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

Abstract

To improve the performance of a lithium secondary battery at high temperatures and high voltages and improve the capacity characteristics, initial charge / discharge efficiency, and high-temperature life characteristics thereof, by introducing an optimal coating layer, as a positive electrode active material including a lithium nickel-manganese-based composite oxide.SOLUTION: The present invention relates to: a positive electrode active material that includes core particles containing a layered lithium nickel-manganese-based composite oxide having a nickel content of greater than or equal to 60 mol% based on 100 mol% of a total metal amount excluding lithium, and a coating layer located on a surface of the core particles and including Al and P; a preparation method thereof; a positive electrode including the positive electrode active material; and a lithium secondary battery.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, research has been actively conducted on 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 suitable for such applications, a variety of positive electrode active materials are being considered. Among these, 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 the rare metal cobalt is expected to be extremely insufficient. In other words, because cobalt is expensive and the remaining reserves are not large, there is a need to develop positive electrode active materials that either exclude cobalt or reduce its content. [Overview of the project] [Problems that the invention aims to solve]

[0004] By introducing an optimal coating layer as a positive electrode active material containing a lithium nickel-manganese composite oxide, the high-temperature and high-voltage performance of lithium secondary batteries is improved, enhancing capacity characteristics, initial charge-discharge efficiency, and high-temperature life characteristics. [Means for solving the problem]

[0005] In one embodiment, provided is a positive electrode active material including core particles containing a layered lithium nickel-manganese composite oxide in which the content of nickel is 60 mol% or more with respect to 100 mol% of the total metal excluding lithium, and a coating layer containing Al and P and located on the surface of the core particles.

[0006] In another embodiment, provided is a method for manufacturing a positive electrode active material, including: (i) preparing core particles containing a layered lithium nickel-manganese composite oxide in which the content of nickel is 60 mol% or more with respect to 100 mol% of the total metal excluding lithium; (ii) preparing a coating solution by adding and mixing an aluminum raw material into an aqueous solvent; (iii) manufacturing a first mixed solution by adding and mixing the core particles into the coating solution; (iv) manufacturing a second mixed solution by adding and mixing a phosphorus-based raw material into the first mixed solution; and (v) removing the aqueous solvent from the mixed solution, and then drying and heat-treating the obtained product to obtain a positive electrode active material.

[0007] In another embodiment, provided is a positive electrode including 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 contains the positive electrode active material described above.

[0008] In another embodiment, provided is a lithium secondary battery including the positive electrode, a negative electrode, and an electrolyte.

Effects of the Invention

[0009] The positive electrode active material according to one embodiment maximizes the capacity while minimizing the production cost, ensures long-life characteristics, and improves characteristics at high voltage and high-temperature characteristics. The lithium secondary battery applying the positive electrode active material can exhibit high initial charge-discharge capacity and efficiency, and can realize excellent high-temperature life characteristics and high-temperature storage characteristics.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a lithium secondary battery according to one embodiment. [Figure 2]FIG. 2 is a cross-sectional view schematically showing a lithium secondary battery according to an embodiment. [Figure 3] FIG. 3 is a cross-sectional view schematically showing a lithium secondary battery according to an embodiment. [Figure 4] FIG. 4 is a cross-sectional view schematically showing a lithium secondary battery according to an embodiment. [Figure 5] FIG. 5 is a scanning electron microscope (SEM) image of the surface of the positive electrode active material coating product of Example 3. [Figure 6] FIG. 6 is an SEM image of the surface of the positive electrode active material of Comparative Example 1. [Figure 7] FIG. 7 is a scanning electron microscope energy dispersive spectroscopy (SEM-EDS) graph of the surface of the positive electrode active material coating product of Example 3. [Figure 8] FIG. 8 is an image obtained by mapping each element by SEM-EDS analysis of the surface of the positive electrode active material coating product of Example 3.

DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, specific embodiments will be described in detail so that those having ordinary knowledge in this technical field can easily implement them. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein.

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

[0013] Here, "these combinations" means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of components.

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

[0015] Thicknesses are shown enlarged in the drawings to clearly represent various 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" or "on" another part, this includes not only when it is "directly on top of" another part, but also when there is another part in between. Conversely, when a part is said to be "directly on top of" 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 a particle whose cumulative volume in the particle size distribution is 50% by volume. 50 This can mean the following. Also, unless otherwise defined, the average particle size is the diameter D of a particle whose cumulative volume in a particle size distribution is 50% by volume, obtained by measuring the size (diameter or length of the major axis) of more than 20 randomly selected particles in a scanning electron microscope image. 50 It may also be taken as the average particle size.

[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.

[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 located on the surface of the core particles and containing Al and P.

[0021] Recently, the price of the rare metal cobalt has surged, creating a demand for the development of cathode active materials that either 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 phosphate (LMO), have limitations in achieving high capacity due to the limited amount of lithium that can be utilized within their structure. Layered nickel-manganese cathode active materials, however, allow for a higher lithium content within their structure, exhibiting excellent capacity and efficiency characteristics, making them suitable for high-capacity batteries. but One problem is that removing cobalt, which plays a key role in the layered structure, reduces structural stability, increases resistance, and makes it difficult to ensure long lifespan. Another problem is that removing cobalt accelerates side reactions between the positive electrode active material and electrolyte under high voltage and high temperature conditions, increasing gas generation and reducing lifespan.

[0022] In one embodiment, to improve the surface stability of a layered nickel-manganese cathode active material in the high-voltage region, a coating layer containing Al and P is introduced to strengthen the particle surface and form a coating layer structurally having 3D lithium channels. This method improves not only the high-voltage high-temperature lifetime characteristics and high-temperature storage characteristics but also the initial charge-discharge efficiency.

[0023] 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 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 satisfies the above range, high capacity can be achieved, and structural safety can be improved even if the cobalt content is reduced.

[0024] The manganese content may 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 and improve structural stability.

[0025] The 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 included 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.

[0026] According to one embodiment, the concentration of aluminum within the core particles can be uniform. That is, it means that aluminum is evenly dispersed within the core particles without having a concentration gradient from the center to the surface direction within the core particles, or without the aluminum concentration being higher or lower outside than inside within the core particles. This can be said to be a structure obtained by synthesizing a composite oxide using a nickel-manganese-aluminum-based hydroxide as a precursor by using an aluminum raw material during the production of the precursor without additionally doping aluminum during the synthesis process of the core particles. The core particles may be in the form of secondary particles in which a plurality of primary particles are aggregated, but it can also be said that the aluminum content inside the primary particles is the same or similar regardless of the position of the primary particles. That is, when a primary particle is selected at an arbitrary position in the cross-section of the secondary particle and the aluminum content inside, not at the interface of the primary particle, is measured, it can be expressed that the aluminum content is the same / similar / uniform regardless of the position of the primary particle, that is, whether the primary particle is close to the center or the surface of the secondary particle. In such a structure, even if cobalt is absent or present in a very small amount, a stable layered structure can be maintained, and no aluminum by-products or aluminum aggregates are generated, so that the capacity, efficiency, and life characteristics of the positive electrode active material can be improved simultaneously.

[0027] The lithium nickel-manganese-based composite oxide is 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

[0028] 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 1is 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.

[0029] In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.5, or 0.9 ≤ a1 ≤ 1.2 may be satisfied. 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.

[0030] 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 be satisfied, 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 be satisfied, 0.01 ≤ z1 ≤ 0.025, 0.01 < z1 ≤ 0.02, or 0.01 < z1 ≤ 0.019 may be satisfied, and 0 ≤ w1 ≤ 0.28, 0 ≤ w1 ≤ 0.27, 0 ≤ w1 ≤ 0.26, 0 ≤ w1 ≤ 0.25, 0 ≤ w1 ≤ 0.24, 0 ≤ w1 ≤ 0.23, 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 be satisfied.

[0031] As an example, the lithium nickel - manganese - based composite oxide may not contain cobalt or may contain a small amount of cobalt, and the content of cobalt relative to 100 mol% of the total metal excluding lithium may be 0 mol% to 0.01 mol%.

[0032] The core particles may be in the form of secondary particles formed by the aggregation of multiple primary particles. The secondary particles may be spherical, ellipsoidal, polyhedronal, or irregular in shape, and the primary particles may be spherical, ellipsoidal, plate-shaped, or a combination thereof.

[0033] The aforementioned core particles are susceptible to chemical attack from components in the electrolyte when the battery is operated under high voltage or high temperature conditions, which can lead to frequent side reactions with the electrolyte. This results in increased gas generation, which reduces battery life and safety. However, by introducing a coating layer according to one embodiment described later, these problems can be resolved.

[0034] coating layer In one embodiment, the positive electrode active material includes a coating layer located on the surface of the core particles and containing Al and P. Such a coating layer improves the structural stability of the core particles containing a layered lithium nickel-manganese composite oxide, effectively suppresses side reactions between the positive electrode active material and the electrolyte, and promotes lithium ion conduction to reduce resistance, thereby increasing the initial discharge capacity and charge / discharge efficiency of the lithium secondary battery, and simultaneously improving high-temperature life characteristics and high-temperature storage characteristics.

[0035] The presence of Al and P in the coating layer can be determined through analysis such as SEM-EDS and XPS. The coating layer may contain one or more of the following: PO bonds, P=O bonds, Al-O bonds, Al=O bonds, and PO-Al bonds. The coating layer may contain, for example, aluminum phosphorus oxide, and more specifically, aluminum oxide and aluminum phosphorus oxide. As an example, the coating layer may contain lithium-aluminum oxide and aluminum phosphorus oxide, for example, Al2O3, LiAlO2 and / or AlPO4.

[0036] In one embodiment, the positive electrode active material may include a first coating layer located on the surface of the core particles and containing aluminum oxide, and a second coating layer located on the first coating layer and containing aluminum phosphorus oxide. In other words, the positive electrode active material may include a double-layered coating structure. The first coating layer may contain aluminum oxide, lithium-aluminum oxide, or a combination thereof, and for example, LiAlO2. The second coating layer may contain both Al and P, and for example, AlPO4.

[0037] In one embodiment, by a manufacturing method described later, core particles are placed in an aluminum-containing coating solution and mixed to perform an Al coating first, and then a phosphorus-based coating raw material is placed and mixed to form a P coating layer on the Al coating layer. According to this method, a positive electrode active material can be provided having a first coating layer containing Al or aluminum oxide on the core particles and a second coating layer located on the first coating layer and containing P, specifically aluminum phosphorus oxide. Unlike one embodiment, when P is coated first, for example, PO4 3- Ions are Li core particles + Lithium phosphate oxides such as Li3PO4 may be formed by reaction with ions, which can result in structural changes on the surface of the positive electrode active material and a decrease in reversible capacity. However, when coating is performed in the order of one embodiment, the structural stability of the core particles is further enhanced, lithium ion conduction is promoted, resistance is reduced, reversible capacity is increased, and lifetime characteristics and high-temperature characteristics are improved. According to the method of one embodiment, the positive electrode active material may contain aluminum oxide, lithium aluminum oxide, aluminum phosphate oxide, or a combination thereof on its surface, although lithium phosphate oxide may not be included.

[0038] In the coating layer, the Al content may be 0.5 mol% to 3 mol% relative to 100 mol% of the total elements excluding lithium and oxygen in the positive electrode active material, for example, 0.5 mol% to 2.5 mol%, 0.5 mol% to 2 mol%, or 0.5 mol% to 1.5 mol%. In addition, the P content in the coating layer may be 0.1 mol% to 2 mol% relative to 100 mol% of the total elements excluding lithium and oxygen in the positive electrode active material, for example, 0.1 mol% to 1.5 mol%, 0.1 mol% to 1 mol%, 0.1 mol% to 0.9 mol%, or 0.1 mol% to 0.5 mol%. When the Al and P content satisfies the above ranges, the structural stability of the layered lithium nickel-manganese composite oxide is improved, lithium ion conduction is promoted, and the initial discharge capacity, charge-discharge efficiency, high-temperature life characteristics, and high-temperature storage characteristics of the lithium secondary battery can be improved simultaneously.

[0039] Furthermore, the Al content relative to 100 at% of the total elements excluding lithium on the surface of the positive electrode active material, as measured by scanning electron microscope energy dispersive spectroscopy (SEM-EDS), may be 5 at% to 35 at%, for example, 5 at% to 30 at%, 5 at% to 25 at%, 6 at% to 20 at%, or 7 at% to 15 at%. Similarly, the P content relative to 100 at% of the total elements excluding lithium on the surface of the positive electrode active material, as measured by SEM-EDS, may be 0.1 at% to 8 at%, for example, 0.5 at% to 7 at%, 1 at% to 6 at%, or 2 at% to 5 at%. The total elements may be, for example, Li, Ni, Mn, Al, Ti, O, and C. When the respective Al and P content on the surface of the positive electrode active material satisfies the above ranges, the initial charge / discharge capacity, initial charge / discharge efficiency, high-temperature lifetime characteristics, and high-temperature storage characteristics of the lithium secondary battery to which this is applied can be simultaneously improved.

[0040] On the surface of the positive electrode active material, the ratio of Al content to P content (Al / P) may be 2 or more, for example, 2 to 10, 2 to 8, 2 to 6, 2 to 4, or 2 to 3. When this ratio is satisfied, the initial charge / discharge capacity, initial charge / discharge efficiency, high-temperature life, and high-temperature storage characteristics of the lithium secondary battery can be improved simultaneously.

[0041] In one embodiment, the coating layer may, for example, 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 completely surround the surface of the core particles and to be very thin and uniform in thickness. As a result, the positive electrode active material does not experience an increase in resistance or a decrease in capacity, its structural stability is improved, side reactions with the electrolyte can be effectively suppressed, and gas generation under high voltage and high temperature conditions is reduced, enabling long-life characteristics.

[0042] The thickness of the coating layer may be 5 nm to 500 nm, for example, 5 nm to 400 nm, 5 nm to 300 nm, 5 nm to 200 nm, 5 nm to 100 nm, or 10 nm to 50 nm. When the coating layer satisfies the above thickness range, the coating does not increase resistance or decrease capacitance, and the structural stability of the positive electrode active material can be improved, effectively suppressing side reactions with the electrolyte. The thickness of the coating layer may be measured, for example, by SEM, TEM, TOF-SIMS, XPS, or EDS analysis, and as an example, it may be measured by EDS line profile analysis of the cross-section of the positive electrode active material.

[0043] One embodiment of the coating layer is characterized by being thin, with a thickness of several tens to several hundred nanometers, and 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 content of the thickness of the coating layer within a single positive electrode active material particle. The thickness deviation of the coating layer can be, for example, calculated 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, 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.

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

[0045] Average particle size D of the positive electrode active material according to one embodiment 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 in a scanning electron microscope image of the positive electrode active material to obtain a particle size distribution, and the diameter D of the particle whose cumulative volume in the particle size distribution is 50 volume%. 50 This 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 is advantageous for forming a coating layer according to one embodiment.

[0046] Furthermore, one embodiment is characterized in that the other positive electrode active material does not contain 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] On the other hand, the positive electrode active material according to one embodiment may contain a sulfur (S) component on its surface, which may be due to a coating material described later.

[0048] 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) preparing a coating solution by adding and mixing aluminum raw material in an aqueous solvent; (iii) producing a first mixed solution by adding and mixing the core particles in the coating solution; (iv) producing a second mixed solution by adding and mixing phosphorus-based raw material in the first mixed solution; and (v) removing the aqueous solvent in the mixed solution, drying the yield, and heat-treating it to obtain a positive electrode active material. The positive electrode active material described above can be produced by this method.

[0049] First, a layered lithium nickel-manganese composite oxide may 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 may be 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 hydroxide may be produced by a general coprecipitation method.

[0050] In nickel-manganese composite hydroxides, the nickel content satisfies 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 satisfies the above range, high capacity can be achieved, and structural safety can be improved even if the cobalt content is reduced.

[0051] In nickel-manganese composite hydroxides, the manganese content may 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.

[0052] Furthermore, if the nickel-manganese composite hydroxide further 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 satisfies the above ranges, high capacity can be achieved, the structural safety of the positive electrode active material can be enhanced, and production costs can be reduced, improving economic efficiency.

[0053] In one embodiment, 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 charging and discharging, even without cobalt. Furthermore, since no aluminum by-products or aluminum aggregates are formed, the capacity, efficiency characteristics, and lifespan characteristics of the positive electrode active material can be improved.

[0054] In nickel-manganese composite hydroxides, the cobalt content may be 0.01 mol% or less, 0.005 mol% or less, or 0.001 mol% or less, relative to 100 mol% of the total metal. Such nickel-manganese composite hydroxides are economical because they avoid the cost increase associated with cobalt, and they can be said to have maximized capacity and improved structural stability.

[0055] Nickel-manganese complex hydroxides are represented, for example, by the following chemical formula 2. [Chemical formula 2] Ni x2 Mn y2 Al z2 M 2 w2 (OH)2

[0056] 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.

[0057] In the aforementioned chemical formula 2, for example, 6≦x2≦0.8, 0.1≦y2≦0.39, 0.01≦z2≦0.03, 0≦ w2 It may also be ≤0.29.

[0058] Nickel-manganese composite hydroxides exist in particulate form, and their average particle size D 50 The particle size may 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.

[0059] The nickel-manganese composite hydroxide and the lithium raw material may 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 may 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. A lithium nickel-manganese composite oxide can be obtained through the heat treatment. The obtained composite oxide is substantially the same as the positive electrode active material described above, specifically the core particles.

[0060] 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. This difference in surface properties makes it impossible to form a uniform, well-formed coating layer using existing coating methods. In one embodiment, we propose a method for coating the surface of layered lithium nickel-manganese composite oxide particles with Al and P to achieve a very uniform thickness.

[0061] In one embodiment, a coating solution is first prepared by adding and mixing aluminum raw materials into an aqueous solvent, and then core particles are added to this coating solution and mixed. This can be described as a salt-dissolution wet coating method, and a pre-addition method in which the positive electrode active material particles are added after the salt of the coating raw material has been completely dissolved.

[0062] The aqueous solvent may include distilled water, an alcoholic solvent, or a combination thereof.

[0063] The aluminum raw material may, for example, be aluminum sulfate. Aluminum sulfate is considered an optimal raw material for forming a uniform Al coating layer on a layered lithium nickel-manganese composite oxide.

[0064] The Al content in the aluminum raw material may be designed to be 0.1 mol% to 3.0 mol% relative to 100 mol% of the total elements in the core particles excluding lithium and oxygen, plus the aluminum in the aluminum raw material. For example, it may be designed to be 0.1 mol% to 2.0 mol%, 0.5 mol% to 1.5 mol%, 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 to be within this range, a thin and uniform coating layer with a thickness of tens to hundreds of nanometers can be formed, reducing the amount of gas generated by the lithium secondary battery under high voltage or high temperature operating conditions, thereby improving high capacity and long life characteristics.

[0065] The mixing of the aluminum raw material into the aqueous solvent may take approximately 1 to 60 minutes, for example, 1 to 30 minutes, 3 to 30 minutes, or 5 to 10 minutes. The mixing speed may 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 raw material can be completely dissolved in the aqueous solvent to produce a colorless and transparent coating solution, and by using such a coating solution, a uniform coating layer according to one embodiment can be effectively formed. The pH of the coating solution after mixing may be, for example, 1.5 to 4, for example, 2.0 to 3.5, 2.5 to 3.3, 2.7 to 3.3, or 2.9 to 3.2.

[0066] 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.

[0067] Furthermore, the time required to introduce the core particles into the coating solution may be 30 seconds / 500g or 2 minutes / 500g, or for example, 30 seconds / 500g or 1.5 minutes / 500g. By appropriately adjusting the rate at which the core particles are introduced, the pH of the supernatant can be appropriately adjusted after the coating is complete, thereby effectively guiding the formation of a uniform coating layer according to one embodiment. If the rate at which the core particles are introduced is excessively slow, the reaction rate for each particle will change, and a uniform coating layer may not be formed. Also, if the rate at which the core particles are introduced is excessively fast, the rate of pH change will be too fast, and a uniform coating layer may not be formed.

[0068] The stirring time after adding all the core particles to the coating solution may 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 until stirring is completed, that is, the time to produce the first mixed solution, can be appropriately adjusted to approximately 1 hour or less.

[0069] In one embodiment, when the core particles are added to the coating solution and mixing is stopped, that is, the pH range of the first mixed solution may be 5.5 to 8.5. If the pH of the first mixed solution 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 8.5, it may become too basic and in this case it may also be difficult to form a uniform Al coating layer.

[0070] In step (iv), a phosphorus-based raw material can be added to the first mixed solution and mixed to perform the P coating. Here, the phosphorus-based raw material may be, for example, phosphoric acid (H3PO4). In one embodiment, in step (iii), core particles are added to the Al coating solution and mixed to induce the Al coating, and then in step (iv), a phosphorus-based raw material is added and mixed to induce the P coating on the outermost surface of the positive electrode active material. As mentioned above, unlike one embodiment, when coating with P first, for example, PO4 3- Ions are Li core particles + Lithium phosphate oxides such as Li3PO4 can be formed by reaction with ions, which can result in structural changes on the surface of the positive electrode active material and a decrease in reversible capacity. However, in one embodiment, it has been confirmed that when P coating is performed after Al coating, the structural stability of the core particles is further enhanced, lithium ion conduction is promoted, resistance is reduced, reversible capacity is increased, and lifetime characteristics and high-temperature characteristics are improved.

[0071] According to a manufacturing method according to one embodiment, a first coating layer containing aluminum oxide, lithium-aluminum oxide, or a combination thereof is formed on the surface of core particles, and a second coating layer containing aluminum phosphorus oxide can be formed on the first coating layer. Since the aluminum oxide of the first coating layer and the aluminum phosphorus oxide of the second coating layer are not well mixed, they may exist as separate layers, and since the phosphate takes on an anionic form, it is expected to be present on the outermost surface of the positive electrode active material rather than diffusing into the interior of the core particles.

[0072] The phosphorus content of the phosphorus-based raw material may be 0.1 mol% to 2 mol% relative to 100 mol% of the total elements in the core particles excluding lithium and oxygen, plus the phosphorus in the phosphorus-based raw material. For example, it may be 0.1 mol% to 1.5 mol%, 0.1 mol% to 1 mol%, 0.1 mol% to 0.9 mol%, or 0.1 mol% to 0.5 mol%. By designing the P coating content within this range, a thin and uniform coating layer with a thickness of tens to hundreds of nanometers can be formed, improving lifespan characteristics under high voltage and high temperature operating conditions, as well as improving initial charge-discharge efficiency.

[0073] After adding the phosphorus-based raw material to the first mixed solution, the mixing time is 15 to 60 minutes, and may be, for example, 20 to 50 minutes, or 30 to 45 minutes. The time until the second mixed solution is produced can be appropriately adjusted to within approximately one hour. When a phosphorus-based raw material, such as phosphoric acid, is added to the first mixed solution, the pH may initially become low and acidic, and after mixing for a while, the pH may rise again. The pH range of the second mixed solution after mixing may be approximately 5.5 to 8.5. If the pH of the second mixed solution is less than 5.5, it may become too acidic and a uniform coating layer may not be formed. If the pH is greater than 8.5, it may become too basic, and in this case, it may also be difficult to form a uniform coating layer.

[0074] After removing the aqueous solvent with the second mixed solution, the product may be dried at, for example, 40°C to 240°C, 100°C to 220°C, or 150°C to 200°C, and may even be carried out under vacuum conditions. Such conditions can yield a good coated product.

[0075] The product obtained after removing the aqueous solvent with the second mixed solution and drying the product can be referred to as a coated product. The coated product includes core particles and a coating layer located on the surface of the core particles that contains Al and P. For example, the coating layer may have a fibrous shape, or it may be a mesh or spiderweb shape. Such a mesh may be formed continuously over the entire surface of the core particles. A 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, improving structural stability, and improving high-temperature and high-voltage characteristics.

[0076] In the above-mentioned process of mixing nickel-manganese composite hydroxide and lithium raw material and heat-treating it is referred to as the first heat treatment, and the heat treatment of the coated product can be referred to as the second heat treatment.

[0077] In one embodiment, the second heat treatment temperature range may be 730°C to 800°C, 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 within the above range, the tendency of aluminum to diffuse into the interior of the secondary particles is reduced, and it mainly remains on the surface of the secondary particles. At the same time, a very thin and uniform shell-shaped coating can be formed on the surface of the secondary particles, and the P element and the surface of the secondary particles can be well coated.

[0078] If the second heat treatment temperature exceeds 800°C, aluminum tends to diffuse more into the secondary particles, making it difficult to form a high-concentration Al-rich coating layer on the surface. This can reduce the initial charge / discharge capacity and efficiency characteristics at high voltages, and may also reduce the lifespan characteristics at high voltages and high temperatures. If the second heat treatment temperature is below 730°C, some of the aluminum and phosphorus components will aggregate or be unevenly distributed on the surface of the secondary particles. This can reduce the lifespan characteristics and initial charge / discharge efficiency under high-temperature and high-voltage conditions.

[0079] The second heat treatment may be carried out, for example, in an oxygen atmosphere for 2 to 20 hours, or 3 to 10 hours.

[0080] The resulting positive electrode active material can be described as comprising 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 and containing Al and P. In this case, the coating layer may also contain layered aluminum oxide and aluminum phosphorus oxide.

[0081] 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 material, or a combination thereof.

[0082] According to one embodiment, the loading level of the positive electrode active material layer is 10 mg / cm³. 2 or 40 mg / cm³ 2 It may also be 10 mg / cm³, for example. 2 or 30 mg / cm³ 2 or 10 mg / cm³ 2 or 20 mg / cm³ 2 It may also be the case that the density of the positive electrode active material layer in the rolled final positive electrode is 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 a loading level and positive electrode density, and a positive electrode satisfying the above range of loading level and positive electrode density is suitable for realizing a high-capacity, high-energy-density lithium secondary battery.

[0083] binder The binder plays a role in ensuring that the positive electrode active material particles adhere well to each other and that the positive electrode active material adheres well 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)acrylic styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0084] conductive material Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not cause chemical changes in the battery that is constructed can be used. Examples of conductive materials 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.

[0085] The content of the binder and conductive material may be 0.5% to 5% by weight, respectively, based on 100% by weight of the positive electrode active material layer.

[0086] Al may be used as the positive electrode current collector, but it is not limited to this.

[0087] Lithium-ion battery In one embodiment, a lithium secondary battery is provided that includes the positive electrode, negative electrode, and electrolyte described above. For 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.

[0088] 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, where 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 may include an electrode assembly 40 with a separator 30 interposed 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 may include a sealing member 60 that seals the case 50, as shown in Figure 1. Also, in Figure 2, the lithium secondary battery 100 may 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 also include electrode tabs 70, namely a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical pathways for guiding the current formed in the electrode assembly 40 to the outside.

[0089] A lithium secondary battery according to one embodiment may be capable of being charged at a high voltage or suitable for being driven 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, etc. 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, and high capacity and long life characteristics can be achieved.

[0090] 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 including a negative electrode active material and further including a binder, a conductive material, or a combination thereof.

[0091] negative electrode active material The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0092] Examples of the material capable of reversibly intercalating / deintercalating lithium ions include carbon-based negative electrode active materials, which may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-shaped, 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.

[0093] As the alloy of 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 may be used.

[0094] As the material capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used. The Si-based negative electrode active material may 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, 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 may be Sn, SnO2, a Sn alloy, or a combination thereof.

[0095] The silicon-carbon composite may also be a composite of silicon and amorphous carbon. Average particle size D of silicon-carbon composite particles 50 The thickness may 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 (cores) assembled from primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of these secondary particles. The amorphous carbon is also 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.

[0096] 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 the 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, etc.

[0097] 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.

[0098] 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) 50may 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 can be represented by SiOx (0 < x < 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation may be 99:1 to 33:67. In this specification, unless otherwise defined, the average particle size D 50 means the diameter of the particles having a cumulative volume of 50% by volume in the particle size distribution.

[0099] The Si-based negative electrode active material or the Sn-based negative electrode active material may be used in mixture with a carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material and the carbon-based negative electrode active material are used in mixture, the mixing ratio may be 1:99 to 90:10 by weight ratio.

[0100] binder The binder serves to well adhere the negative electrode active material particles to each other and also well adhere 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 may be used.

[0101] 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.

[0102] 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.

[0103] When an aqueous binder is used as the negative electrode binder, it may further contain a cellulosic compound capable of imparting viscosity. This cellulosic compound may be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. The alkali metal may be Na, K, or Li.

[0104] 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.

[0105] conductive material Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not cause 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 in the form of metal powders or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0106] 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 material.

[0107] 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.

[0108] electrolyte The electrolyte for lithium secondary batteries may be, for example, an electrolyte solution, which may contain a non-aqueous organic solvent and a lithium salt.

[0109] Non-aqueous organic solvents serve as a medium through which ions involved in the electrochemical reactions of the battery can move. Non-aqueous organic solvents may be carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvents, aprotic solvents, or combinations thereof.

[0110] As carbonate-based solvents, 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), butylene carbonate (BC), etc. may be used. As ester-based solvents, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. may be used. As ether-based solvents, dibutyl ether, tetraglyceride, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran may be used. As ketone-based solvents, cyclohexanone may be used. As alcohol-based solvents, ethyl alcohol and isopropyl alcohol may be used, and as aprotic solvents, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include double bonds, directional rings, or ether groups); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes may be used.

[0111] Non-aqueous organic solvents may 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 should be widely understood by those working in this field.

[0112] When using a carbonate-based solvent, a mixture of cyclic carbonate and linear carbonate may be used, and the cyclic carbonate and linear carbonate may be mixed in a volume ratio of 1:1 to 1:9.

[0113] The non-aqueous organic solvent may further contain an aromatic hydrocarbon organic solvent. For example, the carbonate solvent and the aromatic hydrocarbon organic solvent may be mixed and used in a volume ratio of 1:1 to 30:1.

[0114] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate, or ethylene carbonate compounds to improve battery life.

[0115] 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.

[0116] Lithium salts dissolve in organic solvents and act as a source of lithium ions within 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 SO2) (where x and y are integers from 1 to 20), may contain one or more selected from lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0117] The lithium salt concentration should preferably be 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.

[0118] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such a separator may be polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof. Needless to say, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0119] 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.

[0120] 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.

[0121] The porous substrate may 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.

[0122] The organic substance 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.

[0123] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof. The average particle size D of the inorganic particles 50 This can be 1 nm to 2000 nm, for example, 100 nm to 1000 nm or 100 nm to 700 nm.

[0124] The organic and inorganic materials may be present mixed in a single coating layer, or they may exist in a form in which a coating layer containing organic materials and a coating layer containing inorganic materials are stacked.

[0125] The thickness of the coating layer may be 0.5 μm to 20 μm, for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0126] 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.

[0127] Example 1 1. Manufacturing of positive electrode active material Ni 0.75 Mn 0.24 Al 0.01 (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 0.24 Al 0.01 O2, average particle size D 50 We produced a lithium nickel-manganese composite oxide in the form of secondary particles with a particle size of approximately 14 μm.

[0128] 600g of distilled water and aluminum sulfate were added to a 1L reactor, and the mixture was stirred at approximately 350 rpm for about 5 minutes to dissolve the salt and produce a coating solution. It was confirmed that the salt was completely dissolved in the coating solution and that it was colorless and transparent. 500g of the prepared lithium nickel-manganese composite oxide was added to the continuously stirring coating solution for 1.5 minutes, and the mixture was stirred for about 30 minutes to produce the first mixed solution. At this time, the aluminum content in the aluminum sulfate was designed to be 1 mol% relative to 100 mol% of all elements excluding lithium and oxygen in the final cathode active material. The pH of the first mixed solution after stirring was confirmed to be 6.6. Next, H3PO4 was added to the first mixed solution and stirred for about 30 minutes to produce the second mixed solution. The phosphoric acid content was designed to be 0.1 mol% relative to 100 wt% of all elements excluding lithium and oxygen in the final cathode active material. The pH of the solution decreased with the addition of phosphoric acid, and then increased again after stirring, maintaining a pH of approximately 6.6.

[0129] Subsequently, the solvent was removed with the second mixed solution using an aspirator and filter press, and the coated product was obtained by vacuum drying at 190°C.

[0130] 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.

[0131] 2. Coin Cell Manufacturing 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 material 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. 2The density of the final rolled positive electrode is approximately 3.4 g / cc.

[0132] Coin cells were manufactured using a conventional method, employing lithium metal as the counter electrode, 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.

[0133] Example 2 The positive electrode active material and coin cell were manufactured in substantially the same manner as in Example 1, except that the P content in phosphoric acid was changed to 0.3 mol% relative to 100 wt% of all elements excluding lithium and oxygen in the final positive electrode active material.

[0134] Example 3 The positive electrode active material and coin cell were manufactured in substantially the same manner as in Example 1, except that the P content in phosphoric acid was changed to 0.5 mol% relative to 100 wt% of all elements excluding lithium and oxygen in the final positive electrode active material.

[0135] Comparative Example 1 The positive electrode active material and coin cell were manufactured in substantially the same manner as in Example 1, except that Al and P coatings were not performed in the manufacturing of the positive electrode active material, and the lithium nickel-manganese composite oxide itself was used as the positive electrode active material.

[0136] Comparative Example 2 The positive electrode active material and coin cell were manufactured in substantially the same manner as in Example 1, except that only Al coating was performed without P coating, that is, the positive electrode active material was produced by filtering and drying the first mixed solution and then performing a second heat treatment.

[0137] Evaluation Example 1: SEM-EDS Analysis Figure 5 is an SEM image of the surface of the positive electrode active material coated product manufactured in Example 3, and Figure 6 is an SEM image of the surface of the positive electrode active material manufactured in Comparative Example 1. Comparing Figure 5 and Figure 6, a kind of mesh-like coating pattern can be observed on the surface of the coated product in Example 3.

[0138] Furthermore, SEM-EDS analysis was performed on the surface of the coated product manufactured in Example 3. Figure 7 shows the detection intensity graphs for each element C, O, Mn, Ni, Al, and P, and Figure 8 shows the SEM image (upper left) and an image mapping each of the elements O, Al, Mn, Ni, and P. Referring to Figure 7, it can be confirmed that both Al and P elements are detected on the surface of the positive electrode active material coated product, and referring to Figure 8, it can be confirmed that Al and P elements are distributed very uniformly on the surface of the positive electrode active material coated product.

[0139] Furthermore, the content of each element on the surface of the coated product of Example 3, calculated through SEM-EDS analysis, is shown in Table 1 below. Table 1 can be said to represent the content of each element on the surface of the positive electrode active material, excluding lithium, that is, relative to 100 at% of C+O+Al+P+Mn+Ni.

[0140] [Table 1]

[0141] Referring to Table 1, the Al content relative to the total elements excluding lithium on the surface of the coated product in Example 3 was 7.82 at%, the P content was 3.46 at%, and the Al / P content ratio was confirmed to be approximately 2.26.

[0142] Evaluation Example 2: Evaluation of initial charge / discharge capacity and efficiency of a battery The coin cells manufactured in Examples 1 to 3 and Comparative Examples 1 to 2 were initially charged at 25°C with a constant current of 0.2C up 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. Table 2 below shows the initial charge capacity, initial discharge capacity, and the ratio of the latter to the former, calculated efficiently.

[0143] Evaluation Example 3: Evaluation of High-Temperature Life Characteristics Following on from Evaluation Example 2, the battery underwent more than 50 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 50 cycles to the initial discharge capacity was calculated and is shown as the high-temperature life in Table 2 below.

[0144] Evaluation Example 4: Evaluation of High-Temperature Storage Characteristics In Evaluation Example 1, a battery initially charged to 4.45V was stored at 90°C for 4 hours, and the amount of gas generated inside the battery was measured, as shown in Table 2 below.

[0145] [Table 2]

[0146] Referring to Table 2 above, it can be seen that in Examples 1 to 3, the initial discharge capacity is improved, the initial charge-discharge efficiency is enhanced compared to Comparative Examples 1 and 2, the high-temperature life characteristics are further improved, and the amount of gas generated during high-temperature storage is further reduced.

[0147] 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 using the basic concepts defined in the following claims also fall within the scope of the present invention. [Explanation of Symbols]

[0148] 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 in which the nickel content is 60 mol% or more relative to 100 mol% of the total metals excluding lithium, The core particles include a coating layer located on the surface of the core particles and containing Al and P, A positive electrode active material comprising a layered lithium nickel-manganese composite oxide of core particles, wherein the cobalt content is 0 mol% to 0.01 mol% relative to 100 mol% of the total metals excluding lithium.

2. The coating layer comprises aluminum phosphorus oxide, as described in claim 1.

3. The positive electrode active material according to claim 1, wherein the coating layer comprises aluminum oxide and aluminum phosphorus oxide.

4. The positive electrode active material according to claim 1, wherein the positive electrode active material comprises a first coating layer located on the surface of core particles and containing aluminum oxide, and a second coating layer located on the first coating layer and containing aluminum phosphorus oxide.

5. In the aforementioned coating layer, the Al content is 0.5 mol% to 3 mol% relative to 100 mol% of the total elements excluding lithium and oxygen in the aforementioned positive electrode active material. The positive electrode active material according to claim 1, wherein the P content in the coating layer is 0.1 mol% to 2 mol% relative to 100 mol% of the total elements excluding lithium and oxygen in the positive electrode active material.

6. The Al content on the surface of the positive electrode active material, measured by scanning electron microscopy energy dispersive spectroscopy (SEM-EDS), is 5 at% to 35 at% relative to 100 at% of the total elements excluding lithium, and the P content is 0.1 at% to 8 at%. The positive electrode active material according to claim 1, wherein the ratio of Al content to P content (Al / P) on the surface of the positive electrode active material is 2 or more.

7. The coating layer has a shell shape that continuously surrounds the surface of the core particles. The thickness of the coating layer is 5 nm to 500 nm. 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.

8. In the aforementioned layered lithium nickel-manganese composite oxide of core particles, the nickel content is 60 mol% to 80 mol% relative to 100 mol% of the total metal excluding lithium, and the manganese content is 15 mol% or more. 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%.

9. The layered lithium nickel-manganese composite oxide of the core particles is represented by chemical formula 1, according to claim 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, 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).

10. 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.

11. Prepare 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 metals excluding lithium. Prepare the coating solution by adding aluminum raw material to an aqueous solvent and mixing it. The core particles are added to the coating solution and mixed to produce a first mixed solution. A phosphorus-based raw material is added to the first mixed solution and mixed to produce a second mixed solution. The process involves removing the aqueous solvent with the second mixed solution, drying the product, and then heat-treating it to obtain a positive electrode active material. A method for producing a positive electrode active material, wherein the layered lithium nickel-manganese composite oxide has a cobalt content of 0 mol% to 0.01 mol% relative to 100 mol% of the total metals excluding lithium.

12. A method for producing a positive electrode active material according to claim 11, wherein the layered lithium nickel-manganese composite oxide has a nickel content of 60 mol% to 80 mol%, a manganese content of 15 mol% or more, and an aluminum content of 0 mol% to 3 mol%, based on 100 mol% of the total metals excluding lithium.

13. The aforementioned aluminum raw material is aluminum sulfate. The aforementioned phosphorus-based raw material is phosphoric acid, With respect to 100 mol% of the total metals excluding lithium in the core particles and the aluminum in the aluminum raw material, the aluminum content of the aluminum raw material is 0.5 mol% to 3 mol%. The method for producing a positive electrode active material according to claim 11, wherein the phosphorus content of the phosphorus-based raw material is 0.1 mol% to 2 mol% with respect to a total of 100 mol% of the total elements of the core particles and the phosphorus of the phosphorus-based raw material.

14. The pH of the coating solution is 1.5 to 4. The time required to immerse the core particles in the coating solution is 30 seconds / 500g or 2 minutes / 500g. After adding the core particles to the coating solution, the mixing time is 15 to 60 minutes. The method for producing a positive electrode active material according to claim 11, wherein the pH of the first mixed solution is 5.5 to 8.

5.

15. After adding the phosphorus-based raw material to the first mixed solution, the mixing time is 15 to 60 minutes. The method for producing a positive electrode active material according to claim 11, wherein the pH of the second mixed solution is 5.5 to 8.

5.

16. The method for producing a positive electrode active material according to claim 11, wherein the product is dried after removing the aqueous solvent with a second mixed solution at a vacuum at 40°C to 240°C, and the heat treatment is performed in a temperature range of 730°C to 800°C.

17. The method for producing a positive electrode active material according to claim 11, wherein the coated product obtained by removing the aqueous solvent with a second mixed solution and then drying the product comprises the core particles and a coating layer located on the surface of the core particles and containing Al and P, the coating layer having a mesh or spiderweb shape.

18. Positive electrode current collector and The positive electrode active material layer located on the positive electrode current collector comprises, The positive electrode comprises the positive electrode active material layer according to any one of claims 1 to 10.

19. The loading level of the positive electrode active material layer is 10 mg / cm². 2 or 40 mg / cm³ 2 And, The positive electrode according to claim 18, wherein the density of the positive electrode active material layer is 3.3 g / cc to 3.7 g / cc.

20. The positive electrode described in claim 18, The negative electrode and, A lithium secondary battery comprising an electrolyte, A lithium-ion secondary battery with a charging voltage of 4.45V or higher.

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