Positive electrode active material and method for manufacturing the same, positive electrode containing the same, and lithium secondary battery

Abstract

To provide a positive electrode active material containing lithium nickel manganese complex oxide, in which high-concentration aluminum coating with uniform thickness is achieved, the performance of a lithium secondary battery at high temperature and high voltage is improved, and a capacity characteristic, initial charging and discharging efficiency, and a high-temperature life characteristic are improved.SOLUTION: A positive electrode active material includes a core particle containing layered lithium nickel manganese complex oxide in which the nickel content per 100 mol% of the entire metal excluding lithium is 60 mol% or more, and a coating layer containing Al and existing on a surface of the core particle. The Al content per 100 at% of the total amount of Ni, Mn, and Al on a surface of the positive electrode active material is 20 at% to 33 at%. A manufacturing method for the positive electrode active material, a positive electrode including the positive electrode active material, and a lithium secondary battery are also provided.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a positive electrode active material, a method for producing the same, a positive electrode containing the same, and a lithium secondary battery. [Background technology]

[0002] Lithium-ion batteries, which have high energy density and are easily portable, are primarily used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, there has been active research into using high-energy-density lithium-ion batteries as power sources or energy storage sources for hybrid and electric vehicles.

[0003] To realize lithium secondary batteries that meet these applications, a variety of positive electrode active materials are being considered. Among them, lithium nickel oxides, lithium nickel manganese cobalt composite oxides, lithium nickel cobalt aluminum composite oxides, and lithium cobalt oxides are mainly used as positive electrode active materials. However, recently, while the demand for large, high-capacity, or high-energy-density lithium secondary batteries has been rapidly increasing, the supply of positive electrode active materials containing cobalt, a rare metal, is expected to be extremely insufficient. In other words, since cobalt is expensive and the remaining reserves are not large, there is a need to develop positive electrode active materials that exclude cobalt or reduce its cobalt content. [Overview of the project] [Problems that the invention aims to solve]

[0004] A positive electrode active material containing a lithium nickel-manganese composite oxide, which achieves a uniform thickness and high-concentration aluminum coating, thereby improving the high-temperature and high-voltage performance of lithium secondary batteries and enhancing capacity characteristics, initial charge-discharge efficiency, and high-temperature life characteristics. [Means for solving the problem]

[0005] In one embodiment, a positive electrode active material is provided which includes core particles containing a layered lithium nickel-manganese composite oxide in which the nickel content is 60 mol% or more relative to 100 mol% of the total metal excluding lithium, and a coating layer containing Al located on the surface of the core particles, wherein the Al content on the surface of the positive electrode active material is 20 at% to 33 at% relative to 100 at% of the total amount of Ni, Mn, and Al.

[0006] In another embodiment, a method for producing a positive electrode active material is provided, which includes (i) preparing core particles containing a layered lithium nickel-manganese composite oxide in which the nickel content is 60 mol% or more relative to 100 mol% of the total metal excluding lithium; (ii) adding aluminum sulfate and the core particles to an aqueous solvent and mixing to produce a mixed solution; and (iii) drying the obtained material after removing the aqueous solvent from the mixed solution and heat-treating it at a temperature range of 730°C to 800°C to obtain a positive electrode active material.

[0007] In another embodiment, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, wherein the positive electrode active material layer provides a positive electrode containing the aforementioned positive electrode active material.

[0008] In another embodiment, a lithium secondary battery comprising the positive electrode, negative electrode, and electrolyte is provided. [Effects of the Invention]

[0009] One embodiment of the positive electrode active material minimizes production costs while maximizing capacity, ensuring long-life characteristics, and improving high-voltage and high-temperature storage characteristics. A lithium secondary battery using this positive electrode active material can exhibit high initial charge / discharge capacity and efficiency even under high-voltage driving conditions, achieve long-life characteristics, and effectively suppress gas generation problems caused by high-voltage and high-temperature operation. [Brief explanation of the drawing]

[0010] [Figure 1]It is a cross-sectional view schematically showing a lithium secondary battery according to an embodiment. [Figure 2] It is a cross-sectional view schematically showing a lithium secondary battery according to an embodiment. [Figure 3] It is a cross-sectional view schematically showing a lithium secondary battery according to an embodiment. [Figure 4] It is a cross-sectional view schematically showing a lithium secondary battery according to an embodiment. [Figure 5] It is a scanning electron microscope (SEM) image of the surface of the positive electrode active material of Comparative Example 1. [Figure 6] It is a SEM image of the surface of the positive electrode active material of Example 1. [Figure 7] It is a SEM image of the surface of the positive electrode active material of Example 2. [Figure 8] It is a SEM image of the surface of the positive electrode active material of Example 3. [Figure 9] It is a SEM image of the surface of the positive electrode active material of Example 4. [Figure 10] It is a SEM image of the surface of the positive electrode active material of Comparative Example 4. [Figure 11] It is a SEM image of the cross-section obtained by cutting the positive electrode active material of Comparative Example 1 with a focused ion beam (FIB). [Figure 12] It is an energy-dispersive spectroscopic analysis (EDS) analysis image highlighting the Al element in FIG. 11. [Figure 13] It is a SEM image of the cross-section obtained by cutting the positive electrode active material of Example 1 with FIB. [Figure 14] It is an EDS analysis image highlighting the Al element in FIG. 13. [Figure 15] It is the EP-EDS analysis results for the positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 4, and is a graph showing the ratio (Al / (Ni + Mn + Al)) of the content (at%) of Al to the total amount of 100 at% of Ni, Mn, and Al on the surface of the secondary particles. [Figure 16]This is a transmission electron microscope (TEM) image showing a magnified cross-section of a primary particle located on the outermost side of the secondary particles in the positive electrode active material produced in Example 1. [Figure 17] Figure 16 shows the results of EDS line profile analysis performed on the particle surface in the direction of the particle's interior. [Modes for carrying out the invention]

[0011] The following describes specific embodiments in detail so that they can be easily implemented by a person with ordinary skill in the art. However, the present invention can be implemented in a variety of different forms and is not limited to the embodiments described herein.

[0012] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0013] Here, "these combinations" refers to mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, etc.

[0014] Here, terms such as “include,” “equip,” or “possess” are intended to specify the existence of the implemented features, figures, stages, components, or combinations thereof, and should be understood not to preemptively exclude the existence or possibility of adding one or more other features, figures, stages, components, or combinations thereof.

[0015] In the drawings, thicknesses are shown enlarged to clearly represent multiple layers and regions, and similar parts are denoted by the same reference numerals throughout the specification. When a layer, film, region, plate, or other part is said to be "on top" of another part, this includes not only when it is "directly above" another part, but also when there is another part in between. Conversely, when one part is said to be "directly above" another part, it means that there is no other part in between.

[0016] Furthermore, the term "layer" here includes not only the shapes formed on the entire surface when observed in a plan view, but also the shapes formed on some of the surfaces.

[0017] The average particle size can be measured by methods widely known to those skilled in the art, for example, by a particle size analyzer, or by transmission electron microscope images or scanning electron microscope images. Alternatively, it can be measured using dynamic light scattering, and after performing data analysis to count the number of particles for each particle size range, the average particle size value can be calculated based on this. Unless otherwise defined, the average particle size is the diameter (D) of the particle whose cumulative volume in the particle size distribution is 50% by volume. 50 ) may mean. Also, unless otherwise defined, the average particle size is obtained by measuring the size (diameter or length of the long axis) of more than 20 randomly selected particles in a scanning electron microscope image to obtain a particle size distribution, and from the said particle size distribution, the diameter (D) of the particle whose cumulative volume is 50% by volume. 50 This could be the average particle size taken from ).

[0018] Here, "or" is not interpreted as having an exclusive meaning; for example, "A or B" is interpreted as including A, B, A+B, etc.

[0019] The term "metal" is interpreted as a concept that includes general metals, transition metals, and metalloids (semimetallics).

[0020] positive electrode active material In one embodiment, a positive electrode active material is provided that includes core particles containing a layered lithium nickel-manganese composite oxide in which the nickel content is 60 mol% or more relative to 100 mol% of the total metal excluding lithium, and a coating layer containing Al located on the surface of the core particles. The positive electrode active material is characterized in that the Al content relative to 100 at% of the total amount of Ni, Mn, and Al on its surface is 20 at% to 33 at%.

[0021] The Al content on the surface of the positive electrode active material may be measured by energy profiling energy dispersive spectroscopy (EP-EDS).

[0022] Recently, with the sharp rise in the price of cobalt, a rare metal, there has been a demand for the development of cathode active materials that exclude cobalt or reduce its content. Among these, cathode active materials with olivine-based crystal structures such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), and lithium iron manganese phosphate (LMFP), or spinel crystal structures such as lithium manganese oxide (LMO), have limitations in achieving high capacity because the amount of lithium that can be utilized within the structure is small. Layered nickel-manganese cathode active materials can have a high lithium content within the structure, making them suitable as materials for high-capacity batteries with excellent capacity and efficiency characteristics. However, removing cobalt, which plays a key role in the layered structure, leads to a decrease in structural stability, an increase in resistance, and difficulty in ensuring long life characteristics. Furthermore, excluding cobalt accelerates side reactions between the cathode active material and electrolyte under high voltage and high temperature conditions, increasing gas generation and reducing life characteristics.

[0023] In one embodiment, the surface of the lithium nickel-manganese cathode active material is uniformly coated with aluminum. By optimizing the Al concentration on the surface, the particle surface can be strengthened, maintaining a stable structure even at high voltages, thereby achieving high capacity, long lifespan, and improved high-temperature storage characteristics.

[0024] When coating the secondary particle surface of a positive electrode active material containing a lithium nickel-manganese composite oxide with aluminum to strengthen it, it is not easy to uniformly coat the secondary particle surface with a high concentration of aluminum in a shell form because aluminum tends to diffuse into the interior of the secondary particle. In one embodiment, we propose a coating method best suited to the properties of the lithium nickel-manganese composite oxide, and also propose conditions under which a high concentration of Al can be coated on the secondary particle surface in a thin and uniform thickness without increasing resistance. The resulting Al concentration on the secondary particle surface, i.e., the Al / (Ni+Mn+Al) ratio, is confirmed to be 20at% to 33at%, and we propose a method that can actually achieve such a concentration. A lithium secondary battery using the positive electrode active material according to one embodiment shows improved initial charge / discharge capacity and efficiency under high voltage conditions, as well as improved high-temperature life characteristics and high-temperature storage characteristics.

[0025] core particle The core particles contain a lithium nickel-manganese composite oxide. The nickel content is 60 mol% or more relative to 100 mol% of the total metal excluding lithium in the lithium nickel-manganese composite oxide, and can be, for example, 60 mol% to 80 mol%, 65 mol% to 80 mol%, 70 mol% to 80 mol%, 60 mol% to 79 mol%, 60 mol% to 78 mol%, or 60 mol% to 75 mol%. When the nickel content meets the above range, high capacity can be achieved, and structural safety can be improved even if the cobalt content is reduced.

[0026] The manganese content can be, for example, 15 mol% or more relative to 100 mol% of the total metal excluding lithium in a lithium nickel-manganese composite oxide, and may be, for example, 15 mol% to 40 mol%, 15 mol% to 35 mol%, 15 mol% to 30 mol%, or 20 mol% to 30%. When the manganese content satisfies the above range, the positive electrode active material can achieve high capacity while improving structural stability.

[0027] A lithium nickel-manganese composite oxide may, as an example, be a lithium nickel-manganese-aluminum composite oxide that further contains aluminum in addition to nickel and manganese. When aluminum is contained in the composite oxide, it is advantageous in maintaining a stable layered structure even if the cobalt element is removed from the structure. The aluminum content per 100 mol% of the lithium nickel-manganese-aluminum composite oxide may be 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more, for example, 1 mol% to 3 mol%, 1 mol% to 2.5 mol%, 1 mol% to 2 mol%, or 1.5 mol% to 2.5 mol%. When the aluminum content satisfies the above range, a stable layered structure can be maintained even if cobalt is removed, the problem of structural collapse due to charging and discharging can be suppressed, and the long-life characteristics of the positive electrode active material can be realized.

[0028] According to one embodiment, the concentration of aluminum within the core particles can be uniform. That is, the aluminum concentration within the core particles has a concentration gradient from the center to the surface, or the aluminum concentration within the core particles is neither higher nor lower than the aluminum concentration outside the core particles, meaning that the aluminum is uniformly dispersed within the core particles. This structure can be said to be obtained by synthesizing a composite oxide using nickel-manganese-aluminum hydroxide as a precursor by using aluminum raw materials during the precursor production process, without additional aluminum doping during the core particle synthesis process. The core particles may be in the form of secondary particles formed by the aggregation of multiple primary particles, but the aluminum content inside the primary particles can be said to be the same or similar regardless of the position of the primary particles. In other words, if a primary particle is selected at any position in the cross-section of the secondary particle and the aluminum content is measured inside the primary particle rather than at the interface, it can be said that the aluminum content is the same / similar / uniform regardless of the position of the primary particle, i.e., whether the primary particle is close to the center or the surface of the secondary particle. In such a structure, a stable layered structure can be maintained even if cobalt is absent or present in very small amounts, and since no aluminum by-products or aluminum aggregates are generated, the capacity, efficiency, and lifetime characteristics of the positive electrode active material can be improved simultaneously.

[0029] The lithium nickel-manganese composite oxide can be specifically represented by the following Chemical Formula 1. [Chemical Formula 1] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1

[0030] In Chemical Formula 1, 0.9 ≦ a1 ≦ 1.8, 0.6 ≦ x1 ≦ 0.8, 0.1 ≦ y1 ≦ 0.4, 0 ≦ z1 ≦ 0.03, 0 ≦ w1 ≦ 0.3, 0.9 ≦ x1 + y1 + z1 + w1 ≦ 1.1, and 0 ≦ b1 ≦ 0.1, and M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, and Zr, and X is one or more elements selected from F, P, and S.

[0031] In Chemical Formula 1, 0.9 ≦ a1 ≦ 1.5, or 0.9 ≦ a1 ≦ 1.2 may hold. Also, Chemical Formula 1 may contain aluminum, and in this case, 0.6 ≦ x1 ≦ 0.8, 0.1 ≦ y1 ≦ 0.39, 0.01 ≦ z1 ≦ 0.03, and 0 ≦ w1 ≦ 0.29 can be satisfied, for example, 0.6 ≦ x1 ≦ 0.8, 0.1 ≦ y1 ≦ 0.39, 0.01 < z1 ≦ 0.03, and 0 ≦ w1 ≦ 0.29 can be satisfied.

[0032] In Chemical Formula 1, for example, 0.6 ≦ x1 ≦ 0.79, 0.6 ≦ x1 ≦ 0.78, 0.6 ≦ x1 ≦ 0.75, 0.65 ≦ x1 ≦ 0.8, or 0.7 ≦ x1 ≦ 0.79 may hold, 0.1 ≦ y1 ≦ 0.35, 0.1 ≦ y1 ≦ 0.30, 0.1 ≦ y1 ≦ 0.29, 0.15 ≦ y1 ≦ 0.39, or 0.2 ≦ y1 ≦ 0.3 may hold, 0.01 ≦ z1 ≦ 0.025, 0.01 < z1 ≦ 0.02, or 0.01 < z1 ≦ 0.019 may hold, 0 ≦ w1 ≦ 0.28, 0 ≦ w1 ≦ 0.27, 0 ≦ w1 ≦ 0.26, 0 ≦ w1 ≦ 0.25, 0 ≦ w1 ≦ 0.24, 0 ≦ w1 ≦ 0.23, or 0 ≦ w1 ≦ 0.22, 0 ≦ w1 ≦ 0.21, 0 ≦ w1 ≦ 0.2, 0 ≦ w1 ≦ 0.15, 0 ≦ w1 ≦ 0.1, or 0 ≦ w1 ≦ 0.09, etc. may hold.

[0033] As an example, the lithium nickel-manganese composite oxide may contain no cobalt or a small amount of cobalt, and the content of cobalt based on 100 mol% of the total metal excluding lithium may be 0 mol% to 0.01 mol%.

[0034] The core particles may be in the form of secondary particles formed by aggregation of a plurality of primary particles. The secondary particles may be spherical, ellipsoidal, polyhedral, or irregular in shape, and the primary particles may be spherical, ellipsoidal, plate-like, or a combination thereof.

[0035] Since the core particles are likely to be chemically attacked by components in the electrolyte during battery operation under high voltage or high temperature conditions, there may be many side reactions with the electrolyte, resulting in a large amount of gas generation and problems such as reduced battery life and safety. However, by introducing a coating layer according to an embodiment described later, such problems can be solved.

[0036] coating layer One embodiment of the positive electrode active material includes an Al-rich coating layer located on the surface of the core particles. The Al content, measured on the particle surface of the positive electrode active material, is characterized by being 20 at% to 33 at% relative to the total amount of Ni, Mn, and Al (100 at%). The positive electrode active material particles may be secondary particles formed by the aggregation of multiple primary particles, in which case the Al content can be measured on the surface of the secondary particles.

[0037] The Al content on the surface of the positive electrode active material particles, i.e., Al / (Ni+Mn+Al), can be, for example, 21 at% to 32 at% or 22 at% to 31.5 at%. The content of each element and the Al content on the surface of the positive electrode active material particles can be measured using EP-EDS.

[0038] The Al content of the coating layer relative to 100 mol% of the total metal in the positive electrode active material excluding lithium can be between 0.5 mol% and 1.5 mol%, for example, between 0.6 mol% and 1.4 mol%, between 0.7 mol% and 1.3 mol%, or between 0.8 mol% and 1.2 mol%. This refers only to the aluminum content in the coating layer, separate from the aluminum contained in the core particles. The Al content of the coating layer in the entire positive electrode active material can be measured, for example, by SEM-EDS analysis of the surface or cross-section of the positive electrode active material. When the aluminum content in the coating layer meets the above range, it is possible to form a thin and uniform thickness coating layer, which does not increase the resistance of the positive electrode active material and effectively suppresses side reactions with the electrolyte, thereby improving the life characteristics of lithium secondary batteries under high voltage and high temperature conditions. For example, if the aluminum content of the coating layer is excessively high, a uniform coating layer may not be formed, or resistance may increase, leading to a decrease in charge-discharge efficiency and lifespan characteristics. Conversely, if the aluminum content of the coating layer is excessively low, a coating layer of appropriate thickness may not be formed, which may reduce the effect of suppressing side reactions with the electrolyte.

[0039] One embodiment may involve adjusting the Al content of the coating layer to 0.5 mol% to 1.5 mol% relative to 100 mol% of the total metal excluding lithium in the positive electrode active material, while simultaneously adjusting the coating method and conditions to ensure that the Al / (Ni+Mn+Al) ratio on the positive electrode active material surface satisfies 20 at% to 33 at%. Such an Al coating layer can improve the structural stability of the lithium nickel-manganese composite oxide and enhance its high-voltage characteristics.

[0040] In one embodiment, the coating layer may be in the form of a film that continuously surrounds the surface of the core particles, or it may be in the form of a shell that surrounds the entire surface of the core particles. This is distinct from a structure in which only a part of the surface of the core particles is partially coated. According to one embodiment, the coating layer can be formed to surround the entire surface of the core particles while being very thin and uniform in thickness. As a result, the positive electrode active material can have improved structural stability without an increase in resistance or a decrease in capacity, side reactions with the electrolyte can be effectively suppressed, gas generation at high voltage and high temperature conditions can be reduced, and long-life characteristics can be achieved.

[0041] The thickness of the coating layer can be 5 nm to 200 nm, for example, 5 nm to 150 nm, 5 nm to 100 nm, 5 nm to 80 nm, 5 nm to 50 nm, or 10 nm to 50 nm. When the coating layer meets the aforementioned thickness range, the coating can improve the structural stability of the positive electrode active material without increasing resistance or decreasing capacitance, and effectively suppress side reactions with the electrolyte. The thickness of the coating layer can be measured by methods such as SEM, TEM, TOF-SIMS, XPS, or EDS analysis, and as an example, it can be measured by EDS line profile analysis of the cross-section of the positive electrode active material.

[0042] One embodiment of the coating layer is characterized by its thinness, being at the level of tens to hundreds of nanometers, yet having a uniform thickness. For example, the thickness deviation of the coating layer within a single positive electrode active material particle may be 20% or less, 18% or less, or 15% or less. Here, the thickness deviation of the coating layer refers to the thickness of the coating layer within a single positive electrode active material particle. The thickness deviation of the coating layer may mean, for example, the arithmetic mean obtained by measuring the thickness at more than 10 points in an electron microscope image of the cross-section of a single positive electrode active material particle, calculating the arithmetic mean, and then dividing the absolute value of the difference between one data point and the arithmetic mean by the arithmetic mean and multiplying by 100. When the thickness deviation or standard deviation of the coating layer satisfies the above range, it means that a coating layer of uniform thickness is formed in a good form on the surface of the positive electrode active material particle, thereby improving the structural stability of the positive electrode active material, effectively suppressing side reactions with the electrolyte, and minimizing resistance increase and capacity decrease due to the coating.

[0043] The coating layer may include, for example, a layered aluminum compound, such as aluminum oxide, lithium-aluminum oxide, or a combination thereof, and LiAlO2 may be included as an example.

[0044] The coating layer may also contain nickel, manganese, or a combination thereof, in addition to aluminum.

[0045] Average particle size of positive electrode active material according to one embodiment (D 50 The particle size is not particularly limited, but may be, for example, 1 μm to 25 μm, 5 μm to 25 μm, 10 μm to 25 μm, 11 μm to 20 μm, or 12 μm to 18 μm. The average particle size is obtained by measuring the size (diameter or length of the long axis) of more than 20 random particles from scanning electron microscope images of the positive electrode active material to obtain a particle size distribution, and the diameter (D) of the particle whose cumulative volume is 50 volume% is obtained from the particle size distribution. 50This may be taken as the average particle size. When the average particle size of the positive electrode active material satisfies the above range, high capacity and long life can be achieved, which may be advantageous for forming a coating layer according to one embodiment.

[0046] Furthermore, the positive electrode active material according to one embodiment may be characterized by not containing sodium. Generally, sodium ions may be used in the manufacturing process of positive electrode active materials, but according to the manufacturing method described later, it is possible to form core particles with a stable structure and a coating layer of uniform thickness without using sodium ions.

[0047] Method for manufacturing positive electrode active material In one embodiment, a method for producing a positive electrode active material is provided, which includes (i) preparing core particles containing a layered lithium nickel-manganese composite oxide in which the nickel content is 60 mol% or more relative to 100 mol% of the total metal excluding lithium; (ii) adding aluminum sulfate and the core particles to an aqueous solvent and mixing to produce a mixed solution; and (iii) drying the obtained material after removing the aqueous solvent from the mixed solution and heat-treating it in a temperature range of 730°C to 800°C to obtain a positive electrode active material. The positive electrode active material described above can be produced by this method.

[0048] In step (i) above, a layered lithium nickel-manganese composite oxide can be produced, for example, by mixing a lithium nickel-manganese hydroxide with a lithium raw material and performing a first heat treatment. The nickel-manganese composite hydroxide is a precursor of core particles and may be in the form of secondary particles in which multiple primary particles are aggregated. Nickel-manganese-aluminum composite hydroxides can be produced by a general coprecipitation method.

[0049] In nickel-manganese composite hydroxides, the nickel content must be 60 mol% or more relative to 100 mol% of the total metal, and may be, for example, 60 mol% to 80 mol%, 65 mol% to 80 mol%, 70 mol% to 80 mol%, 60 mol% to 79 mol%, 60 mol% to 78 mol%, or 60 mol% to 75 mol%. When the nickel content meets the above range, high capacity can be achieved, and structural safety can be improved even if the cobalt content is reduced.

[0050] In nickel-manganese composite hydroxides, the manganese content can be 15 mol% or more relative to 100 mol% of the total metal, for example, 15 mol% to 40 mol%, 15 mol% to 39 mol%, 15 mol% to 35 mol%, 15 mol% to 30 mol%, 20 mol% to 30%, etc.

[0051] Furthermore, if the nickel-manganese composite hydroxide also contains aluminum, the aluminum content may be 0.1 mol% or more, 0.5 mol% or more, or 1 mol% or more relative to 100 mol% of the total metal, for example, 1 mol% to 3 mol%, 1 mol% to 2.5 mol%, 1 mol% to 2 mol%, or 1 mol% to 1.9 mol%. When the manganese and aluminum content of the composite hydroxide each meets the above ranges, it is possible to improve the structural safety of the positive electrode active material while achieving high capacity, thereby lowering production costs and improving economic efficiency.

[0052] One embodiment of the method for producing a positive electrode active material may involve using a nickel-manganese-aluminum composite hydroxide as a precursor, in which aluminum is uniformly dispersed within the structure, by using an aluminum raw material during the precursor production process without additional aluminum doping during the production of core particles. When such a precursor is used, a positive electrode active material can be produced in which the layered structure is stably maintained even after repeated charge-discharge cycles, even without cobalt. Furthermore, since no aluminum by-products or aluminum aggregates are formed, the capacity, efficiency, and lifespan characteristics of the positive electrode active material can be improved.

[0053] Nickel-manganese composite hydroxides may contain cobalt at levels of 0.01 mol%, 0.005 mol%, or 0.001 mol% or less relative to 100 mol% of the total metal content. Such nickel-manganese composite hydroxides are economical because they avoid the cost increase associated with cobalt, and they offer maximized capacity and improved structural stability.

[0054] Nickel-manganese composite hydroxides can be represented, for example, by the following chemical formula 2. [Chemical formula 2] Ni x2 Mn y2 Al z2 M 2 w2 (OH)2

[0055] In chemical formula 2, 0.6 ≤ x² ≤ 0.8, 0.1 ≤ y² ≤ 0.40 ≤ z² ≤ 0.03, 0 ≤ w² ≤ 0.3, and 0.9 ≤ x² + y² + z² + w² ≤ 1.1, and M 2 is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, and Zr.

[0056] In the aforementioned chemical formula 2, for example, 6≦x2≦0.8, 0.1≦y2≦0.39, 0.01≦z2≦0.03, and 0≦w2≦0.29 are possible.

[0057] Nickel-manganese composite hydroxides are in particulate form, and their average particle size (D 50 ) can be 1 μm to 25 μm, 5 μm to 20 μm, 10 μm to 20 μm, 11 μm to 18 μm, or 12 μm to 15 μm.

[0058] The nickel-manganese composite hydroxide and lithium raw materials can be mixed in a molar ratio of 1:0.9 to 1:1.8, for example, in a molar ratio of 1:0.9 to 1:1.5 or 1:0.9 to 1:1.2. The first heat treatment can be carried out in an oxygen atmosphere, for example, in a temperature range of 750°C to 950°C, or 780°C to 900°C, or 810°C to 890°C, for 2 to 20 hours, or 4 to 12 hours. Through the heat treatment, a lithium nickel-manganese composite oxide can be obtained. The obtained composite oxide is substantially identical to the description with respect to the core particles in the positive electrode active material portion.

[0059] Layered lithium nickel-manganese composite oxides differ considerably from oxides of other compositions, such as lithium nickel-cobalt-manganese composite oxides, lithium nickel-cobalt-aluminum composite oxides, and lithium cobalt oxides, in terms of residual lithium content on the particle surface. As a result, many surface properties differ, making it impossible to form a good coating layer with a uniform film morphology using existing coating methods. In one embodiment, we propose a method that allows for coating the particle surface of layered lithium nickel-manganese composite oxides with a high concentration of Al to achieve a very uniform thickness.

[0060] In step (ii) above, the aqueous solvent may include distilled water, an alcoholic solvent, or a combination thereof.

[0061] Aluminum sulfate can be considered an optimal raw material for forming a coating layer according to one embodiment. The Al content in the aluminum sulfate can be designed to be 0.5 mol% to 1.5 mol% relative to 100 mol% of the total metal excluding lithium in the final cathode active material, for example, 0.6 mol% to 1.4 mol%, 0.7 mol% to 1.3 mol%, or 0.8 mol% to 1.2 mol%. By designing the Al coating content within the above range, a thin and uniform coating layer with a thickness of tens to hundreds of nanometers can be formed, reducing gas generation in lithium secondary batteries under high voltage or high temperature operating conditions and improving high capacity and long life characteristics.

[0062] In one embodiment, the core particles may be added to the aqueous solvent and mixed, and then aluminum sulfate may be added to produce a mixed solution. This is a wet coating method and can also be described as a post-addition method in which the coating material is added after the core particles are added.

[0063] In another embodiment, a coating solution may be prepared first by adding and mixing aluminum sulfate in an aqueous solvent, and then core particles may be added to this coating solution and mixed to produce a mixed solution. This can be described as a salt-dissolution wet coating method, as well as a pre-addition method in which the salt, which is the coating raw material, is completely dissolved first before the core particles are added.

[0064] In the pre-addition method, the aluminum sulfate is added to the aqueous solvent and mixed for approximately 1 to 60 minutes, for example, 3 to 30 minutes or 5 to 10 minutes. The mixing speed can be 100 rpm to 800 rpm, for example, 200 rpm to 600 rpm or 250 rpm to 500 rpm. Through these mixing conditions, the aluminum sulfate is completely dissolved in the aqueous solvent to produce a colorless and transparent coating solution, and by using such a coating solution, a uniform aluminum coating layer according to one embodiment can be effectively formed. The pH of the completed coating solution can be, for example, 1.5 to 3.5, for example, 2.0 to 3.4, 2.5 to 3.3, 2.7 to 3.3, or 2.9 to 3.2.

[0065] The core particles are added to the manufactured coating solution, and the coating quality can be improved by adding the core particles while the coating solution is being stirred.

[0066] The time required to add core particles to the coating solution can range from 30 seconds / 500g to 2 minutes / 500g, for example, 30 seconds / 500g to 1.5 minutes / 500g. By appropriately adjusting the rate at which the core particles are added, the pH of the supernatant after coating can be appropriately adjusted, thereby effectively guiding the formation of a uniform Al coating layer according to one embodiment. If the rate at which the core particles are added is excessively fast, the pH of the supernatant after coating may become high and basic, which may prevent the formation of a uniform coating layer. Conversely, if the rate at which the core particles are added is excessively slow, the pH of the supernatant may become low and highly acidic, which may also prevent the formation of a uniform coating layer.

[0067] The stirring time after adding all the core particles to the coating solution can be approximately 15 to 60 minutes, for example, 20 to 50 minutes or 30 to 45 minutes. The time from the start of adding the core particles to the coating solution to the completion of stirring, i.e., the coating reaction time, can be appropriately adjusted to approximately 1 hour or less.

[0068] In one embodiment, when the core particles are added to the coating solution and mixing is stopped, that is, when mixing or coating is completed, the pH range of the supernatant liquid may be 5.5 to 7.5. If the pH of the supernatant liquid is less than 5.5, it may become too acidic and a uniform coating layer may not be formed, and if the pH is greater than 7.5, it may become too basic, making it difficult to form a uniform Al coating layer in this case as well.

[0069] In step (iii) above, after removing the aqueous solvent with the mixed solution, the resulting product can be dried at, for example, 40°C to 240°C, 100°C to 220°C, or 150°C to 200°C, and may be carried out under vacuum conditions as an example. Good coated products can be obtained under such conditions.

[0070] The material obtained after removing the aqueous solvent with a mixed solution and then drying can be referred to as a coated product. The coated product comprises core particles and an Al-containing coating layer located on the surface of the core particles. For example, the Al-containing coating layer may have a fibrous structure, such as a mesh or spiderweb structure. Such a mesh can be formed continuously across the entire surface of the core particles. The mesh-shaped coating layer can surround the core particles with a very thin and uniform thickness, thereby strengthening the surface of the positive electrode active material and improving structural stability, thereby improving high-temperature and high-voltage characteristics.

[0071] If the process of mixing nickel-manganese composite hydroxide and lithium raw material and heat-treating them is referred to as the first heat treatment, then the heat treatment of the coated product can be referred to as the second heat treatment.

[0072] One embodiment is characterized by setting the temperature range of the second heat treatment to 730°C to 800°C. The temperature range of the second heat treatment may be, for example, 740°C to 800°C, 750°C to 800°C, 750°C to 780°C, or 750°C to 775°C. When the second heat treatment temperature is set to the above range, the tendency of aluminum to diffuse into the interior of secondary particles is reduced, and it mainly remains on the surface of the secondary particles, and at the same time, it can be coated on the surface of the secondary particles in the form of a very thin and uniform shell. When controlled within the above heat treatment range, the Al content ratio on the surface of the secondary particles, i.e., Al / (Ni+Mn+Al), can be controlled to 20at% to 33at%.

[0073] If the second heat treatment temperature exceeds 800°C, the tendency for aluminum to diffuse into the secondary particles increases, making it difficult to form a high-concentration Al-rich coating layer on the surface. This can lead to a decrease in initial charge / discharge capacity and efficiency characteristics at high voltages, a decrease in lifespan characteristics at high voltages and high temperatures, and an increase in gas generation during high-temperature storage. If the second heat treatment temperature is below 730°C, the tendency for aluminum to diffuse into the secondary particles can be reduced, but the aluminum may partially aggregate or become unevenly distributed on the surface of the secondary particles. This can lead to a decrease in lifespan characteristics under high-temperature and high-voltage conditions, and an increase in gas generation during high-temperature storage.

[0074] The second heat treatment can be carried out, for example, in an oxygen atmosphere, for 2 to 20 hours, or 3 to 10 hours.

[0075] The obtained positive electrode active material can be described as containing core particles with a layered lithium nickel-manganese composite oxide in which the nickel content is 60 mol% or more relative to 100 mol% of the total metal excluding lithium, and a coating layer located on the surface of the core particles that contains aluminum oxide, lithium-aluminum oxide, or a combination thereof.

[0076] positive electrode In one embodiment, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, wherein the positive electrode active material layer provides a positive electrode containing the aforementioned positive electrode active material. The positive electrode active material layer may further contain other types of positive electrode active materials in addition to the aforementioned positive electrode active material. The positive electrode active material layer may also selectively further contain a binder, a conductive agent, or a combination thereof.

[0077] According to one embodiment, the loading level of the positive electrode active material layer is 10 mg / cm³. 2 ~40 mg / cm³ 2 It could be, for example, 10 mg / cm³ 2 ~30 mg / cm³ 2 or 10 mg / cm³ 2 ~20 mg / cm³ 2 This is possible. Furthermore, the density of the positive electrode active material layer in the rolled final positive electrode can be 3.3 g / cc to 3.7 g / cc, for example, 3.3 g / cc to 3.6 g / cc or 3.4 g / cc to 3.58 g / cc. When applying the positive electrode active material according to one embodiment, it is advantageous to achieve such loading levels and positive electrode densities, and a positive electrode that satisfies the above range of loading levels and positive electrode densities is suitable for realizing high-capacity, high-energy-density lithium secondary batteries.

[0078] binder The binder plays a role in ensuring good adhesion between positive electrode active material particles and good adhesion of the positive electrode active material to the current collector. Typical examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylicated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0079] conductive agent Conductive agents are used to impart conductivity to electrodes, and any electronically conductive material that does not undergo chemical changes in the battery that is constructed can be used. Examples of conductive agents include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0080] The binder and conductive agent content may be 0.5% to 5% by weight, respectively, based on 100% by weight of the positive electrode active material layer.

[0081] Al can be used as the positive electrode current collector, but it is not limited to this.

[0082] Lithium-ion battery In one embodiment, a lithium secondary battery is provided that includes the positive electrode, negative electrode, and electrolyte described above. As an example, the lithium secondary battery may include a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte.

[0083] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch-type, coin-type, and other types depending on their form. Figures 1 to 4 are schematic diagrams showing a lithium secondary battery according to one embodiment; Figure 1 is a circular type, Figure 2 is a prismatic type, and Figures 3 and 4 are pouch-type batteries. Referring to Figures 1 to 4, the lithium secondary battery 100 can include an electrode assembly 40 with a separator 30 between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, negative electrode 20, and separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 can include a sealing member 60 that seals the case 50, as shown in Figure 1. Also, in Figure 2, the lithium secondary battery 100 can include a positive electrode lead tab 11 and a positive electrode terminal 12, a negative electrode lead tab 21 and a negative electrode terminal 22. As shown in Figures 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, namely a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical pathways for inducing the current formed in the electrode assembly 40 to the outside.

[0084] A lithium secondary battery according to one embodiment may be rechargeable at a high voltage or suitable for operation at a high voltage. For example, the charging voltage of the lithium secondary battery may be 4.45V or higher, and may be 4.45V to 4.7V, 4.45V to 4.6V, or 4.45V to 4.55V. By applying the positive electrode active material according to one embodiment, the amount of gas generated can be significantly reduced even when charged at a high voltage, thereby achieving high capacity and long life characteristics.

[0085] negative electrode The negative electrode may include a current collector and a negative electrode active material layer located on the current collector, the negative electrode active material layer comprising a negative electrode active material and further comprising a binder, a conductive agent, or a combination thereof.

[0086] negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping with lithium, or a transition metal oxide.

[0087] Examples of the material capable of reversibly inserting / desorbing the lithium ions include carbon-based negative electrode active materials, which can include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0088] As the alloy of the lithium metal, 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 can be used.

[0089] [[ID=1']]

[0090] As the material capable of doping and undoping with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (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 (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, for example, 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), or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn alloy, or a combination thereof. The silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle size (D) of the silicon-carbon composite particles. 50 The particle size can be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, it may include secondary particles (core) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of these secondary particles. The amorphous carbon may also be located between the primary silicon particles, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in the amorphous carbon matrix.

[0091] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of this core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. The amorphous carbon may be soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0092] When the silicon-carbon composite contains silicon and amorphous carbon, the silicon content may be 10% to 50% by weight per 100% by weight of the silicon-carbon composite, and the amorphous carbon content may be 50% to 90% by weight. Furthermore, when the composite contains silicon, amorphous carbon, and crystalline carbon, the silicon content may be 10% to 50% by weight per 100% by weight of the silicon-carbon composite, the crystalline carbon content may be 10% to 70% by weight, and the amorphous carbon content may be 20% to 40% by weight.

[0093] Furthermore, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle size (D) of the silicon particles (primary particles) 50) can be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may exist alone as silicon, or in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon is SiO x (0 < x ≦ 2) can be represented. At this time, the atomic content ratio of Si:O indicating the degree of oxidation can be 99:1 to 33:67. In this specification, unless otherwise defined, the average particle size (D 50 ) means the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution.

[0094] The Si-based negative electrode active material or Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material. When the Si-based negative electrode active material or Sn-based negative electrode active material and the carbon-based negative electrode active material are used in combination, the mixing ratio can be 1:99 to 90:10 by weight ratio.

[0095] binder The binder plays a role of well adhering the negative electrode active material particles to each other and well adhering the negative electrode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder or a combination thereof can be used.

[0096] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide or a combination thereof.

[0097] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylicated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile-ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0098] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulosic compound that can impart viscosity. This cellulosic compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. The alkali metal can be Na, K, or Li.

[0099] The dry binder is a polymeric substance that can be formed into fibers, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0100] conductive agent Conductive agents are used to impart conductivity to electrodes, and any electronically conductive material that does not undergo chemical changes in the battery that is constructed can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0101] The content of the negative electrode active material may be 95% to 99.5% by weight relative to 100% by weight of the negative electrode active material layer, and the content of the binder may be 0.5% to 5% by weight relative to 100% by weight of the negative electrode active material layer. For example, the negative electrode active material layer may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0.5% to 5% by weight of the conductive agent.

[0102] Current collector The negative electrode current collector may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof, and may be in the form of foil, sheet, or foam. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0103] electrolyte The electrolyte for lithium secondary batteries can be, for example, an electrolyte solution, which may contain a non-aqueous organic solvent and a lithium salt.

[0104] Non-aqueous organic solvents act as a medium through which ions involved in the electrochemical reactions of a battery can move. Non-aqueous organic solvents can be carbonate, ester, ether, ketone, or alcoholic solvents, aprotic solvents, or combinations thereof.

[0105] Examples of carbonate-based solvents that can be used 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), and butylene carbonate (BC). Examples of ester-based solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone. As ether-based solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran can be used. As ketone-based solvents, cyclohexanone can be used. As alcohol-based solvents, ethyl alcohol and isopropyl alcohol can be used, and as aprotic solvents, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and can include double bonds, aromatic rings, or ether groups); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes can be used.

[0106] Non-aqueous organic solvents can be used alone or in combination of two or more. When using a mixture of two or more, the mixing ratio can be appropriately adjusted according to the desired battery performance, and this is generally understood by those working in this field.

[0107] When using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed, and the cyclic carbonates and linear carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0108] Non-aqueous organic solvents may further include aromatic hydrocarbon organic solvents. For example, carbonate-based solvents and aromatic hydrocarbon organic solvents can be mixed and used in a volume ratio of 1:1 to 30:1.

[0109] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate, or ethylene carbonate compounds to improve battery life.

[0110] Typical examples of the aforementioned ethylene carbonate compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0111] Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions in batteries, enabling the operation of basic lithium secondary batteries and facilitating the movement of lithium ions between the positive and negative electrodes. Typical examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 It may contain one or more selected from SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0112] The lithium salt concentration is preferably used within the range of 0.1 M to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte has appropriate ionic conductivity and viscosity, resulting in excellent performance and effective lithium ion movement.

[0113] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators can be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers of these materials. Mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, or polypropylene / polyethylene / polypropylene three-layer separators can also be used.

[0114] The separator may include a porous substrate and a coating layer containing organic, inorganic, or a combination thereof located on one or both sides of the porous substrate.

[0115] The porous substrate may be a polymer film formed from one polymer selected from polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon®, and polytetrafluoroethylene, or from a copolymer or mixture of two or more of these polymers.

[0116] The porous substrate can have a thickness of approximately 1 μm to 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 15 μm.

[0117] The organic material may include a (meth)acrylic copolymer comprising a first structural unit derived from (meth)acrylamide, and a second structural unit comprising at least one of a structural unit derived from (meth)acrylic acid or (meth)acrylate and a structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof.

[0118] The inorganic substances mentioned above are Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, and Mg(OH) 2、 This may include, but is not limited to, inorganic particles selected from boehmite and combinations thereof. The average particle size (D) of the inorganic particles. 50 The wavelength can range from 1 nm to 2000 nm, for example, from 100 nm to 1000 nm or from 100 nm to 700 nm.

[0119] The organic and inorganic materials can exist mixed together in a single coating layer, or in a form where a coating layer containing organic materials and a coating layer containing inorganic materials are stacked on top of each other.

[0120] The thickness of the coating layer can be 0.5 μm to 20 μm, for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0121] Examples and comparative examples of the present invention are described below. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0122] Example 1 1. Manufacturing of positive electrode active material Ni 0.75 Mn 0.23 Al 0.02 (OH)2 and LiOH are mixed in a molar ratio of 1:1.05 and subjected to a first heat treatment at 845°C for 8 hours in an oxygen atmosphere, resulting in a composition of Li 1.05 Ni0.75 Mn 0.23 Al 0.02 It is O2 and the average particle size (D 50 We fabricated a lithium nickel-manganese composite oxide in secondary particle form with a particle size of approximately 14 μm.

[0123] 600g of distilled water and 500g of lithium nickel-manganese composite oxide were added to a 1L reactor, and aluminum sulfate was added during stirring, followed by stirring for about 45 minutes. At this time, the aluminum content in the aluminum sulfate was designed to be 1.0 mol% relative to 100% by weight of the total metal excluding lithium in the final cathode active material.

[0124] The solvent was removed using an aspirator and filter press in the mixed solution, and the coated product was obtained by vacuum drying at 190°C.

[0125] The aforementioned coated product was subjected to a second heat treatment at 750°C for 8 hours in an oxygen atmosphere to produce the final cathode active material.

[0126] 2. Manufacturing of lithium-ion batteries A slurry of 98.5% by weight of the manufactured positive electrode active material, 1.0% by weight of polyvinylidene fluoride binder, and 0.5% by weight of carbon nanotube conductive agent was mixed to produce a positive electrode active material layer slurry. This slurry was then coated onto an aluminum foil current collector, dried, and rolled to produce the positive electrode. At this time, the loading level of the positive electrode active material layer was 10 mg / cm². 2 Therefore, the density of the rolled final positive electrode is approximately 3.4 g / cc.

[0127] A slurry of 97.5% by weight of graphite negative electrode active material, 1.5% by weight of carboxymethylcellulose, and 1% by weight of styrene-butadiene rubber was mixed in an aqueous solvent to prepare a negative electrode active material layer slurry. The slurry was coated onto a copper foil current collector, and the negative electrode was produced by drying and rolling.

[0128] A lithium secondary battery was manufactured using a conventional method with a polytetrafluoroethylene separator and an electrolyte solution prepared by dissolving 1M LiPF6 in a solvent containing a 3:7 volume ratio mixture of ethylene carbonate and dimethyl carbonate.

[0129] Example 2 In the production of the positive electrode active material, distilled water and aluminum sulfate were first added to the reactor and mixed at approximately 350 rpm for about 5 minutes to produce a coating solution. Then, 500 g of the lithium nickel-manganese composite oxide produced in Example 1 was added to the coating solution, which was being continuously stirred, over a period of 1.5 minutes, and stirred for about 45 minutes. Except for these steps, the positive electrode active material and lithium secondary battery were produced in substantially the same manner as in Example 1.

[0130] Example 3 The positive electrode active material and lithium secondary battery were manufactured in substantially the same manner as in Example 2, except that the second heat treatment temperature was changed to 775°C.

[0131] Example 4 The positive electrode active material and lithium secondary battery were manufactured in substantially the same manner as in Example 2, except that the second heat treatment temperature was changed to 800°C.

[0132] Comparative Example 1 The positive electrode active material and lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the second heat treatment temperature was changed to 825°C.

[0133] Comparative Example 2 The positive electrode active material and lithium secondary battery were manufactured in substantially the same manner as in Comparative Example 1, except that the aluminum content in the aluminum sulfate was designed to be 1.5 mol% relative to 100 wt% of the total metal excluding lithium in the final positive electrode active material.

[0134] Comparative Example 3 The positive electrode active material and lithium secondary battery were manufactured in substantially the same manner as in Comparative Example 1, except that the aluminum content in the aluminum sulfate was designed to be 2.0 mol% relative to 100% by weight of the total metal excluding lithium in the final positive electrode active material.

[0135] Comparative Example 4 The positive electrode active material and lithium secondary battery were manufactured in substantially the same manner as in Example 2, except that the second heat treatment temperature was changed to 725°C.

[0136] To aid understanding, the design details of the examples and comparative examples are briefly shown in Table 1 below.

[0137] [Table 1]

[0138] Evaluation Example 1: SEM Analysis Figure 5 is an SEM image of the surface of the positive electrode active material of Comparative Example 1, Figure 6 is an SEM image of the surface of the positive electrode active material of Example 1, and Figure 7 is an SEM image of the surface of the positive electrode active material of Example 2.

[0139] Referring to Figure 5, in Comparative Example 1, it can be confirmed that aluminum diffuses into the secondary particles of the positive electrode active material, resulting in a smooth secondary particle surface. On the other hand, in Example 1 (Figure 6) and Example 2 (Figure 7), an Al coating layer is observed on the surface of the secondary particles. In Example 1, a micro-sized island-type coating layer is observed, while in Example 2, a nano-sized Al coating layer is observed.

[0140] Figure 8 is an SEM image of the surface of the positive electrode active material in Example 3, and Figure 9 is an SEM image of the surface of the positive electrode active material in Example 4. Referring to Figures 8 and 9, an Al coating layer can be observed on the surface of the secondary particles.

[0141] Figure 10 is an SEM image of the surface of the positive electrode active material of Comparative Example 4. Due to the low firing temperature of 725°C, a non-uniform coating layer can be seen on the secondary particle surface through the white circle in Figure 10.

[0142] Evaluation Example 2: EDS-Mapping Analysis Figure 11 is an SEM image of a cross-section of the positive electrode active material of Comparative Example 1 obtained by FIB, and Figure 12 is an EDS analysis image of Figure 11 with the Al element highlighted. Referring to Figure 12, in the case of Comparative Example 1, the Al coating region is observed not only on the surface of the secondary particles but also at the internal grain boundaries of the secondary particles.

[0143] Figure 13 is an SEM image of a cross-section of the positive electrode active material of Example 1 obtained by FIB, and Figure 14 is an EDS analysis image of Figure 13 with the Al element highlighted. Referring to Figure 14, it can be seen that in Example 1, the Al coating is distributed uniformly with high content on the surface of the secondary particles rather than diffusing into the internal grain boundaries of the secondary particles, and a thicker and more uniform Al-rich coating layer is observed on the secondary particle surface compared to Comparative Example 1.

[0144] Evaluation Example 3: TEM Analysis On the other hand, HR-TEM analysis of the cross-section of the positive electrode active material produced in Example 1 revealed that a layered structure was observed not only inside the secondary particles but also in the Al coating layer on the surface of the secondary particles. Therefore, it was confirmed that the coating layer contains a layered lithium aluminum oxide, such as LiAlO2.

[0145] Evaluation Example 4: EP-EDS EP-EDS analysis was performed on the positive electrode active materials of Examples 1-4 and Comparative Examples 1-4, and the ratio of the Al content (at%) to the total amount of Ni, Mn, and Al (100 at%) on the surface of the secondary particles (Al / (Ni+Mn+Al)) was calculated and is shown in Figure 15.

[0146] Referring to Figure 15, the Al content ratio on the surface of the examples is confirmed to be approximately 20% to 33%. The Al content on the surface of Examples 1 and 2, where the secondary heat treatment temperature was 750°C, was significantly higher than that of Comparative Example 1 (825°C). In the case of Examples 3 (775°C) and 4 (800°C), it can be seen that the Al content on the surface was also higher than that of Comparative Example 1. In the case of Comparative Examples 2 and 3, which were fired at 825°C as in Comparative Example 1, but with an increased Al coating content, the Al content on the secondary particle surface was lower than that of the examples. It is understood that when firing at 825°C is performed even with an increased coating amount, the Al tends to diffuse into the interior of the secondary particles, resulting in a lower Al content surrounding the surface coating layer than in the examples, and thus the initial charge / discharge capacity and efficiency of the battery were inferior to those of the examples.

[0147] Evaluation Example 5: TEM and EDS line profile analysis Figure 16 shows a TEM image of the cross-section of the primary particle located on the outermost side of the secondary particle in the positive electrode active material produced in Example 1. EDS line profile analysis was performed on the particle surface shown in Figure 16 in the direction of the particle interior, and the results are shown in Figure 17. Referring to Figure 17, an Al-rich coating layer can be confirmed on the surface of the secondary particle, and its thickness was confirmed to be at the 10 nm level.

[0148] Evaluation Example 6: Evaluation of initial charge / discharge capacity and efficiency, high-temperature life characteristics, and high-temperature gas generation amount of a battery. The lithium secondary batteries manufactured in Examples 1-4 and Comparative Examples 1-4 were charged at 25°C with a constant current of 0.2C to an upper voltage limit of 4.45V, then with a constant voltage down to 0.05C, and finally discharged at 0.2C down to a cutoff voltage of 3.0V to complete the initial charge and discharge cycles. Table 1 below shows the initial charge capacity, initial discharge capacity, and the ratio of the latter to the former, calculated using efficiency.

[0149] Next, the battery underwent more than 25 cycles of charging at 1.0C and discharging at 1.0C within a voltage range of 3.0V to 4.45V at 45°C. The ratio of the discharge capacity after 25 cycles to the initial discharge capacity was calculated and is shown in Table 1 below as the high-temperature lifespan.

[0150] On the other hand, the lithium secondary batteries of Examples 1-4 and Comparative Examples 1-4, after initial charging was completed, were stored at 90°C for 4 hours, and the amount of gas generated inside the batteries was measured. The results are shown in Table 2.

[0151] [Table 2]

[0152] In Comparative Example 1, which involved firing at 825°C, the high-temperature life characteristics were inferior to those of the Examples, and the amount of gas generated during high-temperature storage was high. In Comparative Example 2, where the amount of Al coating was increased to 1.5 mol% while firing at 825°C, the initial discharge capacity and high-temperature life characteristics were lower than those of the Examples, and the amount of gas generated was even higher. In Comparative Example 3, where the amount of Al coating was increased to 2.0 mol% while firing at 825°C, the initial charge capacity, initial discharge capacity, and efficiency were inferior to those of the Examples, and the amount of gas generated was also higher than that of the Examples.

[0153] In Comparative Example 4, which involved firing at 725°C, the low firing temperature resulted in unreacted material remaining on the surface of the secondary particles, leading to high gas generation during high-temperature storage and poor high-temperature lifespan characteristics.

[0154] In Examples 1-4, it was confirmed that the formation of a highly concentrated Al-rich coating layer with a very uniform thickness on the surface of the positive electrode active material secondary particles improved the initial charge / discharge capacity, efficiency, and high-temperature life characteristics, and also reduced the amount of gas generated during high-temperature storage. On the other hand, the capacity characteristics were further improved depending on the heat treatment temperature within each example. For example, Examples 1 and 2, which were fired at 750°C, were found to be superior to Examples 3 (775°C) and 4 (800°C) in terms of initial charge / discharge capacity and efficiency.

[0155] Although preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art that utilize the basic concepts defined in the claims also fall within the scope of the present invention. [Explanation of Symbols]

[0156] 100: Lithium-ion rechargeable battery 10: Positive electrode 11: Positive lead tab 12: Positive terminal 20: Negative electrode 21: Negative lead tab 22: Negative terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing member 70: Electrode Tab 71: Positive Tab 72: Negative electrode tab

Claims

1. Core particles containing a layered lithium nickel-manganese composite oxide, wherein the nickel content is 60 mol% or more and the manganese content is 15 mol or more, relative to 100 mol% of the total metal excluding lithium, and A positive electrode active material located on the surface of the core particles and comprising a coating layer containing Al, A positive electrode active material wherein the Al content on the surface of the positive electrode active material is 20 at% to 33 at% relative to the total amount of Ni, Mn, and Al (100 at%).

2. The positive electrode active material according to claim 1, wherein the Al content of the coating layer is 0.5 mol% to 1.5 mol% relative to 100 mol% of the total metal excluding lithium in the positive electrode active material.

3. The positive electrode active material according to claim 1, wherein the coating layer is in the form of a shell that continuously surrounds the surface of the core particles.

4. The positive electrode active material according to claim 1, wherein the thickness of the coating layer is 5 nm to 200 nm.

5. The positive electrode active material according to claim 1, wherein the deviation in the thickness of the coating layer within a single positive electrode active material particle is 20% or less.

6. The positive electrode active material according to claim 1, wherein the coating layer comprises a layered aluminum compound.

7. The positive electrode active material according to claim 1, wherein the coating layer comprises aluminum oxide, lithium-aluminum oxide, or a combination thereof.

8. The aforementioned coating layer is LiAlO 2 The positive electrode active material according to claim 1, comprising:

9. The positive electrode active material according to claim 1, wherein the coating layer further contains nickel, manganese, or a combination thereof.

10. The positive electrode active material according to claim 1, wherein the core particles are a layered lithium nickel-manganese composite oxide, the nickel content is 60 mol% to 80 mol% and the manganese content is 15 mol% to 40 mol% relative to 100 mol% of the total metal excluding lithium.

11. The positive electrode active material according to claim 1, wherein the layered lithium nickel-manganese composite oxide of the core particles further contains aluminum, and the content of aluminum in the core particles relative to 100 mol% of the total metal excluding lithium is 1 mol% to 3 mol%.

12. The positive electrode active material according to claim 11, wherein the concentration of aluminum is uniform within the core particles.

13. The positive electrode active material according to claim 1, wherein the core particles are a layered lithium nickel-manganese composite oxide, and the cobalt content relative to 100 mol% of the total metal excluding lithium is 0 mol% to 0.01 mol%.

14. The positive electrode active material according to claim 1, wherein the layered lithium nickel-manganese composite oxide of the core particles is represented by chemical formula 1. [Chemical formula 1] Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1 (In chemical formula 1, 0.9 ≤ a1 ≤ 1.8, 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.4, 0 ≤ z1 ≤ 0.03, 0 ≤ w1 ≤ 0.3, 0.9 ≤ x1 + y1 + z1 + w1 ≤ 1.1, and 0 ≤ b1 ≤ 0.1, M 1 (where X is one or more elements selected from B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, and Zr, and X is one or more elements selected from F, P, and S.)

15. The aforementioned core particle is a secondary particle form formed by the aggregation of multiple primary particles. The average particle size (D) of the positive electrode active material 50 The positive electrode active material according to claim 1, wherein the particle size is 10 μm to 25 μm.

16. Core particles containing a layered lithium nickel-manganese composite oxide are prepared, wherein the nickel content is 60 mol% or more and the manganese content is 15 mol% or more, relative to 100 mol% of the total metal excluding lithium. A mixed solution is prepared by adding aluminum sulfate and the core particles to an aqueous solvent and mixing them. A method for producing a positive electrode active material, comprising drying the mixture after removing the aqueous solvent and then heat-treating it at a temperature range of 730°C to 800°C to obtain a positive electrode active material.

17. The method for producing a positive electrode active material according to claim 16, wherein the heat treatment is performed in a temperature range of 750°C to 775°C.

18. A method for producing a positive electrode active material according to claim 16, wherein the layered lithium nickel-manganese composite oxide has a nickel content of 60 mol% to 80 mol%, a manganese content of 15 mol% to 40 mol%, an aluminum content of 0 mol% to 3 mol%, and a cobalt content of 0 mol% to 0.01 mol% based on 100 mol% of the total metal excluding lithium.

19. The method for producing a positive electrode active material according to claim 16, wherein the aluminum content of the aluminum sulfate is 0.5 mol% to 1.5 mol% relative to 100 mol% of the total metal excluding lithium in the core particles and the aluminum in the aluminum sulfate.

20. The method for producing a positive electrode active material according to claim 16, wherein the production of the mixed solution involves adding the core particles to the aqueous solvent and mixing them, and then adding aluminum sulfate to produce the mixed solution.

21. The method for producing a positive electrode active material according to claim 16, wherein the production of the mixed solution involves adding aluminum sulfate to the aqueous solvent and mixing to prepare a coating solution, and then adding the core particles to the coating solution and mixing to produce a mixed solution.

22. The time required to immerse the core particles in the coating solution is 30 seconds / 500g to 2 minutes / 500g. The mixing time after adding the core particles to the coating solution is 15 to 60 minutes. The method for producing a positive electrode active material according to claim 21, wherein the pH of the supernatant liquid after mixing is 5.5 to 7.

5.

23. The method for producing a positive electrode active material according to claim 16, wherein the removal of the aqueous solvent with the mixed solution and the subsequent drying of the obtained material are carried out under vacuum conditions at 40°C to 240°C.

24. The method for producing a positive electrode active material according to claim 16, wherein the coated product obtained by drying the mixture after removing the aqueous solvent with the mixed solution comprises the core particles and an Al-containing coating layer located on the surface of the core particles, and the Al-containing coating layer is in the form of a mesh or spiderweb.

25. The method for producing a positive electrode active material according to claim 16, wherein the obtained positive electrode active material comprises core particles containing a layered lithium nickel-manganese composite oxide in which the nickel content is 60 mol% or more relative to 100 mol% of the total metal excluding lithium, and a coating layer located on the surface of the core particles containing aluminum oxide, lithium-aluminum oxide, or a combination thereof.

26. Positive electrode current collector, and The positive electrode active material layer located on the positive electrode current collector is included, The positive electrode active material layer comprises the positive electrode active material described in any one of claims 1 to 15.

27. The loading level of the positive electrode active material layer is 10 mg / cm². 2 ~40 mg / cm³ 2 The positive electrode according to claim 26.

28. The positive electrode according to claim 26, wherein the density of the positive electrode active material layer is 3.3 g / cc to 3.7 g / cc.

29. The positive electrode according to claim 26, Negative electrode, and A lithium secondary battery containing an electrolyte.

30. A lithium secondary battery according to claim 29, wherein the charging voltage is 4.45V or higher.

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