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

Abstract

The present invention relates to a positive electrode active material, a method for preparing the same, and a positive electrode and a lithium secondary battery comprising the same, the positive electrode active material comprising: a lithium composite transition metal oxide in a single particle form formed of one primary particle or less, having a composition represented by Chemical Formula 1 described in the specification; and a coating layer comprising a coating element (M) formed on the lithium composite transition metal oxide, wherein the coating element (M) is at least one selected from the group consisting of Al, W, Cu, Zr, Ni, Co, Sr, Mn, Y, Ti, Mg, Mo, B, Sn, Fe, Zn, and Si, and a single particle formation degree (χ) according to Equation 1 described herein is greater than 0.5.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2023-0151121, filed on November 3, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to positive electrode active materials, their preparation methods, and positive electrodes and lithium secondary batteries containing the same. Background Technology

[0004] Due to technological development and the ever-increasing demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among such secondary batteries, lithium-ion batteries, which exhibit high energy density and voltage, long cycle life, and low self-discharge rate, are now commercially available and widely used.

[0005] Lithium-based composite transition metal oxides have been used as positive electrode active materials for lithium-ion secondary batteries, particularly lithium-cobalt composite metal oxides such as LiCoO2, which exhibit high operating voltage and excellent capacity characteristics. However, LiCoO2 has rather poor thermal properties due to its unstable crystal structure caused by delithiation and is also expensive, thus limiting its widespread use as a power source in fields such as electric vehicles.

[0006] Lithium-manganese composite metal oxides (LiMnO2, LiMn2O4, etc.), lithium iron phosphate compounds (LiFePO4, etc.), or lithium-nickel composite metal oxides (LiNiO2, etc.) have been developed as alternatives to LiCoO2. Among these materials, lithium-nickel composite metal oxides have been studied and developed more actively, as they facilitate the realization of high-capacity batteries due to their high reversible capacity of approximately 200 mAh / g. However, LiNiO2 exhibits worse thermal stability than LiCoO2, and when an internal short circuit occurs during charging due to external pressure, the positive electrode active material itself decomposes, leading to battery rupture and combustion.

[0007] Therefore, as a method to maintain the excellent reversible capacity of LiNiO2 and alleviate its low thermal stability, nickel-cobalt-manganese-based lithium composite transition metal oxides (in which some Ni is replaced by Mn and Co) and nickel-manganese-aluminum-based lithium composite transition metal oxides have been developed.

[0008] Meanwhile, lithium composite transition metal oxides with high nickel content exhibit further deterioration in structural and chemical stability, posing greater challenges in achieving thermal stability and leading to higher costs due to the need for high-temperature processing. Extensive research has been conducted to enhance stability, such as including dopant elements in lithium composite transition metal oxides.

[0009] Therefore, there is a need to develop a cathode active material having improved stability and a high nickel content, thereby allowing a lithium secondary battery to exhibit enhanced capacity and life characteristics.

[0010] [Prior Art Documents]

[0011] [Patent Documents]

[0012] (Patent Document 1) Korean Patent Application Publication No. 10-2021-0007808 Summary of the Invention

[0013] Technical issues

[0014] The present invention aims to overcome the above limitations. Accordingly, one aspect of the present invention provides a cathode active material capable of enhancing battery capacity and life characteristics and a method for preparing the same.

[0015] Another aspect of the present invention provides a cathode and a lithium secondary battery exhibiting excellent capacity and life characteristics, which include the cathode active material.

[0016] Technical solution

[0017] (1) According to one aspect of the present invention, there is provided a cathode active material including: a lithium composite transition metal oxide in the form of a single particle formed of 10 or fewer primary particles, having a composition represented by the following Chemical Formula 1; and a coating including a coating element (M) formed on the lithium composite transition metal oxide, wherein the coating element (M) is at least one selected from Al, W, Cu, Zr, Ni, Co, Sr, Mn, Y, Ti, Mg, Mo, B, Sn, Fe, Zn, and Si, and the single particle formation degree (χ) according to the following Equation 1 is greater than 0.5: [Chemical Formula 1] Li 1+x Ni a Co b Mn c M 1 d O2 Wherein, in the above Chemical Formula 1, M 1 is at least one selected from Zr, Y, W, Cu, Sr, Mn, Ti, Mg, Mo, B, Sn, Fe, Zn, Si, and Al, x, a, b, c, and d satisfy -0.1 ≤ x ≤ 0.1, 0.6 ≤ a < 1, 0 < b < 0.4, 0 < c < 0.4, 0 ≤ d ≤ 0.1, a + b + c + d = 1, and 0.25 ≤ a - c ≤ 0.45, and [Equation 1] .

[0018] (2) The present invention provides a positive electrode active material according to (1) above, wherein in the above chemical formula 1, a is 0.6 to 0.75.

[0019] (3) The present invention provides a positive electrode active material according to (1) or (2) above, wherein in the above chemical formula 1, ac satisfies 0.25. <a-c<0.34。

[0020] (4) The present invention provides a positive electrode active material according to any one of (1) to (3) above, wherein the coating contains the coating element (M) in an amount of 3000 ppm to 5500 ppm relative to the total weight of the lithium composite transition metal oxide.

[0021] (5) The present invention provides a positive electrode active material according to any one of (1) to (4) above, wherein the coating comprises a Li-MO compound and M is at least one selected from Al, W, Cu, Zr, Ni, Co, Sr, Mn, Y, Ti, Mg, Mo, B, Sn, Fe, Zn and Si.

[0022] (6) The present invention provides a positive electrode active material according to any one of (1) to (5) above, wherein the coating element (M) is at least one selected from Al and W.

[0023] (7) The present invention provides a positive electrode active material according to any one of (1) to (6) above, wherein the primary particles have an average particle size (D') of 2 μm to 5 μm. 50 ).

[0024] (8) The present invention provides a positive electrode active material according to any one of (1) to (7) above, wherein the positive electrode active material has an average particle size (D) of 3 μm to 5 μm. 50 ).

[0025] (9) The present invention provides a positive electrode active material according to any one of (1) to (8) above, wherein the degree of single particle formation (χ) is 0.6 to 0.9.

[0026] (10) According to another aspect of the present invention, a method for preparing the positive electrode active material according to (1) above is provided, the method comprising: (A) mixing and calcining a composite transition metal hydroxide and a lithium (Li)-containing raw material to prepare a lithium composite transition metal oxide; and (B) mixing the lithium composite transition metal oxide and a raw material containing a coating element (M), and then heat-treating the mixture to form a coating, wherein the calcination is performed at a temperature of 800°C to 1100°C, and the coating element (M) is at least one selected from Al, W, Cu, Zr, Ni, Co, Sr, Mn, Y, Ti, Mg, Mo, B, Sn, Fe, Zn and Si.

[0027] (11) The present invention provides the method according to (10) above, wherein the raw material containing the coating element (M) is selected from at least one of oxides, carbonates, nitrates, hydroxides, hydroxy oxides and halides containing the coating element (M).

[0028] (12) The present invention provides the method according to (10) or (11) above, wherein the raw material containing the coating element (M) is mixed to obtain the coating element (M) in an amount of 3000 ppm to 5500 ppm relative to the total weight of the lithium composite transition metal oxide.

[0029] (13) The present invention provides a method according to any one of (10) to (12) above, wherein the heat treatment is performed at a temperature of 400°C to 600°C.

[0030] (14) According to another aspect of the invention, a positive electrode is provided, comprising a positive electrode active material according to any one of (1) to (9) above.

[0031] (15) According to another aspect of the present invention, a lithium secondary battery is provided, which includes a positive electrode according to (14) above.

[0032] Beneficial effects

[0033] The positive electrode active material according to the present invention comprises a lithium composite transition metal oxide with a molar fraction difference between nickel and manganese within a specific range, and a coating formed on the lithium composite transition metal oxide. Therefore, electrode density can be maintained by adjusting the average particle size of the primary particles, reducing side reactions with the electrolyte, and improving conductivity. Consequently, positive and secondary batteries incorporating the aforementioned positive electrode active material achieve enhanced capacity and lifetime characteristics.

[0034] Furthermore, the above-mentioned positive electrode active material can be effectively prepared using the method for preparing positive electrode active material according to the present invention. Attached Figure Description

[0035] Figure 1 This is a SEM image (magnification: 5 K) of the positive electrode active material prepared in Example 1; Figure 2 This is a SEM image (magnification: 5 K) of the positive electrode active material prepared in Example 2; Figure 3 This is a SEM image (magnification: 5 K) of the positive electrode active material prepared in Comparative Example 1; Figure 4 This is a SEM image (magnification: 5 K) of the positive electrode active material prepared in Comparative Example 3; Figure 5 This is a SEM image (magnification: 20 K) of the positive electrode active material prepared in Example 1; Figure 6 This is a SEM image (magnification: 50 K) of the positive electrode active material prepared in Example 1. Detailed Implementation

[0036] The invention will be described in detail below to aid in understanding it.

[0037] It should be understood that the words or terms used in the specification and claims should not be interpreted as having the meaning defined in a common dictionary, and it should also be understood that, based on the inventor's ability to appropriately define the meaning of words or terms to best explain the principles of the invention, the words or terms should be interpreted as having a meaning consistent with their meaning in the relevant field and in the context of the technical idea of ​​the invention.

[0038] In this document, it will be further understood that the terms “comprising,” “including,” or “having” specify the presence of the said feature, number, step, element, or combination thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, elements, or combinations thereof.

[0039] In this document, the term "on" refers to a situation where a particular component is formed directly on the upper surface of another component, and a situation where a third component is inserted between these components.

[0040] In this paper, "single-particle form" is the opposite of the spherical secondary particle form (in which dozens to hundreds of primary particles aggregate) formed by typical methods, and refers to a form consisting of fewer than 10 primary particles. Specifically, the single-particle form in this paper can be a single-particle form consisting of one primary particle or a secondary particle form in which 2 to 10 primary particles aggregate.

[0041] In this paper, "primary particle" refers to the smallest unit of a particle identified when observing a positive electrode active material by scanning electron microscopy (SEM), and "secondary particle" refers to a secondary structure in which multiple primary particles are aggregated.

[0042] In this paper, the content of each element in lithium complex transition metal oxides was measured by inductively coupled plasma (ICP) analysis using an inductively coupled plasma optical emission spectrometer (ICP-OES; Optima 7300DV, PerkinElmer).

[0043] In this paper, the area of ​​each primary particle can be calculated based on the number of pixels corresponding to each of the n primary particles present in the SEM image, and the particle size of each primary particle present in the SEM image can be measured using the diameter of a circle with the same area as each primary particle, thereby determining the particle size of the primary particles. Furthermore, in this paper, the average particle size (D') of the primary particles is... 50 The average particle size (D') can be defined as the particle size that constitutes 50% of the cumulative volume distribution in the particle size distribution curve (the curve on the particle size distribution map) of each particle. 50 The particle size at 50% of the cumulative volume distribution can be determined by calculating the particle size from the results of calculating the volume of the primary particle, wherein the volume is defined by the volume of a sphere with a radius half that of the primary particle size.

[0044] In this paper, the average particle size (D) of the positive electrode active material is... 50 The particle size distribution (Dsize) can be defined as the particle size at which the cumulative volume distribution of the particle size distribution curve (the curve on the particle size distribution map) is 50%. After dispersing the target powder in a dispersion medium, the dispersion medium is introduced into a commercial laser diffraction particle size analyzer (e.g., the S3500 from Microtrac). The particle size distribution is calculated by measuring the difference in the diffraction pattern caused by the particle size as it passes through the laser beam, and the average particle size (Dsize) of the positive electrode active material is determined by calculating the particle size at which the cumulative volume distribution of the particle size is 50% using the analyzer. 50 ).

[0045] Positive electrode active material

[0046] The positive electrode active material according to the present invention will be described below.

[0047] The positive electrode active material according to the present invention includes: a lithium composite transition metal oxide in the form of a single particle formed from 10 or fewer primary particles, having a composition represented by the following Chemical Formula 1; and a coating containing a coating element (M) formed on the lithium composite transition metal oxide, wherein the coating element (M) is at least one selected from Al, W, Cu, Zr, Ni, Co, Sr, Mn, Y, Ti, Mg, Mo, B, Sn, Fe, Zn, and Si, and the degree of single particle formation (χ) according to the following Equation 1 is greater than 0.5: [Chemical Formula 1] Li 1+x Ni a Co b Mn c M 1 d O2 Wherein in the above Chemical Formula 1, M 1 is at least one selected from Zr, Y, W, Cu, Sr, Mn, Ti, Mg, Mo, B, Sn, Fe, Zn, Si, and Al, x, a, b, c, and d satisfy -0.1 ≤ x ≤ 0.1, 0.6 ≤ a < 1, 0 < b < 0.4, 0 < c < 0.4, 0 ≤ d ≤ 0.1, a + b + c + d = 1, and 0.25 ≤ a - c ≤ 0.45, and [Equation 1] .

[0048] The present inventors have found that a lithium secondary battery exhibiting improved capacity characteristics and life characteristics can be achieved when including the following positive electrode active material: the positive electrode active material has a difference in molar fractions of nickel and manganese included in a lithium composite transition metal oxide having a high nickel content within a specific range, includes a coating containing a coating element (M) formed on the lithium composite transition metal oxide, and has a degree of single particle formation within a specific range. Specifically, the average particle diameter of the primary particles of the lithium composite transition metal oxide is determined by the difference in molar fractions of nickel and manganese. When the average particle diameter of the primary particles increases, the electrode density decreases and the side reaction with the electrolyte decreases, while when the average particle diameter of the primary particles decreases, the electrode density increases and the side reaction with the electrolyte increases. In addition, by including a coating formed on the lithium composite transition metal oxide, the conductivity can be improved, and the by-products formed through the side reaction with the electrolyte can be controlled. The present inventors have found that the positive electrode active material includes a coating containing a lithium composite transition metal oxide having a difference in molar fractions of nickel and manganese within a specific range and a coating element (M) formed on the lithium composite transition metal oxide, thereby appropriately controlling the average particle diameter (D’ 50Therefore, when the degree of single-particle formation according to Equation 1 described herein is within a certain range, the capacity characteristics, resistance characteristics, and lifetime characteristics of the positive electrode active material can be improved, thereby completing the present invention.

[0049] Meanwhile, when the difference in molar fractions of nickel and manganese in lithium composite transition metal oxides with high nickel content is not within a specific range or the degree of single-particle formation is less than 0.5, the average particle size (D') of the primary particles of lithium composite transition metal oxides is... 50 The small size of the electrolyte leads to poor lifetime characteristics. Furthermore, during rolling for electrode fabrication or battery operation, grain breakage occurs due to grain boundaries, significantly increasing the area of ​​grain boundaries in contact with the electrolyte and increasing gas generation due to side reactions with the electrolyte, resulting in poor lifetime and electrical resistance characteristics. Additionally, when not included in coatings containing the coating element (M) formed on lithium complex transition metal oxides with high nickel content, conductivity is poor, and capacity, electrical resistance, and lifetime characteristics are degraded due to byproducts formed from side reactions with the electrolyte.

[0050] Lithium complex transition metal oxides (LCMOs) are in the form of single particles consisting of fewer than 10 primary particles. In other words, LMOs are either monolithic particles or single particles comprised of 2 to 10 particles. The single-particle form differs from secondary particles comprised of more than 10 primary particles. When in single-particle form, LMOs exhibit excellent stability. Therefore, cathode active materials containing LMOs do not fracture or crack even during rolling, and thus, side reactions between the cathode active material and the electrolyte can be reduced. Consequently, the battery can have improved durability against volume changes during charging and discharging, resulting in enhanced lifespan characteristics. When LMOs are in secondary particle form, the cathode active material fractures or cracks during rolling, leading to side reactions between the cathode active material and the electrolyte, resulting in poor durability against volume changes during charging and discharging, and poor lifespan characteristics.

[0051] M 1 It is a doped element, and specifically, M 1 It can be at least one selected from Zr, Y, W, Cu, Sr, Mn, Ti, Mg, Mo, B, Sn, Fe, Zn, Si, and Al. It does not necessarily include M. 1 However, when containing an appropriate amount of M 1 When this is achieved, the positive electrode active material can exhibit improved particle shape and enhanced crystal structure stability.

[0052] Meanwhile, x can be greater than -0.1, greater than -0.09, greater than -0.08, greater than -0.07, greater than -0.06, greater than -0.05, greater than -0.04, greater than -0.03, greater than -0.02, greater than -0.01, greater than 0, greater than 0, greater than 0, greater than 0.01, greater than 0, greater than 0, greater than 0.02, or greater than 0.03, and can be less than 0.04, less than 0.05, less than 0.06, less than 0.07, less than 0.08, less than 0.09, or less than 0.1. When x meets the above ranges, high capacity characteristics and high energy density per unit volume can be achieved.

[0053] 'a' represents the mole fraction of nickel (Ni) in all metals other than lithium in the lithium-based complex transition metal oxide, and can be 0.6 or more, 0.61 or more, 0.62 or more, 0.63 or more, or 0.64 or more, and can be less than 0.65, 0.66, 0.67, 0.68, 0.69, 0.7, 0.71, 0.72, 0.73, 0.74, 0.75, or 0.76. Values ​​below 0.77, 0.78, 0.79, 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or less than 1, can achieve high capacity characteristics. In particular, when a is between 0.6 and 0.75, high capacity characteristics can be achieved due to the high energy density exhibited under high voltage drive.

[0054] b is the mole fraction of cobalt (Co) in all metals other than lithium in the lithium-ion complex transition metal oxide, and can be greater than 0, 0.01, 0.02, 0.03, 0.04, 0.05, or 0.06, and can be less than 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, or 0.1 Values ​​below 7, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, or less than 0.4. When b meets the above ranges, stability during the charging / discharging process can be improved and rate performance can be enhanced.

[0055] c is the mole fraction of manganese (Mn) in all metals other than lithium in a lithium-ion complex transition metal oxide, and can be greater than 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, or 0. The electrolyte concentration can be 18 or higher, 0.19 or higher, 0.2 or higher, 0.21 or higher, 0.22 or higher, 0.23 or higher, 0.24 or higher, 0.25 or higher, 0.26 or higher, 0.27 or higher, 0.28 or higher, 0.29 or higher, 0.3 or higher, or 0.31 or higher, and can be below 0.32, below 0.33, below 0.34, below 0.35, below 0.36, below 0.37, below 0.38, below 0.39, or less than 0.4. When the above ranges are met, high capacity characteristics can be achieved. Furthermore, high-temperature stability can be improved, and side reactions with the electrolyte can be relatively reduced.

[0056] d is M among all metals other than lithium in lithium complex transition metal oxides. 1 The mole fraction of d can be greater than or equal to 0, 0.001, 0.002, 0.003, or 0.004, and can be less than or equal to 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1. When d meets the above ranges, the positive electrode active material can exhibit enhanced crystal structure stability and improved particle shape.

[0057] Furthermore, for a and c, ac can be greater than 0.25, greater than 0.25, greater than 0.26, greater than 0.27, greater than 0.28, greater than 0.29, greater than 0.3, or greater than 0.31, and can be less than 0.34, less than 0.34, less than 0.35, less than 0.36, less than 0.37, less than 0.38, less than 0.39, less than 0.4, less than 0.41, less than 0.42, less than 0.43, less than 0.44, or less than 0.45. When ac meets the above ranges, the average particle size (D') of the primary particles of the positive electrode active material can be appropriately adjusted. 50 This allows for control of electrode density and side reactions with the electrolyte, and can improve capacity and lifetime characteristics. When AC is less than 0.25, the average particle size (D') of the primary particles in the positive electrode active material... 50When the AC value decreases, side reactions with the electrolyte increase, leading to poor lifetime characteristics. Conversely, when the AC value is greater than 0.45, the electrode density decreases, resulting in poor capacity characteristics. In particular, when the AC value is greater than 0.25 and less than 0.34, lifetime and resistance characteristics can be improved without compromising the charge / discharge capacity of the secondary battery.

[0058] The coating comprises a coating element (M) formed on a lithium complex transition metal oxide, wherein the coating element (M) is at least one selected from Al, W, Cu, Zr, Ni, Co, Sr, Mn, Y, Ti, Mg, Mo, B, Sn, Fe, Zn, and Si. When the coating includes the coating element (M), conductivity can be improved, and byproducts formed through side reactions with the electrolyte can be controlled, thereby improving capacity, resistance, and lifetime characteristics. Specifically, the coating element (M) can be at least one selected from Al and W. In this case, it has the effect of suppressing the generation of byproducts in the form of hydrogen fluoride and exhibiting high capacity characteristics at high rates. Meanwhile, when the coating containing the coating element (M) is not included on the lithium complex transition metal oxide, conductivity is poor, and capacity, resistance, and lifetime characteristics are degraded due to byproducts formed through side reactions with the electrolyte.

[0059] The positive electrode active material according to the present invention has a single particle formation degree (χ) greater than 0.5 according to Equation 1 described herein. Specifically, the single particle formation degree (χ) can be greater than 0.5, 0.51 or more, 0.52 or more, 0.53 or more, 0.54 or more, 0.55 or more, 0.56 or more, 0.57 or more, 0.58 or more, 0.59 or more, 0.6 or more, 0.61 or more, or 0.62 or more, and can be less than 0.87, less than 0.88, less than 0.89, less than 0.90, less than 0.91, less than 0.92, less than 0.93, less than 0.94, less than 0.95, less than 0.96, less than 0.97, less than 0.98, less than 0.99, or less than 1. When the single particle formation degree (χ) is within the above range, it can be seen that the lithium composite transition metal oxide of the present invention is in the form of single particles, wherein the aggregation between primary particles is suppressed. Specifically, when the degree of single-particle formation (χ) is between 0.6 and 0.9, lithium composite transition metal oxides exhibit enhanced structural stability, resulting in suppressed particle breakage during rolling for electrode manufacturing or battery operation, reduced grain boundary area in contact with the electrolyte, and reduced gas generation caused by side reactions with the electrolyte. Consequently, the secondary battery can exhibit improved lifetime and resistivity characteristics. Conversely, when the degree of single-particle formation is below 0.5, particle breakage occurs due to grain boundaries during rolling for electrode manufacturing or cell operation, significantly increasing the grain boundary area in contact with the electrolyte and increasing gas generation caused by side reactions with the electrolyte, leading to deterioration in lifetime characteristics.

[0060] According to an embodiment of the invention, the coating may contain a coating element (M) in an amount of 3,000 ppm to 5,500 ppm relative to the total weight of the lithium composite transition metal oxide. The coating element (M) may be supplied in amounts of 3000 ppm or more or 3100 ppm or more relative to the total weight of the lithium complex transition metal oxide, and in amounts of less than 3200 ppm, less than 3300 ppm, less than 3400 ppm, less than 3500 ppm, less than 3600 ppm, less than 3700 ppm, less than 3800 ppm, less than 3900 ppm, less than 4000 ppm, less than 4100 ppm, less than 4200 ppm, less than 4300 ppm, less than 4400 ppm, less than 4500 ppm, less than 4600 ppm, less than 4700 ppm, less than 4800 ppm, less than 4900 ppm, less than 5000 ppm, less than 5100 ppm, less than 5200 ppm, less than 5300 ppm, less than 5400 ppm, or less than 5500 ppm. When the content of coating element (M) is within the above range, conductivity can be improved and byproducts formed through side reactions with electrolyte can be controlled, thereby improving the capacity, resistance and lifetime characteristics of the positive electrode active material.

[0061] According to embodiments of the present invention, the coating may include a Li-MO compound, and M may be at least one selected from Al, W, Cu, Zr, Ni, Co, Sr, Mn, Y, Ti, Mg, Mo, B, Sn, Fe, Zn, and Si. Specifically, when the coating is a Li-Al-O compound, a Li-WO compound, or a combination thereof, conductivity can be improved, and byproducts formed through side reactions with the electrolyte can be controlled, thereby improving the capacity, resistance, and lifetime characteristics of the positive electrode active material.

[0062] According to embodiments of the present invention, the primary particles may have an average particle size (D') of 2 μm to 5 μm. 50 Specifically, the average particle size (D') of the primary particles. 50 The particle size can be 2 μm or larger, 2.1 μm or larger, 2.2 μm or larger, 2.3 μm or larger, 2.4 μm or larger, 2.41 μm or larger, 2.42 μm or larger, 2.43 μm or larger, 2.44 μm or larger, 2.45 μm or larger, 2.46 μm or larger, 2.47 μm or larger, 2.48 μm or larger, or 2.49 μm or larger, and the average particle size (D') can be 2 μm or larger. 50The particle size can be below 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, or 5 μm. When the average particle size (D') of the primary particles... 50 Within the above range, side reactions between the positive electrode active material and the electrolyte are reduced, thus improving lifetime characteristics, and resistance characteristics are improved due to the reduction of lithium diffusion paths within the particles.

[0063] According to embodiments of the present invention, the positive electrode active material may have an average particle size (D) of 3 μm to 5 μm. 50 Specifically, the average particle size (D) of the positive electrode active material 50 The particle size can be 3 μm or larger, 3.1 μm or larger, 3.2 μm or larger, 3.3 μm or larger, 3.4 μm or larger, 3.5 μm or larger, 3.6 μm or larger, 3.7 μm or larger, 3.8 μm or larger, or 3.9 μm or larger, and the average particle size (D) can be 3 μm or larger. 50 The particle size can be below 4.02 μm, 4.03 μm, 4.04 μm, 4.05 μm, 4.06 μm, 4.07 μm, 4.08 μm, 4.09 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, or 5 μm. When the average particle size (D) of the positive electrode active material... 50 Within the above range, excellent electrode density can be achieved and structural stability can be improved.

[0064] Methods for preparing positive electrode active materials

[0065] Next, a method for preparing the positive electrode active material of the present invention will be described. The method for preparing the positive electrode active material of the present invention is a method for preparing the positive electrode active material according to the present invention.

[0066] The method for preparing the positive electrode active material of the present invention includes: (A) mixing and calcining a composite transition metal hydroxide and a lithium (Li)-containing raw material to prepare a lithium composite transition metal oxide; and (B) mixing the lithium composite transition metal oxide and a raw material containing a coating element (M), and then heat-treating the mixture to form a coating, wherein the calcination is carried out at a temperature of 800°C to 1100°C, and the coating element (M) is at least one selected from Al, W, Cu, Zr, Ni, Co, Sr, Mn, Y, Ti, Mg, Mo, B, Sn, Fe, Zn and Si.

[0067] The positive electrode active material according to the present invention can be prepared by appropriately adjusting the type of raw materials, the mixing ratio of raw materials, the heat treatment temperature, the firing and heat treatment duration, etc.

[0068] The invention will be described in detail below for each step.

[0069] Step A

[0070] The method for preparing positive electrode active materials according to the present invention includes step A, which involves mixing and calcining a composite transition metal hydroxide and a lithium (Li)-containing raw material to prepare a lithium composite transition metal oxide.

[0071] Complex transition metal hydroxides can be prepared by adding an aqueous solution of a complex transition metal, an ammonium cation complexing agent, and a basic compound to a reactor and subjecting the mixture to a coprecipitation reaction.

[0072] Solutions containing complex transition metals may contain nickel (Ni), cobalt (Co), and manganese (Mn).

[0073] Aqueous solutions containing complex transition metals can be prepared by dissolving a transition metal-containing raw material in a solvent (e.g., water), and can be prepared, for example, by dissolving a nickel (Ni), cobalt (Co), and manganese (Mn)-containing raw material in water. In other words, solutions containing complex transition metals may include nickel (Ni), cobalt (Co), and manganese (Mn)-containing raw materials. Furthermore, when desired, solutions containing complex transition metals may further include metal-containing raw materials containing a transition metal other than nickel (Ni), cobalt (Co), and manganese (Mn) (e.g., at least one selected from Zr, Y, W, Cu, Sr, Mn, Ti, Mg, Mo, B, Sn, Fe, Zn, Si, and Al).

[0074] The nickel-containing raw material can be at least one selected from the group consisting of NiSO4, NiO, Ni(OH)2, NiO·OH, NiCO3·2Ni(OH)2·4H2O, NiC2O4·2H2O, Ni(NO3)2·6H2O, nickel fatty acids and nickel halides, and any one or a mixture of two or more of them can be used.

[0075] The cobalt (Co) raw material can be at least one selected from the group consisting of Co(OH)2, Co3O4, CoO·OH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O or Co(SO4)2·7H2O, cobalt fatty acids and cobalt halides, and any one or a mixture of two or more of them can be used.

[0076] The manganese (Mn) raw material can be at least one selected from the group consisting of MnCO3, Mn2O3, MnO2, Mn3O4, Mn(NO3)2, manganese acetate, manganese dicarboxylate, manganese citrate, manganese salts of fatty acids, manganese hydroxyoxide, and manganese halides such as manganese chloride, and any one or a mixture of two or more of them can be used.

[0077] The metal-containing raw material may be selected from at least one of the group consisting of carbonates, nitrates, hydroxides, oxides, hydroxy oxides and halides containing at least one transition metal other than nickel (Ni), cobalt (Co) and manganese (Mn), and may use any one or a mixture of two or more of them.

[0078] Considering the content of each metal element in the prepared composite transition metal hydroxide, nickel (Ni), cobalt (Co), and manganese (Mn) raw materials can be used in appropriate amounts.

[0079] Meanwhile, the ammonium cation complex forming agent may include at least one compound selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and NH4CO3, and may be added to the reactor in solution form (wherein the compound is dissolved in a solvent). In this case, water or a mixture of water and an organic solvent (especially an alcohol, etc.) that can be uniformly mixed with water may be used as the solvent.

[0080] The basic compound can be at least one compound selected from the group consisting of NaOH, KOH, and Ca(OH)2, and can be added to the reactor in solution form (where the compound is dissolved in a solvent). In this case, water or a mixture of water and an organic solvent (especially an alcohol, etc.) that can be homogeneously mixed with water can be used as the solvent.

[0081] As described above, when a solution containing a composite transition metal, an ammonium cation complexing agent, and an alkaline compound are placed in a reactor, precursor particles in the form of a composite transition metal hydroxide are produced due to the coprecipitation reaction between the transition metal in the solution containing the composite transition metal and the hydroxide ions of the alkaline compound.

[0082] The coprecipitation reaction can be carried out for 1 hour to 50 hours. Specifically, the coprecipitation reaction can be carried out for more than 1 hour, more than 5 hours, more than 10 hours, more than 11 hours, more than 12 hours, more than 13 hours, more than 14 hours, more than 15 hours, more than 16 hours, more than 17 hours, more than 18 hours, more than 19 hours, or more than 20 hours, and 30 hours or less, 31 hours or less, 32 hours or less, 33 hours or less, 34 hours or less, 35 hours or less, 36 hours or less, 37 hours or less, 38 hours or less, 39 hours or less, 40 hours or less, 45 hours or less, or 50 hours or less. When the coprecipitation reaction is carried out for a duration within the above range, the crystallinity of the precursor particles can be controlled to a sufficient degree.

[0083] In this case, the alkaline compound can be added in an amount such that the pH of the reaction solution is within the desired range. The coprecipitation reaction can be carried out at a pH of 10 to 13. Specifically, the coprecipitation reaction can be carried out at a pH above 10, a pH above 10.5, a pH above 11, or a pH above 11.5, and a pH below 12, a pH below 12.5, a pH below 12.7, or a pH below 13.

[0084] When precursor particles are formed by the above method, the particles are separated from the reaction solution to obtain a composite transition metal hydroxide. Specifically, the reaction solution can be filtered to separate the precursor particles from the reaction solution, and then the separated precursor particles can be washed and dried to obtain a composite transition metal hydroxide. In this case, processes such as grinding and / or classification can be carried out as needed.

[0085] The composite transition metal hydroxide can have a composition represented by Ni p Co q Mn r M 2 s (OH)2 (where M 2 is at least one selected from Zr, Y, W, Cu, Sr, Mn, Ti, Mg, Mo, B, Sn, Fe, Zn, Si, and Al, and p, q, r, and s satisfy 0.6 ≤ p < 1, 0 < q < 0.4, 0 < r < 0.4, 0 ≤ s ≤ 0.1, and p + q + r + s = 1).

[0086] The lithium (Li)-containing raw material can be at least one selected from LiOH, Li₂CO₃, LiNO₃, LiNO₂, LiOH·H₂O, LiH, LiF, LiCl, LiBr, LiI, CH₃COOLi, Li₂O, lithium acetate, lithium dicarboxylate, lithium citrate, lithium fatty acids, alkyl lithium, and lithium halides, and any one or a mixture of two or more of them can be used. Specifically, considering the similarity between the melting point and firing temperature of the lithium (Li)-containing raw material and economic efficiency, Li₂CO₃ can be used.

[0087] Mixing can be carried out by dry mixing or wet mixing. When each component is mixed by dry mixing, the calcination process can be performed without a separate drying process. When each component is mixed by wet mixing, mixing is carried out by adding a solvent, especially water, or a mixture of water and an organic solvent (especially alcohols, etc.) that can be uniformly mixed with water, or by preparing a solution containing each raw material, especially an aqueous solution, then mixing the solution, spray drying, and then calcining the mixed components. Each raw material and the composite transition metal hydroxide can be used in appropriate amounts, taking into account the content of each metal element in the final prepared lithium composite transition metal oxide.

[0088] According to an embodiment of the present invention, in step A, the composite transition metal hydroxide and the lithium (Li)-containing raw material can be mixed in an amount that achieves the composition represented by the above chemical formula 1.

[0089] Firing is carried out at temperatures between 800°C and 1100°C. Specifically, firing is carried out at temperatures above 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, or 940°C, and at temperatures below 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, 1060°C, 1070°C, 1080°C, 1090°C, or 1100°C. When the firing temperature is within the above range, primary particles can grow to an appropriate extent to improve capacity and lifetime characteristics. When the firing is carried out at temperatures below 800°C, particle growth is insufficient, resulting in the formation of secondary particles of positive electrode active material in which more than 10 primary particles aggregate, leading to deterioration in lifetime characteristics. When the firing is carried out at temperatures above 1100°C, primary particles overgrow and lithium migration decreases, thus increasing resistance and reducing capacity characteristics.

[0090] Firing can be carried out in an air atmosphere, an oxygen atmosphere, or an inert atmosphere. Specifically, firing can be carried out in an air atmosphere due to the ease of maintaining the firing atmosphere and economic benefits.

[0091] The firing process can last from 10 to 18 hours. Specifically, the firing time can be more than 10 hours, more than 11 hours, more than 12 hours, more than 13 hours, or more than 14 hours, or less than 15 hours, less than 16 hours, less than 17 hours, or less than 18 hours. When the firing duration is within the above range, the crystallinity of the lithium composite transition metal oxide particles is sufficiently controlled, which is beneficial to lithium-ion transport.

[0092] Step B

[0093] The method for preparing a positive electrode active material according to the present invention includes: after step (A), mixing a lithium composite transition metal oxide with a raw material containing a coating element (M), and then heat-treating the mixture to form a coating.

[0094] The coating element (M) is selected from at least one of Al, W, Cu, Zr, Ni, Co, Sr, Mn, Y, Ti, Mg, Mo, B, Sn, Fe, Zn, and Si. By forming a coating containing the coating element (M) on lithium composite transition metal oxides, conductivity can be improved, and byproducts formed through side reactions with the electrolyte can be controlled, thereby improving the capacity, resistance, and lifetime characteristics of the positive electrode active material. Conversely, when no coating containing the coating element (M) is formed on the lithium composite transition metal oxide, conductivity is poor, and capacity, resistance, and lifetime characteristics are degraded due to byproducts formed through side reactions with the electrolyte.

[0095] According to embodiments of the present invention, as a raw material containing the coating element (M), at least one selected from oxides, carbonates, nitrates, hydroxides, hydroxy oxides, and halides containing the coating element (M) can be used. Specifically, to exhibit the effect of suppressing the generation of byproducts in the form of hydrogen fluoride and exhibiting high capacity characteristics at high rates, an oxide containing the coating element (M) can be used, and the coating element (M) can be Al or W.

[0096] According to an embodiment of the present invention, raw materials containing coating element (M) can be mixed to obtain a coating element (M) in an amount of 3000 ppm to 5500 ppm relative to the total weight of lithium complex transition metal oxide. Specifically, a coating element (M) can be mixed to achieve a coating element (M) in an amount of 3000 ppm or more, 3100 ppm or more, 3200 ppm or more, 3300 ppm or more, 3400 ppm or more, 3500 ppm or more, 3600 ppm or more, 3700 ppm or more, 3800 ppm or more, 3900 ppm or more, 4000 ppm or more, 4100 ppm or more, 4200 ppm or more, 4300 ppm or more, 4400 ppm or more, or 4500 ppm or more, relative to the total weight of the lithium composite transition metal oxide, or in an amount of less than 4600 ppm, less than 4700 ppm, less than 4800 ppm, less than 4900 ppm, less than 5000 ppm, less than 5100 ppm, less than 5200 ppm, less than 5300 ppm, less than 5400 ppm or less, or less than 5500 ppm. When the mixing amount of raw materials containing coating element (M) is within the above range, conductivity can be improved, and byproducts formed through side reactions with electrolyte can be controlled, thereby improving the capacity and lifetime characteristics of the positive electrode active material.

[0097] Heat treatment can be carried out in an air atmosphere, an oxygen atmosphere, or an inert atmosphere. Specifically, considering the ease of maintaining the heat treatment atmosphere and economic benefits, heat treatment can be carried out in an air atmosphere.

[0098] According to embodiments of the present invention, firing can be performed at a temperature of 400°C to 600°C. Specifically, heat treatment can be performed at temperatures above 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, or 500°C, and at temperatures below 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, or 600°C. When the heat treatment temperature is within the above range, sufficient heat energy can be supplied for coating. When lithium composite transition metal oxide and coating M raw material are mixed and then heat-treated within the above temperature range, a coating containing coating element (M) can be formed on the lithium composite transition metal oxide. The coating containing the coating element (M) can partially (discontinuously) cover at least a portion of the lithium complex transition metal oxide (i.e., at least one region of the lithium complex transition metal oxide) or can (continuously) cover the entire region. The coating can be a film type, an island type, or a combination thereof.

[0099] The heat treatment can be carried out for 3 to 9 hours. Specifically, the heat treatment can be carried out for more than 3 hours, more than 4 hours, or more than 5 hours, and less than 6 hours, less than 7 hours, less than 8 hours, or less than 9 hours. When the heat treatment duration is within the above range, heat energy can be supplied to form a coating to a sufficient extent.

[0100] positive electrode

[0101] Next, the positive electrode according to the present invention will be described.

[0102] The positive electrode according to the present invention comprises a positive electrode active material layer containing the positive electrode active material according to the present invention. Specifically, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector and containing the positive electrode active material. Since the positive electrode active material has already been described above, its detailed description will be skipped, and only the other components will be described below.

[0103] There are no particular limitations on the positive electrode current collector, as long as it is conductive and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel with only surface treatment of one of carbon, nickel, titanium, silver, etc. can be used. Furthermore, the positive electrode current collector can typically have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on its surface to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0104] The positive electrode active material layer may include conductive materials, a binder, and the positive electrode active material. In this case, the content of the positive electrode active material relative to the total weight of the positive electrode active material layer can be from 80% to 99% by weight, for example from 85% to 98.5% by weight, and excellent capacity characteristics can be obtained within this range.

[0105] Conductive materials are used to impart conductivity to the electrodes, and any conductive material can be used without particular limitation, as long as it has electronic conductivity without causing a chemical change in the battery to be constructed. Specific examples may include graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, and carbon fibers; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more of these can be used. The content of the conductive material relative to the total weight of the positive electrode active material layer can be from 0.1% by weight to 15% by weight.

[0106] Adhesives are used to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof may be used. The adhesive content may be from 0.1% by weight to 15% by weight relative to the total weight of the positive electrode active material layer.

[0107] The positive electrode can be prepared according to the general method for preparing a positive electrode, the difference being the use of the aforementioned positive electrode active material. Specifically, a positive electrode active material layer forming composition (prepared by dissolving or dispersing the positive electrode active material and optionally a binder and conductive material in a solvent) can be applied to a positive electrode current collector, followed by drying and rolling to prepare the positive electrode. In this case, the type and amount of the positive electrode active material, binder, and conductive material are as described above. Alternatively, in another method, the positive electrode active material layer forming composition can be cast onto a separate carrier, and then the film layer, separated from the carrier, can be pressed onto the positive electrode current collector to prepare the positive electrode.

[0108] The solvent can be a solvent commonly used in the art, and can be dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, water, etc., and any one or a mixture of two or more of them can be used. Considering the application thickness and preparation yield of the slurry, if the solvent can dissolve or disperse the positive electrode active material, conductive material and binder, the amount of solvent used can be sufficient, and thereafter has a viscosity that can exhibit excellent thickness uniformity when applying to prepare the positive electrode.

[0109] Lithium secondary batteries

[0110] Next, the lithium secondary battery according to the present invention will be described.

[0111] This invention can manufacture electrochemical devices including a positive electrode. Specifically, the electrochemical device can be a battery, a capacitor, etc., and more specifically, a lithium secondary battery.

[0112] Specifically, a lithium secondary battery includes a positive electrode, a negative electrode positioned facing the positive electrode, a separator between the positive and negative electrodes, and an electrolyte. The positive electrode is the same as described above, so its detailed description will be skipped, and only the other components will be described below.

[0113] In addition, the lithium secondary battery may optionally include a battery container that houses the electrode assembly of the positive electrode, the negative electrode and the separator, as well as a sealing member that seals the battery container.

[0114] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material located on the negative electrode current collector.

[0115] There are no particular limitations on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or copper or stainless steel, aluminum-cadmium alloys surface-treated with one of carbon, nickel, titanium, or silver can be used. Furthermore, the negative electrode current collector typically has a thickness from 3 μm to 500 μm, and as in the case of the positive electrode current collector, fine irregularities can be formed on its surface to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0116] In addition to the negative electrode active material, the negative electrode active material layer optionally includes a binder and a conductive material.

[0117] Compounds capable of reversibly inserting and deintercalating lithium can be used as anode active materials. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metallic compounds that can alloy with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and lithium-doped and undoped metal oxides, such as SiO₂. β (0<β<2), SnO2, vanadium oxide and lithium vanadium oxide; or composite materials including metal compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of them can be used. Furthermore, lithium metal films can be used as negative electrode active materials. Additionally, as carbon materials, low-crystallinity carbon and high-crystallinity carbon can be used. Typical examples of low-crystallinity carbon can be soft carbon and hard carbon, while typical examples of high-crystallinity carbon can be irregular, planar, sheet-like, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch and high-temperature calcined carbon, such as coke derived from petroleum or coal tar pitch.

[0118] The content of the negative electrode active material can be 80% to 99% by weight relative to the total weight of the negative electrode active material layer.

[0119] Adhesives are components used to aid in the bonding between conductive materials, active materials, and current collectors, and are typically added in an amount from 0.1% to 10% by weight relative to the total weight of the negative electrode active material layer. Examples of adhesives may include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0120] Conductive materials are components used to further improve the conductivity of the negative electrode active material, and can be added in an amount of less than 10% by weight, particularly less than 5% by weight, relative to the total weight of the negative electrode active material layer. There are no particular limitations on the conductive material, as long as it is conductive without causing chemical changes in the battery, and examples of conductive materials that can be used include: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers, such as carbon fibers or metal fibers; fluorocarbons; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or polyphenylene derivatives.

[0121] The negative electrode active material layer can be prepared by applying a negative electrode active material layer forming composition (which is prepared by dissolving or dispersing the negative electrode active material and optionally a binder and conductive material in a solvent) onto the negative electrode current collector and then drying it; or the negative electrode active material layer can be prepared by casting the negative electrode active material layer forming composition onto a separate carrier and then pressing the film layer separated from the carrier onto the negative electrode current collector.

[0122] Meanwhile, in lithium secondary batteries, the separator is used to separate the negative and positive electrodes and provide a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is commonly used as a separator in lithium secondary batteries. In particular, separators with high water retention capacity for the electrolyte and low resistance to the movement of electrolyte ions are preferred. Specifically, porous polymer membranes can be used, for example, porous polymer membranes prepared using polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures with two or more layers. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from glass fibers or polyethylene terephthalate fibers with high melting points. In addition, coated separators including ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can optionally be used.

[0123] Furthermore, the electrolyte used in this invention can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc., all of which can be used to manufacture lithium secondary batteries, but are not limited thereto.

[0124] Specifically, electrolytes may include organic solvents and lithium salts.

[0125] Any organic solvent can be used without particular limitation, as long as it can serve as a medium through which the ions involved in the electrochemical reactions of the battery can move. Specifically, as organic solvents, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone can be used; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic C2 to C20 hydrocarbon group and may include double-bonded aromatic rings or ether bonds); amides such as dimethylformamide; dioxolane solvents such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constants with linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) with low viscosity are even more preferred, as these mixtures can improve the charge / discharge performance of the battery. In this case, when cyclic carbonates and linear carbonates are mixed in a volume ratio of about 1:1 to about 1:9, the electrolyte can exhibit excellent performance.

[0126] Any compound can be used as a lithium salt without particular limitation, as long as it can provide lithium ions for lithium secondary batteries. Specifically, lithium salts include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, and LiB(C2O4)2. Lithium salts can be used in concentration ranges from 0.1 M to 5.0 M, particularly from 0.1 M to 3.0 M. When the concentration of the lithium salt is within the above range, the electrolyte exhibits suitable conductivity and viscosity, thus demonstrating excellent performance, and lithium ions can move efficiently.

[0127] To improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, the electrolyte may also contain at least one additive, such as alkylene carbonate halogenates (e.g., ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol ethers, triamide hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In this case, the additive content relative to the total weight of the electrolyte can be from 0.1% to 10% by weight, particularly from 0.1% to 5% by weight.

[0128] Lithium secondary batteries, including the positive electrode active material according to the present invention as described above, exhibit excellent life and capacity characteristics, and are therefore suitable for use in portable devices (e.g., mobile phones, laptops, and digital cameras) and electric vehicles (e.g., hybrid electric vehicles (HEVs)).

[0129] Therefore, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the battery module are provided.

[0130] The battery module or battery pack can be used as a power source for at least one of the following medium to large-sized devices: power tools; electric vehicles (including electric vehicles (EVs), hybrid electric vehicles and plug-in hybrid electric vehicles (PHEVs)); or power storage systems.

[0131] The shape of the lithium secondary battery of the present invention is not particularly limited, but it can be cylindrical, prismatic, pouch or coin-shaped.

[0132] The lithium secondary battery according to the present invention can be used in battery cells as power sources for small devices, and is also preferably used as a cell in large and medium-sized battery modules comprising multiple battery cells.

[0133] In the following, embodiments of the invention will be described in detail in a manner readily apparent to those skilled in the art. However, the invention can be embodied in many different forms and is not limited to the embodiments set forth herein.

[0134] Examples and Comparative Examples

[0135] Example 1

[0136] Adding Ni 0.62 Co 0.06 Mn 0.32 (OH)2 represents a complex transition metal hydroxide (product name: nickel-cobalt-manganese hydroxide, D) 503.5 μm, BET: 15 m 2 / g, secondary particles) and Li2CO3 to make the molar ratio of (Ni+Co+Mn):Li 1:1.05, and add Y2O3 and ZrO2 so that the amounts of Y and Zr relative to Ni 0.62 Co 0.06 Mn 0.32 The total weights of (OH)₂ were 1500 ppm and 3000 ppm, respectively, and then calcined at 940 °C for 14 hours in an air atmosphere to prepare a product with LiNi 0.625 Co 0.06 Mn 0.311 Zr 0.003 Y 0.001 O2 represents a lithium complex transition metal oxide.

[0137] A positive electrode active material is prepared by mixing lithium composite transition metal oxide, Al₂O₃, and WO₃ and heat-treating at 500°C for 5 to 7 hours in air atmosphere, wherein an Al and W-containing coating is formed on the lithium composite transition metal oxide. In this case, Al₂O₃ is mixed to obtain a coating relative to LiNi. 0.625 Co 0.06 Mn 0.311 Zr 0.003 Y 0.001 The total weight of O2 is 1500 ppm of Al, and WO3 is mixed in to obtain a relative LiNi 0.625 Co 0.06 Mn 0.311 Zr 0.003 Y 0.001 The total weight of O2 is 3000 ppm (W). The coating includes Li-Al-O compounds, Li-WO compounds, and Li-Al-WO compounds.

[0138] Example 2

[0139] The positive electrode active material was prepared in the same manner as in Example 1, except that a material with Ni was used. 0.65 Co 0.05 Mn 0.30 (OH)2 represents a complex transition metal hydroxide (product name: nickel-cobalt-manganese hydroxide, D) 50 3.5 μm, BET: 15 m 2 / g, secondary particles) replaced by Ni 0.62 Co 0.06 Mn 0.32 (OH)2 represents a complex transition metal hydroxide.

[0140] Comparative Example 1

[0141] The positive electrode active material was prepared in the same manner as in Example 1, except that a material with Ni was used. 0.60 Co 0.05 Mn 0.35 (OH)2 represents a complex transition metal hydroxide (product name: nickel-cobalt-manganese hydroxide, D) 50 3.5 μm, BET: 15 m 2 / g, secondary particles) replaced by Ni 0.62 Co 0.06 Mn 0.32 (OH)2 represents a complex transition metal hydroxide.

[0142] Comparative Example 2

[0143] The lithium composite transition metal oxide of Example 1 was used as the positive electrode active material in Comparative Example 2.

[0144] Comparative Example 3

[0145] The positive electrode active material was prepared in the same manner as in Example 1, except that a material with Ni was used. 0.685 Co 0.095 Mn 0.220 (OH)2 represents a complex transition metal hydroxide (product name: nickel-cobalt-manganese hydroxide, D) 50 3.5 μm, BET: 15 m 2 / g, secondary particles) replaced by Ni 0.62 Co 0.06 Mn 0.32 (OH)2 represents a complex transition metal hydroxide.

[0146] Experimental Example

[0147] Experimental Example 1: Analysis of Lithium-Composite Transition Metal Oxides

[0148] - Composition of lithium complex transition metal oxides

[0149] The composition of the lithium composite transition metal oxides prepared in the above embodiments and comparative examples was confirmed by the following methods and is shown in Table 1 below.

[0150] 1 mL of hydrochloric acid was added to 0.1 g of each lithium complex transition metal oxide particle prepared in the examples and comparative examples, and the mixture was heated to dissolve the lithium complex transition metal oxide. Subsequently, a small amount of hydrogen peroxide was added to promote the reaction, and the lithium complex transition metal oxide was completely dissolved to prepare a solution. The solution was then diluted with deionized water to a total volume of 10 mL to prepare the analytical sample. The composition of the lithium complex transition metal oxide present in the above analytical samples was determined using ICP-OES (Aligent5100, Aligent), and the composition of the lithium complex transition metal oxide and the molar fraction difference (ac) of nickel and manganese are shown in Table 1 below.

[0151] [Table 1]

[0152] As shown in Table 1, the lithium composite transition metal oxides prepared in Examples 1 and 2 were determined to have compositions represented by Chemical Formula 1 as described herein. Furthermore, the difference in molar fractions of nickel and manganese (i.e., the difference (ac) between the molar fraction a of nickel (Ni) and the molar fraction c of manganese (Mn) in the lithium composite transition metal oxides (excluding lithium) as described herein) was determined to be between 0.25 and 0.45 in the lithium composite transition metal oxides prepared in Examples 1 and 2 and Comparative Examples 1 and 2. Meanwhile, in the lithium composite transition metal oxide prepared in Comparative Example 3, ac was determined to be greater than 0.45.

[0153] Experimental Example 2: Analysis of Positive Electrode Active Materials

[0154] - Content of coating element (M) in the coating

[0155] For the positive electrode active materials prepared in the examples and comparative examples, the contents of aluminum (Al) and tungsten (W) contained in the coating were determined by the following methods and are shown in Table 2 below.

[0156] 1 ml of hydrochloric acid was added to 0.1 g of each positive electrode active material particle prepared in the examples and comparative examples, and the mixture was heated to dissolve the positive electrode active material. Subsequently, a small amount of hydrogen peroxide was added to promote the reaction, and the positive electrode active material was completely dissolved to prepare a solution. The solution was then diluted with deionized water to a total volume of 10 mL to prepare the analytical sample. The content (ppm) of aluminum (Al) and tungsten (W) in the positive electrode active material coating present in the above analytical samples was determined using ICP-OES (Optima 7300DV, Perkin Elmer), and the results are shown in Table 2 below.

[0157] [Table 2]

[0158] As shown in Table 2, the total content of aluminum and tungsten (as coating elements in the positive electrode active material coatings prepared in Examples 1 and 2) was determined to be between 3000 ppm and 5500 ppm relative to the total weight of the lithium composite transition metal oxide.

[0159] Particle size and single-particle size formation degree of positive electrode active materials

[0160] The average particle size (D) of the positive electrode active materials prepared in the examples and comparative examples was measured using a PSA (S3500, Microtrac). 50 ), and is shown in Table 3 below.

[0161] Furthermore, SEM images (magnification: 5K) of the positive electrode active materials prepared in the Examples and Comparative Examples were obtained using SEM (FEI, Inspect F), and images of the primary particles present in the SEM images were obtained by dividing and randomly coloring them using an image processing program (LG Chem, DX program). Using the images of the primary particles divided and randomly colored, the area of ​​each primary particle was calculated based on the number of pixels corresponding to each of the n primary particles (at least 50,000 primary particles on average), and the average particle size (D') of the primary particles present in the lithium composite transition metal oxide prepared in Example 1 was measured using the diameter of a circle having the same area as each primary particle. 50 The results are shown in Table 3 below. In addition, the average particle size (D') of the primary particles was calculated. 50 ) relative to the average particle size (D) of lithium composite transition metal oxides 50 The values ​​of χ (single particle formation degree) are shown in Table 3 below.

[0162] [Table 3]

[0163] As shown in Table 3, the primary particles of the positive electrode active materials prepared in Examples 1 and 2 were determined to have an average particle size (D') of 2 μm to 5 μm. 50 Furthermore, the positive electrode active material has an average particle size of 3 μm to 5 μm (D). 50 Furthermore, according to Equation 1 described herein, the positive electrode active materials prepared in Examples 1 and 2 were determined to have a single particle formation degree (χ) greater than 0.5. For reference, it can be seen that, based on the fact that the single particle formation degree is 0.6 to 0.9, the positive electrode active materials prepared in Examples 1 and 2 are in the form of single particles that suppress aggregation between primary particles. Meanwhile, according to Equation 1 described herein, the positive electrode active material prepared in Comparative Example 1 was determined to have a single particle formation degree of less than 0.5.

[0164] Meanwhile, it can be seen that the coating is formed at the nanoscale, because the positive electrode active material prepared in Example 1 including the coating and the positive electrode active material prepared in Comparative Example 2 without the coating have almost the same average particle size (D') of the primary particles. 50 ) and the average particle size (D) of the positive electrode active material 50 ).

[0165] - Shape and coating of positive electrode active material

[0166] For the positive electrode active materials prepared in the examples and comparative examples, SEM images were obtained using a scanning electron microscope (SEM) at a magnification of 5 K. The SEM images of the positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 and 3 were obtained at... Figures 1 to 4 As shown in the figure. Furthermore, for the positive electrode active material prepared in Example 1, SEM images were obtained at magnifications of 20 K and 50 K, and these images were respectively... Figure 5 and 6 As shown in the image.

[0167] Figure 1 This is a SEM image (magnification: 5 K) of the positive electrode active material prepared in Example 1.

[0168] Figure 2 This is a SEM image (magnification: 5 K) of the positive electrode active material prepared in Example 2.

[0169] Figure 3 This is a SEM image (magnification: 5 K) of the positive electrode active material prepared in Comparative Example 1.

[0170] Figure 4 This is a SEM image (magnification: 5 K) of the positive electrode active material prepared in Comparative Example 3.

[0171] Figure 5 This is a SEM image (magnification: 20 K) of the positive electrode active material prepared in Example 1.

[0172] Figure 6 This is a SEM image (magnification: 50 K) of the positive electrode active material prepared in Example 1.

[0173] like Figures 1 to 4As shown, the positive electrode active materials prepared in Examples 1 and 2 according to the present invention were found to be in the form of single particles. The positive electrode active materials consist of a coating on a lithium composite transition metal oxide and a lithium composite transition metal oxide, and since the coating was determined to be formed at the nanoscale in the experimental examples, it can be seen that the lithium composite transition metal oxide prepared in Examples 1 and 2 is in the form of single particles. Furthermore, it was determined that the positive electrode active materials prepared in Examples 1 and 2 have fewer fine particles and a larger particle size compared to the positive electrode active material prepared in Comparative Example 1.

[0174] like Figure 5 and 6 As shown, the positive electrode active material prepared according to Embodiment 1 of the present invention comprises a coating containing coating elements in the form of an island on the positive electrode active material.

[0175] In summary, the average particle size (D') of the primary particles of the positive electrode active materials prepared in Examples 1 and 2 was determined. 50 The coating containing the coating element (M) is larger than the positive electrode active material prepared in Comparative Example 1, and is in the form of partially covering at least a portion of the lithium composite transition metal oxide.

[0176] Experimental Example 3: Evaluation of Battery Properties

[0177] - Manufacturing of coin-type half-cells

[0178] A positive electrode slurry was prepared by mixing 95 wt% of each of the positive electrode active materials prepared in the examples and comparative examples, 2.0 wt% of Super P as a conductive material, and 3.0 wt% of polyvinylidene fluoride (PVDF) as a binder in an N-methylpyrrolidone (NMP) solvent. The prepared positive electrode slurry was applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to prepare the positive electrode.

[0179] An electrode assembly was prepared by using a lithium metal electrode as the negative electrode and placing a porous polyethylene separator between the positive and negative electrodes. The electrode assembly was placed inside a battery casing and an electrolyte (in which 1 M LiPF6 was dissolved in an organic solvent in a volume ratio of 3:4:3 of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC)) was injected to manufacture a coin-shaped half-cell.

[0180] - Evaluation of battery capacity and cycle characteristics

[0181] The coin-shaped half-cell manufactured as described above was charged (0.1 C) to 4.45 V at 25°C in CC-CV mode, and then discharged (0.1 C) to 2.5 V in CC mode for the formation process.

[0182] A single cell is charged at 45°C in CC-CV mode (0.33 C) to 4.45 V, and then discharged in CC mode (0.33 C) to 2.5 V, which is considered as one cycle. This process is repeated for a total of 100 charge and discharge cycles. The discharge capacity of the first cycle and the 100th cycle are measured, and the percentage of the discharge capacity of the 100th cycle relative to the discharge capacity of the first cycle (capacity retention rate (%)) is shown in Table 4 below.

[0183] Furthermore, after measuring the DC internal resistance (DCIR) of the first cycle and the DC internal resistance (DCIR) of the 100th cycle, the percentage (resistance increase rate (%)) of the DCIR value of the 100th cycle relative to the DCIR value of the first cycle was calculated and is shown in Table 4 below. The DCIR value was calculated by dividing the difference between the voltage at 60 seconds and the initial voltage when discharging at a constant current of 0.33 C in each cycle by the applied current.

[0184] The cell was charged (0.1 C) to 4.45 V in CC-CV mode at 25°C, and then discharged (0.1 C) to 2.5 V in CC mode for the initial charge / discharge process, and the charge and discharge capacities were measured under these conditions. The measured charge and discharge capacities, as well as the percentage of discharge capacity relative to charge capacity (efficiency (%)), are shown in Table 4 below.

[0185] [Table 4]

[0186] As shown in Table 4, the battery containing the positive electrode active material prepared in Comparative Example 1 (wherein the degree of single particle formation according to Equation 1 described herein is 5 or less) exhibits high discharge capacity at high temperature during the first and 100th cycles, and high charge / discharge capacity and efficiency at room temperature, but shows low capacity retention and high resistance increase rate at high temperature. Meanwhile, the battery containing the positive electrode active material prepared in Comparative Example 2 without a coating on the lithium composite transition metal oxide exhibits low discharge capacity, capacity retention and efficiency at high temperature during the first and 100th cycles, and high resistance increase rate, as well as low charge / discharge capacity and efficiency at room temperature.

[0187] Furthermore, the battery containing the positive electrode active material prepared in Comparative Example 3 (where the lithium composite transition metal oxide does not have the composition represented by Chemical Formula 1 as described herein, specifically AC greater than 0.45) exhibits high charge / discharge capacity and capacity retention at high temperatures, but shows high-temperature DC internal resistance and high resistance increase rate and low charge / discharge efficiency at room temperature.

[0188] In contrast, batteries containing the positive electrode active materials prepared in Examples 1 and 2 (where the degree of single particle formation according to Equation 1 described herein is greater than 0.5) maintained the charge / discharge capacity at high temperatures and the charge / discharge capacity and efficiency at room temperature (the same level as the battery containing the positive electrode active material prepared in Comparative Example 1), but exhibited excellent capacity retention and resistance increase rate at high temperatures. Furthermore, Examples 1 and 2 included a coating of a coating element (M) on a lithium composite transition metal oxide, thus showing superior discharge capacity and capacity retention, efficiency, and resistance increase rate at high temperatures in the first and 100th cycles compared to the battery containing the positive electrode active material prepared in Comparative Example 2. Batteries containing the positive electrode active materials prepared in Examples 1 and 2 (having a composition represented by Chemical Formula 1 described herein) maintained a capacity retention rate similar to that of the battery manufactured in Comparative Example 3 at high temperatures, but exhibited excellent resistance and resistance increase rate at high temperatures, and excellent charge / discharge efficiency at room temperature.

[0189] In summary, the positive electrode active material according to the present invention has been found to maintain charge / discharge capacity and efficiency at equivalent levels at both high and room temperature, while also exhibiting excellent DC internal resistance and resistivity increase rate at high temperatures. Therefore, it can be seen that the positive electrode active material according to the present invention maintains energy density and remains stable even during charge / discharge cycles with virtually no structural changes.

Claims

1. A positive electrode active material, comprising: A lithium composite transition metal oxide in the form of a single particle formed from 10 or fewer primary particles, having a composition represented by the following Chemical Formula 1; and A coating containing a coating element (M) formed on the lithium composite transition metal oxide, Where the coating element (M) is at least one selected from Al, W, Cu, Zr, Ni, Co, Sr, Mn, Y, Ti, Mg, Mo, B, Sn, Fe, Zn, and Si, and The degree of single particle formation (χ) according to the following Equation 1 is greater than 0.5: [Chemical Formula 1] Li 1+x Ni a Co b Mr c M 1 d O2 Where in the above Chemical Formula 1, M 1 It is selected from at least one of Zr, Y, W, Cu, Sr, Mn, Ti, Mg, Mo, B, Sn, Fe, Zn, Si, and Al. x, a, b, c, and d satisfy -0.1 ≤ x ≤ 0.1, 0.6 ≤ a < 1, 0 < b < 0.4, 0 < c < 0.4, 0 ≤ d ≤ 0.1, a + b + c + d = 1, and 0.25 ≤ a - c ≤ 0.45, and [Equation 1] 。 2. The positive electrode active material according to claim 1, wherein, In the above Chemical Formula 1, a is 0.6 to 0.

75.

3. The positive electrode active material according to claim 1, wherein, In the above Chemical Formula 1, a - c satisfies 0.25 < a - c < 0.

34.

4. The positive electrode active material according to claim 1, wherein, The coating contains the coating element (M) in an amount of 3000 ppm to 5500 ppm relative to the total weight of the lithium composite transition metal oxide.

5. The positive electrode active material according to claim 1, wherein, The coating contains a Li - M - O compound, and M is at least one selected from Al, W, Cu, Zr, Ni, Co, Sr, Mn, Y, Ti, Mg, Mo, B, Sn, Fe, Zn, and Si.

6. The positive electrode active material according to claim 1, wherein, The coating element (M) is at least one selected from Al and W.

7. The positive electrode active material according to claim 1, wherein, The primary particles have an average particle size (D') of 2 μm to 5 μm. 50 ).

8. The positive electrode active material according to claim 1, wherein, The positive electrode active material has an average particle size of 3 μm to 5 μm (D). 50 ).

9. The positive electrode active material according to claim 1, wherein, The degree of single particle formation (χ) is 0.6 to 0.

9.

10. A method for preparing the positive electrode active material according to claim 1, the method comprising: (A) Mixing and firing a composite transition metal hydroxide and a lithium (Li) - containing raw material to prepare a lithium composite transition metal oxide; And (B) Mixing the lithium composite transition metal oxide and a raw material containing a coating element (M), and then subjecting the mixture to a heat treatment to form a coating, Where the firing is carried out at a temperature of 800°C to 1100°C, and The coating element (M) is at least one selected from Al, W, Cu, Zr, Ni, Co, Sr, Mn, Y, Ti, Mg, Mo, B, Sn, Fe, Zn, and Si.

11. The method according to claim 10, wherein, The raw material containing the coating element (M) is at least one selected from oxides, carbonates, nitrates, hydroxides, hydroxyoxides, and halides containing the coating element (M).

12. The method according to claim 10, wherein, Mixing the raw material containing the coating element (M) to obtain the coating element (M) in an amount of 3000 ppm to 5500 ppm relative to the total weight of the lithium composite transition metal oxide.

13. The method according to claim 10, wherein, The heat treatment is carried out at a temperature of 400°C to 600°C.

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

15. A lithium secondary battery comprising the positive electrode according to claim 14.

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