Positive electrode active material, method for preparing the same, and rechargeable lithium battery including the same

Abstract

Disclosed are a positive electrode active material for a rechargeable lithium battery including a lithium nickel-based composite oxide including large-diameter particles and small-diameter particles having different average particle diameters, in which the large-diameter particles include large-diameter secondary particles including a plurality of primary particles and the small-diameter particles include a lithium halide, and the large-diameter particles have an average particle diameter (D50) of 10 to 20 µm and the small-diameter particles have an average particle diameter (D50) of 1 to 8 µm, a method of preparing the same, and a rechargeable lithium battery including the same.

Description

[0001] Cross-references to related applications

[0002] This application claims priority and benefit to Korean Patent Application No. 10-2019-0137853, filed on October 31, 2019, Korean Patent Application No. 10-2020-0127324, filed on September 29, 2020, and Korean Patent Application No. 10-2020-0141836, filed on October 29, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] A positive electrode active material for rechargeable lithium batteries, a method for preparing the material, and a rechargeable lithium battery including the material are disclosed. Background Technology

[0004] With the development of portable electronic devices, communication devices, and the like, there is a need to develop rechargeable lithium batteries with high energy density.

[0005] This rechargeable lithium battery includes a positive electrode and a negative electrode, both of which include an electrode active material layer formed on an electrode current collector. The electrode active material layer comprises an electrode active material. The positive electrode active material is primarily a lithium-ion intercalation material and can be an oxide, such as lithium cobalt oxide (Li₂O₃). x CoO2), lithium nickel oxide (Li x NiO2), lithium nickel cobalt oxide (Li x (NiCo)O2), lithium nickel cobalt manganese oxide (Li x (NiCoMn)O2), spinel-type lithium manganese oxide (Li x Mn2O4), manganese dioxide (MnO2); or olivine-type or NASICON-type phosphates, such as lithium iron phosphate (LiFe). x FePO4), lithium manganese phosphate (Li x MnPO4, etc.; silicates; polymer materials, etc.

[0006] The negative electrode active material can be a compound capable of intercalating lithium ions, lithium metal or its alloy, and can be a polymer material or a carbon material, such as graphite materials (e.g., artificial graphite or natural graphite), non-graphitizable carbon, or graphitizable carbon; carbon nanotubes (CNTs); carbon nanofibers (CNFs); carbon nanowalls (CNWs).

[0007] On the other hand, positive electrode active materials with porous structures have large BET specific surface areas and therefore exhibit very high residual lithium levels on their surfaces. Consequently, side reactions occur, such as gas generation, and ultimately degrade the stability of the battery.

[0008] Conventional techniques involve rinsing the positive electrode active material to reduce residual lithium. However, this requires additional costs and can damage the surface, ultimately degrading battery performance. Alternatively, a coating process can be applied to the positive electrode active material to further reduce residual lithium, but this still results in degradation of the battery's rate performance and capacity characteristics. Summary of the Invention

[0009] The embodiments provide a positive electrode active material for rechargeable lithium batteries, which has reduced residual lithium and gas generation and increased mixture density on the surface of the active material.

[0010] Another embodiment provides a method for preparing a positive electrode active material for a rechargeable lithium battery.

[0011] Another embodiment provides a rechargeable lithium battery including a positive electrode active material for a rechargeable lithium battery.

[0012] The embodiments provide a positive electrode active material for a rechargeable lithium battery, the positive electrode active material comprising: a lithium nickel-based composite oxide comprising large-diameter particles and small-diameter particles with different average particle sizes, wherein the large-diameter particles comprise large-diameter secondary particles containing multiple primary particles, the small-diameter particles comprise lithium halides, and the large-diameter particles have an average particle size (D50) of about 10 μm to about 20 μm, and the small-diameter particles have an average particle size (D50) of about 1 μm to about 8 μm.

[0013] Small-diameter particles may include small-diameter secondary particles that contain multiple primary particles.

[0014] Small-diameter particles can include single-crystal particles.

[0015] Large-diameter secondary particles may include primary particles having an average thickness of about 100 nm to about 200 nm, and the average thickness of the primary particles included in small-diameter secondary particles may be about 200 nm to about 500 nm.

[0016] Based on the total weight of large-diameter and small-diameter particles, large-diameter particles can be included in an amount of about 50 wt% to about 90 wt%.

[0017] Lithium halides can be coated on the surface of small-diameter particles.

[0018] Lithium halides can be coated onto the surface of small-diameter particles in the form of a film.

[0019] Lithium halides may include LiF.

[0020] Based on small-diameter particles of 100 mol, lithium halides can be included in amounts from about 0.1 mol to about 1.0 mol.

[0021] Large-diameter particles and small-diameter particles may include secondary particles in which multiple plate-shaped primary particles are aggregated, and may have a regular array structure in which the (003) facets of the primary particles are oriented in a direction perpendicular to the surface of the secondary particles.

[0022] The positive electrode active material can have a full width at half maximum (FWHM) of the (003) surface peak of about 0.15° to about 0.17° in X-ray diffraction spectroscopy analysis.

[0023] Large-diameter secondary particles and small-diameter secondary particles may have a single-center radial arrangement or a multi-center radial array structure, wherein the single-center radial arrangement has one center and the multi-center radial array structure has multiple centers.

[0024] Lithium-nickel-based composite oxides can be compounds represented by chemical formula 1.

[0025] [Chemical Formula 1]

[0026] Li a Ni x Co y M 1-x-y O2

[0027] In chemical formula 1, 0.9≤a≤1.05, 0.3≤x≤0.95, 0.05≤y≤0.3, and M is at least one metallic element selected from Mn, Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce.

[0028] The positive electrode active material may contain about 1,400 ppm or less of residual lithium on the surface.

[0029] The positive electrode active material can have a content of approximately 3.1 g / cm³. 3 Approximately 3.4 g / cm³ 3 The density of the mixture.

[0030] Another embodiment provides a method for preparing a positive electrode active material for a rechargeable lithium battery, the method comprising: preparing a large-diameter metal hydroxide precursor and a small-diameter metal hydroxide precursor; mixing the large-diameter metal hydroxide precursor and a lithium feedstock and heat-treating the mixture to prepare large-diameter particles; mixing the small-diameter metal hydroxide precursor, the lithium feedstock, and a lithium halide (LiX) feedstock and heat-treating the mixture to prepare small-diameter particles comprising the lithium halide; and mixing the large-diameter particles and the small-diameter particles to prepare the positive electrode active material.

[0031] Another embodiment provides a rechargeable lithium battery comprising a positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material; and an electrolyte.

[0032] Positive electrode active materials can have increased mixture density by including large-diameter and small-diameter particles with different average particle sizes.

[0033] Because the positive electrode active material includes lithium halides, residual lithium on the surface of the positive electrode active material can be reduced and gas generation can be suppressed, thereby providing a rechargeable lithium battery with improved cycle life characteristics. Attached Figure Description

[0034] Figure 1 This is a schematic diagram showing the positive electrode active material containing a mixture of large-diameter and small-diameter secondary particles.

[0035] Figure 2 This is a schematic diagram showing the positive electrode active material, which contains a mixture of large-diameter secondary particles and small-diameter single-crystal particles.

[0036] Figure 3 This is a schematic diagram showing the oriented primary particles that make up the large-diameter secondary particles.

[0037] Figures 4A to 4C A schematic diagram illustrating the shape of a primary particle according to an embodiment of the present disclosure.

[0038] Figure 5 A perspective view illustrating a representative structure of a rechargeable lithium battery.

[0039] Figure 6 A graph showing the amount of gas generated at high temperature in button cells manufactured according to Examples 2-1 to 2-3, Example 3 and Comparative Example 2.

[0040] <Symbol Description>

[0041] 1: Positive electrode active material

[0042] 1a: Positive electrode active material

[0043] 10: Small-diameter secondary particles

[0044] 10a: Small diameter single crystal particles

[0045] 11: Small-diameter primary particles

[0046] 13: Lithium halides

[0047] 20: Large-diameter secondary particles

[0048] 21: Large-diameter primary particles

[0049] 100: Rechargeable lithium battery

[0050] 50: Negative electrode; 60: Positive electrode

[0051] 70: Separator; 80: Battery casing

[0052] 90: Cover component Detailed Implementation

[0053] Embodiments of the present invention are described in detail below. However, these embodiments are exemplary, and this disclosure is not limited thereto and is defined by the scope of the claims.

[0054] As used in this article, "large-diameter secondary particles" and "small-diameter secondary particles" refer to "large-diameter lithium-nickel-based composite oxide secondary particles" and "small-diameter lithium-nickel-based composite oxide secondary particles," respectively.

[0055] As used herein, "secondary particles" refers to either "large-diameter lithium-nickel-based composite oxide secondary particles" or "small-diameter lithium-nickel-based composite oxide secondary particles," and "primary particles" refers to either "large-diameter lithium-nickel-based composite oxide primary particles" or "small-diameter lithium-nickel-based composite oxide primary particles."

[0056] For example, secondary particles can be relatively large particles comprising multiple physical and / or chemically aggregated primary particles, and primary and secondary particles can be mixed, or secondary particles can exist alone. Additionally, as used herein, D50 refers to the particle size corresponding to the 50% of the total number of particles when the measured particles are arranged in ascending order of size.

[0057] The following text is for reference only. Figures 1 to 3 and Figures 4A to 4C Describe the positive electrode active material according to the embodiments.

[0058] Figure 1 This is a schematic diagram illustrating the positive electrode active material, which contains a mixture of large-diameter and small-diameter secondary particles. Figure 2 This is a schematic diagram illustrating the positive electrode active material, which contains a mixture of large-diameter secondary particles and small-diameter single-crystal particles. Figure 3 This is a schematic diagram showing the oriented primary particles that make up the large-diameter secondary particles. Figures 4A to 4C A schematic diagram showing the sheet-like shape of the primary particles.

[0059] Specifically, the positive electrode active material for a rechargeable lithium battery according to the embodiments includes a lithium nickel-based composite oxide, which comprises large-diameter particles and small-diameter particles with different average particle sizes.

[0060] Large-diameter particles may include large-diameter secondary particles 20 comprising multiple primary particles, and small-diameter particles may include single-crystal particles 10a, small-diameter secondary particles 10 comprising multiple primary particles, or combinations thereof.

[0061] In this article, a single crystal grain refers to a monolithic structure that exists as an independent phase (where the grains do not aggregate with each other in the morphological phase), exists alone without grain boundaries inside the grain, and can be formed by a single grain.

[0062] refer to Figure 1 According to the embodiment, the positive electrode active material 1 includes a lithium-nickel-based composite oxide, which comprises large-diameter secondary particles 20 and small-diameter secondary particles 10. Additionally, refer to... Figure 2 The positive electrode active material 1a according to the embodiment may include a lithium nickel-based composite oxide comprising large-diameter secondary particles 20 and small-diameter single-crystal particles 10a with different average particle sizes. Including large-diameter secondary particles 20 and small-diameter secondary particles 10 or small-diameter single-crystal particles 10a can increase the mixture density of the positive electrode active material. The large-diameter and small-diameter particles may include secondary particles in which a plurality of plate-like primary particles are aggregated, and may have a regular array structure in which the (003) facets of the primary particles are oriented in a direction perpendicular to the surface of the secondary particles.

[0063] refer to Figure 3 The array structure of the primary particles is described below. (Refer to...) Figure 3 The large-diameter secondary particle 20 is described, but it is clear that the small-diameter secondary particle 10 can also be applied in the same manner. Specifically, the (003) facet of the primary particle 21 can be oriented in a direction perpendicular to the surface of the large-diameter secondary particle 20. Surface refers to the outermost surface of the large-diameter secondary particle 20. The (003) facet refers to the lattice facet corresponding to the Miller index (003). Perpendicular direction means that the long axis (a-axis) or short axis (b-axis) of the (003) facet intersects the surface of the large-diameter secondary particle 20 at an angle of about 70° to about 110°, for example, about 80° to about 100°. When the (003) facet of the primary particle 21 is oriented perpendicular to the surface of the large-diameter secondary particle 20, a relatively large number of lithium diffusion pathways between boundaries are formed on the surface side of the large-diameter secondary particle 20, and the degree of lithium diffusion is increased by exposing a large number of crystal faces capable of transporting lithium. Therefore, high initial efficiency and capacity can be ensured. In addition, by suppressing the stress caused by the volume change of the large-diameter secondary particles 20 during charging and discharging, the occurrence of cracks can be suppressed, and the cycle life characteristics of the battery can be improved.

[0064] In the positive electrode active material according to the embodiment, the full width at half maximum (FWHM) of the (003) plane can be about 0.15° to about 0.17° in X-ray diffraction spectroscopy analysis. As used herein, full width at half maximum (FWHM) means the value of the peak width at the position of half the maximum peak intensity of the (003) plane obtained by X-ray diffraction spectroscopy (XRD) analysis of the positive electrode active material. When the FWHM of the (003) plane is within the above range, the size of the small-diameter particles included in the positive electrode active material increases, improving the high initial efficiency and capacity characteristics of the rechargeable lithium battery including the positive electrode active material, and suppressing deformation due to changes in the volume of large-diameter and small-diameter particles during the charging and discharging of the rechargeable lithium battery, thereby suppressing the occurrence of cracks in the battery.

[0065] Large-diameter secondary particles 20 and / or small-diameter secondary particles 10 may have a single-center radial arrangement (with one center) or a multi-center radial array structure (with multiple centers). Primary particles 21, oriented as described above, aggregate to form large-diameter secondary particles 20. For example, multiple primary particles 21 may aggregate to provide large-diameter secondary particles 20 with a radial array structure. Multiple primary particles 21 may be oriented toward a single center to form a surface contact along the c-axis (thickness) direction of the primary particles 21 to provide large-diameter secondary particles 20 with a radial array structure. In another embodiment, the large-diameter secondary particles 20 may have a multi-center radial array structure (with multiple centers). When the large-diameter secondary particles 20 have a single-center radial arrangement or a multi-center radial array structure as described above, lithium can be readily intercalated / deintercalated into the center of the large-diameter secondary particles 20.

[0066] Lithium-nickel based composite oxides can be compounds represented by chemical formula 1:

[0067] [Chemical Formula 1]

[0068] Li a Ni x Co y M 1-x-y O2

[0069] In chemical formula 1, 0.9≤a≤1.05, 0.3≤x≤0.95, 0.05≤y≤0.3, and M is at least one metallic element selected from Mn, Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce.

[0070] In chemical formula 1, 0.98≤a≤1.02, 0.5≤x≤0.8, 0.1≤y≤0.3, or 0.98≤a≤1.02, 0.6≤x≤0.8, 0.1≤y≤0.3, and M can be Mn or Al.

[0071] For example, lithium-nickel-based composite oxides can be selected from LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2 and LiNi 0.8 Co 0.1 Mn 0.1 At least one of O2.

[0072] The small-diameter secondary particles 10 and the small-diameter single crystals 10a include lithium halide 13. When lithium halide 13 is included in the small-diameter secondary particles 10 and the small-diameter single crystals 10a, residual lithium generated on the surface of the positive electrode active material can be reduced, and gas generation due to side reactions can be suppressed. Therefore, the cycle life characteristics of the battery can be improved by preventing side reactions between the positive electrode active material and the electrolyte during battery operation.

[0073] Specifically, when the positive electrode active materials 1 and 1a include lithium halide 13 only in the small-diameter particles (i.e., small-diameter single-crystal particles 10a, small-diameter secondary particles 10, and / or primary particles 11 constituting the small-diameter secondary particles 10), the aforementioned effects are more pronounced compared to when lithium halide is included in the large-diameter secondary particles 20 or simultaneously in both the large-diameter secondary particles 20 and the small-diameter particles. Compared to the large-diameter secondary particles 20, the small-diameter secondary particles 10 and the small-diameter single crystals 10a have a larger BET (Brunauer-Emmett-Teller) specific surface area per unit weight and exhibit more residual lithium and more gas generation. In other words, when lithium halide 13 is included only in the small-diameter secondary particles 10 and the small-diameter single crystals 10a, residual lithium generation and gas generation can be effectively suppressed with a relatively smaller amount of lithium halide 13.

[0074] On the other hand, lithium halide 13 can be coated on at least one of the small-diameter single-crystal particles 10a, small-diameter secondary particles 10, and primary particles 11 constituting the small-diameter secondary particles 10. For example, lithium halide 13 can be coated on the surface of the small-diameter single-crystal particles 10a; on both the surface of the small-diameter secondary particles 10 and the surface of the primary particles 11 constituting the small-diameter secondary particles 10; or only on the surface of the small-diameter primary particles 11. Accordingly, lithium halide 13 can increase the average particle size (D50) of the small-diameter particles and thus reduce the BET specific surface area of ​​the small-diameter particles. Accordingly, the generation of residual lithium and gas on the surface of the positive electrode active material can be effectively suppressed. Lithium halide 13 can be coated in film form on the surface of at least one of the small-diameter single-crystal particles 10a, small-diameter secondary particles 10, and primary particles 11 constituting the small-diameter secondary particles 10. According to the method for preparing the positive electrode active material according to the embodiment, lithium halide 13 can be uniformly coated on the surface of the particles in film form. During the high-temperature firing of the positive electrode active material, lithium halide 13 can act as a flux, thus promoting the growth of primary particles 11 and more effectively increasing the BET specific surface area of ​​the particles.

[0075] The lithium halide 13 may include at least one selected from LiF, LiCl, LiBr and LiI, and in embodiments, LiF may be used.

[0076] Based on small-diameter particles of about 100 mol, lithium halide 13 can be used in amounts of about 0.1 mol to about 1.0 mol, for example, about 0.2 mol to about 0.8 mol, or about 0.25 mol to about 0.75 mol. When the amount of lithium halide 13 exceeds this range, it can accelerate the cycle life degradation of rechargeable lithium batteries including positive electrode active materials, and therefore lithium halide 13 should be appropriately adjusted within this range.

[0077] Large-diameter particles may have an average particle size (D50) of about 10 μm to about 20 μm, for example, greater than or equal to about 10 μm, greater than or equal to about 11 μm, greater than or equal to about 12 μm, greater than or equal to about 13 μm, or greater than or equal to about 14 μm and less than or equal to about 20 μm, less than or equal to about 19 μm, less than or equal to about 18 μm, less than or equal to about 17 μm, less than or equal to about 16 μm, or less than or equal to about 15 μm. Small-diameter particles may have an average particle size (D50) of about 1 μm to about 8 μm, for example, greater than or equal to about 1 μm, greater than or equal to about 2 μm, greater than or equal to about 3 μm, or greater than or equal to about 4 μm and less than or equal to about 8 μm, less than or equal to about 7 μm, less than or equal to about 6 μm, or less than or equal to about 5 μm. When large-diameter particles and small-diameter particles each have an average particle size within this range, the mixture density of the positive electrode active material can be increased. Correspondingly, the capacity characteristics of the battery can be improved.

[0078] Large-diameter particles (D50) and small-diameter particles (D50) can have an average particle size difference (D50-D50) of about 9 μm to about 12 μm, for example, about 9 μm to about 10 μm. Accordingly, the mixture density of the positive electrode active material is increased, and the capacity characteristics of the battery can be improved.

[0079] The primary particles 21 constituting the large-diameter secondary particles 20 may have an average particle size of about 200 nm to about 900 nm, for example, 200 nm to 800 nm, or 200 nm to 700 nm, or 300 nm to 600 nm, or 300 nm to 500 nm. The primary particles 11 constituting the small-diameter secondary particles may have an average particle size of about 100 nm to about 900 nm, for example, 100 nm to 800 nm, or 100 nm to 700 nm, or 100 nm to 600 nm, or 100 nm to 500 nm. When the primary particles 21 constituting the large-diameter secondary particles 20 and the primary particles 11 constituting the small-diameter secondary particles have average particle sizes within this range, high initial efficiency and capacity can be obtained, and crack initiation during charging and discharging can be suppressed by suppressing stress according to the volume change of the secondary particles. The average particle size of the primary particles can be measured by electron microscopy using a scanning electron microscope or a field emission scanning electron microscope.

[0080] The primary particles 21 constituting the large-diameter secondary particles 20 and the primary particles 11 constituting the small-diameter secondary particles 10 can be in the form of thin sheets. Figures 4A to 4C A schematic diagram illustrating the shape of primary particles according to embodiments of the present disclosure. Reference Figures 4A to 4CThe primary particles according to embodiments of this disclosure may have any suitable shape, such as (A) a polygonal nanoplate shape (e.g., hexagonal), (B) a nanodisk shape and / or (C) a cuboid shape, each having a basic sheet-like structure.

[0081] exist Figures 4A to 4C In this context, "a" refers to the length of the major axis, such as the length of its longest axis (e.g., the major axis in the planar direction), "b" refers to the length of the minor axis, such as the length of its shortest axis (e.g., the minor axis in the planar direction), and "t" refers to the thickness. The thickness t of the primary particle can be less than the planar lengths a and b. The planar length a can be greater than b, or can be the same as b. The major axis length, minor axis length, and thickness of the primary particle can be measured by electron microscopy using a scanning electron microscope or a field emission scanning electron microscope.

[0082] The primary particles 21 constituting the large-diameter secondary particles 20 may have an average thickness of about 100 nm to about 200 nm, for example, about 100 nm to about 150 nm, greater than or equal to about 100 nm, greater than or equal to about 110 nm, greater than or equal to about 120 nm, or greater than or equal to about 130 nm and less than or equal to about 200 nm, less than or equal to about 190 nm, less than or equal to about 180 nm, or less than or equal to about 170 nm, or less than or equal to about 160 nm, or less than or equal to about 150 nm. When the large-diameter primary particles 21 have an average thickness within this range, high initial efficiency and capacity can be ensured, and crack initiation can be suppressed during charging and discharging by suppressing stresses caused by changes in the volume of the secondary particles. Accordingly, cycle life characteristics can be improved. The primary particles 21 constituting the large-diameter secondary particles 20 may have an average major axis length of about 200 nm to about 900 nm, for example, 200 nm to 800 nm, or 200 nm to 700 nm, or 300 nm to 600 nm, or 300 nm to 500 nm. When the primary particles 21 constituting the large-diameter secondary particles 20 have an average major axis length within this range, high initial efficiency and capacity can be obtained, and crack initiation during charging and discharging can be suppressed by suppressing stress according to the volume change of the secondary particles.

[0083] The primary particles 11 aggregated in the small-diameter secondary particles 10 may have an average thickness of about 200 nm to about 500 nm, for example, greater than or equal to about 200 nm, greater than or equal to about 210 nm, greater than or equal to about 220 nm, or greater than or equal to about 230 nm and less than or equal to about 500 nm, less than or equal to about 490 nm, less than or equal to about 480 nm, or less than or equal to about 470 nm. When the primary particles 11 constituting the small-diameter secondary particles 10 have an average thickness within this range, high initial efficiency and capacity characteristics of the rechargeable lithium battery including the positive electrode active material can be ensured, and crack initiation can be suppressed during the charging and discharging of the rechargeable lithium battery by suppressing volume changes of the secondary particles.

[0084] The primary particles 11 constituting the small-diameter secondary particles can have an average major axis length of about 100 nm to about 900 nm, for example, 100 nm to 800 nm, or 100 nm to 700 nm, or 100 nm to 600 nm, or 100 nm to 500 nm. When the primary particles 11 constituting the small-diameter secondary particles have an average major axis length within this range, high initial efficiency and capacity can be obtained, and crack initiation during charging and discharging can be suppressed by suppressing stress according to the volume change of the secondary particles.

[0085] The average thickness and average major axis length of primary particles can be measured by electron microscopy using a scanning electron microscope or a field emission scanning electron microscope.

[0086] Large-diameter secondary particles 20 can have a diameter of approximately 0.100 μm. 2 / g to approximately 0.600m 2 / g, for example, greater than or equal to about 0.100m 2 / g, greater than or equal to approximately 0.200m 2 / g, or greater than or equal to approximately 0.300m 2 / g, and less than or equal to approximately 0.600m 2 / g, less than or equal to approximately 0.500m 2 / g, or less than or equal to approximately 0.400m 2 / g BET specific surface area. When the large-diameter secondary particles 20 have a BET specific surface area within this range, high initial efficiency and capacity can be ensured, and crack initiation can be suppressed during battery charging and discharging by suppressing stress caused by changes in the volume of the secondary particles. Accordingly, the cycle life characteristics of the battery can be improved.

[0087] Small-diameter secondary particles 10 can have a diameter of approximately 0.300 μm. 2 / g to approximately 1,000m 2 / g, for example, greater than or equal to about 0.300m 2 / g, greater than or equal to approximately 0.400m 2 / g, or greater than or equal to approximately 0.500m 2 / g, and less than or equal to about 1,000m 2 / g, less than or equal to approximately 0.900m 2 / g, less than or equal to approximately 0.800m 2 / g, or less than or equal to approximately 0.700m 2 / g BET specific surface area. When the small-diameter secondary particles 10 have a BET specific surface area within this range, the level of residual lithium compounds on the surface can be reduced, and gas generation can be reduced during battery operation by reducing side reactions on the surface of the positive electrode active material.

[0088] Based on the total weight of large-diameter and small-diameter particles, large-diameter particles may be included in an amount of about 50 wt% to about 90 wt%, for example, greater than or equal to about 50 wt%, greater than or equal to about 55 wt%, greater than or equal to about 60 wt%, or greater than or equal to about 65 wt%, and less than or equal to about 90 wt%, less than or equal to about 85 wt%, less than or equal to about 80 wt%, or less than or equal to about 75 wt%.

[0089] The positive electrode active materials 1 and 1a may include less than or equal to about 1,400 ppm, for example, less than or equal to about 1,350 ppm, less than or equal to about 1,300 ppm, less than or equal to about 1,290 ppm, less than or equal to about 1,280 ppm, less than or equal to about 1,270 ppm, less than or equal to about 1,260 ppm, less than or equal to about 1,250 ppm, less than or equal to about 1,230 ppm, less than or equal to about 1,200 ppm, or less than or equal to about 1,150 ppm of residual lithium on the surface.

[0090] Positive electrode active materials 1 and 1a can have a concentration of approximately 3.1 g / cm³. 3 Approximately 3.4 g / cm³ 3 or approximately 3.2 g / cm 3 Approximately 3.3 g / cm³ 3 The density of the mixture. Because the positive electrode active materials 1 and 1a include large-diameter particles and small-diameter particles with different average particle sizes, their mixture density can be increased.

[0091] The following provides a method for preparing a positive electrode active material according to an embodiment.

[0092] A method for preparing positive electrode active materials for rechargeable lithium batteries includes preparing large-diameter metal hydroxide precursors and small-diameter metal hydroxide precursors; mixing the large-diameter metal hydroxide precursors and lithium feedstock and heat-treating the mixture to prepare large-diameter particles; mixing the small-diameter metal hydroxide precursors, lithium feedstock and lithium halide (LiX) feedstock and heat-treating the mixture to prepare small-diameter particles including lithium halide; and mixing large-diameter particles and small-diameter particles to prepare positive electrode active materials.

[0093] In the embodiments, large-diameter particles may be secondary particles comprising multiple primary particles, and small-diameter particles may be single-crystal particles, secondary particles comprising multiple primary particles, or combinations thereof.

[0094] The method for preparing the metal hydroxide precursor can be carried out in three steps: a first step, a second step, and a third step, based on the formation of a core, an intermediate layer, and a shell structure. In the first, second, and third steps, the process conditions (such as the concentration and amount of the metal raw material, the concentration and amount of ammonia as a complexing agent, and the amount of pH control agent) can differ.

[0095] On the other hand, "core" refers to the region comprising approximately 65% ​​to approximately 85% of the total distance from the center of the secondary particles 10 and 20 to the surface. For example, in lithium nickel-based composite oxides, it may be the remaining region outside the area within approximately 2 μm to approximately 6 μm from the outermost edge. Additionally, "shell" refers to the region comprising approximately 5% to approximately 15% of the total distance from the center of the lithium nickel-based composite oxide to the surface, or the region within approximately 2 μm from the outermost edge. "Intermediate layer" refers to the remaining region outside the core and shell. As used herein, the orientation of primary particles 11 and 21 may be primarily within the shells of secondary particles 10 and 20.

[0096] (First step) Formation of the nucleus of the metal hydroxide precursor:

[0097] A complexing agent and a pH control agent are placed in the reactor, and a metal feedstock is added and reacted. This can be achieved at approximately 0.1 kW / m³. 2 Approximately 6kW / m 2 For example, approximately 1 kW / m 2 Approximately 3kW / m 2 The stirring power of the reactor can be adjusted within a certain range, and the reaction can proceed from about 5 hours to about 30 hours, or from about 10 hours to about 30 hours.

[0098] The complexing agent plays a role in controlling the reaction rate of precipitate formation in the coprecipitation reaction, and can be ammonia or citric acid, with ammonia being preferred in the embodiments. The amount of complexing agent used is typically within acceptable limits. For example, the concentration of the complexing agent can be from about 0.1 M to about 0.7 M, such as from about 0.2 M to about 0.5 M.

[0099] A pH control agent can control the pH of the reaction mixture to form a precipitate from it, and can be, for example, sodium hydroxide (NaOH), sodium carbonate (Na₂CO₃), sodium oxalate (Na₂C₂O₄), etc., with sodium hydroxide (NaOH) being preferred. If the pH of the reaction mixture in the reactor changes as the reaction proceeds, the pH can be controlled by adding a pH control agent if necessary, and the pH of the reaction mixture can be maintained in the range of about 10 to about 12.

[0100] Metal raw materials are obtained by mixing nickel compounds, manganese compounds, cobalt compounds, etc., in pure water and stirring them. The concentration of the metal raw materials can be from about 0.1M to about 0.5M, for example, about 0.3M, and the input rate of the metal raw materials can be from about 50 ml / min to about 100 ml / min.

[0101] Examples of nickel compounds may include Ni(OH)₂, NiO, NiOOH, NiCO₃·2Ni(OH)₂·4H₂O, NiC₂O₄·2H₂O, Ni(NO₃)₂·6H₂O, NiSO₄, NiSO₄·6H₂O, nickel salts of fatty acids, or nickel halides. Among these, none produce harmful substances (such as NO) during the firing process. x and SO x From the perspective of [missing information], it is desirable that the nickel compound does not contain nitrogen or sulfur atoms during the calcination process, and therefore Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O and NiC2O4·2H2O are desired. These nickel compounds can be used alone or in combination of two or more.

[0102] Examples of manganese compounds include manganese oxides such as Mn₂O₃, MnO₂, and Mn₃O₄; manganese salts such as MnCO₃, Mn(NO₃)₂, MnSO₄, manganese acetate, manganese dicarboxylate, manganese citrate, and fatty acid manganese salts; manganese hydroxides; and manganese halides such as manganese chloride. Among these, MnO₂, Mn₂O₃, and Mn₃O₄ are desirable because they do not produce gases such as NO₂ during the firing process. x and SO x And CO2, and is available cheaply as an industrial raw material. These manganese compounds can be used alone or in combination of two or more.

[0103] Examples of cobalt compounds may include Co(OH)₂, CoOOH, CoO, Co₂O₃, Co₃O₄, Co(OCOCH₃)₂·4H₂O, CoCl₂, Co(NO₃)₂·6H₂O, and Co(SO₄)₂·7H₂O. Among these, those that do not produce harmful substances (such as NO₂) during the firing process... x and SO x From the perspective of [unclear meaning], Co(OH)₂, CoOOH, CoO, Co₂O₃, and Co₃O₄ are desirable. From the perspective of industrial inexpensiveness and high reactivity, Co(OH)₂ and CoOOH are more desirable. These cobalt compounds can be used alone or in combination of two or more.

[0104] (Second step) Formation of the intermediate layer of the metal hydroxide precursor:

[0105] The metal feedstock and complexing agent are added to the material obtained from the first step reaction, and the reaction is carried out after controlling the pH of the reaction mixture.

[0106] The stirring power in the second step can be reduced compared to the stirring power in the first step, and is the same as the stirring power in the third step. The stirring power in the second step is approximately 0.1 kW / m³. 2 Approximately 6kW / m 2 For example, approximately 1 kW / m 2 Approximately 3kW / m 2 Within the range. The reaction time for the second step can be approximately 5 to approximately 30 hours, or approximately 10 to approximately 30 hours.

[0107] The second step can be performed under the following specific conditions: for example, using a complexing agent at an input rate of about 8 ml / min to about 20 ml / min, or about 8 ml / min to about 12 ml / min, at a concentration of about 0.3 M to about 1.0 M, and injecting the metal feedstock at an input rate of about 90 ml / min to about 120 ml / min. In the second step, the input amount and concentration of the metal feedstock and the complexing agent are increased to prevent a decrease in the growth rate due to particle growth after a certain period of reaction of the product from the first step.

[0108] (Step 3) Prepare the final metal hydroxide precursor, which includes a shell forming the metal hydroxide precursor:

[0109] After adding the metal raw material and complexing agent to the material obtained from the second step reaction and then controlling the pH of the reaction mixture, a reaction to form a shell of the metal hydroxide precursor is carried out, and the obtained precursor is washed several times with deionized water (DI water), filtered under reduced pressure, and finally dried at a high temperature of greater than or equal to about 80°C to prepare the metal hydroxide precursor.

[0110] By minimizing the exposure of the (001) crystal planes, the metal hydroxide precursor appropriately maintains the porosity between the (001) crystal planes and thus can have excellent structural stability.

[0111] The stirring power in the third step can be reduced compared to the stirring power in the first step, and is the same as the stirring power in the second step. The stirring power in the third step can be approximately 0.1 kW / m³. 2 Approximately 6kW / m 2 For example, approximately 1 kW / m 2 Approximately 3kW / m 2 Within the range. The reaction in the third step can take approximately 3 to 30 hours, or approximately 10 to 30 hours.

[0112] Increase the input amount and concentration of metal raw materials and complexing agents to prevent the growth rate from decreasing due to particle growth after a certain period of reaction from the reaction products of the second step.

[0113] The third step is carried out under the following specific process conditions: a complexing agent is used at an input rate of about 12 ml / min to about 25 ml / min, about 12 ml / min to about 18 ml / min, and a concentration of about 0.35 M to about 1.0 M; and then, the metal feedstock is injected at an input rate of about 120 ml / min to about 150 ml / min. These reaction conditions of the third step have a significant impact on the surface depth of the porous layer in the metal hydroxide precursor.

[0114] Subsequently, a large-diameter metal hydroxide precursor and lithium raw material are mixed and heat-treated to prepare large-diameter particles.

[0115] Large-diameter metal hydroxide precursor powder obtained by spray drying is thoroughly mixed with lithium raw materials (such as Li₂CO₃, LiNO₃, LiNO₂, LiOH, LiOH·H₂O, LiH, LiF, LiCl, LiBr, LiI, CH₃OOLi, Li₂O, Li₂SO₄, lithium dicarboxylate, lithium citrate, fatty acid lithium salts, and alkyllithium). Here, the molar ratio of Li:(Ni+Co+Mn) can exceed about 1:1. Specifically, it can be about 1.01:1 to about 1.06:1, and more specifically about 1.02:1 to about 1.05:1.

[0116] In the step of obtaining large-diameter particles, the dopant material may be further mixed with the large-diameter metal hydroxide precursor and the lithium feedstock. The dopant material may include compounds comprising Ba, Mg, Al, Fe, Ti, W, B, Zr or combinations thereof, and specifically, may be compounds comprising Al, Zr or combinations thereof.

[0117] The obtained powder mixture undergoes primary calcination (heat treatment). The conditions for primary calcination are determined depending on the composition and the lithium feedstock used. The temperature used for primary calcination is generally greater than or equal to about 800°C and less than or equal to about 1000°C, preferably less than or equal to about 950°C, and more preferably less than or equal to about 900°C. The temperature conditions during primary calcination are maintained for a predetermined time and then decreased at a predetermined rate to about 10°C to about 40°C to complete the primary calcination.

[0118] Subsequently, a small-diameter metal hydroxide precursor, lithium feedstock, and lithium halide (LiX) feedstock are mixed and then heat-treated to prepare small-diameter particles comprising lithium halide.

[0119] The small-diameter metal hydroxide precursor powder obtained by spray drying is mixed with lithium feedstock, and then thoroughly mixed with lithium halide feedstock.

[0120] In the step of obtaining small-diameter particles, the dopant material, along with the lithium raw material and the lithium halide raw material, can be further mixed with a small-diameter metal hydroxide precursor. The dopant material can be a compound including Ba, Mg, Al, Fe, Ti, W, B, Zr, or combinations thereof, and specifically, a compound including Al, Zr, or combinations thereof.

[0121] The types and mixing of lithium feedstocks are the same as those described in the preparation of large-diameter particles.

[0122] The raw materials for lithium halides refer to materials that can be used to prepare small-diameter lithium halide particles by mixing with a small-diameter metal hydroxide precursor and a lithium raw material and then heat-treating. Raw materials for lithium halides may include: fluorinated polymer compounds, including polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), or combinations thereof; or hydrogen fluoride, oxygen fluoride, hydrofluoric acid, hydrogen chloride, hydrochloric acid, chlorine oxide, chlorine fluoride oxidase, bromine oxide, fluorosulfuric acid, bromine, hydrogen iodide, iodine oxide, periodic acid, etc., such as compounds including NH4F, NH4Cl, NH4Br, NH4I, LiF, LiCl, LiBr, LiI, MnF2, MnCl2, MnBr2, MnI2, or combinations thereof, and specifically, compounds including PVdF or LiF.

[0123] Based on the total amount of small-diameter metal hydroxide precursors, the lithium halide (LiX) feedstock can be mixed in amounts from about 0.1 mol% to about 1 mol%, for example, from about 0.2 mol% to about 0.8 mol%.

[0124] On the other hand, lithium fluoride (LiF), an example of a lithium halide feedstock, has a very high melting point of about 835°C or higher. Therefore, it does not fully melt within the heat treatment temperature range (about 800°C to about 900°C) for preparing high-nickel-based cathode active materials, but exists as a solid phase, making it difficult to uniformly coat onto the surface of the cathode active material. However, compared to when LiF exists as a single phase, when LiF is mixed with lithium feedstock, the melting point of LiF can be significantly reduced, and it thus exists in a molten state within the temperature range used for preparing high-nickel-based cathode active materials. Consequently, it can be uniformly coated as a film onto the surface of the cathode active material.

[0125] In addition, during the process of preparing lithium nickel-based composite oxides, when small-diameter particles are generated by the above process, the lithium halide raw material reacts with the precursor and thus penetrates into the secondary particles of lithium nickel-based composite oxides and is coated as a film on the surface of the primary particles constituting the secondary particles and on the surface of the secondary particles.

[0126] The resulting powder mixture is then subjected to a secondary firing (heat treatment). This secondary firing is carried out under the same conditions as the primary firing used to prepare large-diameter particles.

[0127] Subsequently, the positive electrode active material according to the embodiment can be prepared by mixing large-diameter particles and small-diameter particles.

[0128] Another embodiment provides a rechargeable lithium battery including a positive electrode comprising a positive electrode active material; a negative electrode comprising a negative electrode active material; and an electrolyte.

[0129] The positive electrode includes a current collector and a layer of positive active material formed on the current collector and including positive active material.

[0130] In the positive electrode active material layer, the amount of positive electrode active material can be from about 90 wt% to about 98 wt%, based on the total weight of the positive electrode active material layer. Additionally, the positive electrode active material layer may further include a binder and a conductive material. The amounts of the binder and the conductive material, respectively, can be from about 1 wt% to about 5 wt%, based on the total weight of the positive electrode active material layer.

[0131] The positive electrode active material is as described above.

[0132] Adhesives may include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic styrene-butadiene rubber, epoxy resin, nylon, etc.

[0133] Examples of the conductive material include carbon materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber; metal powders or metal fibers including copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0134] The current collector may be aluminum foil, nickel foil, or a combination thereof, but is not limited thereto.

[0135] The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector and including a negative electrode active material.

[0136] The negative electrode active material may include a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / de-doping lithium, or a transition metal oxide.

[0137] The material that reversibly intercalates / deintercalates lithium ions may include a carbon-containing material. The carbon-containing material may be any commonly used carbon-based negative electrode active material in a rechargeable lithium-ion battery. Examples thereof may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be amorphous, or natural graphite or artificial graphite in the form of flakes, scales, spheres, or fibers. The amorphous carbon may be soft carbon, hard carbon, a mesophase pitch carbonized product, calcined coke, etc.

[0138] The lithium metal alloy includes an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0139] The material capable of doping / de-doping lithium may be Si, SiO x (0 < x < 2), a Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, but not Si), Sn, SnO2, a Sn-R alloy (where R is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, but not Sn), etc. At least one of these materials may be mixed with SiO2. The elements Q and R may be selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0140] The transition metal oxide may be vanadium oxide, lithium vanadium oxide, or lithium titanium oxide.

[0141] In the negative electrode active material layer, the negative electrode active material may be included in an amount of about 95 wt% to about 99 wt% based on the total weight of the negative electrode active material layer.

[0142] In one embodiment, the negative electrode active material layer includes a binder and may optionally further include a conductive material. Based on the total weight of the negative electrode active material layer, the amount of binder in the negative electrode active material layer may be from about 1 wt% to about 5 wt%. When the negative electrode active material layer further includes a conductive material, the negative electrode active material layer comprises about 90 wt% to about 98 wt% of negative electrode active material, about 1 wt% to about 5 wt% of binder, and about 1 wt% to about 5 wt% of conductive material.

[0143] Binders improve the bonding properties between negative electrode active material particles and between the negative electrode active material particles and the current collector. Binders include non-water-soluble binders, water-soluble binders, or combinations thereof.

[0144] Non-water-soluble adhesives may include styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polyacrylonitrile, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0145] Water-soluble adhesives may include acrylic styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or combinations thereof.

[0146] When a water-soluble binder is used as a negative electrode binder, a cellulose compound may be further used as a thickener to provide viscosity. Cellulose compounds include one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or their alkali metal salts. The alkali metal may be Na, K, or Li. Based on 100 parts by weight of the negative electrode active material, this thickener may be included in an amount from about 0.1 to about 3 parts by weight.

[0147] Conductive materials may include: carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metallic materials, including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0148] The current collector may include at least one selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0149] Electrolytes include non-aqueous organic solvents and lithium salts.

[0150] Non-aqueous organic solvents are used as media for transporting ions that participate in the electrochemical reactions of the battery.

[0151] Non-aqueous organic solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolactone, mevalonolactone, caprolactone, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, cyclohexanone, ethanol, isopropyl alcohol, nitriles (such as R-CN (where R can be a C2 to C20 straight-chain, branched, or cyclic hydrocarbon group and R may include double bonds, aromatic rings, or ether bonds)), amides (such as dimethylformamide), dioxolane (such as 1,3-dioxolane), sulfolane, etc.

[0152] Non-aqueous organic solvents can be used alone or in mixtures of two or more, and when used in mixtures of two or more, the mixing ratio can be appropriately adjusted according to the desired battery performance, as is widely understood by those working in the field.

[0153] In addition, non-aqueous organic solvents may further include aromatic hydrocarbon organic solvents. Specific examples of aromatic hydrocarbon organic solvents may be selected from benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, and fluoromethylbenzene. Benzene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

[0154] The electrolyte may further include additives such as vinylene carbonate or ethylene carbonate compounds as cycle life improving additives.

[0155] Examples of ethylene carbonate compounds include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, and fluoroethylene carbonate. The amount of additives used to improve cycle life can be within an appropriate range.

[0156] Lithium salts dissolved in non-aqueous organic solvents supply lithium ions to the battery, enabling basic operation of rechargeable lithium batteries and improving lithium ion transport between the positive and negative electrodes. Examples of lithium salts include at least one supporting salt selected from the following: LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2 (where x and y are natural numbers, such as integers from 1 to 20), LiCl, LiI, and LiB(C2O4)2 (lithium bis(oxalate)borate, LiBOB). The concentration of lithium salts can range from about 0.1 M to about 2.0 M. When lithium salts are included within the above concentration range, the electrolyte exhibits excellent performance and lithium-ion mobility due to optimal electrolyte conductivity and viscosity.

[0157] Depending on the type of battery, rechargeable lithium batteries may further include a separator between the negative and positive electrodes. Examples of suitable separator materials include polyethylene, polypropylene, polyvinylidene fluoride, and multilayers thereof, such as polyethylene / polypropylene double-layer separators, polyethylene / polypropylene / polypropylene triple-layer separators, and polypropylene / polypropylene / polypropylene triple-layer separators.

[0158] Figure 5 A perspective view illustrating a typical structure of a rechargeable lithium battery according to an embodiment.

[0159] refer to Figure 5 The rechargeable lithium battery 100 includes a positive electrode 60, a negative electrode 50, and a separator 70 containing a positive electrode active material according to an exemplary embodiment. The positive electrode 60, negative electrode 50, and separator 70 are wound or folded to be housed in a battery casing 80. Subsequently, an organic electrolyte is injected into the battery casing 80 and sealed to complete the rechargeable lithium battery 100. The battery casing 80 may be cylindrical, rectangular, or a thin film, etc.

[0160] The rechargeable lithium battery 100 can be a lithium-ion battery.

[0161] A separator 70 may be disposed between the positive electrode 60 and the negative electrode 50, and may be wound or stacked to form an electrode assembly. When the electrode assembly is housed in the battery casing 80, it is impregnated with an organic electrolyte, and the resulting product is sealed to complete the rechargeable lithium battery 100.

[0162] Furthermore, rechargeable lithium batteries are formed into battery packs with circuitry, and single or multiple packs can be used in any device requiring high capacity and high power. For example, they can be used in laptops, smartphones, electric vehicles, etc. Additionally, rechargeable lithium batteries exhibit excellent storage stability, cycle life characteristics, and high rate performance at high temperatures, and are therefore suitable for use in electric vehicles (EVs). For example, they can be used in hybrid electric vehicles, such as plug-in hybrid electric vehicles (PHEVs).

[0163] The following describes embodiments and comparative examples of the present invention. However, these embodiments are not to be construed as limiting the scope of the invention in any way.

[0164] Example

[0165] Synthesis Example 1: Synthesis of large-diameter metal hydroxide precursor (Ni 0.6 Co 0.2 Mn 0.2 (OH)2)

[0166] In the following preparation process, nickel sulfate, cobalt sulfate, and manganese sulfate are used as metallic raw materials for forming the metal hydroxide precursor. The synthesis is carried out in two sequential steps:

[0167] [First Step]

[0168] First, ammonia water (NH3) with a concentration of 0.30M is placed in the reactor. At a power output of 1.5 kW / m³... 3 Under stirring power, at 50°C, the reaction was initiated while adding the metal raw material and complexing agent (ammonia) at a concentration ratio of 9:1. NaOH was added to maintain the pH between 10 and 11. The resulting core particles had an average size of approximately 5.5 μm to 6.5 μm, and then the second step was carried out as follows.

[0169] [Second Step]

[0170] The second step is performed using the same method as the first step, except that the stirring power is reduced to 1.0 kW / m³. 3 The concentration ratio of the metal raw material to the complexing agent was changed to 7:1, and the concentration of the complexing agent was changed to 0.35M.

[0171] The particles produced from this reaction, which have a core and an intermediate layer, have an average size of 12 μm to 13 μm, and then the reaction is terminated.

[0172] The obtained material was rinsed and hot-air dried at approximately 150°C for 24 hours to obtain a large-diameter metal hydroxide precursor (Ni). 0.6 Co 0.2 Mn 0.2 (OH)2).

[0173] Synthesis Example 2: Synthesis of small-diameter metal hydroxide precursor (Ni 0.6 Co 0.2 Mn 0.2 (OH)2)

[0174] In the following preparation process, nickel sulfate, cobalt sulfate, and manganese sulfate are used as metallic raw materials for forming metal hydroxide precursors.

[0175] Ammonia solution (NH3) with a concentration of 0.30M was added to the reactor. The reactor was operated at 2.0 kW / m³ at 40°C. 3 The reaction was initiated by adding the metal raw material and the complexing agent (ammonia) at a concentration ratio of 5:1 under stirring power. NaOH was added to maintain the pH between 12 and 13. The average size of the resulting core particles was approximately 2.5 μm to 3.0 μm, and then the reaction was terminated.

[0176] The obtained material was rinsed and then dried with hot air at approximately 150°C for 24 hours to obtain a small-diameter metal hydroxide precursor (Ni). 0.6 Co 0.2 Mn 0.2 (OH)2).

[0177] Example 1-1

[0178] (1) Preparation of positive electrode active material

[0179] (i) Preparation of large-diameter secondary particles

[0180] According to Ni from Synthesis Example 1 0.6 Co 0.2 Mn 0.2 A large-diameter metal hydroxide precursor of (OH)₂ and LiOH are mixed in a 1:1 molar ratio and heat-treated to obtain a lithium-nickel based composite oxide (LiNi). 0.6 Co 0.2 Mn 0.2 Large-diameter secondary particles (O2). Heat treatment was performed by increasing the temperature from 25°C to 830°C at a rate of 2.0°C / min under an oxygen atmosphere, maintaining the temperature at 830°C for 6 hours, and then decreasing the temperature from 830°C to 25°C at a rate of 2.0°C / min.

[0181] (ii) Preparation of small-diameter secondary particles

[0182] According to Ni from Synthesis Example 2 0.6 Co 0.2 Mn 0.2 (OH)₂, a small-diameter metal hydroxide precursor, LiOH, and LiF are mixed in a molar ratio of 1:1:0.0025 and then heat-treated to obtain a lithium-nickel based composite oxide (LiNi). 0.6 Co 0.2 Mn 0.2 Small-diameter secondary particles of O2 and LiF were obtained. The heat treatment was carried out by increasing the temperature from 25°C to 830°C at a rate of 2.0°C / min in an oxygen atmosphere, maintaining the temperature at 830°C for 6 hours, and then decreasing the temperature from 830°C to 25°C at a rate of 2.0°C / min.

[0183] (iii) Preparation of positive electrode active material

[0184] Large-diameter secondary particles (D50: 11.7 μm) and small-diameter secondary particles (D50: 2.8 μm) were mixed at a weight ratio of 7:3 to prepare the positive electrode active material. The average particle size (D50) of the large-diameter and small-diameter secondary particles was measured using a PSD (particle size distribution) measuring device.

[0185] (2) Manufacturing button cell batteries

[0186] A slurry was prepared by mixing positive electrode active material, carbon black conductive agent (product name: Denka Black, Denka Korea Co., Ltd.), and polyvinylidene fluoride (PVdF) in a weight ratio of 92:4:4, and then mixing it with N-methylpyrrolidone (NMP). The slurry was coated onto a 15 μm thick aluminum current collector, dried at room temperature, and then dried under vacuum at 120°C, compressed, and stamped to produce a 45 μm thick positive electrode plate.

[0187] A button cell is manufactured using a positive electrode plate, lithium metal as a counter electrode, a PTFE separator, and a solution prepared by dissolving 1.3 M LiPF6 in a mixed solvent of EC (ethylene carbonate), DEC (diethyl carbonate), and EMC (ethyl methyl carbonate) (in a volume ratio of 3:4:3) as the electrolyte.

[0188] Examples 1-2

[0189] Button single cells were manufactured according to the same method as in Examples 1-1, except that Ni from Synthesis Example 2 was used. 0.6 Co 0.2 Mn 0.2A small-diameter metal hydroxide precursor (OH)2, LiOH, and LiF were mixed in a molar ratio of 1:1:0.005 to prepare a positive electrode active material.

[0190] Examples 1-3

[0191] Button single cells were manufactured according to the same method as in Examples 1-1, except that Ni from Synthesis Example 2 was used. 0.6 Co 0.2 Mn 0.2 (OH)2, a small-diameter metal hydroxide precursor, LiOH, and LiF were mixed in a molar ratio of 1:1:0.0075 to prepare the positive electrode active material.

[0192] Example 2-1

[0193] The positive electrode active material and button cell were manufactured according to the same method as in Examples 1-1, except that (i) the heat treatment temperature of the large-diameter secondary particles and (ii) the heat treatment temperature of the small-diameter secondary particles were changed to 850°C instead of 830°C.

[0194] Example 2-2

[0195] The positive electrode active material and button cell were manufactured according to the same method as in Examples 1-1, except that (i) the heat treatment temperature of the large-diameter secondary particles and (ii) the heat treatment temperature of the small-diameter secondary particles were changed to 850°C instead of 830°C, and the Ni according to Synthesis Example 2 was used... 0.6 Co 0.2 Mn 0.2 (OH)2 small-diameter metal hydroxide precursor, LiOH and LiF are mixed in a molar ratio of 1:1:0.005.

[0196] Example 2-3

[0197] The positive electrode active material and button cell were manufactured according to the same method as in Examples 1-1, except that (i) the heat treatment temperature of the large-diameter secondary particles and (ii) the small-diameter secondary particles was changed to 850°C instead of 830°C, and the Ni according to Synthesis Example 2 was used... 0.6 Co 0.2 Mn 0.2 (OH)2 small-diameter metal hydroxide precursor, LiOH and LiF are mixed in a molar ratio of 1:1:0.0075.

[0198] Example 3

[0199] Small-diameter single-crystal positive electrode active material (product name: Xiamen Tungsten Co., Ltd.) and LiF were mixed at a molar ratio of 1:0.025 and then heat-treated to obtain LiNi containing lithium nickel-based composite oxide. 0.83Co 0.11 Mn 0.06 Small-diameter single-crystal particles of O2 and LiF were obtained. Heat treatment was performed by increasing the temperature from 25°C to 850°C at a rate of 2.0°C / min under an oxygen atmosphere, maintaining the temperature at 850°C for 6 hours, and then decreasing the temperature from 850°C to 25°C at a rate of 2.0°C / min.

[0200] The positive electrode active material was prepared by mixing large-diameter secondary particles (D50: 11.7 μm) and small-diameter single-crystal particles (D50: 2.8 μm) at a weight ratio of 7:3 according to step (i) of Example 1-1. The average particle size (D50) of the small-diameter single-crystal particles was measured using a PSD (particle size distribution) measuring device.

[0201] The positive electrode active material is used to manufacture a button cell using the same method as step (2) of Example 1-1.

[0202] Comparative Example 1

[0203] The positive electrode active material was prepared by mixing a large-diameter metal hydroxide precursor according to Synthesis Example 1 and a small-diameter metal hydroxide precursor according to Synthesis Example 2 at a weight ratio of 7:3. This mixture was then mixed with LiOH at a molar ratio of Li:metal (transition metal) = 1:1, and the resulting mixture was subjected to heat treatment. The heat treatment was carried out under an oxygen atmosphere, increasing the temperature from 25°C to 830°C at a rate of 2.0°C / min, maintaining the temperature at 830°C for 6 hours, and then decreasing the temperature from 830°C to 25°C at a rate of 2.0°C / min.

[0204] The positive electrode active material is used to manufacture a button cell using the same method as step (2) of Example 1-1.

[0205] Comparative Example 2

[0206] The positive electrode active material and the button cell were manufactured using the same method as in Comparative Example 1, except that the heat treatment was performed at 850°C instead of 830°C.

[0207] Comparative Example 3

[0208] The positive electrode active material of Comparative Example 2 and PVDF were mixed at a molar ratio of 1:0.0075, and then heat-treated to obtain the final positive electrode active material. The heat treatment was performed by increasing the temperature from 25°C to 400°C at a rate of 2.0°C / min under an oxygen atmosphere, maintaining the temperature at 400°C for 6 hours, and then decreasing the temperature from 400°C to 25°C at a rate of 2°C / min.

[0209] The positive electrode active material is used to manufacture a button cell using the same method as step (2) of Example 1-1.

[0210] Comparative Example 4

[0211] The large-diameter metal hydroxide precursor of Synthesis Example 1 and the small-diameter metal hydroxide precursor of Synthesis Example 2 were mixed at a weight ratio of 7:3 to prepare a mixed precursor. The mixed precursor, LiOH, and LiF were then mixed at a molar ratio of 1:1:0.0075, and subsequently heat-treated to prepare a positive electrode active material comprising small-diameter secondary particles, large-diameter secondary particles, and LiF. The heat treatment was performed by increasing the temperature from 25°C to 850°C at a rate of 2.0°C / min under an oxygen atmosphere, maintaining the temperature at 850°C for 6 hours, and then decreasing the temperature from 850°C to 25°C at a rate of 2.0°C / min.

[0212] The prepared positive electrode active material is used to manufacture a button cell in the same manner as step (2) of Example 1-1.

[0213] Comparative Example 5

[0214] The positive electrode active material was prepared using the same method as in Comparative Example 4, except that the large-diameter metal hydroxide precursor of Synthesis Example 1 and the small-diameter metal hydroxide precursor of Synthesis Example 2 were used in a weight ratio of 7:3, and the mixed precursor was mixed with LiOH and LiF in a molar ratio of 1:1:0.025.

[0215] The prepared positive electrode active material is used to manufacture a button cell in the same manner as step (2) of Example 1-1.

[0216] Assessment 1

[0217] X-ray diffraction analysis (scan rate: 0.96 degrees / min, scan step: 0.01 degrees 2θ, scan range: 10 degrees to 90 degrees) was performed on the positive electrode active materials according to Examples 1-1 to 1-3, Examples 2-1 to 2-3, Example 3, and Comparative Examples 1 to 5 using Cu Kα rays, with respect to sintering temperature and LiF content. The full width at half maximum (FWHM) of the (003) plane XRD peaks and the c-axis lattice constant were measured, and the results are shown in Table 1.

[0218] (Table 1)

[0219]

[0220] Referring to Table 1, compared with the full width at half maximum (FWHM) of the (003) plane XRD peak of the positive electrode active material of Comparative Example 1, the full WHM of the (003) plane XRD peak of the positive electrode active materials of Examples 1-1 to 1-3 is reduced, and the results show that the size of the primary particles included in the small-diameter secondary particles of the positive electrode active materials of Examples 1-1 to 1-3 is increased.

[0221] Specifically, when the full width at half maximum (FWHM) of the (003) plane XRD peak of the positive electrode active material in Examples 1-1 to 1-3 was detected, the size of the primary particles included in the small-diameter secondary particles increased with the increase of LiF content. Furthermore, when the full width at half maximum (FWHM) of the (003) plane XRD peak of the positive electrode active material in Examples 1-1 and 2-1 was detected, the size of the primary particles included in the small-diameter secondary particles also increased even with the increase of firing temperature.

[0222] Furthermore, since the c-axis lattice constant of Examples 1-1 to 1-3, Examples 2-1 to 2-3, and Example 3 showed almost no change, even with an increase in LiF content or firing temperature, structural changes in the positive electrode active material due to expansion towards the c-axis were suppressed, and correspondingly, the cycle life characteristics of the battery cell including the positive electrode active material according to the examples were improved. Conversely, compared to the positive electrode active material of the examples, the positive electrode active material of Comparative Example 4 showed a significantly degraded full width at half maximum (FWHM) of the (003) plane XRD peak, and correspondingly, because the large-diameter and small-diameter secondary particles of the positive electrode active material of Comparative Example 4 exhibited increased size and excessive inclusion of LiF, the cycle life characteristics of the battery cell deteriorated.

[0223] Assessment 2

[0224] Unreacted residual lithium on the surface of the positive electrode active materials of Examples 1-1 to 1-3, Examples 2-1 to 2-3, Example 3, and Comparative Examples 1 to 2 was measured by HCl titration, and the results are shown in Table 2. The unreacted residual lithium was measured as follows: 10 g of each positive electrode active material was placed in 100 ml of distilled water, and then stirred at 300 rpm for 30 minutes. The pH was measured by partially removing the solution while HCl was added. Because the unreacted residual lithium exists in the form of Li₂CO₃ and LiOH, the pH value increased when HCl was added. + CO3 2- and OH - The ionic reaction and titration of the solution, wherein the input volume of HCl solution is measured, is used to calculate the content of unreacted residual lithium.

[0225] (Table 2)

[0226]

[0227] Referring to Table 2, compared with Comparative Examples 1 and 2 which do not contain lithium halides, the positive electrode active materials of Examples 1-1 to 1-3, Examples 2-1 to 2-3 and Example 3 showed reduced residual lithium content.

[0228] Assessment 3

[0229] In the first cycle at room temperature (25°C), button cell batteries according to Examples 2-1 to 2-3, Example 3, and Comparative Example 2 were charged at a constant current rate of 0.1C until a voltage of 4.3V (relative to Li), and then cut off at a rate of 0.05C while maintaining a constant voltage at 4.3V. The charged cell was disassembled, and the five positive electrode plates buffered at 4.3V were placed together with the electrolyte solution in a bag, and then stored in an 80°C oven. The volume change of the bag was then measured and converted into a mass change using the Archimedes method. The results showed... Figure 6 middle.

[0230] refer to Figure 6 Compared to the single cell of Comparative Example 2, which does not contain lithium halides in small-diameter particles, the single cells of Examples 2-1 to 2-3 and Example 3 exhibited reduced gas generation due to side reactions.

[0231] Although this disclosure has been described in conjunction with exemplary embodiments now considered to be practical, it should be understood that the invention is not limited to the disclosed embodiments, but rather, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A positive electrode active material for a rechargeable lithium battery, comprising: a lithium nickel-based composite oxide including large-diameter particles and small-diameter particles having different average particle diameters, wherein the large-diameter particles include large-diameter secondary particles including a plurality of primary particles having an average particle diameter of 200 nm to 900 nm, only the small-diameter particles include a lithium halide, and the large-diameter particles have an average particle diameter of 10 μm to 20 μm, and the small-diameter particles have an average particle diameter of 1 μm to 8 μm. 2.The positive electrode active material of claim 1, wherein the small-diameter particles include small-diameter secondary particles including a plurality of primary particles. 3.The positive electrode active material of claim 1, wherein the small-diameter particles include single-crystal particles. 4.The positive electrode active material of claim 1, wherein the large-diameter secondary particles include primary particles having an average thickness of 100 nm to 200 nm. 5.The positive electrode active material of claim 2, wherein the small-diameter secondary particles include primary particles having an average thickness of 200 nm to 500 nm. 6.The positive electrode active material of claim 1, wherein the large-diameter particles are included in an amount of 50 wt% to 90 wt% based on the total weight of the large-diameter particles and the small-diameter particles. 7.The positive electrode active material of claim 1, wherein the lithium halide is coated on a surface of the small-diameter particles. 8.The positive electrode active material of claim 7, wherein the lithium halide is coated on the surface of the small-diameter particles in the form of a film. 9.The positive electrode active material of claim 1, wherein the lithium halide includes LiF. 10.The positive electrode active material of claim 1, wherein the lithium halide is included in an amount of 0.1 mol to 1.0 mol based on 100 mol of the small-diameter particles. 11.The positive electrode active material of claim 1, wherein the large-diameter particles include large-diameter secondary particles in which a plurality of plate-shaped primary particles are aggregated, and have a regular array structure in which (003) planes of the primary particles are oriented in a direction perpendicular to a surface of the large-diameter secondary particles. 12.The positive electrode active material of claim 2, wherein the small-diameter particles include small-diameter secondary particles in which a plurality of plate-shaped primary particles are aggregated, and have a regular array structure in which (003) planes of the primary particles are oriented in a direction perpendicular to a surface of the small-diameter secondary particles. 13.The positive electrode active material of claim 1, wherein the positive electrode active material has a full width at half maximum of a (003) plane peak of 0.15° to 0.17° in X-ray diffraction spectroscopy. 14.The positive electrode active material of claim 11, wherein the large-diameter secondary particles have a one-center radial arrangement having one center or a multi-center radial array structure having a plurality of centers.

15. The positive electrode active material of claim 12, wherein the small-diameter secondary particles have a one-center radial arrangement having one center or a multi-center radial array structure having a plurality of centers.

16. The positive electrode active material of claim 1, wherein the lithium nickel-based composite oxide is a compound represented by Chemical Formula 1: [Chemical Formula 1] Li a Ni x Mn y M z O 2 Chemical Formula 1 in which 0.9≤a≤1.05, 0.3≤x≤0.95, 0.05≤y≤0.3, and M is at least one metal element selected from the group consisting of Mn, Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce.

17. The positive electrode active material of claim 1, wherein the positive electrode active material includes 1,400 ppm or less of residual lithium on a surface. Li a Ni x Co y M 1-x-y O2 wherein, 19. A method of preparing a positive electrode active material for a rechargeable lithium battery according to any one of claims 1-18, comprising: preparing a large-diameter metal hydroxide precursor and a small-diameter metal hydroxide precursor; 18. The positive electrode active material according to claim 1, wherein the positive electrode active material has a mixture density of 3.1 g / cm 3 to 3.4 g / cm 3 . mixing the large-diameter metal hydroxide precursor and a lithium raw material and heat-treating the mixture to prepare large-diameter particles; mixing the small-diameter metal hydroxide precursor, a lithium raw material, and a lithium halide raw material and heat-treating the mixture to prepare small-diameter particles including a lithium halide; and mixing the large-diameter particles and the small-diameter particles to prepare a positive electrode active material.

20. A rechargeable lithium battery, comprising: a positive electrode including the positive electrode active material according to any one of claims 1-18; a negative electrode including a negative electrode active material; and an electrolyte. ​ ​

Images