Positive electrode active material and method for producing same

Abstract

The present invention relates to a positive electrode active material capable of improving the performance and stability of a lithium-rich manganese-based oxide, thereby improving the performance of a battery comprising the same, and particularly, to a positive electrode active material and a method for manufacturing the same, the positive electrode active material comprising: a core part comprising a lithium-rich manganese-based oxide having a layered structure, the lithium-rich manganese-based oxide simultaneously comprises a Li2MnO3 phase and a LiMO2 phase, wherein M is an element comprising at least one selected from the group consisting of Ni, Co and Mn; a first layer continuously formed on the core portion and including a crystal structure belonging to an R-3m space group; and a second layer continuously formed on the first layer and including a rock salt type crystal structure belonging to an Fm-3m space group.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0135434, filed on October 11, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to a positive electrode active material and its manufacturing method. Background Technology

[0004] Lithium-ion batteries consist of four main components: the positive electrode, the negative electrode, the separator, and the electrolyte. Among these, the positive electrode active material plays a crucial role in determining the battery's capacity, output, and lifespan. Improving the performance of the positive electrode active material is essential for achieving high energy density, output, and lifespan in lithium-ion batteries; therefore, extensive research has recently been conducted to develop high-performance positive electrode active materials.

[0005] Lithium-rich layered oxides (a type of positive electrode active material) are mixed phases containing Li₂MnO₃ and LiMO₂ (M = Ni, Mn, Co) phases, and exhibit high operating voltage (>3.5V vs. Li / Li). + This provides a very large capacity of 250 mAh / g. Therefore, lithium-rich layered oxides are attracting attention as low-cost, high-capacity cathode active materials.

[0006] However, lithium-rich layered oxides have problems due to their mixed two-phase structural characteristics. Specifically, when batteries containing lithium-rich layered oxides are driven at high voltages, there is an irreversible capacity loss during the first formation process, leading to reduced efficiency, and there is also a problem of voltage decay and O2 gas generation during charge / discharge cycles as the layered structure transforms from a spinel structure to a rock salt structure.

[0007] Therefore, it is necessary to ensure the technology used to improve the performance and stability of lithium-rich layered oxides. Summary of the Invention

[0008] Technical issues

[0009] One objective of this invention is to improve the performance and stability of lithium-rich layered oxides, thereby improving the performance of batteries containing them.

[0010] Another object of the present invention is to provide a method for manufacturing positive electrode active materials.

[0011] Technical solution

[0012] To achieve the above objectives, the present invention provides a positive electrode active material and a method for manufacturing the positive electrode active material.

[0013] (1) This invention provides a positive electrode active material, the positive electrode active material comprising: The core comprises a lithium-rich manganese oxide having a layered structure, the lithium-rich manganese oxide comprising both a Li2MnO3 phase and a LiMO2 phase, wherein M is an element comprising at least one selected from Ni, Co and Mn. The first layer, which is continuously formed on the core, contains a crystal structure belonging to the R-3m space group; and The second layer is formed continuously on the first layer and contains a rock salt-type crystal structure belonging to the Fm-3m space group.

[0014] (2) The present invention provides a positive electrode active material according to (1) above, wherein the lithium-rich manganese oxide contains at least one doping element selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta and Zr.

[0015] (3) The present invention provides a positive electrode active material according to (1) or (2) above, wherein the lithium-rich manganese oxide contains a crystal structure belonging to the C2 / m space group and the R-3m space group.

[0016] (4) The present invention provides a positive electrode active material according to any one of (1) to (3) above, wherein the lithium-rich manganese oxide has a manganese (Mn) content of more than 50 mol% in all metals other than lithium.

[0017] (5) The present invention provides a positive electrode active material according to any one of (1) to (4) above, wherein the lithium-rich manganese oxide has a composition represented by the following chemical formula 1: [Chemical Formula 1] Li a Ni b Co c Mn d Me e O2 in: Me is selected from at least one of Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr, and 1.09≤a≤1.20, 0≤b≤0.50, 0≤c≤0.10, 0.50≤d≤1.0, 0 <e≤0.10。

[0018] (6) The present invention provides a positive electrode active material according to any one of (1) to (5) above, wherein the lithium-rich manganese oxide is in the form of secondary particles.

[0019] (7) The present invention provides a positive electrode active material according to any one of (1) to (6) above, wherein the average particle size (D) of the lithium-rich manganese oxide is... 50 The range is from 5μm to 15μm.

[0020] (8) The present invention provides a positive electrode active material according to any one of (1) to (7) above, wherein the positive electrode active material further comprises a coating formed on a second layer and comprises at least one selected from carbon and sulfur.

[0021] (9) The present invention provides a positive electrode active material according to (8) above, wherein the coating further comprises boron.

[0022] (10) The present invention provides a positive electrode active material according to (8) or (9) above, wherein the carbon is derived from urea and the sulfur is derived from thiourea.

[0023] (11) The present invention provides a positive electrode active material according to any one of (1) to (10) above, wherein the thickness of the first layer is 0.5 nm to 20 nm.

[0024] (12) The present invention provides a positive electrode active material according to any one of (1) to (11) above, wherein the thickness of the second layer is 0.5 nm to 20 nm.

[0025] (13) The present invention provides a method for manufacturing a positive electrode active material according to (1) above, the method comprising the following steps: (A) A complex transition metal hydroxide is dry-mixed with a lithium-containing raw material, followed by a first calcination at 400°C to 500°C and a second calcination at 800°C to 1000°C to produce a lithium-rich manganese oxide; and (B) At least one selected from urea and thiourea is dry-mixed with a lithium-rich manganese oxide by mechanical melting, followed by heat treatment at 300°C to 550°C.

[0026] (14) The present invention provides a method for manufacturing a positive electrode active material according to (13) above, wherein in step (A), when the composite transition metal hydroxide is dry-mixed with the lithium-containing raw material, a doped raw material containing at least one doping element selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta and Zr is further mixed.

[0027] (15) The present invention provides a method for manufacturing a positive electrode active material according to (13) or (14) above, wherein the composite transition metal hydroxide has a composition represented by the following chemical formula 2: [Chemical Formula 2] Ni b' Co c' Mn d' Me e' (OH)2 in: Me is selected from at least one of Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr, and 0≤b'≤0.50, 0≤c'≤0.10, 0.50≤d'≤1.0, 0≤e'≤0.10, b'+c'+d'+e'=1.

[0028] (16) The present invention provides a method for manufacturing a positive electrode active material according to any one of (13) to (15) above, wherein the first calcination and the second calcination are each carried out independently in an atmospheric atmosphere or an oxygen atmosphere.

[0029] (17) The present invention provides a method for manufacturing a positive electrode active material according to any one of (13) to (16) above, wherein in step (B), at least one selected from urea and thiourea is mixed in an amount of 0.3 to 3 parts by weight based on 100 parts by weight of lithium-rich manganese oxide.

[0030] (18) The present invention provides a method for manufacturing a positive electrode active material according to any one of (13) to (17) above, wherein the heat treatment is performed in an N2 atmosphere.

[0031] (19) The present invention provides a method for manufacturing a positive electrode active material according to any one of (13) to (18) above, wherein in step (B), when at least one selected from urea and thiourea is dry-mixed with a lithium-rich manganese oxide, a boron-containing raw material is further mixed.

[0032] (20) The present invention provides a method for manufacturing a positive electrode active material according to (19) above, wherein the boron-containing raw material is mixed in an amount of 0.2 to 2 parts by weight based on 100 parts by weight of lithium-rich manganese oxide.

[0033] Beneficial effects

[0034] The positive electrode active material of the present invention comprises a first layer comprising a crystal structure belonging to the R-3m space group continuously formed on a lithium-rich manganese oxide, and a second layer comprising a rock salt type crystal structure belonging to the Fm-3m space group continuously formed on the first layer, thereby stabilizing the structure of the positive electrode active material. Therefore, the performance of the lithium secondary battery containing it can be improved, such as its lifespan characteristics, and gas generation can be reduced. Attached Figure Description

[0035] Figure 1 This is a HAADF-STEM image of the cross-section of the positive electrode active material manufactured in Example 5.

[0036] Figure 2 a / I is the cross-section of the positive electrode active material manufactured in Example 5. MnL3 Compare the images.

[0037] Figure 3 This is an OK front-edge / main-edge ratio diagram of the cross-section of the positive electrode active material manufactured in Example 5.

[0038] Figure 4 This is a HAADF-STEM image of the cross-section of the positive electrode active material manufactured in Comparative Example 1.

[0039] Figure 5 a / I is the cross-section of the positive electrode active material manufactured in Comparative Example 1. MnL3 Compare the images.

[0040] Figure 6 This is an OK front / main side ratio diagram of the cross-section of the positive electrode active material manufactured in Comparative Example 1.

[0041] Figure 7 The EELS analysis data for the OK edge is shown.

[0042] Figure 8 The EELS analysis data for the Mn L3 edge is shown.

[0043] Figure 9 This is an HR-(S)TEM image of the positive electrode active material of Example 5 of the present invention.

[0044] Figure 10 This is an HR-(S)TEM image of the positive electrode active material of Comparative Example 1.

[0045] Figure 11 This is an HR-(S)TEM image of the positive electrode active material of Comparative Example 3.

[0046] Figure 12 These are HAADF-STEM images and EDS data of the positive electrode active material of Example 5 of the present invention.

[0047] Figure 13 This is a graph showing the amount of gas produced during 50 charge and discharge cycles.

[0048] Figure 14 This is a graph showing the amount of gas produced during storage in a chamber at 60°C for 4 weeks.

[0049] Figure 15 It is a graph of charge and discharge curves based on repeated charge / discharge cycles.

[0050] Figure 16 It is a specific capacity diagram based on the repeated charge / discharge cycles after the formation cycle and the 0th cycle.

[0051] Figure 17 It is a graph based on the average discharge voltage of repeated charge / discharge cycles.

[0052] Figure 18 It is a graph based on the energy density of repeated charge / discharge cycles. Detailed Implementation

[0053] In the following description, the invention will be presented in more detail to aid in understanding.

[0054] The terms or words used in the specification and claims of this invention should not be construed as limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts consistent with the technical idea of ​​the invention, based on the principle that the inventor can appropriately define the concepts of the terms to best describe his invention.

[0055] It should be understood that terms such as “comprising,” “including,” and “having” as used herein are intended to indicate the presence of the said features, numbers, steps, constituent elements, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, constituent elements, or combinations thereof.

[0056] In this specification, the term "on" means not only that one component is directly formed on another component, but also that a third component is formed between these components.

[0057] In this specification, "primary particle" refers to the smallest particle unit identified when observing positive electrode active material using a scanning electron microscope (SEM), and "secondary particle" refers to a secondary structure formed by the aggregation of multiple primary particles.

[0058] In this specification, the term "average particle size (D)" is used. 50 "" refers to the particle size at the 50% point of the cumulative volume distribution based on particle size. Average particle size (D) 50The particle size distribution can be measured by dispersing the powder to be tested in a dispersion medium and then introducing it into a commercially available laser diffraction particle size measurement device (e.g., Microtrac's Bluewave). The particle size distribution is obtained by measuring the difference in the diffraction pattern of the particle size as the particles pass through the laser beam, and the particle size at the point where the cumulative volume distribution of the particle size is calculated in the measurement device.

[0059] Positive electrode active material

[0060] This invention provides a positive electrode active material, the positive electrode active material comprising: The core comprises a lithium-rich manganese oxide having a layered structure, the lithium-rich manganese oxide comprising both a Li2MnO3 phase and a LiMO2 phase, wherein M is an element comprising at least one selected from Ni, Co and Mn. The first layer, which is continuously formed on the core, contains a crystal structure belonging to the R-3m space group; and The second layer is formed continuously on the first layer and contains a rock salt-type crystal structure belonging to the Fm-3m space group.

[0061] The inventors have discovered that when the positive electrode active material comprises a first layer containing a crystal structure belonging to the R-3m space group continuously formed on a lithium-rich manganese oxide and a second layer containing a rock-salt type crystal structure belonging to the Fm-3m space group continuously formed on the first layer, the surface structure of the positive electrode active material is stabilized, thereby suppressing the migration of transition metals, suppressing phase transitions, and improving lithium mobility. As a result, the lifespan characteristics of batteries containing the positive electrode active material according to the present invention can be improved, gas generation can be reduced, and discharge capacity, capacity retention (de-rating), etc., can be improved, thus completing the present invention. The first and second layers are relatively reduced layers compared to the lithium-rich manganese oxide, and are a reduced bilayer.

[0062] On the other hand, when the positive electrode active material does not contain the first and second layers, there is a problem caused by the structural characteristics of lithium-rich manganese oxides having two mixed phases, so the performance of batteries containing it is problematic.

[0063] According to the present invention, the lithium-rich manganese oxide may contain at least one doping element selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr. That is, the lithium-rich manganese oxide may be doped with at least one doping element selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr. When the lithium-rich manganese oxide is doped with a doping element, the binding energy between the doping element and oxygen can be increased, thereby suppressing oxygen desorption in the cathode active material structure and thus preventing gas generation.

[0064] Specifically, when lithium-rich manganese oxides are doped with molybdenum (Mo), not only can the particle size of the positive electrode active material be increased, but the particle shape can also be improved. On the other hand, based on lithium-rich manganese oxides, the doping amount of molybdenum (Mo) can be below 5,000 ppm.

[0065] According to the present invention, lithium-rich manganese oxides may contain crystal structures belonging to the C2 / m space group and the R-3m space group.

[0066] According to the present invention, lithium-rich manganese oxides can have an Mn content of 50 mol% or more, specifically 60 mol% or more, and more specifically 65 mol% or more in all metals other than lithium. In this case, high capacity can be exhibited even when charging at high voltage.

[0067] According to the present invention, lithium-rich manganese oxides can have a composition represented by the following chemical formula 1. In this case, the capacity of Li2MnO3 can be further achieved at high voltages exceeding 4.4V, thereby exhibiting excellent capacity characteristics.

[0068] [Chemical Formula 1]

[0069] Li a Ni b Co c Mn d Me e O2

[0070] in: Me is selected from at least one of Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr, and 1.09≤a≤1.20, 0≤b≤0.50, 0≤c≤0.10, 0.50≤d≤1.0, 0 <e≤0.10。

[0071] Lithium-rich manganese oxides can be made without expensive cobalt and can improve the performance of lithium secondary batteries without cobalt.

[0072] The above chemical formula 1 can be represented as the following chemical formula 2: [Chemical Formula 2] Li(Li a' Ni b Co c Mn d Me e )O2 Where: Me is at least one selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr, and 0.09 ≤ a' ≤ 0.20, 0 ≤ b ≤ 0.50, 0 ≤ c ≤ 0.10, 0.50 ≤ d ≤ 1.0, 0 < e ≤ 0.10. In this case, a' + b + c + d + e = 1 can be satisfied above.

[0073] According to the present invention, the lithium-rich manganese-based oxide can be in the form of secondary particles. In this case, since the diffusion of lithium (Li) is improved, not only the capacity but also the rate performance is excellent compared to single particles. The secondary particles are secondary structures formed by the aggregation of multiple primary particles, and according to the present invention, the first layer containing a crystal structure belonging to the R-3m space group and continuously formed on the first layer and the second layer containing a rock salt-type crystal structure belonging to the Fm-3m space group can be formed not only on the secondary particles but also on the primary particles.

[0074] According to the present invention, the average particle diameter (D 50 ) of the lithium-rich manganese-based oxide can be 5 μm to 15 μm. Specifically, the average particle diameter (D 50 ) of the lithium-rich manganese-based oxide can be 5 μm or more, 6 μm or more, or 7 μm or more, and can be 10 μm or less, 11 μm or less, 12 μm or less, 13 μm or less, 14 μm or less, or 15 μm or less. In this case, electrode failure caused by particle aggregation during electrode manufacturing can be prevented.

[0075] The positive electrode active material according to the present invention may further include a coating formed on the second layer and containing at least one selected from carbon and sulfur. Specifically, the coating may contain at least one selected from carbon-containing compounds and sulfur-containing compounds. Here, the carbon may be derived from urea, and the sulfur may be derived from thiourea. The coating can be formed not only on the secondary particles of the lithium-rich manganese-based oxide but also on the primary particles.

[0076] According to the present invention, the coating may also contain boron. That is, in addition to carbon and / or sulfur, the coating may also contain boron. Specifically, the coating may contain at least one selected from carbon-containing compounds and sulfur-containing compounds, and compounds in which lithium, boron, and oxygen are chemically bonded to each other. When the coating contains both carbon and boron, the structural stability of the surface is further improved, thereby suppressing the formation of the surface modification layer. As a result, there is an advantage in further improving the lifespan characteristics of the battery containing the positive electrode active material.

[0077] According to the present invention, the thickness of the first layer can be from 0.5 nm to 20 nm. Specifically, the thickness of the first layer can be 0.5 nm or more, 1 nm or more, 1.5 nm or more, 2 nm or more, 2.5 nm or more, 3 nm or more, 3.5 nm or more, 4 nm or more, 4.5 nm or more, or 5 nm or more, and less than 10 nm, less than 11 nm, less than 12 nm, less than 13 nm, less than 14 nm, less than 15 nm, less than 16 nm, less than 17 nm, less than 18 nm, less than 19 nm, or less than 20 nm. In this case, there is the advantage of maintaining high capacity while effectively preventing the generation of gas on the particle surface.

[0078] According to the present invention, the thickness of the second layer can be from 0.5 nm to 20 nm. Specifically, the thickness of the second layer can be 0.5 nm or more, 1 nm or more, 1.5 nm or more, 2 nm or more, 2.5 nm or more, 3 nm or more, 3.5 nm or more, 4 nm or more, 4.5 nm or more, or 5 nm or more, and less than 10 nm, less than 11 nm, less than 12 nm, less than 13 nm, less than 14 nm, less than 15 nm, less than 16 nm, less than 17 nm, less than 18 nm, less than 19 nm, or less than 20 nm. In this case, there is the advantage of maintaining high capacity while effectively preventing the generation of gas on the particle surface.

[0079] In this specification, the thickness of the first layer and the thickness of the second layer can be values ​​measured by HR-TEM image analysis.

[0080] Methods for manufacturing positive electrode active materials

[0081] This invention provides a method for manufacturing the above-mentioned positive electrode active material, the method comprising the following steps: (A) A complex transition metal hydroxide is dry-mixed with a lithium-containing raw material, followed by a first calcination at 400°C to 500°C and a second calcination at 800°C to 1000°C to produce a lithium-rich manganese oxide; and (B) At least one selected from urea and thiourea is dry-mixed with a lithium-rich manganese oxide by mechanical melting, followed by heat treatment at 300°C to 500°C.

[0082] Step (A)

[0083] Step (A) involves dry mixing a complex transition metal hydroxide with a lithium-containing raw material, followed by a first calcination at 400°C to 500°C and a second calcination at 800°C to 1000°C to produce lithium-rich manganese oxides.

[0084] Step (A) comprises the following steps: dry mixing of a composite transition metal hydroxide with a lithium-containing raw material, performing a first calcination at a temperature near the melting point of the lithium-containing raw material, and performing a second calcination at a high temperature, thereby forming a lithium-rich layered oxide containing both Li₂MnO₃ and LiMO₂ phases. The mixing in step (A) is dry mixing, and is carried out in a dry manner because the lithium-containing raw material exists in the form of a solid powder. Wet mixing results in high processing costs; therefore, a dry mixing method is used in this invention.

[0085] According to the present invention, when the composite transition metal hydroxide is dry-mixed with the lithium-containing raw material in step (A), a doping raw material containing at least one doping element selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr can be further mixed. The doping raw material can be, for example, molybdenum oxide, ammonium molybdate, lithium molybdate, etc.

[0086] According to the present invention, the composite transition metal hydroxide can have a composition represented by the following chemical formula 2: [Chemical Formula 2] Ni b' Co c' Mn d' Me e' (OH)2 in: Me is selected from at least one of Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr, and 0≤b'≤0.50, 0≤c'≤0.10, 0.50≤d'≤1.0, 0≤e'≤0.10, b'+c'+d'+e'=1.

[0087] Composite transition metal hydroxides can be made without expensive cobalt and can improve the performance of lithium secondary batteries without cobalt.

[0088] Lithium-containing raw materials are lithium-containing raw materials commonly used to manufacture positive electrode active materials, and can be, for example, lithium carbonate (Li2CO3), lithium hydroxide (LiOH), LiNO3, CH3COOLi, Li2(COO)2 or their hydrates.

[0089] The composite transition metal hydroxide and the lithium-containing raw material can be mixed in an amount such that the molar ratio of the transition metal present in the composite transition metal hydroxide to the lithium present in the lithium-containing raw material is 1:1.2 to 1.4, specifically 1:1.2 to 1.4, 1:1.2 to 1.35, 1:1.25 to 1.4, 1:1.25 to 1.35, 1:1.3 to 1.4, 1:1.3 to 1.35, or 1.35 to 1.4. In this case, the Li2MnO3 phase and the LiMO2 phase can be formed simultaneously in an appropriate ratio.

[0090] According to the present invention, when a mixture of a composite transition metal hydroxide and a lithium-containing raw material is first calcined at 400°C to 500°C, the lithium-containing raw material can be melted and uniformly mixed with the composite transition metal hydroxide. Furthermore, when the mixture that has undergone the first calcination is subjected to a second calcination at 800°C to 1000°C, a lithium-rich layered oxide containing both Li₂MnO₃ and LiMO₂ phases can be well formed.

[0091] The first calcination temperature can be specifically above 400℃, above 410℃, above 420℃, above 430℃, above 440℃, or above 450℃, and can be below 450℃, below 460℃, below 470℃, below 480℃, below 490℃, or below 500℃.

[0092] The second calcination temperature can be specifically above 800℃, above 810℃, above 820℃, above 830℃, above 840℃, or above 850℃, and below 950℃, below 960℃, below 970℃, below 980℃, below 990℃, or below 1000℃.

[0093] On the other hand, when the first calcination temperature is below 400°C, there may be a problem of not forming a layered cathode material with excellent crystallinity, because the reaction will not proceed after the composite transition metal hydroxide and lithium-containing raw materials are uniformly mixed. When the first calcination temperature exceeds 500°C, there may be a problem of cathode material synthesis reaction occurring before the lithium-containing raw materials are uniformly mixed. In addition, when the second calcination temperature is below 800°C, lithium-rich layered oxides may not be completely formed, and when it exceeds 1000°C, particle growth and agglomeration may increase, thereby reducing electrochemical characteristics.

[0094] According to the present invention, the first calcination and the second calcination can be carried out independently in an atmospheric atmosphere or an oxygen atmosphere.

[0095] The first calcination can last for 3 to 5 hours, and the second calcination can last for 10 to 15 hours.

[0096] Step (B)

[0097] Step (B) involves dry mixing at least one selected from urea and thiourea with a lithium-rich manganese oxide via mechanical fusion, followed by heat treatment at 300°C to 500°C. When at least one selected from urea and thiourea is dry mixed with the lithium-rich manganese oxide via mechanical fusion and then heat-treated within the aforementioned temperature range, the urea and / or thiourea undergo thermal decomposition, generating ammonia gas during the decomposition process to form a reducing atmosphere. This reducing atmosphere reduces the surface layer of the lithium-rich manganese oxide, resulting in surface modification. Therefore, a first layer comprising a crystal structure belonging to the R-3m space group and a second layer comprising a rock-salt-type crystal structure belonging to the Fm-3m space group, i.e., a reduced bilayer, are formed on the lithium-rich manganese oxide.

[0098] Furthermore, since urea has a carbonyl group (C(=O) group), it undergoes thermal decomposition and carbonization under a nitrogen (N2) atmosphere, thereby forming a carbon-containing coating on lithium-rich manganese oxides. Similarly, since thiourea has a C(=S) group, it undergoes thermal decomposition under a nitrogen (N2) atmosphere, thereby forming a sulfur-containing coating on lithium-rich manganese oxides. In this case, either the carbon-containing coating or the sulfur-containing coating can be formed on the (outermost) surface of the positive electrode active material. That is, it can be formed on a second layer.

[0099] According to the present invention, dry mixing is carried out by mechanical melting, thus simultaneously and uniformly delivering impact / compression / shear to each particle while mixing the base material and coating material, allowing for uniform coating. On the other hand, when dry mixing is performed by methods such as ball milling, only a simple mixing process of the base material and coating material occurs.

[0100] According to the present invention, in step (B), at least one selected from urea and thiourea can be mixed in an amount of 0.3 to 3 parts by weight based on 100 parts by weight of lithium-rich manganese oxide. Specifically, at least one selected from urea and thiourea can be mixed in an amount of 0.3 parts by weight or more, 0.4 parts by weight or more, 0.5 parts by weight or more, 0.6 parts by weight or more, 0.7 parts by weight or more, 0.8 parts by weight or more, 0.9 parts by weight or more, or 1.0 parts by weight or more, and less than 2.0 parts by weight, less than 2.1 parts by weight, less than 2.2 parts by weight, less than 2.3 parts by weight, less than 2.4 parts by weight, less than 2.5 parts by weight, less than 2.6 parts by weight, less than 2.7 parts by weight, less than 2.8 parts by weight, less than 2.9 parts by weight, or less than 3.0 parts by weight. In this case, a stable surface layer with improved structural stability can be formed without reducing the capacity.

[0101] According to the present invention, the heat treatment can be carried out under a N2 atmosphere to form a reducing atmosphere through thermal decomposition.

[0102] According to the present invention, the heat treatment in step (B) can be performed at a temperature between 300°C and 550°C. Specifically, the heat treatment temperature can be above 300°C, above 310°C, above 320°C, above 330°C, above 340°C, above 350°C, above 360°C, above 370°C, above 380°C, above 390°C, or above 400°C, and below 450°C, below 460°C, below 470°C, below 480°C, below 490°C, below 500°C, below 510°C, below 520°C, below 530°C, below 540°C, or below 550°C. In this case, a stable surface layer (reduced bilayer and coating) with improved structural stability can be formed without reducing the capacity.

[0103] On the other hand, if the heat treatment temperature is below 300°C, the urea and / or thiourea are not properly thermally decomposed, and therefore the surface modification layer is not properly formed. If it exceeds 500°C, there is a problem that the carbon coating is not properly formed because the carbon burns at high temperatures.

[0104] The heat treatment can last for 3 to 5 hours.

[0105] According to the present invention, when at least one selected from urea and thiourea is dry-mixed with a lithium-rich manganese oxide in step (B), a boron-containing raw material can be further mixed. The boron-containing raw material can be, for example, boric acid, B₂O₃, etc.

[0106] According to the present invention, the boron-containing raw material can be mixed in an amount of 0.2 to 2 parts by weight based on 100 parts by weight of lithium-rich manganese oxide. Specifically, the boron-containing raw material can be mixed in an amount of 0.2 parts by weight or more, 0.3 parts by weight or more, 0.4 parts by weight or more, 0.5 parts by weight or more, and less than 0.8 parts by weight, less than 0.9 parts by weight, less than 1.0 parts by weight, less than 1.1 parts by weight, less than 1.2 parts by weight, less than 1.3 parts by weight, less than 1.4 parts by weight, less than 1.5 parts by weight, less than 1.6 parts by weight, less than 1.7 parts by weight, less than 1.8 parts by weight, less than 1.9 parts by weight, or less than 2.0 parts by weight based on 100 parts by weight of lithium-rich manganese oxide. In this case, a coating containing boron and at least one selected from carbon and sulfur and having a suitable thickness can be formed.

[0107] positive electrode

[0108] The present invention provides a positive electrode comprising a positive electrode active material.

[0109] The positive electrode may include a positive current collector and a positive active material layer formed on the positive current collector, wherein the positive active material layer may contain a positive active material.

[0110] The positive electrode current collector can contain a highly conductive metal, and there are no particular limitations, as long as the positive electrode active material layer can easily adhere to it and it is non-reactive within the battery's voltage range. The positive electrode current collector can be, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc. Furthermore, the thickness of the positive electrode current collector can typically range from 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0111] In addition to the positive electrode active material, the positive electrode active material layer may optionally contain conductive materials and binders as needed. In this case, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be from 80% to 99% by weight, more specifically from 85% to 98.5% by weight, and within this range, excellent capacity characteristics can be exhibited.

[0112] Conductive materials are used to impart conductivity to the electrodes and can be any material without particular limitation, as long as they are electronically conductive without causing chemical changes in the battery to be constructed. Specific examples may include: graphite, such as natural or artificial graphite; carbonaceous materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, and carbon fibers; powders or fibers of metals such as copper, nickel, aluminum, silver, etc.; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more thereof may be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material can be from 0.1% by weight to 15% by weight.

[0113] Adhesives are used to improve the bonding between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples may include: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers wherein hydrogen is substituted by Li, Na, or Ca, or various copolymers thereof, and any one or a mixture of two or more thereof may be used. Based on the total weight of the positive electrode active material layer, the adhesive content may be from 0.1% by weight to 15% by weight.

[0114] In addition to using the aforementioned positive electrode active material, the positive electrode can be manufactured according to conventional positive electrode manufacturing methods. Specifically, the aforementioned positive electrode active material, along with a binder, conductive material, and dispersant as needed, can be dissolved or dispersed in a solvent to prepare a composition for forming a positive electrode active material layer. This composition can then be coated onto a positive electrode current collector, dried, and calendered to manufacture the positive electrode. Alternatively, the positive electrode can be manufactured by casting the composition onto a separate support, peeling it off from the support to obtain a film, and then stacking the film onto a positive electrode current collector.

[0115] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, water, etc., and any one or a mixture of two or more thereof can be used. The amount of solvent used can be sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into account the coating thickness and manufacturing yield of the slurry, and to allow the slurry to have a viscosity that exhibits excellent thickness uniformity when applied to subsequent positive electrode manufacturing.

[0116] Lithium secondary batteries

[0117] The present invention provides a lithium secondary battery, wherein the lithium secondary battery includes the above-mentioned positive electrode.

[0118] A lithium secondary battery may include: a positive electrode; a negative electrode; and a separator and an electrolyte between the positive and negative electrodes. Additionally, a lithium secondary battery may optionally include a battery container for housing an electrode assembly formed by the positive electrode, negative electrode, and separator; and a sealing member for sealing the battery container.

[0119] The negative electrode may include a negative electrode current collector and a layer of negative electrode active material disposed on the negative electrode current collector.

[0120] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and will not cause chemical changes in the battery. It can be, for example, made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatments of carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloys. Furthermore, the thickness of the negative electrode current collector can typically range from 3 μm to 500 μm, and similar to the positive electrode current collector, fine irregularities can be formed on its surface to increase the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0121] In addition to the negative electrode active material, the negative electrode active material layer may optionally include a binder and a conductive material.

[0122] As anode active materials, compounds capable of reversibly inserting and deintercalating lithium can be used. Specific examples can include: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; (semi-)metallic materials capable of forming alloys with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and (semi-)metal oxides capable of doping or dedoping lithium, such as SiO₂. β (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composite materials containing (semi-)metallic materials and carbonaceous materials, such as Si-C composite materials or Sn-C composite materials, and any one or a mixture of two or more thereof can be used. Furthermore, lithium metal films can also be used as the negative electrode active material. Additionally, as carbon materials, low-crystallinity carbon, high-crystallinity carbon, etc., can be used. Representative examples of low-crystallinity carbon can include soft carbon and hard carbon, and representative examples of high-crystallinity carbon can include irregular, plate-like, sheet-like, spherical, or fibrous natural or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and high-temperature calcined carbon such as coke derived from petroleum or coal tar pitch. Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be from 80% to 99% by weight.

[0123] The binder for the negative electrode active material layer is a component that facilitates the bonding between the conductive material, the active material, and the current collector, and is typically added in amounts ranging from 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include: polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0124] The conductive material in the negative electrode active material layer is a component that further improves the conductivity of the negative electrode active material, and the amount added based on the total weight of the negative electrode active material layer can be less than 10% by weight, preferably less than 5% by weight. There are no particular limitations on the conductive material, as long as it is conductive and will not cause chemical changes in the battery, and it can be, for example, graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal cracking black; conductive fibers, such as carbon fibers and metal fibers; fluorocarbons; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; conductive materials, such as polyphenylene derivatives.

[0125] A negative electrode active material, along with optional binders and conductive materials, can be dissolved or dispersed in a solvent to prepare a composition for forming a negative electrode active material layer. This composition can then be coated onto a negative electrode current collector and dried to manufacture a negative electrode. Alternatively, the negative electrode can be manufactured by casting the composition onto a separate support, peeling the film off the support, and then laminating the film onto the negative electrode current collector.

[0126] The separator is used to separate the negative and positive electrodes and provides a channel for lithium-ion movement. Any separator can be used without particular limitation, as long as it is commonly used as a separator in lithium secondary batteries. In particular, separators with excellent electrolyte retention while exhibiting low resistance to electrolyte ion migration are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or membranes having two or more layers. Alternatively, conventional porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, to ensure heat resistance or mechanical strength, separators coated with ceramic components or polymer materials can be used, or optionally, they can be used in single-layer or multi-layer structures.

[0127] Electrolytes can be organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., but are not limited to these. As a specific example, an electrolyte can contain an organic solvent and a lithium salt.

[0128] As an organic solvent, any solvent can be used without particular limitation, as long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, the organic solvent can be an ester solvent, such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether solvent, such as dibutyl ether or tetrahydrofuran; a ketone solvent, such as cyclohexanone; an aromatic solvent, such as benzene or fluorobenzene; a carbonate solvent, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (PC); an alcohol solvent, such as ethanol or isopropanol; a nitrile, such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may contain double bonds, aromatic rings, or ether bonds); an amide, such as dimethylformamide; a dioxolane, such as 1,3-dioxolane; or sulfolane. Carbonate solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate, propylene carbonate, etc.) with high ionic conductivity and high dielectric constant that can increase the charging / discharging performance of the battery and low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) are even more preferred.

[0129] Lithium salts can be any compound without particular limitation, as long as they can provide lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt can be at least one selected from the following: F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N -The lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. The lithium salt is preferably used at a concentration ranging from 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, thereby exhibiting excellent electrolyte performance, and lithium ions can move efficiently.

[0130] To improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, in addition to the electrolyte components mentioned above, the electrolyte may also contain one or more additives, such as alkylene carbonate halide compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (condensed) glycol dimethyl ethers, hexamethylphosphoric triamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted sulfadiazine ketones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, based on the total weight of the electrolyte, the content of the additives may be from 0.1% by weight to 5% by weight.

[0131] Since lithium secondary batteries containing the positive electrode active material according to the present invention stably exhibit excellent capacity, output and life characteristics, they can be used in portable devices such as mobile phones, laptops, digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0132] There are no particular limitations on the shape of the lithium secondary battery of the present invention, but it can be cylindrical, prismatic, pouch-shaped or coin-shaped.

[0133] The lithium secondary battery according to the present invention can be used not only in battery cells as power sources for small devices, but also preferably as unit cells in medium and large battery modules containing multiple battery cells.

[0134] Therefore, a battery module comprising a lithium secondary battery as a unit cell and a battery pack comprising the battery module are provided.

[0135] Battery modules or battery packs can be used as power sources for any one or more medium to large-sized devices in power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles and plug-in hybrid electric vehicles (PHEVs); or systems for storing electricity.

[0136] Preferred Implementation

[0137] Embodiments of the invention will be described in detail below to enable those skilled in the art to readily implement the invention. However, the invention can be practiced in various forms and is not limited to the embodiments described herein.

[0138] Preparation Example

[0139] Preparation Example 1

[0140] Manganese sulfate (MnSO4) and nickel sulfate (NiSO4) were mixed in distilled water in amounts such that the molar ratio of Mn:Ni was 65:35, thereby preparing a 2.0 M aqueous solution of transition metals. A co-precipitation reaction was then carried out by adding 4 M NaOH and 15.3 M NH4OH aqueous solutions to the above transition metal aqueous solution while maintaining the pH at approximately 11. Subsequently, the precipitate was separated and washed, and dried at 120 °C for 24 hours to prepare a product containing Ni... 0.65 Mn 0.35 (OH)2 represents a complex transition metal hydroxide.

[0141] Example

[0142] Example 1 (Urea-coated LMRO)

[0143] The composite transition metal hydroxide prepared in Preparation Example 1 was mixed with LiOH·H2O such that the ratio of the total molar number of transition metals (Ni + Mn) in the composite transition metal hydroxide to the molar number of lithium (Li) in LiOH ((Ni + Mn):Li) was 1:1.35. Then, a first calcination was performed at 450°C for 5 hours under atmospheric atmosphere, followed by a second calcination at 900°C for 12 hours to produce a lithium-rich manganese oxide (composition: Li). 1.13 Ni 0.3 Mn 0.57 O2, average particle size (D) 50 : 7μm).

[0144] By means of mechanical melting, lithium-rich manganese oxide is mixed with urea (Sigma Aldrich) in an amount of 2 parts by weight based on 100 parts by weight of lithium-rich manganese oxide, and then heat-treated at 400°C for 5 hours under N2 atmosphere to produce a positive electrode active material with the formed coating.

[0145] For reference, mechanical fusion was performed using a Hosokawa Micron Novilta, and was carried out by placing a batch of 50g of raw material (lithium-rich manganese oxide + urea) in a mixing container and rotating the rotor at 1A, 2000rpm and 5L / min under N2 atmosphere.

[0146] Example 2 (Mo-doped / urea-coated LMRO)

[0147] The composite transition metal hydroxide prepared in Preparation Example 1 was mixed with LiOH·H2O such that the ratio of the total molar number of transition metals (Ni + Mn) in the composite transition metal hydroxide to the molar number of lithium (Li) in LiOH ((Ni + Mn):Li) was 1:1.35. Furthermore, 0.5 mol% of MoO3 (Sigma-Aldrich) relative to the composite transition metal hydroxide was mixed in. Then, a first calcination was performed at 450°C for 5 hours under atmospheric conditions, followed by a second calcination at 900°C for 12 hours to produce a lithium-rich manganese oxide (composition: Li). 1.13 (Ni 0.3 Mn 0.57 ) 0.994 Mo 0.005 O2, average particle size (D) 50 : 7μm).

[0148] By means of mechanical melting, lithium-rich manganese oxide is mixed with urea in an amount of 2 parts by weight based on 100 parts by weight of lithium-rich manganese oxide, and then heat-treated at 400°C for 5 hours under N2 atmosphere to produce a positive electrode active material with the formed coating.

[0149] For reference, mechanical fusion was performed using Hosokawa Micron's Novilta, and was carried out by placing a batch of 50g of raw material (lithium-rich manganese oxide + urea) in a mixing container and rotating the rotor at 1A, 2000rpm and 5L / min under N2 atmosphere.

[0150] Example 3 (Mo-doped / urea, B-coated LMRO)

[0151] The lithium-rich manganese oxide prepared in Example 2 was mixed with urea in an amount of 2 parts by weight based on 100 parts by weight of the lithium-rich manganese oxide, and further mixed with boric acid (H3BO3) (Sigma-Aldrich) in an amount of 0.57 parts by weight based on 100 parts by weight of the lithium-rich manganese oxide, and then heat-treated at 400°C for 5 hours under N2 atmosphere to produce a positive electrode active material having the formed coating.

[0152] For reference, mechanical fusion was performed using Hosokawa Micron's Novilta, and was carried out by placing a batch of 50g of raw material (lithium-rich manganese oxide + urea) in a mixing container and rotating the rotor at 1A, 2000rpm and 5L / min under N2 atmosphere.

[0153] Example 4 (Thiourea-coated LMRO)

[0154] The lithium-rich manganese oxide prepared in Example 1 was mixed with thiourea (Sigma-Aldrich) in an amount of 2 parts by weight based on 100 parts by weight of the lithium-rich manganese oxide, and then heat-treated at 400°C for 5 hours under N2 atmosphere to produce a positive electrode active material having the formed coating.

[0155] Example 5 (Mo-doped / thiourea-coated LMRO)

[0156] The lithium-rich manganese oxide prepared in Example 2 was mixed with thiourea in an amount of 2 parts by weight based on 100 parts by weight of the lithium-rich manganese oxide, and then heat-treated at 400°C for 5 hours under N2 atmosphere to produce a positive electrode active material having the formed coating.

[0157] Comparative Example 1 (Naked LMRO)

[0158] The lithium-rich manganese oxide prepared in Example 1 was used as the positive electrode active material in Comparative Example 1.

[0159] Comparative Example 2 (Mo-doped LMRO)

[0160] The lithium-rich manganese oxide prepared in Example 2 was used as the positive electrode active material in Comparative Example 2.

[0161] Comparative Example 3

[0162] The composite transition metal hydroxide prepared in Preparation Example 1 was mixed with LiOH·H2O such that the ratio of the total molar number of transition metals (Ni + Mn) in the composite transition metal hydroxide to the molar number of lithium (Li) in LiOH ((Ni + Mn):Li) was 1:1.35. Then, a first calcination was performed at 450°C for 5 hours under atmospheric atmosphere, followed by a second calcination at 900°C for 12 hours to produce a lithium-rich manganese oxide (composition: Li). 1.13 Ni 0.3 Mn 0.57 O2, average particle size (D) 50 : 7μm).

[0163] Using a ball mill, lithium-rich manganese oxides were mixed with urea (Sigma-Aldrich) in an amount of 2 parts by weight based on 100 parts by weight of lithium-rich manganese oxides, and then heat-treated at 400°C for 5 hours under N2 atmosphere to produce a positive electrode active material with the formed coating.

[0164] For reference, after loading the zirconia balls and powder into a Nalzen bottle at a weight ratio of 10:1, the mixture was ball-milled at 300 rpm for 12 hours.

[0165] Refer to Example 1 (NCMA positive electrode active material)

[0166] Using LiNi 0.86 Co 0.05 Mn 0.07 Al 0.02 The composition of O2 and its average particle size of 10 μm (D 50 Lithium nickel cobalt manganese aluminum oxide was used as the positive electrode active material in Reference Example 1.

[0167] Experimental Example

[0168] Experiment Example 1: Analysis of STEM-EELS Data

[0169] Electron energy loss spectroscopy (EELS) was performed on the electrodes containing the positive electrode active materials manufactured in Example 5 and Comparative Example 1, and the EELS data are then presented. Figures 1 to 8 middle.

[0170] Specifically, thin samples for STEM-EELS analysis were prepared using a TFS Helios 5 UX (accelerating voltages: 30 kW, 5 kW, and 2 kW), and HAADF-STEM images and EELS maps were obtained using a TFS Spectra 300 STEM at an accelerating voltage of 200 kV. The degree of Mn reduction was confirmed from the obtained images to verify the presence of a reduced layer. In this case, the dispersion was 0.15 eV / ch, the aperture of the GIF (Gatan image filter) camera was 1 mm, and the full width at half maximum (FWHM) of the zero-loss peak per image pixel ranged from 0.7 to 0.85 eV.

[0171] Figures 1 to 8 This is a HAADF-STEM image showing the cross-section of each positive electrode active material manufactured in Example 5 and Comparative Example 1, a / I MnL3 Comparison charts, OK front / main side comparison charts, and EELS analysis data charts.

[0172] Specifically, Figure 1 , 2 3 and 4 are HAADF-STEM images of the cross-section of the positive electrode active material manufactured in Example 5, respectively, and a / I. MnL3 Compare the image with the front / main side of the OK image; Figure 4 , 5 6 and 6 are HAADF-STEM images of the cross-section of the positive electrode active material manufactured in Comparative Example 1, respectively, and a / I MnL3 Compare the image with the front / main side of the OK image; Figure 7This is EELS analysis data for OK edges; and Figure 8 This is the EELS analysis data for the Mn L3 edge.

[0173] On the other hand, the OK front / main edge ratio and a / I in the EELS graph MnL3 The comparison chart is obtained using the following method.

[0174] Specifically, background is removed from the EELS ratio plot to remove noise; the OK leading edge signal at approximately 530 eV (hereinafter referred to as the OK leading edge), the OK main edge signal at approximately 541 eV to 542 eV (hereinafter referred to as the OK main edge), and the signal corresponding to Mn at approximately 644 eV are obtained. 4+ The side signal of the main peak (hereinafter referred to as a), and the integral signal of all L3 peaks (L3 sides) of Mn between 635eV and 650eV (hereinafter referred to as I). MnL3 The color is displayed differently depending on the ratio of the OK front edge to the OK main edge in the OK front / main edge ratio chart, and the color is displayed differently depending on the ratio of the front edge to the main edge in the OK front / main edge ratio chart. MnL3 Compare graph a and I MnL3 Different ratio values ​​represent different colors.

[0175] In this case, for Mn L3, the background is set to approximately 20 eV in front of the starting point of the L3 edge, approximately 10 eV away, and for the OK edge, the background is set to approximately 20 eV in front of the starting point. Furthermore, when obtaining the signal from the edge of the peak, an integral signal with a width (width) corresponding to 0.75 eV is obtained while including the peak, and when obtaining the integral signal from the L3 edge, the integral signal is obtained by setting the width to 10.05 eV to include the entire L3 edge.

[0176] Reference Figures 1 to 8 It can be confirmed that, in the case of Example 5, the OK front / main side ratio is low for the entire secondary particle, and in all L3 peaks of Mn, particularly as Mn 4+ The intensity of the main peak is slightly lower.

[0177] This is because the reduction layer is uniformly formed on the surface of the primary particles.

[0178] Experiment Example 2: Analysis of HR-TEM Images

[0179] For each positive electrode active material manufactured in Example 5, Comparative Example 1, and Comparative Example 3, HR-(S)TEM image analysis was performed, and the images are shown below. Figures 9 to 11 middle.

[0180] HR-(S)TEM analysis was specifically performed using a Spectra 300 (w / dual Cs corrector, monochromator) from Thermo Fisher Scientific at an accelerating voltage of 200 kV and with a shielding current of approximately 20 pA.

[0181] Figure 9 , 10 Figures 1 and 11 are HR-TEM (left) and HR-STEM (right) images, respectively, measured by magnifying the surface of primary particles in cross-sectional samples of the positive electrode active materials manufactured in Example 5, Comparative Example 1, and Comparative Example 2.

[0182] Reference Figures 9 to 11 It can be confirmed that, in the case of the positive electrode active material of Example 5, a first layer comprising a crystal structure belonging to the R-3m space group and a second layer formed on the first layer comprising a rock salt-type crystal structure belonging to the Fm-3m space group are formed. Furthermore, it can be confirmed that the first and second layers are formed continuously. Conversely, it can be confirmed that, in the case of the positive electrode active material of Comparative Example 1, the first and second layers according to the present invention do not exist, and in the case of the positive electrode active material of Comparative Example 3, the first layer according to the present invention does not exist. That is, when observing… Figures 9 to 11 When the particle surface was exposed to a single particle, it was confirmed that a double reduction layer was formed in Example 5, but no double reduction layer was found in Comparative Examples 1 and 3.

[0183] For reference, the reason for the difference in thickness between the first and second layers in the HR-TEM and HR-STEM images of Example 5 is that the STEM image mainly reflects information about the particle surface.

[0184] Experimental Example 3: EDS Analysis

[0185] HAADF-STEM images and EDS data of the cross-section of the positive electrode active material fabricated in Example 5 were obtained using a TFS Spectra300 and a quadrupole EDS detector (accelerating voltage: 200 kV), and are shown below. Figure 12 middle.

[0186] The results of EDS analysis confirm that sulfur (S) is coated on the surface of both the secondary and primary particles of the positive electrode active material.

[0187] Experiment Example 4: Evaluation of Battery Characteristics

[0188] Evaluation of gas production

[0189] A positive electrode slurry was prepared by mixing 92.5% by weight of each of the positive electrode active materials prepared in Examples 1 to 5, Comparative Examples 1 and 2, and Reference Example 1, 3% by weight of carbon black as a conductive material, and 4.5% by weight of polyvinylidene fluoride (PVDF) as a binder in N-methylpyrrolidone (NMP) solvent. The positive electrode slurry was coated on one surface of an aluminum current collector, dried at 130°C, and calendered to manufacture a positive electrode.

[0190] An electrode assembly is fabricated by using graphite as the negative electrode and inserting a porous polyethylene separator between the negative and positive electrodes. The electrode assembly is placed inside a battery casing, and a single cell is fabricated by injecting an electrolyte (additives: 2% LiBF4 and 5% FEC) obtained by dissolving 1M LiPF6 in an organic solvent containing ethylene carbonate (EC): ethyl methyl carbonate (EMC) in a 3:7 volume ratio.

[0191] 1) Evaluation of gas generation during charging and discharging

[0192] The single cell was charged to 4.65V at 45°C under CC (0.1C)-CV (cutoff current: 0.05C) conditions, and then discharged to 2.0V at 0.1C (first cycle) for formation. The single cell that underwent the above formation process was charged to 4.4V at 25°C under CC (0.1C)-CV (cutoff current: 0.05C) conditions, and then discharged to 2.5V at 0.1C (second cycle). Then, it was charged to 4.4V at 25°C under CC (0.33C)-CV (cutoff current: 0.05C) conditions, and then discharged to 2.5V at 0.33C. This was counted as one cycle and repeated 48 times, for a total of 50 charge and discharge cycles.

[0193] In addition, the amount of gas produced during 50 cycles was measured using a hydrometer (Matsuhaku Co., Ltd., TWD-150DM), and the results are shown in Table 1 below. Figure 13 The difference between the initial weight of the single cell and its weight in water is measured to calculate the volume change of the single cell. The volume change (ml) is then divided by the weight (g) of the positive electrode active material to calculate the amount of gas produced per 1g of positive electrode active material.

[0194] [Table 1]

[0195] 2) Evaluation of gas generation during high-temperature storage

[0196] The single cell was charged to 4.65V at 45°C under CC (0.1C)-CV (cutoff current: 0.05C) conditions, discharged to 2.0V at 0.1C, and charged to 4.4V at 25°C under CC (0.1C)-CV (cutoff current: 0.05C) conditions. Subsequently, the generated gas was degassed and removed, and the single cell was then recovered and stored in a chamber at 60°C. After two weeks of storage, the single cells were removed from the chamber at weekly intervals. The difference between the initial weight of the single cell and its weight in water was measured using a hydrometer (Matsushiki Co., Ltd., TWD-150DM). The volume change of the single cell was calculated, and the volume change (ml) was divided by the weight of the positive electrode active material (g) to calculate the amount of gas generated per 1g of positive electrode active material. The results are shown in Table 2 below. Figure 14 middle.

[0197] [Table 2]

[0198] Refer to Table 1 and Table 2. Figure 13 and Figure 14 It can be confirmed that in the case of batteries containing the positive electrode active materials manufactured in Examples 1 and 2, since they have a uniform first layer and a second layer formed continuously, the amount of gas generated during repeated charge / discharge cycles at high temperature and the amount of gas generated when stored at high temperature for a long time are less than those in batteries containing the positive electrode active materials manufactured in Comparative Example 1.

[0199] That is, it can be seen that the positive electrode active material according to the present invention has a uniform first layer and a second layer, and therefore can improve the stability of the battery when applied to a battery.

[0200] Electrochemical performance evaluation

[0201] A positive electrode slurry was prepared by mixing 92.5% by weight of the positive electrode active materials prepared in the above examples and comparative examples, 3% by weight of carbon black as a conductive material, and 4.5% by weight of polyvinylidene fluoride (PVDF) as a binder in N-methylpyrrolidone (NMP) solvent. The positive electrode slurry was coated on one surface of an aluminum current collector, dried at 130°C, and calendered to manufacture the positive electrode.

[0202] An electrode assembly is manufactured by using a lithium metal electrode as the negative electrode and inserting a porous polyethylene separator between the positive and negative electrodes. The electrode assembly is placed inside the battery casing, and an electrolyte (additives: 2% LiBF4 and 5% FEC) obtained by dissolving 1M LiPF6 in an organic solvent containing ethylene carbonate (EC): ethyl methyl carbonate (EMC) in a 3:7 volume ratio is injected to manufacture a half-cell.

[0203] The half-cell was charged to 4.65V at 45°C under CC (0.1C)-CV (cutoff current: 0.05C) conditions, and then discharged to 2.0V at 0.1C (hereinafter, "formation cycle") for a formation process. The half-cell formed in the above process was charged to 4.4V at 25°C under CC (0.1C)-CV (cutoff current: 0.05C) conditions, and then discharged to 2.5V at 0.1C (hereinafter, cycle 0). Then, it was charged to 4.4V at 25°C under CC (0.33C)-CV (cutoff current: 0.05C) conditions, and then discharged to 2.5V at 0.33C, which was considered one cycle and repeated 50 times (cycles 1 to 50).

[0204] In this case, Figures 15 to 18 The diagram shows a repeated charge / discharge curve based on the cycle. Figure 15 ), specific capacity diagram ( Figure 16 ), average discharge voltage diagram ( Figure 17 ) and energy density map ( Figure 18 The charge / discharge capacity of the formation cycle, the charge / discharge capacity of cycle 0, the discharge capacity of cycle 1, and the capacity retention rate were confirmed and are shown in Table 3 below. Furthermore, the resistance increase rate at 10, 30, and 50 cycles was confirmed and is shown in Table 4 below. For reference, the capacity retention rate is a value showing the discharge capacity of cycle 1 relative to the discharge capacity of cycle 0.

[0205] [Table 3]

[0206] [Table 4]

[0207] Refer to Tables 3 and 4 and Figures 15 to 18 It can be confirmed that, compared with the battery containing the positive electrode active material manufactured in Comparative Example 1, the battery containing the positive electrode active material manufactured in Examples 1 and 4 exhibits superior discharge capacity after formation, high capacity retention, and low resistance increase rate. Furthermore, it can be confirmed that, compared with the battery containing the positive electrode active material manufactured in Comparative Example 2, the battery containing the positive electrode active material manufactured in Examples 2, 3, and 5 exhibits superior discharge capacity after formation, high capacity retention, and low resistance increase rate.

[0208] As can be seen from these, the positive electrode active material according to the present invention has a uniform first layer and a second layer, and therefore can improve various battery performances when applied to a battery.

Claims

1. A positive electrode active material, said positive electrode active material comprising: The core comprises a lithium-rich manganese oxide having a layered structure, the lithium-rich manganese oxide comprising both a Li2MnO3 phase and a LiMO2 phase, wherein M is an element comprising at least one selected from Ni, Co and Mn. The first layer, which is continuously formed on the core and contains a crystal structure belonging to the R-3m space group; and The second layer is formed continuously on the first layer and contains a rock salt-type crystal structure belonging to the Fm-3m space group.

2. The positive electrode active material according to claim 1, wherein the lithium-rich manganese oxide contains at least one doping element selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta and Zr.

3. The positive electrode active material according to claim 1, wherein the lithium-rich manganese oxide comprises a crystal structure belonging to the C2 / m space group and the R-3m space group.

4. The positive electrode active material according to claim 1, wherein the lithium-rich manganese oxide has a manganese (Mn) content of more than 50 mol% in all metals other than lithium.

5. The positive electrode active material according to claim 1, wherein the lithium-rich manganese oxide has a composition represented by the following chemical formula 1: [Chemical Formula 1] Li a Ni b Co c Mr d Along with e O2 in: Me is selected from at least one of Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr, and 1.09≤a≤1.20, 0≤b≤0.50, 0≤c≤0.10, 0.50≤d≤1.0, 0 <e≤0.10。 6. The positive electrode active material according to claim 1, wherein the lithium-rich manganese oxide is in the form of secondary particles.

7. The positive electrode active material according to claim 1, wherein the average particle size (D) of the lithium-rich manganese oxide is... 50 The range is from 5μm to 15μm.

8. The positive electrode active material according to claim 1, wherein the positive electrode active material further comprises a coating formed on the second layer and comprises at least one selected from carbon and sulfur.

9. The positive electrode active material according to claim 8, wherein the coating further comprises boron.

10. The positive electrode active material according to claim 8 or claim 9, wherein the carbon is derived from urea, and the sulfur is derived from thiourea.

11. The positive electrode active material according to claim 1, wherein the thickness of the first layer is from 0.5 nm to 20 nm.

12. The positive electrode active material according to claim 1, wherein the thickness of the second layer is from 0.5 nm to 20 nm.

13. A method for manufacturing the positive electrode active material according to claim 1, the method comprising the following steps: (A) A complex transition metal hydroxide is dry-mixed with a lithium-containing raw material, followed by a first calcination at 400°C to 500°C and a second calcination at 800°C to 1000°C to produce a lithium-rich manganese oxide; and (B) The lithium-rich manganese oxide is dry-mixed with at least one selected from urea and thiourea by mechanical melting, followed by heat treatment at 300°C to 550°C.

14. The method for manufacturing a positive electrode active material according to claim 13, wherein in step (A), when the composite transition metal hydroxide is dry-mixed with the lithium-containing raw material, a doped raw material comprising at least one doping element selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta and Zr is further mixed.

15. The method for manufacturing a positive electrode active material according to claim 13, wherein the composite transition metal hydroxide has a composition represented by the following chemical formula 2: [Chemical Formula 2] Ni b' Co c' Mr d' Along with e' (OH)2 in: Me is selected from at least one of Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr, and 0≤b'≤0.50, 0≤c'≤0.10, 0.50≤d'≤1.0, 0≤e'≤0.10, b'+c'+d'+e'=1.

16. The method for manufacturing a positive electrode active material according to claim 13, wherein the first calcination and the second calcination are each carried out independently in an atmospheric atmosphere or an oxygen atmosphere.

17. The method for manufacturing a positive electrode active material according to claim 13, wherein in step (B), at least one selected from urea and thiourea is mixed in an amount of 0.3 to 3 parts by weight based on 100 parts by weight of the lithium-rich manganese oxide.

18. The method for manufacturing a positive electrode active material according to claim 13, wherein the heat treatment is performed under a N2 atmosphere.

19. The method for manufacturing a positive electrode active material according to claim 13, wherein in step (B), when at least one selected from urea and thiourea is dry-mixed with the lithium-rich manganese oxide, a boron-containing raw material is further mixed.

20. The method for manufacturing a positive electrode active material according to claim 19, wherein the boron-containing raw material is mixed in an amount of 0.2 to 2 parts by weight based on 100 parts by weight of the lithium-rich manganese oxide.

Images