganese acetate and combinations thereof.

[0037] The atmosphere with reduced oxygen content can be obtained by injecting an inert gas, and the inert gas can be nitrogen (N2).

[0038] The injection rate of the inert gas can be 50 sccm to 5000 sccm.

[0039] Drying can be carried out at 100℃~200℃.

[0040] The preparation method may further include: heat treatment at 350°C to 600°C before mixing the nickel-based composite metal compound coated with manganese salt with a lithium source.

[0041] Another embodiment provides a lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte.

[0042] Further specific details of the implementation methods are included in the detailed description below.

[0043] In positive electrode active materials, coating manganese at the grain boundaries between primary particles at a certain depth within the secondary particles of the positive electrode active material can maximize capacity, improve cycle life, and simultaneously increase initial charge / discharge efficiency. Furthermore, uniformly coating manganese at the grain boundaries of the primary particles of the positive electrode active material using a wet process ensures a functional layer with high surface activity. Attached Figure Description

[0044] Figure 1 This is a schematic cross-sectional view showing a positive electrode active material in which the grain boundaries of primary particles are coated, according to an embodiment.

[0045] Figure 2 It is a perspective view that schematically illustrates the representative structure of a lithium secondary battery.

[0046] Figure 3 This is a STEM image (HAADF) showing the cross-section of multiple primary particles of the positive electrode active material.

[0047] Figure 4 It shows the distribution in Figure 3 A graph showing the manganese content in multiple primary particles (A, B, and C).

[0048] Figure 5 These are scanning transmission electron microscopy (STEM) images (high-angle annular dark field (HAADF)) of the surface and central portions of the positive electrode active material.

[0049] Figure 6 This is a STEM image of the surface of the primary particles in the surface portion of the secondary particles of the positive electrode active material in Example 1.

[0050] Figure 7 This is a STEM image of the interior of the primary particles in the surface portion of the secondary particles of the positive electrode active material in Example 1.

[0051] Figure 8This is a STEM image of the primary particles of the positive electrode active material of Comparative Example 1. Detailed Implementation

[0052] Embodiments of the invention are described in detail below. However, these are presented by way of example and are not intended to limit the invention, which is defined only by the scope of the claims described later.

[0053] As used herein, unless otherwise specifically defined, it will be understood that when an element (such as a layer, film, region, or substrate) is referred to as being “on” another element, it may be directly on the other element or there may be an intervening element.

[0054] In this invention, "particle size" or "particle diameter" can be defined as the average particle diameter (D50) based on 50% of the volumetric accumulation in the particle size distribution curve. Particle diameter can be measured, for example, by electron microscopy using a scanning electron microscope (SEM) or a field emission scanning electron microscope (FE-SEM), or by laser diffraction methods. It can be measured by laser diffraction as follows: The particles to be measured are dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size measurement device (e.g., Microtrac MT 3000), irradiated with ultrasound at approximately 28 kHz with an output of 60 W, and the average particle diameter (D50) based on 50% of the particle size distribution in the measurement device can be calculated.

[0055] In this specification, "center" means the point that bisects the longest axis of the particle.

[0056] "Primary grains" can be crystalline grains or crystals. Multiple primary grains form grain boundaries and aggregate together to form secondary grains. Primary grains can have various shapes, such as spherical or spherical shapes (plate-like shapes, etc.).

[0057] "Secondary particles" refer to particles that include multiple primary particles but are not aggregates of other particles or particles that no longer aggregate, and can have a spherical or pseudo-spherical shape.

[0058] In the following text, see references Figure 1 Describes the positive electrode active material used in lithium secondary batteries. Figure 1 This is a schematic cross-sectional view showing a positive electrode active material in which the grain boundaries of primary particles are coated, according to an embodiment.

[0059] refer to Figure 1 According to the embodiments, the positive electrode active material includes a nickel-based composite metal oxide containing secondary particles 1 in which a plurality of primary particles 3 are aggregated.

[0060] The secondary particle 1 includes a central portion 5b and a surface portion 5a, and the surface portion 5a includes a manganese-doped nickel-based composite metal oxide (hereinafter also referred to as manganese-doped nickel-based composite metal oxide) present at the grain boundaries 7 of the plurality of primary particles 3. That is, the positive electrode active material may include manganese-doped nickel-based composite metal oxide coated at the grain boundaries of the surface portion 5a corresponding to a predetermined depth.

[0061] The central portion 5b can refer to the region that is less than or equal to 50% to less than or equal to 80% of the total distance (100% of length) from the center of the secondary particle 1 to the outermost surface (e.g., less than or equal to 75%, 70%, 65%, 60%, 55%, or 50%) from the center, or it can refer to the region other than the region within 2 μm from the outermost surface of the secondary particle 1.

[0062] Surface portion 5a is the portion other than the central portion 5b and the area that is less than or equal to 20% of the length from the outermost surface relative to the total distance (100% of length) from the center to the outermost surface (e.g., less than or equal to 25%, less than or equal to 30%, less than or equal to 20%, less than or equal to 40%, less than or equal to 45%, or less than or equal to 50%).

[0063] In an embodiment, the region from the surface portion 5a of the secondary particle to the central portion 5b of the secondary particle can be a region less than or equal to 1000 nm (e.g., less than or equal to 400 nm, less than or equal to 450 nm, less than or equal to 500 nm, less than or equal to 550 nm, less than or equal to 600 nm, less than or equal to 650 nm, less than or equal to 700 nm, less than or equal to 750 nm, less than or equal to 800 nm, less than or equal to 850 nm, less than or equal to 900 nm, or less than or equal to 950 nm).

[0064] The surface portion 5a is the region where the grain boundary coating of the primary particles 3 is formed. In this document, based on the cross-section of the surface portion 5a of the secondary particles 1, it may include 2 to 3 primary particles. In embodiments, the size of the primary particles 3 may be 100 nm to 800 nm. The size of the primary particles 3 may be greater than or equal to 50 nm, greater than or equal to 100 nm, greater than or equal to 150 nm, greater than or equal to 200 nm, greater than or equal to 250 nm, greater than or equal to 300 nm, greater than or equal to 350 nm, greater than or equal to 400 nm, greater than or equal to 450 nm, greater than or equal to 500 nm, greater than or equal to 550 nm, greater than or equal to 600 nm, greater than or equal to 650 nm, greater than or equal to 700 nm, or greater than or equal to 750 nm. In another embodiment, the size of the primary particle 3 may be less than or equal to 800 nm, less than or equal to 750 nm, less than or equal to 700 nm, less than or equal to 650 nm, less than or equal to 600 nm, less than or equal to 550 nm, less than or equal to 500 nm, less than or equal to 450 nm, less than or equal to 400 nm, less than or equal to 350 nm, less than or equal to 300 nm, less than or equal to 250 nm, less than or equal to 200 nm, or less than or equal to 150 nm.

[0065] The surface portion 5a includes a manganese-doped nickel-based composite metal oxide located between the primary particles 3 (i.e., grain boundaries), and the amount of manganese present at the grain boundaries 7 of the primary particles 3 in the surface portion 5a is higher than the amount of manganese present inside the primary particles 3. In other words, the amount of manganese coated at the grain boundaries of the primary particles 3 is higher than the amount of manganese coated inside the primary particles 3.

[0066] "Grain boundary" refers to the interface between two adjacent primary particles 3. In embodiments, a grain boundary may refer to a region less than or equal to 20% of the length from the outermost surface (the interface between adjacent primary particles 3) to less than or equal to 40% of the length from the outermost surface (e.g., a region less than or equal to 25%, 30%, or 35% of the length from the outermost surface). The interior of a primary particle 3 refers to the portion excluding the grain boundary. In an implementation, the interior of a primary particle 3 may refer to a region that is less than or equal to 60% of the length from the center of the primary particle 3 to less than or equal to 80% of the length from the center of the primary particle 3, based on the total distance from the center of the primary particle to the outermost surface (the interface between adjacent primary particles 3). (For example, less than or equal to 40%, less than or equal to 45%, less than or equal to 50%, less than or equal to 55%, less than or equal to 60%, less than or equal to 65%, less than or equal to 70%, less than or equal to 75%, or less than or equal to 80% of the length from the center of the primary particle.)

[0067] In this embodiment, based on the total amount (mol%) of metals (excluding lithium) in the nickel-based composite metal oxide, the manganese-doped nickel-based composite metal oxide may include 0.1 mol% to 5 mol% of manganese. The amount by which the manganese concentration in the surface portion 5a of the secondary particle 1 is higher than the manganese concentration in the central portion 5b can be equal to the manganese content of the manganese-doped nickel-based composite metal oxide. That is, the manganese concentration in the surface portion 5a of the secondary particle 1, relative to the manganese concentration in the central portion 5b, may further include 0.1 mol% to 5 mol% of manganese. By including 0.1 mol% to 5 mol% of manganese in the total amount (mol%) of metals in the nickel-based composite metal oxide, the structural stability and cycle characteristics of the positive electrode active material can be improved.

[0068] In embodiments, relative to the total amount (mol%) of metals (excluding lithium) in the manganese-doped nickel-based composite metal oxide, the manganese content of the manganese-doped nickel-based composite metal oxide may be greater than or equal to 0.1 mol%, greater than or equal to 0.2 mol%, greater than or equal to 0.3 mol%, greater than or equal to 0.4 mol%, greater than or equal to 0.5 mol%, greater than or equal to 0.6 mol%, greater than or equal to 0.7 mol%, greater than or equal to 0.8 mol%, greater than or equal to 0.9 mol%, greater than or equal to 1.0 mol%, greater than or equal to 1.1 mol%, greater than or equal to 1.2 mol%, greater than or equal to 1.3 mol%, greater than or equal to 1.4 mol%, greater than or equal to 1.5 mol%, greater than or equal to 1.6 mol%, greater than or equal to 1.7 mol%, greater than or equal to 1.8 mol%, greater than or equal to 1.9 mol%, greater than or equal to 2.0 mol%, greater than or equal to 2.1 mol%, greater than or equal to 2.2 mol%, greater than or equal to 2. 3 mol%, greater than or equal to 2.4 mol%, greater than or equal to 2.5 mol%, greater than or equal to 2.6 mol%, greater than or equal to 2.7 mol%, greater than or equal to 2.8 mol%, greater than or equal to 2.9 mol%, greater than or equal to 3.0 mol%, greater than or equal to 3.1 mol%, greater than or equal to 3.2 mol%, greater than or equal to 3.3 mol%, greater than or equal to 3.4 mol%, greater than or equal to 3.5 mol%, greater than or equal to 3.6 mol%, greater than or equal to 3.7 mol%, greater than or equal to 3.8 mol%, greater than or equal to 3.9 mol%, greater than or equal to 4.0 mol%, greater than or equal to 4.1 mol%, greater than or equal to 4.2 mol%, greater than or equal to 4.3 mol%, greater than or equal to 4.4 mol%, greater than or equal to 4.5 mol%, greater than or equal to 4.6 mol%, greater than or equal to 4.7 mol%, greater than or equal to 4.8 mol%, greater than or equal to 4.9 mol%, or greater than or equal to 5.0 mol%.

[0069] In embodiments, relative to the total amount (mol%) of metals (excluding lithium) in the manganese-doped nickel-based composite metal oxide, the manganese content of the manganese-doped nickel-based composite metal oxide may be less than or equal to 5.0 mol%, less than or equal to 4.9 mol%, less than or equal to 4.8 mol%, less than or equal to 4.7 mol%, less than or equal to 4.6 mol%, less than or equal to 4.5 mol%, less than or equal to 4.4 mol%, less than or equal to 4.3 mol%, less than or equal to 4.2 mol%, less than or equal to 4.1 mol%, less than or equal to 4.0 mol%, less than or equal to 3.9 mol%, less than or equal to 3.8 mol%, less than or equal to 3.7 mol%, less than or equal to 3.6 mol%, less than or equal to 3.5 mol%, less than or equal to 3.4 mol%, less than or equal to 3.3 mol%, less than or equal to 3.2 mol%, less than or equal to 3.1 mol%, less than or equal to 3.0 mol%, less than or equal to 2.9 mol%, and less than or equal to 2. 8 mol%, less than or equal to 2.7 mol%, less than or equal to 2.6 mol%, less than or equal to 2.5 mol%, less than or equal to 2.4 mol%, less than or equal to 2.3 mol%, less than or equal to 2.2 mol%, less than or equal to 2.1 mol%, less than or equal to 2.0 mol%, less than or equal to 1.9 mol%, less than or equal to 1.8 mol%, less than or equal to 1.7 mol%, less than or equal to 1.6 mol%, less than or equal to 1.5 mol%, less than or equal to 1.4 mol%, less than or equal to 1.3 mol%, less than or equal to 1.2 mol%, less than or equal to 1.1 mol%, less than or equal to 1.0 mol%, less than or equal to 0.9 mol%, less than or equal to 0.8 mol%, less than or equal to 0.7 mol%, less than or equal to 0.6 mol%, less than or equal to 0.5 mol%, less than or equal to 0.4 mol%, less than or equal to 0.3 mol%, less than or equal to 0.2 mol% or less than or equal to 0.1 mol%.

[0070] In one embodiment, the positive electrode active material may have a concentration gradient in which the concentration of manganese continuously decreases from the surface portion 5a to the central portion 5b of the secondary particle 1. The surface portion 5a of the secondary particle 1 may include a first surface portion near the outermost surface and a second surface portion near the center, and the first surface portion may have a higher manganese concentration than the second surface portion.

[0071] In an embodiment, the manganese content ratio (molar ratio) of the surface portion 5a to the central portion 5b of the secondary particle 1 can be 5 to 15. For example, the manganese content ratio of the surface portion 5a to the central portion 5b of the secondary particle 1 can be greater than or equal to 5, greater than or equal to 6, greater than or equal to 7, greater than or equal to 8, greater than or equal to 9, greater than or equal to 10, greater than or equal to 11, greater than or equal to 12, greater than or equal to 13, or greater than or equal to 14, and less than or equal to 15, less than or equal to 14, less than or equal to 13, less than or equal to 12, less than or equal to 11, less than or equal to 10, less than or equal to 9, less than or equal to 8, less than or equal to 7, or less than or equal to 6. In an embodiment, the manganese content ratio of the surface portion 5a to the central portion 5b of the secondary particle 1 can be 10.

[0072] In another embodiment, the central portion 5b of the secondary particle may not include a manganese-doped nickel-based composite metal oxide.

[0073] As described above, the positive electrode active material according to the embodiment comprises a high concentration of a nickel-based composite metal oxide doped with manganese, present between primary particles in a surface portion 5a extending from the outermost surface of the secondary particles 1 to a specific depth. This differs from conventional structures that coat the surface of the secondary particles, and by coating the primary particles at a specific depth on the outermost surface, the structural stability of the positive electrode active material can be improved.

[0074] By including a manganese-doped nickel-based composite metal oxide (nickel-based lithium metal oxide) at the grain boundaries 7 of the primary particles 3, lithium can diffuse smoothly into the central portion 5b of the secondary particles 1, and the elution of nickel ions from the central portion 5b of the secondary particles 1 can be suppressed. Furthermore, side reactions between the primary particles and the electrolyte in the central portion 5b of the secondary particles 1 can be suppressed. Therefore, the cycle characteristics of lithium secondary batteries including positive electrode active materials with the above structure can be improved.

[0075] Furthermore, reducing the residual lithium content on the surface of the multiple primary particles 3 within the secondary particles 1 suppresses the degradation of the positive electrode active material and reduces gas generation, thereby improving the thermal stability of the lithium secondary battery. The manganese-doped nickel-based composite metal oxide disposed at the grain boundaries between adjacent primary particles 3 prevents damage to the surface of the primary particles during the cleaning process of the positive electrode active material, thus preventing degradation of the cycle life characteristics of the lithium secondary battery.

[0076] The manganese-doped nickel-based composite metal oxide arranged at grain boundaries 7 between adjacent primary particles 3 can absorb volume changes caused by charging and discharging of the primary particles, and suppress cracking between primary particles over a long period of time. Even after discharging, deterioration of the lithium secondary battery can be prevented by suppressing the reduction in mechanical strength of the positive electrode active material. In addition, by doping the primary particles with manganese, the crystal structure of the nickel-based composite metal oxide is stabilized, and the cycle characteristics of the lithium secondary battery including the positive electrode active material can be further improved.

[0077] In an embodiment, the surface portion 5a of the secondary particle may further include lithium manganese oxide. The lithium manganese oxide may be selected from LiMnO₂, Li₂Mn₂O₃, LiMn₂O₄, or a combination thereof.

[0078] In an embodiment, the manganese-doped nickel-based composite metal oxide may be a layered oxide, a spinel oxide, a rock-salt oxide, or a combination thereof. In another embodiment, the manganese-doped nickel-based composite metal oxide is mainly a layered oxide, and may be partially mixed with a spinel-structured oxide and a rock-salt-structured oxide.

[0079] The manganese-doped nickel-based composite metal oxide may be represented by Chemical Formula 1:

[0080] [Chemical Formula 1]

[0081] LiNi 1-x-y-z Co x Mn y M z O₂

[0082] In Chemical Formula 1,

[0083] 0 < x ≤ 0.05, 0.001 ≤ y ≤ 0.05 and 0 ≤ z ≤ 0.02, and M is at least one metal element selected from the group consisting of Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, B, Ta, Pr, Si, Ba and Ce.

[0084] In an embodiment, the compound of Chemical Formula 1 may be LiNi 1-x-y Co x Mn y O₂, LiNi 1-x-y-z Co x Mn y Al z O₂ or LiNi 1-x-y-z Co x Mn y+z O₂.

[0085] Because manganese-doped nickel-based composite metal oxides have a high nickel content, their capacity can be maximized. While high nickel content can lead to high capacity but low cycle life, this degradation can be mitigated by doping with a specific amount of manganese.

[0086] In this embodiment, y in Formula 1 can be 0.001 ≤ y ≤ 0.03. When y in Formula 1 exceeds 0.05, manganese may aggregate. In this embodiment, the manganese-doped nickel-based composite metal oxide can be Li[(NiCoAl)]. 0.995 Mn 0.005 O2, Li[(NiCoAl)] 0.99 Mn 0.01 O2, Li[(NiCoAl)] 0.985 Mn 0.015 O2, Li[(NiCoAl)] 0.98 Mn 0.02 O2, Li[(NiCoAl)] 0.975 Mn 0.025 O2, Li[(NiCoAl)] 0.97 Mn 0.03 O2, etc.

[0087] In the implementation, when XRD is measured on a positive electrode active material powder including a nickel-based composite metal oxide doped with manganese, the full width at half maximum (FWHM) of the (003) peak is... (003) The value can be 0.1° to 0.2° (2θ).

[0088] In an implementation, the full width at half maximum (FWHM) value can be greater than or equal to 0.1°, for example greater than or equal to 0.11°, greater than or equal to 0.12°, greater than or equal to 0.13°, greater than or equal to 0.14°, greater than or equal to 0.15°, greater than or equal to 0.16°, greater than or equal to 0.17°, greater than or equal to 0.18°, or greater than or equal to 0.19°, and for example less than or equal to 0.20°, less than or equal to 0.19°, less than or equal to 0.18°, less than or equal to 0.17°, less than or equal to 0.16°, less than or equal to 0.15°, less than or equal to 0.14°, less than or equal to 0.13°, less than or equal to 0.12°, or less than or equal to 0.11°.

[0089] Even when fired at the same temperature, the full width at half maximum (FWHM) increases with the amount of manganese coating. When the FWHM is 0.1° to 0.2° (2θ) or greater, it can be seen that manganese is coated on the positive electrode active material. However, when the FWHM is less than 0.1° (2θ), it cannot be considered that manganese is uniformly coated.

[0090] In this embodiment, the c-axis length (d-spacing) of the primary particles present in the surface portion 5a of the secondary particles 1 of the positive electrode active material, including a nickel-based composite metal oxide doped with manganese, can be greater than or equal to... Since the c-axis length increases with manganese coating, it can be confirmed whether manganese has been coated by comparing the c-axis lengths. When manganese is coated at the grain boundaries of the primary particles present in the surface portion 5a of secondary particles 1, the c-axis length of the primary particles increases with manganese coating, but the c-axis length of the primary particles in the central portion 5b of secondary particles 1 remains almost unchanged. That is, by comparing the c-axis lengths of the primary particles in the central portion 5b and the surface portion 5a of secondary particles 1, it can be confirmed whether manganese is coated only on the surface or at the grain boundaries of the primary particles 3 in the surface portion 5a of secondary particles. This shows that the manganese content is high at the surface or grain boundaries of the primary particles in the surface portion 5a of secondary particles, while the nickel content is relatively lower.

[0091] In this embodiment, the c-axis length of the primary particle in the surface portion 5a of the secondary particle can be greater than or equal to... Greater than or equal to Greater than or equal to Greater than or equal to Greater than or equal to Greater than or equal to Greater than or equal to Greater than or equal to Greater than or equal to Greater than or equal to Greater than or equal to Greater than or equal to or greater than or equal to

[0092] In this embodiment, the c-axis length of the primary particles present in the surface portion 5a of the secondary particle 1 can be greater than the c-axis length of the primary particles present in the central portion 5b of the secondary particle 1. For example, the c-axis length of the primary particles present in the surface portion 5a of the secondary particle 1 can be... The c-axis length of the primary particle in the central part 5b of secondary particle 1 can be...

[0093] In this embodiment, the c-axis length of the primary particle in the central portion 5b of the secondary particle 1 and the c-axis length of the interior of the primary particle in the surface portion of the secondary particle can be the same.

[0094] The positive electrode active material is prepared according to the following preparation method.

[0095] First, a nickel-based composite metal compound, including secondary particles in which multiple primary particles are aggregated, and a solvent are placed in a reactor and dispersed to prepare a dispersion.

[0096] The solvent may be distilled water.

[0097] The nickel-based composite metal compound (i.e., the positive electrode active material precursor) may be a compound represented by Chemical Formula 2 or Chemical Formula 3:

[0098] [Chemical Formula 2]

[0099] Ni 1-x-y-z Co x M y (OH)2Mn w O q

[0100] In Chemical Formula 2,

[0101] 0 < x ≤ 0.05, 0 ≤ y ≤ 0.02, 0 < w ≤ 3, 0 < q ≤ 4, and M is at least one metal element selected from the group consisting of Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, B, Ta, Pr, Si, Ba and Ce,

[0102] [Chemical Formula 3]

[0103] Ni 1-x-y-z Co x M y O2Mn w O q

[0104] wherein in Chemical Formula 3,

[0105] 0 < x ≤ 0.05, 0 ≤ y ≤ 0.02, 0 < w ≤ 3, 0 < q ≤ 4, and M is at least one metal element selected from the group consisting of Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, B, Ta, Pr, Si, Ba and Ce.

[0106] The compound represented by Chemical Formula 2 may be Ni 1-x Co x (OH)2Mn w O q , Ni 1-x-y Co x Al y (OH)2Mn w O q or Ni 1-x-y Co x Mn y (OH)2Mn w O q , and the compound represented by Chemical Formula 3 may be Ni1-x Co x O2Mn w O q Ni 1-x- y Co x Al y O2Mn w O q or Ni 1-x-y Co x Mn y O2Mn w O q .

[0107] The compound represented by chemical formula 2 is prepared by coprecipitation.

[0108] A nickel composite metal compound and a solvent are placed in a reactor and stirred to prepare a dispersion. During stirring, an inert gas can be injected into the reactor. By injecting the inert gas into the reactor, the partial pressure of dissolved oxygen can be reduced. When dissolved oxygen is high, manganese exists as an oxide rather than a hydroxide, making it difficult to coat the surface of the nickel composite metal compound. Therefore, to prevent this, the reaction between the nickel composite metal compound and dissolved oxygen can be minimized by injecting an inert gas into the reactor to reduce the partial pressure of dissolved oxygen.

[0109] Inactive gases can be selected from N2, He, Ar and combinations thereof.

[0110] The injection rate of the inactive gas can be from 50 sccm to 5000 sccm. For example, the injection rate of the inactive gas can be greater than or equal to 500 sccm, greater than or equal to 1000 sccm, greater than or equal to 1500 sccm, greater than or equal to 2000 sccm, greater than or equal to 2500 sccm, greater than or equal to 3000 sccm, greater than or equal to 3500 sccm, greater than or equal to 4000 sccm, or greater than or equal to 4500 sccm.

[0111] During stirring, the reactor temperature can be between 30°C and 60°C, for example, between 40°C and 50°C or between 40°C and 45°C.

[0112] The stirring speed of the reactor can be from 300 rpm to 600 rpm. For example, the stirring speed of the reactor can be greater than or equal to 300 rpm, greater than or equal to 350 rpm, greater than or equal to 400 rpm, greater than or equal to 450 rpm, greater than or equal to 500 rpm, or greater than or equal to 550 rpm, and less than or equal to 600 rpm, less than or equal to 550 rpm, less than or equal to 500 rpm, less than or equal to 450 rpm, less than or equal to 400 rpm, or less than or equal to 350 rpm.

[0113] By injecting an inert gas, an aqueous solution of manganese salt and a precipitant are added to a dispersion in an atmosphere with reduced oxygen content to prepare nickel-based composite metal compounds coated with manganese salts via a co-precipitation method.

[0114] At this point, manganese salts can be coated, in the form of manganese hydroxide, onto the grain boundaries of the primary particles on the surface portion of the secondary particles present in the nickel-based complex metal hydroxide. The manganese salts can be selected from manganese sulfate (MnSO4), manganese nitrate, manganese acetate, and their hydrates.

[0115] The precipitant can be NaOH. When the precipitant is NaOH, it can act as a pH adjuster in the reactor.

[0116] The reactor pH can be maintained between 8 and 13. The reactor pH is greater than or equal to 8, greater than or equal to 8.5, greater than or equal to 9, greater than or equal to 9.5, greater than or equal to 10, greater than or equal to 10.5, greater than or equal to 11, greater than or equal to 11.5, greater than or equal to 12, or greater than or equal to 12.5, and less than or equal to 13, less than or equal to 12.5, less than or equal to 12, less than or equal to 11.5, less than or equal to 11, less than or equal to 10.5, less than or equal to 10, less than or equal to 9.5, less than or equal to 9, or less than or equal to 8.5.

[0117] The reactor temperature can be maintained between 20℃ and 50℃. The reactor temperature can be greater than or equal to 20℃, greater than or equal to 30℃, or greater than or equal to 40℃, and less than or equal to 50℃, less than or equal to 40℃, or less than or equal to 30℃.

[0118] The nickel-based composite metal compound coated with manganese salt in the reactor can be dried in a vacuum dryer at a temperature of 100°C to 200°C. Drying can be performed using convection. When using convection drying, oxygen can flow in, and manganese hydroxide can react with oxygen to form oxides. Manganese hydroxide can react with oxygen to form manganese oxides (such as MnO2, Mn2O3, and Mn3O4).

[0119] After drying, the dried nickel-based composite metal compound can be heat-treated at a temperature of 400℃ to 600℃. Through heat treatment, manganese hydroxide can be converted into oxide. Specifically, manganese hydroxide can be converted into manganese oxide (MnO2) through heat treatment.

[0120] Subsequently, a lithium source is mixed with a nickel-based composite metal compound, and then calcined to obtain a positive electrode active material of a nickel-based composite metal oxide. The lithium source can be LiOH, Li₂CO₃, or their hydrates.

[0121] The firing temperature can be 600℃ to 800℃, for example, greater than or equal to 600℃, greater than or equal to 625℃, greater than or equal to 650℃, greater than or equal to 675℃, greater than or equal to 700℃, greater than or equal to 725℃, greater than or equal to 750℃, greater than or equal to 775℃, and less than or equal to 800℃, less than or equal to 775℃, less than or equal to 750℃, less than or equal to 725℃, less than or equal to 700℃, less than or equal to 675℃, less than or equal to 650℃, or less than or equal to 625℃.

[0122] In another embodiment, the lithium secondary battery includes: a positive electrode, including a positive electrode active material; a negative electrode, including a negative electrode active material; and an electrolyte.

[0123] In the following description, a lithium secondary battery according to an embodiment will be described with reference to the accompanying drawings. Figure 2 This is a perspective view that schematically illustrates a typical structure of a lithium secondary battery according to an embodiment.

[0124] refer to Figure 2 The lithium secondary battery 31 includes a positive electrode 33, a negative electrode 32, and a separator 34 containing positive electrode active material according to an embodiment. The aforementioned positive electrode 33, negative electrode 32, and separator 34, including the positive electrode active material, are wound or folded and housed in a battery casing 35. Then, an organic electrolyte is injected into the battery casing 35 and sealed using a cover assembly 36 to complete the lithium secondary battery 31. The battery casing 35 may have a cylindrical shape, a square shape, a thin film shape, etc.

[0125] A lithium secondary battery can be a lithium-ion battery.

[0126] The positive and negative electrodes are manufactured by coating the composition for forming the positive electrode active material layer and the composition for forming the negative electrode active material layer onto a current collector and drying them respectively.

[0127] The composition for forming the positive electrode active material is prepared by mixing the positive electrode active material, a conductive agent, a binder, and a solvent, wherein the positive electrode active material is as described above.

[0128] The binder is a component that facilitates the adhesion of the active material and conductive agent to the current collector, and is added in an amount of 1 to 50 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material. Non-limiting examples of binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene copolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers. Based on 100 parts by weight of the total weight of the positive electrode active material, the binder may be included in an amount of 2 to 5 parts by weight. When the amount of binder is within this range, the adhesion of the active material layer to the current collector can be suitable or good.

[0129] The conductive agent is not particularly limited, as long as it does not cause a chemical change in the battery and is conductive. Non-limiting examples of conductive agents may include: graphite (such as natural graphite and / or artificial graphite); carbon-based materials (such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, etc.); conductive fibers (such as carbon fibers, metal fibers, etc.); fluorides; metal powders (such as aluminum powder and / or nickel powder); conductive whiskers (such as zinc oxide, potassium titanate, etc.); conductive metal oxides (such as titanium oxide); and conductive materials (such as polyphenylene derivatives, etc.). Based on the total weight of 100 parts by weight of the positive electrode active material, the amount of conductive agent can be 2 to 5 parts by weight. When the amount of conductive agent is within this range, the conductivity characteristics of the obtained electrode can be improved.

[0130] Non-limiting examples of solvents include N-methylpyrrolidone, etc. The amount of solvent can be from 10 to 100 parts by weight, based on the total weight of 100 parts by weight of the positive electrode active material. When the amount of solvent is within this range, the active material layer can be easily formed.

[0131] The positive electrode current collector can have a thickness of 3 μm to 500 μm, and the material of the positive electrode current collector is not particularly limited, as long as it does not cause chemical changes in the battery and has high conductivity. It can be, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, and / or aluminum or stainless steel surface-treated with carbon, nickel, titanium, and / or silver. The current collector can have fine irregularities formed on its surface to increase adhesion to the positive electrode active material, and can be provided in any suitable form such as a film, sheet, foil, mesh, porous body, foam, and / or nonwoven fabric.

[0132] The negative electrode active material, binder, conductive agent, and solvent can be separately mixed to prepare a composition for forming the negative electrode active material layer. The negative electrode active material can be or includes materials capable of intercalating and deintercalating lithium ions. Non-limiting examples of negative electrode active materials can be carbon-based materials (such as graphite and / or carbon), lithium metal, alloys thereof, silicon oxide-based materials, etc. According to embodiments of the present invention, silicon oxide is used.

[0133] The binder, conductive agent, and solvent can be the same type of materials used in manufacturing the positive electrode. Based on 100 parts by weight of the total weight of the negative electrode active material, a binder can be added in an amount of 1 to 50 parts by weight. Based on 100 parts by weight of the total weight of the negative electrode active material, a conductive agent can be used in an amount of 1 to 5 parts by weight. When the content of the conductive agent is within the above range, the conductivity characteristics of the final electrode are improved. Based on 100 parts by weight of the total weight of the negative electrode active material, a solvent can be used in an amount of 1 to 10 parts by weight. When the amount of solvent is within this range, a layer of the negative electrode active material can be easily formed.

[0134] The negative electrode current collector can have a thickness of 3 μm to 500 μm. The materials used for the negative electrode current collector are not particularly limited, as long as they do not cause chemical changes in the battery and have high conductivity. Non-limiting examples may include: copper; stainless steel; aluminum; nickel; titanium; heat-treated carbon; copper and / or stainless steel surface-treated with carbon, nickel, titanium, and / or silver; aluminum-cadmium alloys, etc. The negative electrode current collector may have fine irregularities formed on its surface to increase adhesion to the negative electrode active material, and similar to the positive electrode current collector, it can be provided in any suitable form such as a film, sheet, foil, mesh, porous body, foam, and / or nonwoven fabric.

[0135] A separator can be disposed between the positive and negative electrodes by winding or laminating it to form an electrode assembly. The separator can have a pore size of 0.01 μm to 10 μm and a thickness of 5 μm to 300 μm. Specific examples may include: olefin polymers (such as polypropylene, polyethylene, etc.); or sheets or nonwoven fabrics formed from glass fibers. Solid electrolytes, such as polymers, can also be used as separators when they are used as the electrolyte itself.

[0136] When the electrode assembly is housed in a casing, an electrolyte is injected and the resulting product is sealed, completing the lithium secondary battery. The electrolyte can be a non-aqueous electrolyte including non-aqueous solvents and lithium salts, an organic solid electrolyte, an inorganic solid electrolyte, etc. Non-aqueous electrolytes can be or include, for example, aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, N,N-dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate, etc. Lithium salts can be materials that are readily soluble in non-aqueous electrolytes, and non-limiting examples include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB. 10 Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborate, low aliphatic carboxylic acid lithium, lithium tetraphenylborate, lithium imino, etc.

[0137] Non-limiting examples of organic solid electrolytes may include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, etc.

[0138] Non-limiting examples of inorganic solid electrolytes may include Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, etc.

[0139] Furthermore, lithium-ion batteries can be formed into battery packs with circuitry, and single or multiple packs can be used as needed for all devices requiring high capacity and high power. For example, they can be used in laptops, smartphones, electric vehicles, etc. Additionally, lithium-ion batteries exhibit excellent storage stability, cycle life characteristics, and high rate capability at high temperatures, making them suitable for use in electric vehicles (EVs). For instance, they can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs).

[0140] The invention is explained in more detail in the following embodiments and comparative examples. However, it should be understood that these embodiments are for illustrative purposes only and should not be construed as limiting the invention.

[0141] Example

[0142] Example 1

[0143] (Preparation of positive electrode active material)

[0144] Ni was added to it 0.945 Co 0.04 Al 0.015 In a reactor containing (OH)₂ and distilled water, N₂ gas was supplied at 4000 sccm, and the aqueous solution in the reactor was stirred at 300-600 rpm while maintaining the aqueous solution at 45°C. Subsequently, 2M manganese sulfate aqueous solution and 5.5M NaOH aqueous solution were continuously added to the reactor for 30 minutes to 1 hour. While maintaining the pH concentration of the reactor at 10-12, 2 mol% of a Mn compound was coated onto a nickel-based composite metal hydroxide. The Mn compound-coated nickel-based composite metal hydroxide was dried in a vacuum dryer at a final temperature of 120°C.

[0145] Subsequently, nickel-based composite metal hydroxides were mixed with lithium hydroxide at a 1:1 molar ratio, and then calcined at 720°C for 5 hours to obtain Li[Ni] 0.926 Co 0.039 Al 0.015 Mn 0.02 O2 positive electrode active material powder.

[0146] (The manufacture of the positive electrode)

[0147] A positive electrode active material slurry was prepared by mixing 94 wt% of positive electrode active material, 3 wt% of Ketjen black, and 3 wt% of polyvinylidene fluoride in an N-methylpyrrolidone solvent. The positive electrode active material slurry was coated onto an Al foil, then dried and pressed to manufacture the positive electrode.

[0148] (Manufacturing of coin cell batteries)

[0149] The coin cell is manufactured using a positive electrode, lithium metal as the counter electrode, a PTFE membrane, and an electrolyte (which is a solution of 1.15M LiPF6 dissolved in a mixed solvent of EC (ethylene carbonate), DEC (diethyl carbonate), and EMC (ethyl methyl carbonate) in a volume ratio of 3:4:3).

[0150] Example 2

[0151] Except that Mn was changed to 0.5 mol% coating, the positive electrode and coin cell were manufactured in the same manner as in Example 1.

[0152] Example 3

[0153] Except that Mn was changed to 1 mol% coating, the positive electrode and coin cell were manufactured in the same manner as in Example 1.

[0154] Example 4

[0155] In addition to using Ni 0.945 Co 0.04 Al 0.015 O2 replaces Ni 0.945 Co 0.04 Al 0.015 (OH)2 and Mn were changed to be coated with 0.5 mol% in addition to the positive electrode and coin cell, which were manufactured in the same manner as in Example 1.

[0156] Comparative Example 1

[0157] (Preparation of positive electrode active material)

[0158] Ni 0.945 Co 0.04 Al 0.015 (OH)₂ and distilled water were placed in a reactor and stirred for a predetermined time. Manganese acetate and C₄H₆MnO₄ were then added and stirred simultaneously. The stirred mixture was dried at 80°C to obtain a nickel-based composite metal hydroxide coated with a Mn compound. Subsequently, the hydroxide was heat-treated at 450°C to obtain a nickel-based composite metal oxide coated with MnO₂.

[0159] Subsequently, nickel-based composite metal oxides were used to manufacture the positive electrode and coin cell in the same manner as in Example 1.

[0160] Assessment 1. EDS (Energy Dispersive X-ray Spectroscopy) measurement

[0161] Evaluation 1-1. Measurement of manganese distribution among primary particles

[0162] To confirm whether Mn is well distributed at the interface between the primary particles and the secondary particles of the positive electrode active material, EDS analysis was performed on the cross-section of the positive electrode active material of Example 1. Figure 3 This is a STEM image (HAADF) showing cross-sections of multiple primary particles in the positive electrode active material used for EDS analysis, and Figure 4 It shows the distribution in Figure 3 A graph showing the manganese content in multiple primary particles (A, B, and C).

[0163] refer to Figure 3 and Figure 4The arrow points to a portion corresponding to the interface between the primary particles and the secondary particles, indicating that manganese is present at the corresponding interface at a significantly higher mol% concentration than inside the primary particles. This result suggests that manganese is coated at the grain boundaries of the primary particles on the surface portion of the secondary particles.

[0164] Assessment 1-2. Measurement of manganese distribution in the surface and central portions of the positive electrode active material

[0165] To confirm the distribution of Mn on the surface and central portions of the positive electrode active material, EDS analysis was performed on the cross-section of the positive electrode active material of Example 1. Figure 5 This is a STEM image (HAADF) showing the surface and central portions of the cross-section of the positive electrode active material. Figure 5 In the diagram, regions 1 to 3 correspond to the surface portion of the positive electrode active material, and regions 4 to 8 correspond to the central portion of the positive electrode active material. Additionally, measurements... Figure 5 The mol% of the metal at each region is shown in Table 1. In Table 1, the content of each metal is based on the total content of metals other than lithium.

[0166] (Table 1)

[0167] Ni 85.03 88.76 87.89 94.71 87.34 93.79 92.69 94.35 Co 3.71 3.39 4.54 3.47 4.71 3.72 2.13 2.24 Al 1.45 4.74 5.71 0.00 7.15 1.44 4.21 2.81 Mn 9.81 3.11 1.86 1.82 0.80 1.05 0.97 0.60

[0168] As shown in Table 1, the higher the Mn content, the closer it is to the surface of the positive electrode active material. Therefore, the positive electrode active material of Example 1 exhibits a concentrated coating of manganese on the surface portion.

[0169] Assessment 2. c-axis length (d - spacing) measurement

[0170] To confirm whether Mn was coated on the grain boundaries of the primary particles, STEM analysis was used to measure the c-axis lengths of the primary particles in the surface portion and the central portion (bulk portion) of the secondary particles of the positive electrode active material in Example 1. Figure 6 and Figure 7 The results are shown in the figure. Figure 6 This is a STEM image of the primary particles on the surface portion of the secondary particles of the positive electrode active material in Example 1, and... Figure 7 This is a STEM image of the primary particles in the central portion of the secondary particles of the positive electrode active material of Comparative Example 1. Furthermore, for comparison, the c-axis length of the primary particles of the positive electrode active material of Comparative Example 1 was measured by STEM analysis, and... Figure 8 The results are shown in the figure. Figure 8 This is a STEM photograph showing the primary particles of the positive electrode active material of Comparative Example 1.

[0171] refer to Figure 6 and Figure 7 Depending on the position of the primary particles within the secondary particles, their c-axis lengths differ. In other words, the c-axis length of the primary particles in the surface portion of the secondary particles is... This is compared to the c-axis length of the primary particles in the central part of the secondary particles. The length of the c-axis is thus confirmed to be long, indicating that manganese is coated on the grain boundaries of the primary particles in the surface portion of the secondary particles and extends the c-axis length.

[0172] on the other hand, Figure 8 The c-axis length of the primary particles of the uncoated manganese positive electrode active material is shown, where the c-axis length is... This is almost equal to the c-axis length of the primary particle in the center of the secondary particle in Example 1. This result shows that manganese is coated at the interface between the primary and secondary particles of the positive electrode active material, that is, at their grain boundaries.

[0173] Assessment 3. X-ray diffraction (XRD) data measurement

[0174] X-ray diffraction analysis was performed as follows. Measurements were taken using an X-ray diffraction apparatus with Cu-Ka wavelength at a scan rate of 0.2θ / step. The X-ray tube voltage and current were 40 kV and 40 mA, respectively, with the divergence slit set at 0.5°, the Soler slit at 0.04 rad, and the wavelength at 8.05 keV (at 50% PHD).

[0175] The FWHM was then obtained by Rietveld refinement of the acquired measurements using the HighScore Plus program.

[0176] Table 2 shows the XRD data results of the positive electrode active materials of Examples 2 to 4 and Comparative Example 1.

[0177] (Table 2)

[0178] <![CDATA[FWHM (003) ]]> 0.152° 0.162° 0.158° 0.121°

[0179] Generally, a larger full width at half maximum (FWHM) indicates a greater amount of manganese coating. As shown in Table 2, Examples 2 to 4 exhibit a higher FWHM than Comparative Example 1, indicating that the positive electrode active materials of Examples 2 to 4 prepared in the co-precipitation method are coated with manganese.

[0180] Assessment 4. Evaluation of initial charge and discharge capacity and charge and discharge efficiency

[0181] The coin cell battery according to Examples 2 to 4 and Comparative Example 1 was charged and discharged once at 0.2C, and then the charging capacity, discharging capacity, and charging and discharging efficiency were measured. The results are shown in Table 3.

[0182] (Table 3)

[0183]

[0184] As shown in Table 3, the coin cell according to Examples 2 to 4 exhibits superior charging and discharging efficiency compared to the cell according to Comparative Example 1.

[0185] Assessment 5. Evaluation of cycle life characteristics

[0186] The coin cell from Examples 2-4 and Comparative Example 1 was charged at 45°C with a constant current rate of 1.0C to a voltage of 4.30V (relative to Li). Then, while maintaining 4.30V, it was cut off in constant voltage mode with a current rate of 0.05C. Subsequently, the coin cell was discharged at a constant current rate of 1.0C to a voltage of 3.0V (relative to Li). This was considered one cycle and repeated until the 50th cycle. A 10-minute pause was set after each charge / discharge cycle in all charge and discharge cycles. At the 50th cycle, the cycle life (capacity retention) of the coin cell was measured, and the results are shown in Table 4.

[0187] Calculate the capacity retention rate according to Equation 1:

[0188] [Equation 1]

[0189] Capacity retention at the 50th cycle [%] = [Discharge capacity at the 50th cycle / Discharge capacity at the 1st cycle] × 100 [%]

[0190] (Table 4)

[0191] Cycle life at the 50th cycle 97.2％ 97.5％ 96.3％ 88.3％

[0192] As shown in Table 4, it can be seen that the cycle life of the coin battery cells manufactured in Examples 2 to 4 is better than that of Comparative Example 1.

[0193] While the invention has been described in conjunction with exemplary embodiments now considered practical, it should be understood that the invention is not limited to the disclosed embodiments. Rather, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the claims.

Claims

1. A positive electrode active material for a lithium secondary battery, comprising: a nickel-based composite metal oxide comprising secondary particles in which a plurality of primary particles are aggregated, wherein the secondary particles comprise a central portion and a surface portion, the surface portion comprises a manganese-doped nickel-based composite metal oxide, the amount of manganese present at grain boundaries of the plurality of primary particles in the surface portion is greater than the amount of manganese present inside the primary particles, wherein based on the total amount (mol%) of metals other than lithium in the nickel-based composite metal oxide, the manganese-doped nickel-based composite metal oxide comprises 0.1 mol% to 5 mol% of manganese, the size of the primary particles of the positive electrode active material is 100 nm to 800 nm, the central portion of the secondary particles does not comprise the manganese-doped nickel-based composite metal oxide, and the central portion refers to a region of less than or equal to 50 length% to less than or equal to 80 length% relative to the total distance (100 length%) from the center of the secondary particle to the outermost surface.

2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material has a concentration gradient in which the concentration of manganese continuously decreases from the surface portion of the secondary particle to the central portion of the secondary particle.

3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the surface portion of the secondary particle is a region of less than or equal to 20 length% to less than or equal to 50 length% of the total distance from the center of the secondary particle to the outermost surface in a direction from the outermost surface toward the center.

4. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the manganese-doped nickel-based composite metal oxide is a compound represented by Chemical Formula 1: [Chemical Formula 1] LiNi 1-x-y-z Co x Mr y M z O2 wherein in Chemical Formula 1, 0 < x ≤ 0.05, 0.001 ≤ y ≤ 0.05 and 0 ≤ z ≤ 0.02, and M is at least one metal element selected from the group consisting of Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, B, Ta, Pr, Si, Ba and Ce.

5. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the manganese-doped nickel-based composite metal oxide comprises a layered structure oxide, a spinel structure oxide, a rock-salt structure oxide, or a combination thereof.

6. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the surface portion further comprises lithium manganese oxide.

7. The positive electrode active material for a lithium secondary battery according to claim 6, wherein the lithium manganese oxide comprises LiMnO2, LiMn2O4, or a combination thereof.

8. The positive electrode active material for a lithium secondary battery according to claim 1, wherein X-ray diffraction analysis was performed on the FWHM of the positive electrode active material. (003) The value is in the range of 0.1° to 0.2° (degrees).

9. The positive electrode active material for a lithium secondary battery according to claim 1, wherein The c-axis length (d-spacing) value of the primary particles present in the surface portion of the secondary particles of the positive electrode active material is greater than or equal to 4.88Å.

10. A method for preparing a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 9, comprising: preparing a dispersion, in which a nickel-based composite metal compound comprising secondary particles formed by aggregation of a plurality of primary particles is dispersed in a solvent, wherein the secondary particles have a central portion and a surface portion, adding an aqueous solution of a manganese salt and a precipitant to the dispersion in an atmosphere with reduced oxygen content to prepare a nickel-based composite metal compound coated with the manganese salt, wherein the manganese salt is coated on the primary particles of the surface portion, and drying the nickel-based composite metal compound coated with the manganese salt, mixing the nickel-based composite metal compound coated with the manganese salt with a lithium source, and then performing heat treatment.

11. The method for preparing a positive electrode active material for a lithium secondary battery according to claim 10, wherein the nickel-based composite metal compound is represented by Chemical Formula 2 or Chemical Formula 3: [Chemical Formula 2] Ni 1-x-y-z Co x M y (OH)2Mn w O q wherein, in Chemical Formula 2, 0<x≤0.05, 0≤y≤0.02, 0<w≤3, 0<q≤4, and M is at least one metal element selected from the group consisting of Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La and Ce, [Chemical Formula 3] Ni 1-x-y-z Co x M y O2Mn w O q wherein, in Chemical Formula 3, 0<x≤0.05, 0≤y≤0.02, 0<w≤3, 0<q≤4, and M is at least one metal element selected from the group consisting of Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La and Ce.

12. The method for preparing a positive electrode active material for a lithium secondary battery according to claim 10, wherein the manganese salt is selected from the group consisting of manganese sulfate, manganese nitrate, manganese acetate, and combinations thereof.

13. The method for preparing a positive electrode active material for a lithium secondary battery according to claim 10, wherein the atmosphere with reduced oxygen content is obtained by injecting an inert gas, and the inert gas is nitrogen (N2).

14. The method for preparing a positive electrode active material for a lithium secondary battery according to claim 13, wherein the injection rate of the inert gas is 50 sccm to 5000 sccm.

15. The method for preparing a positive electrode active material for a lithium secondary battery according to claim 10, wherein the drying is performed at 100°C to 200°C.

16. The method for preparing a positive electrode active material for a lithium secondary battery according to claim 10, wherein the method further comprises: performing heat treatment at 350°C to 600°C before mixing the nickel-based composite metal compound coated with the manganese salt with a lithium source.

17. A lithium secondary battery, comprising: a positive electrode comprising the positive electrode active material according to any one of claims 1 to 9; Negative electrode, including the negative electrode active material; as well as Electrolytes.

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