Positive electrode active material and method for manufacturing the same

Abstract

The present invention relates to a cathode active material capable of improving the performance and stability of lithium peroxide, and as a result, improving the performance of a battery containing the same. The present invention relates to a layered lithium-rich transition metal oxide containing a Li2MnO3 phase and a LiMO2 phase (where M is an element containing one or more selected from Ni, Co, and Mn) at the same time, and a coating layer containing boron and carbon formed on the lithium-rich transition metal oxide, and relates to a cathode active material, a method for producing the same, a cathode containing the same, and a lithium secondary battery that satisfy at least one of the following conditions (1) to (3). - Condition (1): The atomic ratio (B / Mn) of boron (B) to manganese (Mn) present on the surface analyzed by XPS is 1 to 5 - Condition (2): In the XPS spectrum of the surface, peak I at 287.5 to 288.5 eV Carbonate,1 and peak I at 284 to 285 eV C-C The intensity ratio I Carbonate,1 :I C-C is 0.05 to 0.15:1 - Condition (3): In the XPS spectrum of the surface, peak I at 288.6 to 290.5 eV Carbonate,2 and peak I at 284 to 285 eV C-C The intensity ratio I Carbonate,2 :I C-C is 0.05 to 0.15:1

Description

[Technical Field]

[0001] This application claims priority rights under Korean Patent Application No. 10-2023-0087326 dated July 5, 2023, and Korean Patent Application No. 10-2023-0086034 dated July 3, 2023, and all content disclosed in the documents of the said Korean patent applications is incorporated herein by reference.

[0002] 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]

[0003] Lithium-ion batteries consist of four main components: a positive electrode, a negative electrode, a separator, and an electrolyte. Of these, the positive electrode active material plays a major role in determining the battery's capacity, output, and lifespan. Improving the performance of the positive electrode active material is essential for lithium-ion batteries to have high energy density, output, and lifespan, and therefore, a lot of research has recently been conducted to develop high-performance positive electrode active materials.

[0004] Lithium-rich layered oxide (Li-rich layered oxide), a type of positive electrode active material, is a mixed phase in which the Li2MnO3 phase and the LiMO2 (M=Ni, Mn, Co) phase are mixed, and has a high operating voltage (>3.5V vs. Li / Li + It possesses the characteristic of providing a very large capacity of 250 mAh / g. For this reason, the lithium excess oxide is attracting attention as a low-cost, high-capacity cathode active material.

[0005] However, the lithium excess oxide presents problems due to its structural characteristics, namely the mixing of two phases. Specifically, when a battery containing the lithium excess oxide is driven under high voltage, irreversible capacity loss occurs during the first formation process, leading to a decrease in efficiency. Furthermore, during charge-discharge cycles, the structure changes from a layered structure to a spinel structure and then to a rock salt structure, resulting in voltage fading and the generation of O2 gas.

[0006] Therefore, it is necessary to secure technologies that improve the performance and stability of the aforementioned lithium excess oxide. [Overview of the project] [Problems that the invention aims to solve]

[0007] The problem that this invention aims to solve is to improve the performance and stability of lithium excess oxides, and as a result improve the performance of batteries containing them.

[0008] Furthermore, the present invention aims to provide a method for producing the positive electrode active material.

[0009] Furthermore, the present invention aims to provide a positive electrode containing the positive electrode active material and a lithium secondary battery. [Means for solving the problem]

[0010] To solve the above problems, the present invention provides a positive electrode active material, a method for producing a positive electrode active material, a positive electrode, and a lithium secondary battery.

[0011] (1) The present invention provides a positive electrode active material comprising a layered lithium-excess transition metal oxide containing a Li2MnO3 phase and a LiMO2 phase (where M is an element containing one or more selected from Ni, Co, and Mn) and a coating layer containing boron and carbon formed on the lithium-excess transition metal oxide, which satisfies at least one of the following conditions (1) to (3). - Condition (1): The atomic ratio (B / Mn) of boron (B) to manganese (Mn) present on the surface analyzed by XPS is 0.3 to 5 - Condition (2): In the XPS spectrum of the surface, peak I at 287.5 to 288.5 eV Carbonate,1 and peak I at 284 to 285 eV C-C The intensity ratio I Carbonate,1 : I C-C is 0.05 to 0.15:1 - Condition (3): In the XPS spectrum of the surface, peak I at 288.6 to 290.5 eV Carbonate,2 and peak I at 284 to 285 eV C-C The intensity ratio I Carbonate,2 : I C-C is 0.05 to 0.15:1

[0012] (2) The present invention provides a positive electrode active material in which, in the above (1), the lithium-excess transition metal oxide is in a single particle form.

[0013] (3) The present invention provides a positive electrode active material in which, in the above (1), the lithium-excess transition metal oxide has an average particle size (D 50 ) of 0.75 μm to 10 μm.

[0014] (4) The present invention provides a positive electrode active material in which, in any one of the above (1) to (3), the content of Mn among all the metals other than lithium in the lithium-excess transition metal oxide is 50 mol% or more.

[0015] (5) The present invention provides a positive electrode active material in which, in any one of the above (1) to (4), the lithium-excess transition metal oxide has a composition represented by the following chemical formula 1. [Chemical formula 1] Li(Li a Ni b Co c Mn d Me e )O2 In the above chemical formula 1, Me is one or more elements selected from W, Mo, Zn, Mg, Nb, and Al. 0.01≦a≦0.20, 0≦b≦0.50, 0≦c≦0.10, 0.50≦d≦1.0, 0≦e≦0.10, and a+b+c+d+e=1.

[0016] (6) The present invention provides a positive electrode active material in which, in any one of (1) to (5) above, the lithium-rich transition metal oxide is doped with W, Mo, or a combination thereof.

[0017] (7) In any one of (1) to (6) above, the present invention provides a positive electrode active material in which the coating layer comprises a compound in which lithium, boron, and oxygen are chemically bonded to each other and a compound containing carbon.

[0018] (8) The present invention provides a positive electrode active material in any one of (1) to (7) above, wherein the coating layer has a thickness of 1 nm to 80 nm.

[0019] (9) The present invention provides a method for producing a positive electrode active material according to any one of (1) to (8) above, comprising the steps of (A) dry mixing a lithium-containing raw material and a transition metal-containing raw material, and then calcining to produce a lithium-excess transition metal oxide, and (B) dry mixing the lithium-excess transition metal oxide and a boron-containing raw material, and then heat-treating to form a coating layer on the lithium-excess transition metal oxide.

[0020] (10) The present invention provides a method for producing a positive electrode active material, wherein the firing described in (9) above is carried out at a temperature of 850°C to 1,050°C.

[0021] (11) The present invention provides a method for producing a positive electrode active material in which, in (9) or (10) above, the boron-containing raw material is mixed in an amount such that boron (B) is present in an amount of 300 ppm to 1,500 ppm relative to the total weight of the lithium-rich transition metal oxide.

[0022] (12) The present invention provides a method for producing a positive electrode active material in any one of (9) to (11) above, wherein the heat treatment is performed at a temperature of 300°C to 450°C.

[0023] (13) The present invention provides a method for producing a positive electrode active material in which, in any one of (9) to (12) above, a doping element-containing raw material is further mixed when the lithium-containing raw material and the transition metal-containing raw material are dry-mixed.

[0024] (14) The present invention provides a positive electrode comprising a positive electrode active material according to any one of (1) to (8) above.

[0025] (15) The present invention provides a lithium secondary battery including a positive electrode according to (14) above. [Effects of the Invention]

[0026] The positive electrode active material of the present invention comprises a coating layer containing boron and carbon formed on a lithium-rich transition metal oxide, satisfies at least one of the conditions (1) to (3) described herein with respect to XPS data, and can improve the performance of lithium secondary batteries containing it, such as efficiency during the activation process, 0.33C discharge capacity, and resistance performance. [Brief explanation of the drawing]

[0027] [Figure 1] This is the EELS data for the positive electrode active material of Example 1 of the present invention. [Figure 2] These are the XRD spectra of the positive electrode active materials of Examples 1 to 4 of the present invention. [Figure 3] These are the XPS spectra of Examples 1-3 and Comparative Example 1 of the present invention. [Modes for carrying out the invention]

[0028] The present invention will be described in more detail below to facilitate understanding of it.

[0029] The terms and words used in the description and claims of this invention should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​this invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0030] In this specification, "single-particle form" is a concept contrasted with secondary particle forms, which are formed by the aggregation of tens to hundreds of primary particles, and refers to a form consisting of 10 or fewer primary particles. Specifically, "single-particle form" may be a single-particle form consisting of one primary particle, or it may be a secondary particle form formed by the aggregation of several primary particles.

[0031] In this specification, "primary particle" refers to the smallest particle unit recognized when observing a 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.

[0032] 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 by particle size. The average particle size is calculated by dispersing the powder to be measured in a dispersion medium, introducing it into a commercially available laser diffraction particle size analyzer (for example, a Bluewave from Microtrac), measuring the difference in diffraction patterns due to particle size as the particles pass through the laser beam to calculate the particle size distribution, and then calculating the particle diameter at the point where the cumulative volume distribution by particle size in the measuring device reaches 50%. 50 It can be measured.

[0033] positive electrode active material The present invention relates to a Li2MnO3 phase and LiMO2 (where M is an element selected from Ni, Co, and Mn, specifically M=Ni x Co y Mn z The present invention provides a positive electrode active material comprising a lithium-rich transition metal oxide having a layered structure containing the phases , 0≦x≦0.9, 0≦y≦0.1, 0.1≦z≦1.0, and x+y+z=1, and a coating layer containing boron and carbon formed on the lithium-rich transition metal oxide, and satisfying at least one of the following conditions (1) to (3).

[0034] -Condition (1): The atomic ratio (B / Mn) of boron (B) to manganese (Mn) present on the surface analyzed by XPS is 0.3-5 -Condition (2): In the surface XPS spectrum, peak I at 287.5~288.5 eV Carbonate,1 and peak I at 284-285 eV C-C Intensity ratio I Carbonate,1 :I C-C The ratio is 0.05~0.15:1 -Condition (3): In the surface XPS spectrum, peak I at 288.6~290.5 eV Carbonate,2 and peak I at 284-285 eV C-C Intensity ratio I Carbonate,2 :I C-C The ratio is 0.05~0.15:1

[0035] The inventors of the present invention have found that if the positive electrode active material includes a coating layer containing boron and carbon formed on the lithium-rich transition metal oxide, and at least one of the above conditions (1) to (3) is satisfied when the surface of the positive electrode active material is analyzed by XPS, then the discharge capacity and efficiency of the battery containing the positive electrode active material can be improved in the first formation step, the 0.33C discharge capacity can be improved, and the resistance characteristics can also be improved, thus completing the present invention.

[0036] XPS is equipment for analyzing the components or chemical bonding state from the surface to a depth of 10 nm, and in this specification, the surface analyzed by XPS may be the region from the outermost edge of the positive electrode active material to a depth of 10 nm.

[0037] On the other hand, if the positive electrode active material does not contain the coating layer, problems arise due to the structural characteristics of the mixture of the two phases, resulting in a decrease in the initial activation efficiency and 0.33C discharge capacity of batteries containing this material. Furthermore, if the coating layer does not contain carbon, there is a problem of low conductivity in the coating layer and high resistance in the positive electrode active material. In addition, the positive electrode active material is a Mn-rich positive electrode active material, and when the surface of the positive electrode active material is analyzed by XPS, the manganese content on the surface is higher than that of NCM-based positive electrode active materials, and the atomic ratio of boron (B) to manganese (Mn) on the surface (B / Mn) is relatively small. Specifically, the atomic ratio of boron (B) to manganese (Mn) on the surface (B / Mn) may be 0.30 or more, 0.40 or more, 4.50 or less, or 5.00 or less.

[0038] According to the present invention, the positive electrode active material may have lower resistance than the lithium-rich transition metal oxide. That is, the coating layer contained in the positive electrode active material may contain a low-resistance substance that improves the electronic conductivity and ionic conductivity of the positive electrode active material.

[0039] According to the present invention, the positive electrode active material exhibits a peak I at 287.5-288.5 eV in the surface XPS spectrum. Carbonate,1 and peak I at 284-285 eV C-C Intensity ratio I Carbonate,1 :I C-C The ratio may be 0.05 to 0.15:1. Furthermore, the positive electrode active material exhibits a peak I at 288.6 to 290.5 eV in the surface XPS spectrum. Carbonate,2 and peak I at 284-285 eV C-C Intensity ratio I Carbonate,2 :I C-CThe ratio may be 0.05 to 0.15:1. This is because, in the case of the positive electrode active material according to the present invention, a coating layer is formed on the lithium-rich transition metal oxide, and the Li2CO3 content of the by-products (residual lithium) present in the lithium-rich transition metal oxide is significantly reduced, and the carbonate content on the surface of the positive electrode active material becomes significantly lower. On the other hand, in the XPS spectrum of the surface of the positive electrode active material, Carbonate,1 :I C-C and / or I Carbonate,2 :I C-C If the above range is met, the battery containing the positive electrode active material according to the present invention can have improved charge-discharge efficiency, discharge capacity at 0.33C, and resistance characteristics.

[0040] Peak I at 287.5-288.5 eV Carbonate,1 and peak I at 284-285 eV C-C Intensity ratio I Carbonate,1 :I C-C Specifically, this could be 0.05~0.15:1, 0.06~0.15:1, 0.07~0.14:1, 0.08~0.13:1, or 0.09~0.12:1. Also, the peak I at 288.6~290.5eV Carbonate,2 and peak I at 284-285 eV C-C Intensity ratio I Carbonate,2 :I C-C Specifically, this could be 0.05-0.15:1, 0.06-0.14:1, 0.07-0.13:1, or 0.08-0.12:1.

[0041] According to the present invention, the lithium-rich transition metal oxide may be in single-particle form, which improves the energy density of the lithium secondary battery and reduces gas generation.

[0042] According to the present invention, the lithium-rich transition metal oxide has an average particle size (D 50 The particle size may be 0.75 μm to 10 μm, specifically 0.9 μm to 10 μm or less. In this case, electrode defects due to particle aggregation during electrode manufacturing can be prevented.

[0043] On the other hand, if the lithium-rich transition metal oxide is in single-particle form, the average particle size (D 50 ) may be 0.75 μm to 2 μm.

[0044] Furthermore, if the lithium-rich transition metal oxide is in a secondary particle form formed by the aggregation of tens to hundreds of primary particles, the average particle size (D) of the lithium-rich transition metal oxide is... 50 The diameter may be 3 μm to 10 μm.

[0045] According to the present invention, the lithium-rich transition metal oxide may have a Mn content of 50 mol% or more, specifically 60 mol% or more, or more specifically 65 mol% or more, among the total metals other than lithium. In this case, high capacity can be achieved even when charging at high voltage.

[0046] According to the present invention, the lithium-rich transition metal oxide may have a composition represented by the following chemical formula 1. In this case, the charge-discharge efficiency in the first formation step and the discharge capacity after the activation step (particularly the discharge capacity at 0.33C) of the battery containing the positive electrode active material according to the present invention can be improved.

[0047] [Chemical formula 1] Li(Li a Ni b Co c Mn d Me e )O2

[0048] In the above chemical formula 1, Me is one or more elements selected from W, Mo, Zn, Mg, Nb, and Al. 0.01≦a≦0.20, 0≦b≦0.50, 0≦c≦0.10, 0.50≦d≦1.0, 0≦e≦0.10, and a+b+c+d+e=1.

[0049] The aforementioned lithium-rich transition metal oxide does not need to contain expensive cobalt, and can improve the performance of lithium secondary batteries while being cobalt-free.

[0050] According to the present invention, the lithium-rich transition metal oxide may be doped with W, Mo, or a combination thereof. When the lithium-rich transition metal oxide is doped with tungsten (W), the performance of the battery can be improved, and when it is 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, tungsten (W) can be doped with the lithium-rich transition metal oxide at a content of 14,700 ppm or less, and molybdenum (Mo) can also be doped with the lithium-rich transition metal oxide at a content of 5,500 ppm or less.

[0051] The tungsten (W) content may be 6,300 ppm or more, 7,500 ppm or more, 8,500 ppm or more, or 9,000 ppm or more relative to the total content of the lithium-rich transition metal oxide, and may also be 10,500 ppm or less, 12,000 ppm or less, 13,000 ppm or less, 14,000 ppm or less, or 14,700 ppm or less. When the tungsten (W) content is within the above range, the W ions form WO bonds, thereby improving structural stability. Specifically, during the initial charge, when all the lithium in the transition metal layer is desorbed from the Li2MnO3 phase, oxygen is released to match the chemical equivalents, but the WO bond reduces the amount of oxygen released on the surface. Furthermore, the WO bond suppresses the cation mixing phenomenon during the charge-discharge process, preventing deformation of the layered structure, thereby improving the capacity characteristics and resistance characteristics of the secondary battery containing the positive electrode active material.

[0052] The molybdenum (Mo) content may be 1,100 ppm or more, 1,500 ppm or more, 2,000 ppm or more, or 2,500 ppm or more relative to the total content of the lithium-rich transition metal oxide, and may also be 3,300 ppm or less, 3,500 ppm or less, 4,000 ppm or less, 4,500 ppm or less, or 5,500 ppm or less. When the molybdenum (Mo) content is within the above range, the Mo ions have a relatively large cation radius, which improves the particle size and particle shape of the positive electrode active material, and improves the life characteristics of the secondary battery containing the positive electrode active material.

[0053] According to the present invention, the coating layer may contain compounds in which lithium, boron, and oxygen are chemically bonded to each other, as well as compounds containing carbon. That is, amorphous compounds containing lithium, boron, and oxygen and carbon-based compounds can coexist.

[0054] According to the present invention, the coating layer may have a thickness of 1 nm to 80 nm, more specifically 1 nm to 50 nm, and more specifically 2 nm to 20 nm. In this case, the coating layer can help improve electrical properties, in particular, reduce resistance.

[0055] Method for manufacturing positive electrode active material The present invention provides a method for producing a positive electrode active material according to the present invention, comprising the steps of (A) dry mixing a lithium-containing raw material and a transition metal-containing raw material, and then calcining them to produce a lithium-excess transition metal oxide, and (B) dry mixing the lithium-excess transition metal oxide and a boron-containing raw material, and then heat-treating them to form a coating layer on the lithium-excess transition metal oxide.

[0056] (A) Step (A) Step involves dry mixing the lithium-containing raw material and the transition metal-containing raw material, followed by calcination to form the Li2MnO3 phase and LiMO2(M=Ni x Co y Mn zThis is a step to produce a lithium-excess transition metal oxide with a layered structure that simultaneously contains phases (0≦x≦0.9, 0≦y≦0.1, 0.1≦z≦1.0, x+y+z=1).

[0057] According to the present invention, in step (A), when the lithium-containing raw material and the transition metal-containing raw material are dry-mixed, a doping element-containing raw material may be further mixed in. That is, the doping element-containing raw material may be added selectively.

[0058] The lithium-containing raw material may be a lithium-containing raw material used in the production of a positive electrode active material, such as lithium hydroxide, lithium carbonate, or lithium oxide.

[0059] The transition metal-containing raw material may include nickel compounds, cobalt compounds, manganese compounds, and the like.

[0060] The nickel compound is a nickel raw material used in the production of the positive electrode active material, and may be, for example, nickel carbonate, sulfate, nitrate, hydroxide, or oxide.

[0061] The aforementioned cobalt compound is a cobalt raw material used in the production of the positive electrode active material, and may be, for example, a cobalt carbonate, sulfate, nitrate, hydroxide, or oxide.

[0062] The manganese compound is a manganese raw material used in the production of the positive electrode active material, and may be, for example, a manganese carbonate, sulfate, nitrate, or oxide.

[0063] The doping element-containing raw material comprises one or more selected from W and Mo, and may include tungsten oxide, molybdenum oxide, ammonium molybdate, lithium molybdate, etc.

[0064] For example, tungsten (W)-containing raw materials include WO3, WC, WS2, and C8H 16At least one selected from the group consisting of O8W may be used, and one or more mixtures of these may be used. Specifically, WO3 can be used, taking into consideration economics, the amount of gas generated during heat treatment, and the heat treatment temperature.

[0065] Furthermore, molybdenum (Mo)-containing raw materials include Li2MoO4, MoO3, and (NH4)6Mo7O 24 At least one can be selected from the group consisting of the above, and one or more mixtures of these can be used. Specifically, Li2MoO4 can be used, taking into consideration the raw materials used during mixing, the Mo content, and the heat treatment temperature.

[0066] The lithium-containing raw material, transition metal-containing raw material, and doping element-containing raw material can be added in amounts such that the resulting lithium-rich transition metal oxide has the composition represented by the chemical formula 1.

[0067] According to the present invention, the firing in step (A) can be carried out at a temperature of 850°C to 1,050°C. In this case, the crystallinity of the positive electrode active material can be increased.

[0068] The firing process can be carried out for 1 to 15 hours.

[0069] Specifically, step (A) may involve dry mixing a lithium-containing raw material and a transition metal-containing raw material, followed by primary calcination (corresponding to the calcination) to produce a primary calcined product, primary grinding of the primary calcined product, secondary calcination to remove the fine powder generated by the grinding to produce a secondary calcined product, and secondary grinding of the secondary calcined product to produce a lithium-rich transition metal oxide. Here, the secondary calcination is a heat treatment process that does not affect the phase of the lithium-rich transition metal oxide and is performed to cause very small particles to solidify upon receiving thermal energy, and can be carried out at a temperature lower than the primary calcination temperature (700-800°C).

[0070] The primary grinding is performed to reduce the size distribution among multiple particles, as the primary fired product contains multiple particles (several to tens of particles) randomly aggregated. The primary grinding is a process of grinding particles with weak force and has similarities to the disintegration process.

[0071] The secondary grinding is a process of separating the multiparticles contained in the secondary calcined product one by one and grinding the particles with strong force so that they exist in single-particle form. When the secondary grinding is completed, the particles have a single-particle form, and in this specification, the average particle size of the lithium-rich transition metal oxide may be the average particle size of the lithium-rich transition metal oxide in single-particle form after the secondary grinding is completed.

[0072] (B) Step Step (B) is a step in which the lithium-rich transition metal oxide and the boron-containing raw material are dry-mixed and then heat-treated to form a coating layer on the lithium-rich transition metal oxide.

[0073] Although by-products such as residual lithium exist on the surface of the lithium-rich transition metal oxide produced in step (A) above, in the present invention, even without the step of washing the residual lithium with water, the amount of residual lithium decreases as the process goes through step (B) above, and in particular the content of Li2CO3 decreases significantly, resulting in superior performance of the cathode active material produced.

[0074] Specifically, when the lithium-rich transition metal oxide boron-containing raw material is dry-mixed and then heat-treated, the boron-containing raw material melts, and Li2CO3, a by-product (residual lithium) present in the lithium-rich transition metal oxide, also participates in the reaction, forming a coating layer containing boron and carbon. That is, the boron present in the coating layer originates from the boron-containing raw material, and the carbon may originate from Li2CO3, a by-product (residual lithium) present in the lithium-rich transition metal oxide. As a result, the positive electrode active material according to the present invention may have a remarkably low carbonate content on its surface. In addition to boron and carbon, the coating layer may further contain lithium and oxygen, and the coating layer may also contain compounds in which lithium, boron, and oxygen are chemically bonded to each other, as well as compounds containing carbon.

[0075] According to the present invention, in step (B), the boron-containing raw material may be mixed in an amount such that the boron (B) content is 300 ppm to 1,500 ppm relative to the total weight of the lithium-excess transition metal oxide. Specifically, the boron-containing raw material may be mixed in an amount such that the boron (B) content is 300 ppm or more, 500 ppm or more, 1,000 ppm or more, or 1,500 ppm or less relative to the total weight of the lithium-excess transition metal oxide. In this case, a coating layer containing boron and carbon of appropriate thickness is formed, and the electrical properties of the manufactured positive electrode active material can be improved.

[0076] According to the present invention, the heat treatment in step (B) can be carried out at a temperature of 300°C to 450°C. Specifically, the heat treatment temperature may be 300°C or higher, 310°C or higher, 320°C or higher, 330°C or higher, 340°C or higher, 360°C or lower, 380°C or lower, 400°C or lower, or 450°C or lower. In this case, a coating layer with high electrical conductivity and improved battery performance can be formed.

[0077] The aforementioned heat treatment can be carried out for 3 to 7 hours, specifically 3 to 5 hours.

[0078] positive electrode The present invention provides a positive electrode containing the positive electrode active material.

[0079] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer may include the positive electrode active material.

[0080] The positive electrode current collector is not particularly limited as long as it contains a highly conductive metal, allows for easy adhesion of the positive electrode active material layer, and is unreactive within the battery voltage range. Examples of materials that can be used for the positive electrode current collector include stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, or silver. Furthermore, the positive electrode current collector can typically have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous materials, foams, and nonwoven fabrics.

[0081] The positive electrode active material layer may optionally contain a conductive material and a binder along with the positive electrode active material. Here, the positive electrode active material can be included in an amount of 80% to 99% by weight, more specifically 85% to 98.5% by weight, relative to the total weight of the positive electrode active material layer, and within this range, excellent capacitance characteristics can be observed.

[0082] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations in the battery it is configured in, as long as it does not cause chemical changes and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; 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. Of these, one or more can be used. The conductive material can be included in an amount of 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0083] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which the hydrogen atoms of these materials are substituted with Li, Na, or Ca, or various copolymers thereof. One of these materials alone or a mixture of two or more materials can be used. The binder can be present in an amount of 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0084] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except that the positive electrode active material is used. Specifically, the positive electrode can be manufactured by coating a positive electrode active material layer-forming composition, which is prepared by dissolving or dispersing the positive electrode active material and, if necessary, selectively, a binder, a conductive material, and a dispersant in a solvent, onto a positive electrode current collector, followed by drying and rolling; or by casting the positive electrode active material layer-forming composition onto another support, peeling it off the support, and laminating the resulting film onto the positive electrode current collector.

[0085] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and one or more of these can be used individually or in mixtures of two or more. The amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode.

[0086] Lithium-ion battery The present invention provides a lithium secondary battery including the positive electrode.

[0087] The lithium secondary battery may include a positive electrode, a negative electrode, a separator interposed between the positive and negative electrodes, and an electrolyte. The lithium secondary battery may also selectively further include a battery container for housing the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0088] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0089] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. The negative electrode current collector can usually have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0090] The negative electrode active material layer may selectively include a binder and a conductive material together with the negative electrode active material.

[0091] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. βExamples include metallic oxides that can be doped and dedoped with lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more mixtures thereof can be used. A metallic lithium thin film can also be used as the negative electrode active material. Furthermore, both low-crystallinity carbon and high-crystallinity carbon can be used as the carbon material. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbons such as petroleum or coal tar pitch-derived cokes. The anode active material can be present in an amount of 80% to 99% by weight relative to the total weight of the anode active material layer.

[0092] The binder in the negative electrode active material layer is a component that helps to bond the conductive material, active material, and current collector, and is usually added in an amount of 0.1% to 10% by weight relative to the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0093] The conductive material in the negative electrode active material layer is a component for further improving the conductivity of the negative electrode active material, and can be added in an amount of 10% by weight or less, preferably 5% by weight or less, relative to the total weight of the negative electrode active material layer. Such conductive materials are not particularly limited as long as they do not cause chemical changes in the battery and are conductive, and 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 black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used.

[0094] The negative electrode can be manufactured by coating a negative electrode active material layer-forming composition, which is prepared by dissolving or dispersing a negative electrode active material and, selectively, a binder and a conductive material in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode active material layer-forming composition onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0095] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a separator commonly used in lithium secondary batteries. Particularly preferred is one that exhibits low resistance to ion movement of the electrolyte and has excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as those made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof, can be used. Alternatively, ordinary porous nonwoven fabrics, such as those made from high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used in single-layer or multi-layer structures.

[0096] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries. Specifically, the electrolyte may contain an organic solvent and a lithium salt.

[0097] The aforementioned organic solvent can be used without particular limitations, as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the aforementioned organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0098] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the anion of the lithium salt is 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 may be selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably in the range of 0.1M to 2.0M. When the concentration of the lithium salt falls within this range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0099] In addition to the components of the electrolyte, the electrolyte may also contain one or more additives, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethyl alcoholamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethyl alcohol, or aluminum trichloride, for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. Here, the additive may be present in an amount of 0.1% to 5% by weight relative to the total weight of the electrolyte.

[0100] The lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent capacity characteristics, output characteristics, and life characteristics in a stable manner, making it useful in fields such as portable devices like mobile phones, notebook computers, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0101] The external shape of the lithium secondary battery of the present invention is not particularly limited, but it may be cylindrical, rectangular, pouch-type, or coin-type, using a can.

[0102] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also preferably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0103] This provides a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

[0104] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0105] Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0106] Examples Example 1 Li2CO3, NiCO3, and MnCO3 were dry-mixed to a lithium:nickel:manganese molar ratio of 1.143:0.287:0.57, and then calcined at 1,000°C for 12 hours in an air atmosphere to produce a calcined product. The calcined product was then pulverized using a UCM (Retsch ZM200, 18,000 rpm), and then calcined at 750°C for 5 hours in an air atmosphere to remove fine particles. Finally, it was pulverized using a Jet-mill (ISAACENC Micron-master air jetmill, 3.5 bar) to obtain single-particle lithium-rich transition metal oxide (composition: Li 1.143 Ni 0.287 Mn 0.57 O2, average particle size (D 50 A sample of 1.05 μm was produced.

[0107] The lithium-rich transition metal oxide was mixed with H3BO3 such that the amount of boron (B) was 1,200 ppm relative to the total weight of the lithium-rich transition metal oxide. This mixture was then heat-treated at 350°C for 5 hours to form a coating layer (thickness: 2-10 nm) containing lithium, boron, carbon, and oxygen on the lithium-rich transition metal oxide, thereby producing a positive electrode active material.

[0108] Example 2 Li2CO3, NiCO3 and MnCO3 were dry-mixed so that the molar ratio of lithium:nickel:manganese was 1.143:0.287:0.57 to prepare a mixture. WO3 was further mixed with the mixture so that tungsten (W) was 10,500 ppm with respect to the total weight of the lithium-excess transition metal oxide finally produced, and then fired at 1,050 °C for 12 hours to produce a fired product. The fired product was pulverized with a UCM apparatus (ZM200, manufactured by Retsch, 18,000 rpm), and then fired at 750 °C for 5 hours in an air atmosphere for removal of fine powder, and pulverized with a Jet-mill apparatus (Micron-master air jetmill, manufactured by ISAACENC, 3.5 bar) to obtain a lithium-excess transition metal oxide in single-particle form (composition: Li 1.143 Ni 0.287 Mn 0.565 W 0.005 O2, average particle size (D 50 ): 0.93 μm) was produced.

[0109] H3BO3 was mixed with the lithium-excess transition metal oxide so that boron (B) was 1,200 ppm with respect to the total weight of the lithium-excess transition metal oxide, and then heat-treated at 350 °C for 5 hours to form a coating layer (thickness: 2 to 10 nm) containing lithium, boron, carbon and oxygen on the lithium-excess transition metal oxide to produce a positive electrode active material.

[0110] Example 3 Li2CO3, NiCO3 and MnCO3 were dry-mixed in a lithium:nickel:manganese molar ratio of 1.143:0.287:0.57 to prepare a mixture. WO3 and Li2MoO4 were further mixed into the mixture such that tungsten (W) and molybdenum (Mo) were 10,500 ppm and 3,300 ppm, respectively, based on the total weight of the finally produced lithium-excess transition metal oxide. After that, the mixture was calcined at 1,050 °C for 12 hours to produce a calcined product. The calcined product was pulverized with a UCM device (ZM200, manufactured by Retsch, 18,000 rpm), and then, for the removal of fine powder, it was calcined at 750 °C for 5 hours in an air atmosphere and pulverized with a Jet-mill device (Micron-master air jetmill, manufactured by ISAACENC, 3.5 bar) to produce lithium-excess transition metal oxide in the form of single particles (composition: Li 1.143 Ni 0.287 Mn 0.562 W 0.005 Mo 0.003 O2, average particle size (D 50 ): 1.05 μm).

[0111] H3BO3 was mixed into the lithium-excess transition metal oxide such that boron (B) was 1,450 ppm based on the total weight of the lithium-excess transition metal oxide. After that, it was heat-treated at 350 °C for 5 hours to form a coating layer (thickness: 2 - 10 nm) containing lithium, boron, carbon and oxygen on the lithium-excess transition metal oxide to produce a positive electrode active material.

[0112] Example 4 Li2CO3, NiCO3 and MnCO3 were added to pure water in amounts such that the lithium:nickel:manganese molar ratio was 1.145:0.282:0.572 (solid content: 20 wt%). Wet mixing was carried out using a zirconia ball for 1 hour with a ball mill. Next, the zirconia balls were removed, and the solid content was pulverized using a wet pulverization device (MiniCer, manufactured by NETZCH) to obtain an average particle size (D 50A slurry with a particle size of 0.2 μm was prepared. Next, using a spray dryer (Buchi B-290), the slurry was spray-dried to obtain a dried product by setting the input hot air temperature to 200°C and the exhaust hot air temperature to 90°C or higher. The dried product was calcined in an air atmosphere at 975°C for 12 hours to produce a calcined product. The calcined product was pulverized using a jet mill (ISAACENC Micron-master air jetmill, 1.7 bar) to obtain single-particle lithium-rich transition metal oxide (composition: Li 1.145 Ni 0.282 Mn 0.572 O2, average particle size (D 50 A sample of 1.01 μm was produced.

[0113] The lithium-rich transition metal oxide was mixed with H3BO3 so that the amount of boron (B) was 300 ppm relative to the lithium-rich transition metal oxide, and then heat-treated at 350°C for 5 hours to form a coating layer (thickness: 1-10 nm) containing lithium, boron, carbon, and oxygen on the lithium-rich transition metal oxide, thereby producing a positive electrode active material.

[0114] Comparative Example 1 The lithium-rich transition metal oxide produced in Example 1 was used as the positive electrode active material in Comparative Example 1.

[0115] Comparative Example 2 The lithium-rich transition metal oxide produced in Example 2 was used as the positive electrode active material in Comparative Example 2.

[0116] Comparative Example 3 The lithium-rich transition metal oxide produced in Example 3 was used as the cathode active material in Comparative Example 3.

[0117] Comparative Example 4 It is a secondary particle form, and LiNi 0.88 Co 0.05 Mn 0.07 Layered structure of high-Ni lithium transition metal oxide having a composition represented by O2 (average particle size (D 50 A 10μm (size) was prepared.

[0118] The lithium transition metal oxide was mixed with H3BO3 so that the amount of boron (B) was 1000 ppm relative to the lithium transition metal oxide, and then heat-treated at 350°C for 5 hours to form a coating layer (thickness: 2-10 nm) containing lithium, boron, carbon, and oxygen on the lithium-rich transition metal oxide, thereby producing a positive electrode active material.

[0119] Comparative Example 5 The lithium-rich transition metal oxide produced in Example 4 was used as the cathode active material in Comparative Example 5.

[0120] Comparative Example 6 In Example 4, H3BO3 was mixed with the lithium-rich transition metal oxide so that the amount of boron (B) was 150 ppm relative to the lithium-rich transition metal oxide. This mixture was then heat-treated at 350°C for 5 hours to form a coating layer (thickness: 1-10 nm) containing lithium, boron, carbon, and oxygen on the lithium-rich transition metal oxide, thereby producing a positive electrode active material.

[0121] Experimental example Experimental Example 1: EELS Analysis After performing EELS analysis on electrodes containing the positive electrode active material manufactured in Examples 1 to 4, the EELS data for Example 1 is shown in Figure 1.

[0122] Specifically, samples for cross-sectional imaging for STEM-EELS analysis were prepared using a TFS Helios 5 UX (acceleration voltages of 30, 5, and 2 kW, with Pt coating). Using a TFS Spectra 300 STEM, HAADF and EELS images were acquired at an acceleration voltage of 200 kV. The acquired images were then line-scanned to confirm the thickness of the coating layer and the presence or absence of constituent elements.

[0123] Referring to Figure 1, it can be confirmed that the thickness of the coating layer in the analyzed area is approximately 2 nm, and that boron and carbon are present in the coating layer.

[0124] Experimental Example 2: XRD Analysis The positive electrode active materials produced in Examples 1 to 4 were subjected to XRD analysis, and the XRD spectra are shown in Figure 2.

[0125] Specifically, XRD analysis was performed using a Bruker D8 endeavor under the conditions of λ=1.5418 Å (Cu target), 40 kV, 40 mA, and 2 theta:15~80 degrees.

[0126] Referring to Figure 2, it can be confirmed that the positive electrode active materials produced in Examples 1 to 4 all have peaks corresponding to regions A, B, and C, which are shaded in Figure 2, indicating that they simultaneously contain the Li2MnO3 phase and the LiMO2 phase, forming a layered lithium excess oxide structure.

[0127] Experiment Example 3: XPS Analysis - Elemental content analysis of the surface of the positive electrode active material XPS analysis was performed on the positive electrode active materials produced in Examples 1-4 and Comparative Examples 4 and 6. The content of O, C, Li, Mn, Ni, and B elements present on the surface was then analyzed and is shown in Table 1 below. The atomic ratio of boron (B) to manganese (Mn) (B / Mn) was also calculated and is shown in Table 1 below.

[0128] Specifically, a Nexsa system manufactured by Thermo Fisher Scientific Inc. was used, with a monochromatic Al Ka ​​(1486.6 eV) as the X-ray source, CAE (Constant Analyzer Energy) mode as the operation mode, and Avantage software (version 5.9925) was used. After filling the powder holder with the sample, it was fixed onto Cu foil with carbon tape and loaded into the equipment. After loading the sample, once the vacuum of the load lock had decreased sufficiently, the experiment was performed according to the K-Alpha standard operating procedure (SOP-0524-0k). After a survey scan of the surface of each sample (as-received state), qualitative analysis was performed, and based on the qualitative analysis results, narrow scans (snaps) were obtained at three points per sample for each element to perform quantitative analysis.

[0129] [Table 1]

[0130] Referring to Table 1, it can be confirmed that, in the case of the positive electrode active materials of Examples 1 to 4, a large amount of manganese is present on the surface, and the B / Mn value is relatively significantly lower compared to the NCM-based positive electrode active material of Comparative Example 4. Furthermore, it can be confirmed that the positive electrode active materials of Examples 1 to 4 satisfy a B / Mn value of 0.3 to 5, while the positive electrode active material of Comparative Example 6 has a B / Mn value of less than 0.3.

[0131] - Analysis of carbonate content on the surface of positive electrode active material Figure 3 shows the XPS spectra obtained by performing XPS analysis on the positive electrode active materials produced in Examples 1-3 and Comparative Example 1 using the same method as for elemental content analysis of the positive electrode active material surface. Furthermore, in the surface XPS spectrum, a peak I at 287.5-288.5 eV is observed. Carbonate,1 and peak I at 284-285 eV C-C Intensity ratio I Carbonate,1 :I C-CAnd peak I at 288.6~290.5eV Carbonate,2 and peak I at 284-285 eV C-C Intensity ratio I Carbonate,2 :I C-C The calculations were performed and are shown in Table 2 below.

[0132] [Table 2]

[0133] Referring to Figure 3 and Table 2, it can be seen that in the case of the positive electrode active materials of Examples 1 to 3, the intensity of the carbonate peak is significantly lower compared to the positive electrode active material of Comparative Example 1, indicating a significant decrease in carbonate content.

[0134] Experimental Example 4: Analysis of Residual Lithium Content The residual lithium content of the positive electrode active materials produced in Examples 1-4 and Comparative Examples 1-6 was analyzed using the following method, and the results are shown in Table 3 below. Furthermore, the lithium transition metal oxide of Comparative Example 4 was used as the positive electrode active material, and the residual lithium content was analyzed using the same method as in Experimental Example 4, and the results are shown in Table 3 below as Reference Example 1.

[0135] Specifically, for the analysis of residual lithium content, we used a Metrohm 888 Titrandeo, 814 USM Sample Processor, and tiamo 2.5 software. 2.5 g of cathode active material was added to 100 ml of ultrapure water, and the mixture was stirred at 300 rpm for 5 minutes. The stirred solution was then filtered under reduced pressure using a PES04547A filter, and the residual lithium content of the filtered liquid was analyzed using 0.1 N HCl.

[0136] [Table 3]

[0137] Referring to Table 3 above, it can be confirmed that the total amount of residual lithium decreased in the case of the positive electrode active material of Example 1 compared to the positive electrode active material of Comparative Example 1, in the case of the positive electrode active material of Example 2 compared to the positive electrode active material of Comparative Example 2, in the case of the positive electrode active material of Example 3 compared to the positive electrode active material of Comparative Example 3, and in the case of the positive electrode active material of Example 4 compared to the positive electrode active materials of Comparative Examples 5 and 6. In particular, it can be confirmed that the content of Li2CO3 among the residual lithium decreased significantly. Furthermore, it can be confirmed that the rate of decrease in Li2CO3 content is significantly higher in the positive electrode active materials of Examples 1 to 4 compared to NCM-based positive electrode active materials containing a coating layer containing boron.

[0138] Experimental Example 5: Evaluation of Battery Characteristics A positive electrode slurry was prepared by mixing 92.5% by weight of the positive electrode active material produced in Examples 1-4 and Comparative Examples 1-6, 3% by weight of Super P as a conductive material, and 4.5% by weight of polyvinylidene fluoride (PVDF) as a binder in an N-methylpyrrolidone (NMP) solvent. The prepared positive electrode slurry was applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to produce a positive electrode.

[0139] An electrode assembly was manufactured using a lithium metal electrode as the negative electrode, with a porous polyethylene separator interposed between the positive and negative electrodes. This assembly was placed inside a battery case, and an electrolyte solution (additives: LiBF 42%, FEC 5%) was injected, which consisted of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed in a volume ratio of 3:7, with 1M LiPF6 dissolved in it, to manufacture a coin-type half-cell.

[0140] Using coin-type half-cells containing the positive electrode active materials of Examples 1-4 and Comparative Examples 1-3, 5, and 6 manufactured above, the cells were charged to 4.65V at 45°C with a constant current of 0.1C, and then discharged to 2.0V with a constant current of 0.1C to perform an activation process (formation). The charge and discharge capacities at this time are shown in Table 4 below, and the percentage of the discharge capacity to the charge capacity at this time is defined as the efficiency of the activation process, as shown in Table 4 below.

[0141] After the activation process, the battery was charged to 4.4V at 25°C with a constant current of 0.1C, and then discharged to 2.5V with a constant current of 0.1C to confirm the initial charge and discharge performance. The charge and discharge process was then repeated, changing the current from 0.1C to 0.33C. This cycle was considered one cycle, and the discharge capacity was measured while repeating the charging and discharging process for a total of 30 cycles. The discharge capacity per cycle is shown in Table 4 below, and the capacity retention rate is defined as the percentage of the discharge capacity after 30 cycles relative to the discharge capacity after 1 cycle, also shown in Table 4 below.

[0142] The batteries, after undergoing the activation process, were charged to 4.4V at 25°C with a constant current of 0.1C, and then discharged to 2.5V with a constant current of 0.1C. The initial voltage and the voltage at 60 seconds were measured, and the DC internal resistance (DCIR) was calculated and is shown in Table 4 below. For reference, the DCIR value is calculated by dividing the difference between the voltage at 60 seconds of discharge with a constant current of 0.1C and the initial voltage by the applied current.

[0143] On the other hand, the coin-type half-cell containing the positive electrode active material of Comparative Example 4 manufactured above had a different type of positive electrode material, and was evaluated under different battery evaluation conditions. Specifically, a battery that had not undergone the activation process was charged to 4.25V at 25°C with a constant current of 0.1C, and while discharging to 2.5V with a constant current of 0.1C, the initial voltage and the voltage at 60 seconds were measured, and the DC internal resistance (DCIR) was calculated and shown in Table 4 below.

[0144] For reference, when the lithium transition metal oxide of Comparative Example 4 was used as the positive electrode active material, a battery was manufactured using the same method as in Experimental Example 5, and the DCIR value obtained using the same method as the battery evaluation method of Comparative Example 4 was 18.6 Ω.

[0145] [Table 4]

[0146] Referring to Table 4 above, it can be confirmed that the battery containing the positive electrode active material of Example 1 exhibits superior efficiency during the activation process, superior discharge capacity per cycle (discharge capacity of 0.33C), and significantly lower DC internal resistance compared to the battery containing the positive electrode active material of Comparative Example 1. Similarly, the battery containing the positive electrode active material of Example 2 exhibits superior efficiency during the activation process, superior discharge capacity per cycle (discharge capacity of 0.33C), and significantly lower DC internal resistance compared to the battery containing the positive electrode active material of Comparative Example 2. Furthermore, the battery containing the positive electrode active material of Example 3 exhibits superior efficiency during the activation process, superior discharge capacity per cycle (discharge capacity of 0.33C), and significantly lower DC internal resistance compared to the battery containing the positive electrode active material of Comparative Example 3. Finally, the battery containing the positive electrode active material of Example 4 exhibits superior efficiency during the activation process, superior discharge capacity per cycle (discharge capacity of 0.33C), and significantly lower DC internal resistance compared to the battery containing the positive electrode active material of Comparative Example 5.

[0147] From this, it can be confirmed that the positive electrode active material according to the present invention has lower resistance compared to lithium-rich transition metal oxides without a coating layer. Furthermore, it can be confirmed that the overall performance of the battery is improved when the atomic ratio of boron (B) to manganese (Mn) present on the surface, as analyzed by XPS, satisfies 0.3 to 5.

[0148] On the other hand, in the case of the battery containing the positive electrode active material of Comparative Example 4, which includes a coating layer formed on a high-Ni lithium transition metal oxide, it can be confirmed that the DC internal resistance is higher compared to the battery containing a high-Ni lithium transition metal oxide.

[0149] This is thought to be because the coating layer in the positive electrode active material of the present invention contains a substance with low resistance, while the coating layer in the positive electrode active material of Comparative Example 4 contains a substance with high resistance.

[0150] As a result, it is found that the positive electrode active material of the present invention includes a coating layer containing boron and carbon formed on a lithium-rich transition metal oxide with a layered structure containing both a Li2MnO3 phase and a LiMO2 phase, satisfies at least one of the following conditions (1) to (3), and can improve the performance of a lithium secondary battery containing it.

[0151] -Condition (1): The atomic ratio (B / Mn) of boron (B) to manganese (Mn) present on the surface analyzed by XPS is 0.3-5 -Condition (2): In the surface XPS spectrum, peak I at 287.5~288.5 eV Carbonate,1 and peak I at 284-285 eV C-C Intensity ratio I Carbonate,1 :I C-C The ratio is 0.05~0.15:1 -Condition (3): In the surface XPS spectrum, peak I at 288.6~290.5 eV Carbonate,2 and peak I at 284-285 eV C-C Intensity ratio I Carbonate,2 :I C-C The ratio is 0.05~0.15:1

Claims

1. Li ２ MnO ３ Ai and LiMO ２ A lithium-rich transition metal oxide with a layered structure containing phases simultaneously (where M is an element containing one or more selected from Ni, Co, and Mn), The lithium-rich transition metal oxide comprises a coating layer containing boron and carbon formed on the lithium-rich transition metal oxide, A positive electrode active material that satisfies at least one of the following conditions (1) to (3). -Condition (1): The atomic ratio (B / Mn) of boron (B) to manganese (Mn) present on the surface analyzed by XPS is 0.3 to 5 - Condition (2): In the surface XPS spectrum, peak I at 287.5–288.5 eV Ｃａｒｂｏｎａｔｅ，１ and peak I at 284-285 eV Ｃ－Ｃ Intensity ratio I Ｃａｒｂｏｎａｔｅ，１ : I Ｃ－Ｃ The ratio is 0.05 to 0.15:1 - Condition (3): In the XPS spectrum of the surface, peak I at 288.6 - 290.5 eV Ｃａｒｂｏｎａｔｅ，２ and peak I at 284 - 285 eV Ｃ－Ｃ have an intensity ratio I Ｃａｒｂｏｎａｔｅ，２ : I Ｃ－Ｃ of 0.05 - 0.15:1

2. The positive electrode active material according to claim 1, wherein the lithium-rich transition metal oxide is in single-particle form.

3. The lithium-rich transition metal oxide has an average particle size (D ５０ The positive electrode active material according to claim 1, wherein the diameter is 0.75 μm to 10 μm.

4. The lithium-rich transition metal oxide has a Mn content of 50 mol% or more among the total metals other than lithium, as described in claim 1.

5. The positive electrode active material according to claim 1, wherein the lithium-rich transition metal oxide has a composition represented by the following chemical formula 1. [Chemical formula 1] Li(Li ａ Ni ｂ Co ｃ Mn ｄ Me ｅ )O ２ In the aforementioned chemical formula 1, Me is one or more elements selected from W, Mo, Zn, Mg, Nb, and Al. 0.01 ≤ a ≤ 0.20, 0 ≤ b ≤ 0.50, 0 ≤ c ≤ 0.10, 0.50 ≤ d ≤ 1.0, 0 ≤ e ≤ 0.10, and a + b + c + d + e = 1.

6. The positive electrode active material according to claim 1, wherein the lithium-rich transition metal oxide is doped with W, Mo, or a combination thereof.

7. The positive electrode active material according to claim 1, wherein the coating layer comprises a compound in which lithium, boron, and oxygen are chemically bonded to each other, and a compound containing carbon.

8. The positive electrode active material according to claim 1, wherein the coating layer has a thickness of 1 nm to 80 nm.

9. (A) A step of producing a lithium-rich transition metal oxide by dry mixing a lithium-containing raw material and a transition metal-containing raw material, followed by calcination, (B) A method for producing a positive electrode active material according to claim 1, comprising the steps of (B) dry mixing the lithium-excess transition metal oxide and the boron-containing raw material, and then heat-treating them to form a coating layer on the lithium-excess transition metal oxide.

10. The method for producing a positive electrode active material according to claim 9, wherein the firing is carried out at a temperature of 850°C to 1,050°C.

11. The method for producing a positive electrode active material according to claim 9, wherein the boron-containing raw material is mixed in such an amount that the boron (B) contained in the boron-containing raw material is 300 ppm to 1,500 ppm relative to the total weight of the lithium excess transition metal oxide.

12. The method for producing a positive electrode active material according to claim 9, wherein the heat treatment is performed at a temperature of 300°C to 450°C.

13. The method for producing a positive electrode active material according to claim 9, wherein when dry mixing the lithium-containing raw material and the transition metal-containing raw material, a doping element-containing raw material is further mixed.

14. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 8.

15. A lithium secondary battery comprising the positive electrode described in claim 14.

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