Cathode active material and preparation method therefor

Abstract

The present invention relates to a cathode active material capable of improving the performance and stability of a lithium-rich manganese-based oxide, thereby improving the performance of a battery comprising same, and, to a cathode active material and a preparation method therefor, the material comprising: a core part comprising a lithium-rich manganese-based oxide of a layered structure that includes both a Li2MnO3 phase and a LiMO2 (here, M is at least one element selected from among Ni, Co and Mn) phase; a first layer which is continuously formed on the core part and which has a crystal structure belonging to the R-3m space group; and a second layer which is continuously formed on the first layer and which has a rock-salt crystal structure belonging to the Fm-3m space group.

Description

Positive electrode active material and method for producing the same

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2023-0135434, filed October 11, 2023, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a positive electrode active material and a method for producing the same.

[0005]

[0006] Lithium secondary batteries are composed of four major components: a cathode, an anode, a separator, and an electrolyte. Among these, the cathode active material contained in the cathode plays a significant role in determining the battery's capacity, output, and lifespan. For lithium secondary batteries to achieve high energy density, output, and lifespan, improving the performance of the cathode active material is essential. Consequently, extensive research has been conducted recently to develop high-performance cathode active materials.

[0007] Li-rich layered oxide, a type of cathode active material, is a mixed phase of Li2MnO3 phase and LiMO2 (M=Ni, Mn, Co) phase and has a high operating voltage (>3.5 V vs. Li / Li). + ) has the characteristic of providing a very large capacity of 250 mAh / g. Therefore, the lithium excess oxide is attracting attention as a low-cost, high-capacity cathode active material.

[0008] However, the lithium-excess oxide has problems that arise due to its structural characteristic of being a mixture of two phases. Specifically, when a battery containing the lithium-excess oxide is operated under high voltage, there is a problem that irreversible capacity loss occurs in the first formation process, resulting in reduced efficiency, and during charge / discharge cycles, voltage fading occurs as the layered structure changes to a spinel structure and then to a rock salt structure, resulting in problems such as the generation of O2 gas.

[0009] Therefore, it is necessary to secure a technology to improve the performance and stability of the lithium-excess oxide.

[0010]

[0011] The problem to be solved in the present invention is to improve the performance and stability of lithium-excess oxide, thereby improving the performance of a battery containing the same.

[0012] In addition, the present invention aims to provide a method for manufacturing the positive electrode active material.

[0013]

[0014] To solve the above problem, the present invention provides a positive electrode active material and a method for producing the positive electrode active material.

[0015]

[0016] (1) The present invention provides a cathode active material comprising a core portion including a lithium-excess manganese oxide having a layered structure simultaneously including a Li2MnO3 phase and a LiMO2 (wherein M is an element including at least one selected from Ni, Co, and Mn) phase; a first layer formed continuously on the core portion and including a crystal structure belonging to the R-3m space group; and a second layer formed continuously on the first layer and including a rock salt-type crystal structure belonging to the Fm-3m space group.

[0017] (2) The present invention provides a positive electrode active material in (1) above, wherein the lithium-excess manganese oxide includes at least one doping element selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr.

[0018] (3) The present invention provides a positive electrode active material in (1) or (2), wherein the lithium-excess manganese oxide includes a crystal structure belonging to the C2 / m space group and the R-3m space group.

[0019] (4) The present invention provides a positive electrode active material in any one of the above (1) to (3), wherein the lithium-excess manganese oxide has a manganese (Mn) content of 50 mol% or more among all metals excluding lithium.

[0020] (5) The present invention provides a positive electrode active material in any one of the above (1) to (4), wherein the lithium-excess manganese oxide has a composition represented by the following chemical formula 1.

[0021] [Chemical Formula 1]

[0022] Li a Ni b Co c Mn d Me e O2

[0023] In the above chemical formula 1,

[0024] Me is one or more selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr,

[0025] 1.09≤a≤1.20, 0≤b≤0.50, 0≤c≤0.10, 0.50≤d≤1.0, 0 <e≤0.10이다.

[0026] (6) The present invention provides a positive electrode active material according to any one of the above (1) to (5), wherein the lithium-excess manganese oxide is in the form of secondary particles.

[0027] (7) In any one of the above (1) to (6), the lithium-excess manganese oxide has an average particle diameter (D 50 ) provides a positive electrode active material having a diameter of 5㎛ to 15㎛.

[0028] (8) The present invention provides a positive electrode active material according to any one of the above (1) to (7), wherein the positive electrode active material further includes a coating layer formed on the second layer and including at least one selected from carbon and sulfur.

[0029] (9) The present invention provides a positive electrode active material according to (8), wherein the coating layer further contains boron.

[0030] (10) The present invention provides a positive electrode active material in (8) or (9), wherein the carbon is derived from urea and the sulfur is derived from thiourea.

[0031] (11) The present invention provides a positive electrode active material in any one of the above (1) to (10), wherein the first layer has a thickness of 0.5 nm to 20 nm.

[0032] (12) The present invention provides a positive electrode active material according to any one of (1) to (11), wherein the second layer has a thickness of 0.5 nm to 20 nm.

[0033] (13) The present invention provides a method for producing a cathode active material according to claim 1, comprising the steps of: (A) dry mixing a composite transition metal hydroxide and a lithium-containing raw material, then performing a first calcination at 400°C to 500°C and a second calcination at 800°C to 1000°C to produce a lithium-excess manganese oxide; and (B) dry mixing at least one selected from urea and thiourea and the lithium-excess manganese oxide using a mechanofusion method, and then heat treating the mixture at 300°C to 550°C.

[0034] (14) The present invention provides a method for manufacturing a cathode active material, wherein, in step (13), when dry mixing a composite transition metal hydroxide and a lithium-containing raw material in the 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 is further mixed.

[0035] (15) The present invention provides a method for producing a positive electrode active material, wherein the composite transition metal hydroxide in (13) or (14) above has a composition represented by the following chemical formula 2.

[0036] [Chemical Formula 2]

[0037] Ni b' Co c' Mn d' Me e' (OH)2

[0038] In the above chemical formula 2,

[0039] Me is one or more selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr,

[0040] 0≤b'≤0.50, 0≤c'≤0.10, 0.50≤d'≤1.0, 0≤e'≤0.10, b'+c'+d'+e'=1.

[0041] (16) The present invention provides a method for manufacturing a positive electrode active material, wherein the first firing and the second firing are each independently performed under an air atmosphere or an oxygen atmosphere in any one of the above (13) to (15).

[0042] (17) The present invention provides a method for producing a positive electrode active material, wherein in any one of the above (13) to (16), in the step (B), at least one selected from urea and thiourea is mixed in an amount of 0.3 to 3 parts by weight per 100 parts by weight of the lithium-excess manganese oxide.

[0043] (18) The present invention provides a method for manufacturing a positive electrode active material, wherein the heat treatment is performed under an N2 atmosphere in any one of the above (13) to (17).

[0044] (19) The present invention provides a method for producing a positive electrode active material, wherein, in any one of the above (13) to (18), when dry mixing at least one selected from urea and thiourea and the lithium-excess manganese oxide in step (B), a boron-containing raw material is further mixed.

[0045] (20) The present invention provides a method for producing a positive electrode active material, wherein, in the above (19), the boron-containing raw material is mixed in an amount of 0.2 to 2 parts by weight per 100 parts by weight of the lithium-excess manganese oxide.

[0046]

[0047] The cathode active material of the present invention comprises a first layer including a crystal structure belonging to the R-3m space group formed continuously on a lithium-excess manganese oxide, and a second layer including a rock salt-type crystal structure belonging to the Fm-3m space group formed continuously on the first layer, so that the structure of the cathode active material is stabilized, and thus the performance of a lithium secondary battery including the cathode active material, for example, the life characteristics, can be improved and gas generation can be reduced.

[0048]

[0049] Figure 1 is a HAADF-STEM image of a cross-section of the positive electrode active material manufactured in Example 5.

[0050] Figure 2 shows the a / I of the cross-section of the positive electrode active material manufactured in Example 5. MnL3 It's a ratio map.

[0051] Figure 3 is an OK pre-edge / main edge ratio map of a cross-section of a positive electrode active material manufactured in Example 5.

[0052] Figure 4 is a HAADF-STEM image of a cross-section of the positive electrode active material manufactured in Comparative Example 1.

[0053] Figure 5 shows the a / I of the cross-section of the positive electrode active material manufactured in Comparative Example 1. MnL3 It's a ratio map.

[0054] Figure 6 is an OK pre-edge / main edge ratio map of a cross-section of a positive electrode active material manufactured in Comparative Example 1.

[0055] Figure 7 is EELS analysis data of OK edge.

[0056] Figure 8 is EELS analysis data of Mn L3edge.

[0057] Figure 9 is an HR-(S)TEM image of the positive electrode active material of Example 5 of the present invention.

[0058] Figure 10 is an HR-(S)TEM image of the positive electrode active material of Comparative Example 1.

[0059] Figure 11 is an HR-(S)TEM image of the positive electrode active material of Comparative Example 3.

[0060] Figure 12 is a HAADF-STEM image and EDS data of the positive electrode active material of Example 5 of the present invention.

[0061] Figure 13 is a graph showing the amount of gas generated during 50 cycles of charging and discharging.

[0062] Figure 14 is a graph showing the amount of gas generated during storage in a chamber at 60°C for 4 weeks.

[0063] Figure 15 is a graph of the charge / discharge profile according to repeated charge / discharge cycles.

[0064] Figure 16 is the formation cycle, 0 th This is a graph of the specific capacity as the charge and discharge cycles are repeated after each cycle.

[0065] Figure 17 is a graph of the average discharge voltage as the charge and discharge cycle is repeated.

[0066] Figure 18 is a graph of energy density as the charge and discharge cycle is repeated.

[0067]

[0068] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0069] The terms or words used in the description and claims of the present invention should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0070]

[0071] It should be understood that the terms “include,” “have,” or “have” used in this specification are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0072] In this specification, the term 'on' means not only when a configuration is formed directly on the top surface of another configuration, but also when a third configuration is interposed between these configurations.

[0073] In this specification, 'primary particle' means the smallest particle unit recognized when observing a positive electrode active material using a scanning electron microscope (SEM), and 'secondary particle' means a secondary structure formed by the aggregation of multiple primary particles.

[0074] In this specification, the term 'average particle diameter (D 50 )' means the particle size at the 50% point of the volume cumulative distribution according to particle size. The above 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 measuring device (e.g., Bluewave of Microtrac), and measuring the difference in diffraction pattern according to particle size when the particles pass through the laser beam to calculate the particle size distribution, and calculating the particle diameter at the point where it becomes 50% of the volume cumulative distribution according to particle size in the measuring device, thereby obtaining D 50 can be measured.

[0075]

[0076] positive electrode active material

[0077] The present invention provides a cathode active material comprising: a core portion including a lithium-excess manganese oxide having a layered structure simultaneously including a Li2MnO3 phase and a LiMO2 (wherein M is an element including at least one selected from Ni, Co, and Mn) phase; a first layer formed continuously on the core portion and including a crystal structure belonging to the R-3m space group; and a second layer formed continuously on the first layer and including a rock salt-type crystal structure belonging to the Fm-3m space group.

[0078] The inventors of the present invention have found that when a positive electrode active material includes a first layer including a crystal structure belonging to the R-3m space group continuously formed on a lithium-excess manganese oxide and a second layer including 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, migration of a transition metal is suppressed, phase change is suppressed, and lithium mobility is improved, and as a result, the life characteristics of a battery including the positive electrode active material according to the present invention can be improved, gas generation can be reduced, and discharge capacity, de-rating, etc. can be improved, and the present invention has been completed. The first layer and the second layer are relatively reduced layers compared to the lithium-excess manganese oxide, and are reduced double layers.

[0079] Meanwhile, when the positive electrode active material does not include the first layer and the second layer, problems arise due to the structural characteristics of the lithium-excess manganese oxide being a mixture of two phases, and thus there are problems with the performance of the battery including it.

[0080]

[0081] According to the present invention, the lithium-excess manganese oxide may include at least one doping element selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr. That is, the lithium-excess 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 doping element is doped into the lithium-excess manganese oxide, the binding energy between the doping element and oxygen increases, thereby suppressing desorption of oxygen within the positive electrode active material structure, and consequently, preventing gas from being generated.

[0082] Specifically, when molybdenum (Mo) is doped into the lithium-excess manganese oxide, not only can the particle size of the positive electrode active material increase, but the particle shape can also be improved. Meanwhile, molybdenum (Mo) can be doped into the lithium-excess manganese oxide in an amount of 5,000 ppm or less.

[0083]

[0084] According to the present invention, the lithium-excess manganese oxide may include a crystal structure belonging to the C2 / m space group and the R-3m space group.

[0085] According to the present invention, the lithium-excess manganese oxide may have a manganese content of 50 mol% or more, specifically 60 mol% or more, and more specifically 65 mol% or more, of the total metal excluding lithium. In this case, high capacity can be exhibited even when charged at high voltage.

[0086] According to the present invention, the lithium-excess manganese oxide may have a composition represented by the following chemical formula 1. In this case, the capacity of Li2MnO3 can be additionally realized at a high voltage exceeding 4.4 V, thereby exhibiting excellent capacity characteristics.

[0087] [Chemical Formula 1]

[0088] Lia Ni b Co c Mn d Me e O2

[0089] In the above chemical formula 1,

[0090] Me is one or more selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr,

[0091] 1.09≤a≤1.20, 0≤b≤0.50, 0≤c≤0.10, 0.50≤d≤1.0, 0 <e≤0.10이다.

[0092] The above lithium-excess manganese oxide may not contain expensive cobalt, and may improve the performance of a lithium secondary battery without containing cobalt.

[0093] The above chemical formula 1 can be expressed as the following chemical formula 2.

[0094] [Chemical Formula 2]

[0095] Li(Li a' Ni b Co c Mn d Me e )O2

[0096] In the above chemical formula 2,

[0097] Me is one or more selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr,

[0098] 0.09≤a'≤0.20, 0≤b≤0.50, 0≤c≤0.10, 0.50≤d≤1.0, 0 <e≤0.10이다. 이 때, 상기 a'+b+c+d+e=1을 만족할 수 있다.

[0099]

[0100] According to the present invention, the lithium-excess manganese oxide may be in the form of secondary particles. In this case, lithium diffusion is improved, so that not only capacity but also rate characteristics are superior to those of single particles. The secondary particles are secondary structures formed by agglomeration of a plurality of primary particles, and a first layer including a crystal structure belonging to the R-3m space group formed continuously according to the present invention and a second layer including a rock salt-type crystal structure belonging to the Fm-3m space group formed continuously on the first layer may be formed not only on the secondary particles but also on the primary particles.

[0101]

[0102] According to the present invention, the lithium-excess manganese oxide has an average particle diameter (D 50 ) may be 5 μm to 15 μm. Specifically, the average particle diameter (D) of the lithium-excess manganese oxide 50 ) may be 5㎛ or more, 6㎛ or more, or 7㎛ or more, and may be 10㎛ or less, 11㎛ or less, 12㎛ or less, 13㎛ or less, 14㎛ or less, or 15㎛ or less. In this case, electrode defects due to particle agglomeration during electrode manufacturing can be prevented.

[0103]

[0104] The cathode active material according to the present invention may further include a coating layer formed on the second layer and containing at least one selected from carbon and sulfur. Specifically, the coating layer may contain at least one selected from a carbon-containing compound and a sulfur-containing compound. In this case, the carbon may be derived from urea, and the sulfur may be derived from thiourea. The coating layer may be formed not only on secondary particles of the lithium-excess manganese oxide, but also on primary particles.

[0105] According to the present invention, the coating layer may further contain boron. That is, the coating layer may further contain boron in addition to carbon and / or sulfur. Specifically, the coating layer may contain at least one selected from a carbon-containing compound and a sulfur-containing compound, and a compound in which lithium, boron, and oxygen are chemically bonded to each other. When the coating layer contains both carbon and boron, the structural stability of the surface is further improved, and as a result of suppressing the formation of a surface-denatured layer, there is an advantage in that the life characteristics of a battery including a positive electrode active material are further improved.

[0106]

[0107] According to the present invention, the first layer may have a thickness of 0.5 nm to 20 nm. Specifically, the thickness of the first layer may 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 mm or more, 3.5 nm or more, 4 nm or more, 4.5 nm or more, or 5 nm or more, and may be 10 nm or less, 11 nm or less, 12 nm or less, 13 nm or less, 14 nm or less, 15 nm or less, 16 nm or less, 17 nm or less, 18 nm or less, 19 nm or less, or 20 nm or less. In this case, there is an advantage in that high capacity can be maintained while effectively preventing gas generation on the particle surface.

[0108] According to the present invention, the second layer may have a thickness of 0.5 nm to 20 nm. Specifically, the thickness of the second layer may 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 mm or more, 3.5 nm or more, 4 nm or more, 4.5 nm or more, or 5 nm or more, and may be 10 nm or less, 11 nm or less, 12 nm or less, 13 nm or less, 14 nm or less, 15 nm or less, 16 nm or less, 17 nm or less, 18 nm or less, 19 nm or less, or 20 nm or less. In this case, there is an advantage in that high capacity can be maintained while effectively preventing gas generation on the particle surface.

[0109] In this specification, the thickness of the first layer and the thickness of the second layer may be values ​​measured through HR-TEM image analysis.

[0110]

[0111] Method for manufacturing positive electrode active material

[0112] The present invention provides a method for producing a cathode active material according to the present invention, comprising the steps of (A) dry mixing a composite transition metal hydroxide and a lithium-containing raw material, performing a first calcination at 400°C to 500°C, and a second calcination at 800°C to 1000°C to produce a lithium-excess manganese oxide; and (B) dry mixing at least one selected from urea and thiourea and the lithium-excess manganese oxide using a mechanofusion method, and then heat-treating the resultant mixture at 300°C to 500°C.

[0113]

[0114] (A) Step

[0115] (A) A step for producing a lithium-excess manganese oxide by dry mixing a composite transition metal hydroxide and a lithium-containing raw material, first calcining at 400°C to 500°C, and second calcining at 800°C to 1000°C.

[0116] The above step (A) is a step of dry mixing a composite transition metal hydroxide and a lithium-containing raw material, first calcining at a temperature near the melting point of the lithium-containing raw material, and second calcining at a high temperature so as to form a lithium-rich oxide in which the Li2MnO3 phase and the LiMO2 phase are mixed. The mixing in the above step (A) is a dry mixing, and since the lithium-containing raw material exists in the form of a solid powder, it is performed dry. In the case of wet mixing, there is a problem that the process cost is high, so the present invention uses a dry mixing method.

[0117]

[0118] According to the present invention, when dry mixing a composite transition metal hydroxide and a lithium-containing raw material in step (A), a doping raw material including at least one doping element selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr may be further mixed. The doping raw material may be, for example, molybdenum oxide, ammonium molybdate, lithium molybdate, or the like.

[0119]

[0120] According to the present invention, the composite transition metal hydroxide may have a composition represented by the following chemical formula 2.

[0121] [Chemical Formula 2]

[0122] Ni b' Co c' Mn d' Me e' (OH)2

[0123] In the above chemical formula 2,

[0124] Me is one or more selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr,

[0125] 0≤b'≤0.50, 0≤c'≤0.10, 0.50≤d'≤1.0, 0≤e'≤0.10, b'+c'+d'+e'=1.

[0126] The above-mentioned composite transition metal hydroxide may not contain expensive cobalt, and may improve the performance of a lithium secondary battery without containing cobalt.

[0127]

[0128] The above lithium-containing raw material is a lithium-containing raw material typically used in the manufacture of a cathode active material, and may be, for example, lithium carbonate (Li2CO3), lithium hydroxide (LiOH), LiNO3, CH3COOLi, Li2(COO)2, or a hydrate thereof.

[0129]

[0130] The above composite transition metal hydroxide and the lithium-containing raw material may be mixed in an amount such that the molar ratio of the transition metal present in the composite transition metal hydroxide and 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 may be formed simultaneously in an appropriate ratio.

[0131]

[0132] According to the present invention, when a mixture of the composite transition metal hydroxide and a lithium-containing raw material is first fired at 400°C to 500°C, the lithium-containing raw material can be evenly mixed with the composite transition metal hydroxide as it melts. In addition, when the mixture that has undergone the first firing is second fired at 800°C to 1000°C, a lithium-rich oxide in which the Li2MnO3 phase and the LiMO2 phase are mixed can be well formed.

[0133] The above first firing temperature may specifically be 400°C or higher, 410°C or higher, 420°C or higher, 430°C or higher, 440°C or higher, or 450°C or higher, and may be 450°C or lower, 460°C or lower, 470°C or lower, 480°C or lower, 490°C or lower, or 500°C or lower.

[0134] The above secondary firing temperature may specifically be 800°C or higher, 810°C or higher, 820°C or higher, 830°C or higher, 840°C or higher, or 850°C or higher, and may be 950°C or lower, 960°C or lower, 970°C or lower, 980°C or lower, 990°C or lower, or 1000°C or lower.

[0135] Meanwhile, if the first sintering temperature is less than 400℃, there is a problem that a layered cathode material with excellent crystallinity is not formed properly because the reaction does not proceed after the composite transition metal hydroxide and the lithium-containing raw material are evenly mixed, and if it exceeds 500℃, there may be a problem that the cathode material synthesis reaction occurs before the lithium-containing raw material is evenly mixed. In addition, if the second sintering temperature is less than 800℃, lithium-excess oxide may not be completely formed, and if it exceeds 1000℃, particle growth and agglomeration may increase, which may reduce the electrochemical characteristics.

[0136] According to the present invention, the first firing and the second firing may each be independently performed under an air atmosphere or an oxygen atmosphere.

[0137] The above first firing can be performed for 3 to 5 hours, and the above second firing can be performed for 10 to 15 hours.

[0138]

[0139] (B) Step

[0140] (B) A step of dry mixing at least one selected from urea and thiourea with the lithium-excess manganese oxide by a mechanofusion method, and then heat treating at 300°C to 500°C. When at least one selected from urea and thiourea with the lithium-excess manganese oxide is dry mixed by a mechanofusion method, and then heat treating within the temperature range, urea and / or thiourea undergoes thermal decomposition, and ammonium gas is generated during the decomposition process to form a reducing atmosphere, thereby reducing the surface layer of the lithium-excess manganese oxide, and thus surface modification occurs. Accordingly, a first layer including a crystal structure belonging to the R-3m space group and a second layer including a rock salt-type crystal structure belonging to the Fm-3m space group, i.e., a reduced double layer, are formed on a lithium-excess manganese oxide.

[0141] In addition, since urea has a carbonyl group (C(=O) group), it is carbonized when thermally decomposed in a nitrogen (N2) atmosphere, thereby forming a carbon-containing coating layer on the lithium-excess manganese oxide. In addition, since thiourea has a C(=S) group, it forms a sulfur-containing coating layer on the lithium-excess manganese oxide when thermally decomposed in a nitrogen (N2) atmosphere. At this time, the carbon-containing coating layer or the sulfur-containing coating layer can be formed on the surface (outermost layer) of the positive electrode active material. That is, it can be formed on the second layer.

[0142] According to the present invention, the dry mixing is performed using a mechanofusion method, whereby the base material and the coating raw material are mixed, while at the same time, impact / compression / shear force is uniformly transmitted to each particle, so that the coating can proceed uniformly. On the other hand, when dry mixing is performed using a method such as a ball mill, only the process of mixing the base material and the coating raw material occurs.

[0143]

[0144] According to the present invention, in the step (B), at least one selected from urea and thiourea may be mixed in an amount of 0.3 to 3 parts by weight per 100 parts by weight of the lithium-excess manganese oxide. Specifically, the amount of at least one selected from urea and thiourea may be 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 2.0 parts by weight or less, 2.1 parts by weight or less, 2.2 parts by weight or less, 2.3 parts by weight or less, 2.4 parts by weight or less, 2.5 parts by weight or less, 2.6 parts by weight or less, 2.7 parts by weight or less, 2.8 parts by weight or less, 2.9 parts by weight or less, or 3.0 parts by weight or less, with respect to 100 parts by weight of the lithium-excess manganese oxide. In this case, a stable surface layer with improved structural stability can be formed without reducing the capacity.

[0145]

[0146] According to the present invention, the heat treatment may be performed under an N2 atmosphere to form a reducing atmosphere through thermal decomposition.

[0147] According to the present invention, the heat treatment of step (B) can be performed at 300°C to 550°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, 350°C or higher, 360°C or higher, 370°C or higher, 380°C or higher, 390°C or higher, or 400°C or higher, and 450°C or lower, 460°C or lower, 470°C or lower, 480°C or lower, 490°C or lower, 500°C or lower, 510°C or lower, 520°C or lower, 530°C or lower, 540°C or lower, or 550°C or lower. In this case, a stable surface layer (reduced double layer and coating layer) with improved structural stability can be formed without reducing capacity.

[0148] Meanwhile, if the heat treatment temperature is less than 300°C, urea and / or thiourea are not properly thermally decomposed, so a surface modification layer is not properly formed. If the temperature is more than 500°C, there is a problem in that the carbon is burned at a high temperature, so a proper carbon coating is not formed.

[0149] The above heat treatment can be performed for 3 to 5 hours.

[0150]

[0151] According to the present invention, when dry mixing at least one selected from urea and thiourea and the lithium-excess manganese oxide in step (B), a boron-containing raw material may be further mixed. The boron-containing raw material may be, for example, boric acid, B2O3, etc.

[0152] According to the present invention, the boron-containing raw material may be mixed in an amount of 0.2 parts by weight to 2 parts by weight relative to 100 parts by weight of the lithium-excess manganese oxide. Specifically, the mixing amount of the boron-containing raw material may be 0.2 parts by weight or more, 0.3 parts by weight or more, 0.4 parts by weight or more, or 0.5 parts by weight or more, and 0.8 parts by weight or less, 0.9 parts by weight or less, 1.0 parts by weight or less, 1.1 parts by weight or less, 1.2 parts by weight or less, 1.3 parts by weight or less, 1.4 parts by weight or less, 1.5 parts by weight or less, 1.6 parts by weight or less, 1.7 parts by weight or less, 1.8 parts by weight or less, 1.9 parts by weight or less, or 2.0 parts by weight or less relative to 100 parts by weight of the lithium-excess manganese oxide. In this case, a coating layer containing at least one selected from carbon and sulfur and boron of an appropriate thickness can be formed.

[0153]

[0154] anode

[0155] The present invention provides a positive electrode comprising the positive electrode active material.

[0156] 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.

[0157] The positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it is easily adhered to by the positive electrode active material layer and does not react within the voltage range of the battery. The positive electrode current collector may be made of, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the positive electrode current collector may typically have a thickness of 3 ㎛ to 500 ㎛, and fine unevenness may 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 may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0158] The above-mentioned positive electrode active material layer may optionally include a conductive material and a binder, together with the positive electrode active material, as needed. In this case, the positive electrode active material may be included in an amount of 80 wt% to 99 wt%, more specifically 85 wt% to 98.5 wt%, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics may be exhibited within this range.

[0159] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. 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 or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0160] The above binder serves to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylalcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and polymers in which hydrogens of these are substituted with Li, Na, or Ca, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The above binder may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0161] The positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material described above is used. Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, which is manufactured by dissolving or dispersing the positive electrode active material and optionally a binder, a conductive agent, and a dispersant in a solvent as needed, onto a positive electrode current collector, followed by drying and rolling, or by casting the composition for forming a positive electrode active material layer onto a separate support, peeling the film from the support, and laminating the resulting film onto a positive electrode current collector.

[0162] The solvent may be a solvent generally used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0163]

[0164] lithium secondary battery

[0165] The present invention provides a lithium secondary battery including the positive electrode.

[0166]

[0167] The lithium secondary battery may include the positive electrode; the negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte. In addition, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0168] The above negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0169] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0170] The above negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material.

[0171] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may 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 alloy, Sn alloy, or Al alloy; SiO β(0<β<2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical or fibrous shapes, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes. The negative electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0172] The binder of the above-described negative electrode active material layer is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1 wt% to 10 wt% 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 polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0173] The conductive material of the above-described negative electrode active material layer is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include 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 fiber or metal fiber; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0174] The above negative electrode can be manufactured by applying and drying a composition for forming a negative electrode active material layer prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent, on a negative electrode current collector, or by casting the composition for forming a negative electrode active material layer on a separate support, and then laminating the film obtained by peeling it off from the support on a negative electrode current collector.

[0175] The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0176] 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. As a specific example, the electrolyte may include an organic solvent and a lithium salt.

[0177] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may 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; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylenecarbonate (EC), and propylene carbonate (PC); alcohol 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 may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0178] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the anion of the above 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 - At least one selected from the group consisting of may be used, and the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. It is preferable to use the concentration of the lithium salt within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0179] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0180]

[0181] A lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent capacity characteristics, output characteristics, and life characteristics, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0182] There is no particular limitation on the external shape of the lithium secondary battery of the present invention, but it may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0183] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells.

[0184] Accordingly, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0185] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0186]

[0187] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0188]

[0189] Manufacturing example

[0190] Manufacturing Example 1

[0191] Manganese sulfate (MnSO4) and nickel sulfate (NiSO4) were mixed in distilled water in an amount such that the molar ratio of Mn:Ni was 65:35 to prepare a 2.0 M concentration transition metal aqueous solution. 4 M NaOH aqueous solution and 15.3 M NH4OH aqueous solution were added to the above transition metal aqueous solution, and the pH was maintained at about 11, followed by coprecipitation. The precipitate was separated and washed, and dried at 120°C for 24 hours to obtain Ni. 0.65 Mn 0.35 A complex transition metal hydroxide having a composition represented by (OH)2 was prepared.

[0192]

[0193] Example

[0194] Example 1 (Urea-coated LMRO)

[0195] The composite transition metal hydroxide manufactured in Manufacturing Example 1 and LiOH·H2O were mixed so that the ratio of the total mole number of transition metals included in the composite transition metal hydroxide (Ni+Mn) and the mole number of lithium included in LiOH (Li) ((Ni+Mn):Li) was 1:1.35, and then the mixture was first calcined at 450°C for 5 hours in an air atmosphere, and second calcined at 900°C for 12 hours to obtain a lithium-excess manganese oxide (composition: Li 1.13 Ni 0.3 Mn 0.57 O2, average particle size (D 50 ): 7㎛) was manufactured.

[0196] By mechanofusion method, 2 parts by weight of urea (Sigma Aldrich) was mixed with 100 parts by weight of the lithium-excess manganese oxide, and then heat-treated at 400°C for 5 hours under a N2 atmosphere to produce a cathode active material having a coating layer formed thereon.

[0197] For reference, the above mechanofusion was performed using Hosokawa Micron's Novilta, and 50 g batches of raw materials (lithium-excess manganese oxide + urea) were placed in a mixing vessel, and the rotor was rotated at 1 A, 2000 rpm, and 5 L / min under a N2 atmosphere.

[0198]

[0199] Example 2 (Mo-doped / urea-coated LMRO)

[0200] The composite transition metal hydroxide manufactured in Manufacturing Example 1 and LiOH·H2O were mixed so that the ratio of the total mole number of transition metals (Ni+Mn) included in the composite transition metal hydroxide and the mole number of lithium included in LiOH (Li) ((Ni+Mn):Li) was 1:1.35, and MoO3 (Sigma Aldrich) was further mixed in an amount of 0.5 mol% relative to the composite transition metal hydroxide, and then the mixture was first calcined at 450°C for 5 hours in an air atmosphere and second calcined at 900°C for 12 hours to obtain a lithium-excess manganese oxide (composition: Li 1.13 (Ni 0.3 Mn 0.57 ) 0.994 Mo 0.005 O2, average particle size (D 50 ): 7㎛) was manufactured.

[0201] By mechanofusion method, 2 parts by weight of urea was mixed with 100 parts by weight of the lithium-excess manganese oxide, and then heat-treated at 400°C for 5 hours under a N2 atmosphere to produce a cathode active material having a coating layer formed thereon.

[0202] For reference, the above mechanofusion was performed using Hosokawa Micron's Novilta, and 50 g batches of raw materials (lithium-excess manganese oxide + urea) were placed in a mixing vessel, and the rotor was rotated at 1 A, 2000 rpm, and 5 L / min under a N2 atmosphere.

[0203]

[0204] Example 3 (Mo-doped / urea,B-coated LMRO)

[0205] By the mechanofusion method, 2 parts by weight of urea was mixed with respect to 100 parts by weight of the lithium-excess manganese oxide prepared in Example 2, and 0.57 parts by weight of boric acid (H3BO3) (Sigma Aldrich) was further mixed with respect to 100 parts by weight of the lithium-excess manganese oxide, and then heat-treated at 400°C for 5 hours under a N2 atmosphere to prepare a cathode active material having a coating layer formed thereon.

[0206] For reference, the above mechanofusion was performed using Hosokawa Micron's Novilta, and 50 g batches of raw materials (lithium-excess manganese oxide + urea) were placed in a mixing vessel, and the rotor was rotated at 1 A, 2000 rpm, and 5 L / min under a N2 atmosphere.

[0207]

[0208] Example 4 (Thiourea-coated LMRO)

[0209] In Example 1, 2 parts by weight of thiourea (Sigma Aldrich) was mixed with 100 parts by weight of the lithium-excess manganese oxide, and then heat-treated at 400°C for 5 hours under an N2 atmosphere to produce a cathode active material having a coating layer formed thereon.

[0210]

[0211] Example 5 (Mo-doped / thiourea-coated LMRO)

[0212] In Example 2, 2 parts by weight of thiourea was mixed with 100 parts by weight of the lithium-excess manganese oxide, and then heat-treated at 400°C for 5 hours under a N2 atmosphere to produce a cathode active material having a coating layer formed thereon.

[0213]

[0214] Comparative Example 1 (Bare LMRO)

[0215] The lithium-excess manganese oxide manufactured in Example 1 was used as the positive electrode active material of Comparative Example 1.

[0216]

[0217] Comparative Example 2 (Mo-doped LMRO)

[0218] The lithium-excess manganese oxide manufactured in Example 2 was used as the positive electrode active material of Comparative Example 2.

[0219]

[0220] Comparative Example 3

[0221] The composite transition metal hydroxide manufactured in Manufacturing Example 1 and LiOH·H2O were mixed so that the ratio of the total mole number of transition metals included in the composite transition metal hydroxide (Ni+Mn) and the mole number of lithium included in LiOH (Li) ((Ni+Mn):Li) was 1:1.35, and then the mixture was first calcined at 450°C for 5 hours in an air atmosphere, and second calcined at 900°C for 12 hours to obtain a lithium-excess manganese oxide (composition: Li 1.13 Ni 0.3 Mn 0.57 O2, average particle size (D 50 ): 7㎛) was manufactured.

[0222] A cathode active material having a coating layer was manufactured by mixing 2 parts by weight of urea (Sigma Aldrich) per 100 parts by weight of the lithium-excess manganese oxide using a ball mill, and then heat-treating at 400°C for 5 hours under a N2 atmosphere.

[0223] For reference, the ball-mill mixing was performed by loading zirconia balls and powder into a Nalzen bottle at a weight ratio of 10:1 and then performing the mixing at 300 rpm for 12 hours.

[0224]

[0225] Reference Example 1 (NCMA positive electrode active material)

[0226] Composition: LiNi 0.86 Co 0.05 Mn 0.07 Al0.02 O2, and the average particle size (D 50 ) Lithium nickel cobalt manganese aluminum oxide having a particle size of 10 μm was used as the positive electrode active material of Reference Example 1.

[0227]

[0228] Experimental example

[0229] Experimental Example 1: STEM-EELS Data Analysis

[0230] Electron energy loss spectroscopy (EELS) was performed on the electrodes containing each of the positive electrode active materials manufactured in Example 5 and Comparative Example 1, and the EELS-related data are shown in FIGS. 1 to 8.

[0231] Specifically, thin sections for STEM-EELS analysis were prepared using a TFS Helios 5 UX (acceleration voltages of 30, 5, and 2 kW), and HAADF-STEM images and EELS maps were obtained at an acceleration voltage of 200 kV using a TFS Spectra 300 STEM. The degree of reduction of Mn was determined from the obtained maps to confirm the existence of a reduced layer. At this time, the dispersion was 0.15 eV / ch, the aperture of the GIF (Gatan Image Filter) camera was 1 mm, and the full width half maximum (FWHM) of the zero-loss peak for each pixel of the image was 0.7 to 0.85 eV.

[0232] Figures 1 to 8 are HAADF-STEM images, a / I, of the cross-sections of the positive electrode active materials manufactured in Example 5 and Comparative Example 1, respectively. MnL3 This diagram shows the ratio map, OK pre-edge / main edge ratio map, and EELS analysis data.

[0233] Specifically, FIG. 1, FIG. 2, and FIG. 3 are HAADF-STEM images, a / I, of the cross-section of the positive electrode active material manufactured in Example 5, respectively. MnL3ratio map, OK pre-edge / main edge ratio map, and Fig. 4, Fig. 5, and Fig. 6 are HAADF-STEM images of the cross-section of the positive electrode active material manufactured in Comparative Example 1, respectively, a / I MnL3 ratio map, OK pre-edge / main edge ratio map, Fig. 7 is EELS analysis data of OK edge, and Fig. 8 is EELS analysis data of Mn L3edge.

[0234] Meanwhile, in the EELS map, the OK pre / main edge ratio map and a / I MnL3 The ratio map was obtained in the following way.

[0235] Specifically, the background is removed from the EELS map to remove noise, and the OK pre-edge signal (hereinafter, OK pre-edge) is detected at approximately 530 eV, the 0 K main edge signal (hereinafter, 0 K main edge) is detected at approximately 541–542 eV, and the Mn is detected at approximately 644 eV. 4+ The edge signal corresponding to the main peak (hereinafter, a), and the integral signal (hereinafter, I) of all L3 peaks (L3edge) of Mn existing between 635 eV and 650 eV MnL3 ) was obtained, and the color was expressed differently according to the ratio value of the OK pre edge and the 0 K main edge, and the OK pre / main edge ratio map was expressed, and the a and I MnL3 Colors are expressed differently depending on the ratio of a / I MnL3 It is displayed as a ratio map.

[0236] At this time, the background was set to ~20 eV in front of the L3 edge onset point ~10 eV for Mn L3, and to ~20 eV in front of the onset point for OK edge. Then, when obtaining the edge signal from the peak, an integral signal corresponding to a width of 0.75 eV was obtained while including the peak, and when obtaining the integral signal of the L3 edge, the width was set to 10.05 eV so as to include the entire L3 edge, thereby obtaining the integral signal.

[0237]

[0238] Referring to FIGS. 1 to 8, in the case of Example 5, the OK pre-edge / main edge ratio is low for the entire secondary particle, and among all L3 peaks of Mn, in particular, Mn 4+ It can be seen that the intensity of the main peak, peak a, is slightly lower.

[0239] This is because a reduction layer was uniformly formed on the surface of the primary particles.

[0240]

[0241] Experimental Example 2: HR-TEM Image Analysis

[0242] For each of the positive electrode active materials manufactured in Example 5, Comparative Example 1, and Comparative Example 3, HR-(S)TEM image analysis was performed, and the images are shown in FIGS. 9 to 11.

[0243] Specifically, HR-(S)TEM analysis was performed using a Spectra 300 (w / double Cs corrector, monochromator) from Thermo Fisher Scientific at an acceleration voltage of 200 kV, and STEM was performed under a screen current of ~20 pA.

[0244] FIG. 9, FIG. 10, and FIG. 11 are drawings showing HR-TEM images (left) and HR-STEM images (right) respectively, which are measured by enlarging the primary particle surface in cross-sectional samples of the positive electrode active materials manufactured in Example 5, Comparative Example 1, and Comparative Example 2.

[0245]

[0246] Referring to FIGS. 9 to 11, in the case of the positive electrode active material of Example 5, it can be confirmed that a first layer including a crystal structure belonging to the R-3m space group and a second layer formed on the first layer and including a rock salt-type crystal structure belonging to the Fm-3m space group are formed. In addition, it can be confirmed that the first layer and the second layer are formed continuously. In contrast, in the case of the positive electrode active material of Comparative Example 1, it can be confirmed that the first layer and the second layer according to the present invention do not exist, and in the case of the positive electrode active material of Comparative Example 3, it can be confirmed that the first layer according to the present invention does not exist. That is, looking at the primary particle surface of FIGS. 9 to 11, it can be confirmed that a double reduction layer was formed in the case of Example 5, but a double reduction layer did not exist in the cases of Comparative Examples 1 and 3.

[0247] For reference, the reason why the difference in thickness between the first and second layers appears in the HR-TEM image and HR-STEM image of Example 5 is because the STEM image mainly reflects information on the particle surface.

[0248]

[0249] Experimental Example 3: EDS Analysis

[0250] Using a TFS Spectra300 quadruple EDS detector (acceleration voltage: 200 kV), HAADF-STEM images and EDS data of the cross-section of the positive electrode active material manufactured in Example 5 were obtained, and are shown in Fig. 12.

[0251]

[0252] EDS analysis results show that sulfur (S) is coated on the surface of the secondary particles and primary particles of the positive electrode active material.

[0253]

[0254] Experimental Example 4: Battery Characteristics Evaluation

[0255] - Gas generation assessment

[0256] A positive electrode slurry was prepared by mixing 92.5 wt% of each of the positive electrode active materials manufactured in Examples 1 to 5, Comparative Examples 1 and 2, and Reference Example 1, 3 wt% of carbon black as a conductive material, and 4.5 wt% of polyvinylidene fluoride (PVDF) as a binder in an N-methylpyrrolidone (NMP) solvent. The positive electrode slurry was applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to prepare a positive electrode.

[0257] An electrode assembly was manufactured using graphite as the cathode and a porous polyethylene separator interposed between the cathode and the anode. The electrode assembly was placed inside a battery case, and an electrolyte solution (additives: LiBF 42%, FEC 5%) in which 1 M LiPF6 was dissolved in an organic solvent mixed with ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 was injected to manufacture a monocell.

[0258]

[0259] 1) Evaluation of gas generation during charging and discharging

[0260] The above monocell was charged to 4.65 V under CC (0.1 C)-CV (Cut off current: 0.05 C) conditions at 45°C, and then discharged to 2.0 V at 0.1 C (first cycle) to perform an activation process (formation). The monocell that went through the activation process was charged to 4.4 V under CC (0.1 C)-CV (Cut off current: 0.05 C) conditions at 25°C, and then discharged to 2.5 V at 0.1 C (second cycle), and then charged to 4.4 V under CC (0.33 C)-CV (Cut off current: 0.05 C) conditions at 25°C, and then discharged to 2.5 V at 0.33 C. This process was repeated 48 times as one cycle, and a total of 50 charge-discharge cycles were performed.

[0261] Then, using a hydrometer (MATSUHAKU, TWD-150DM), the amount of gas generated during 50 cycles was measured, and the results are shown in Table 1 and Fig. 13 below. The difference between the original weight of the monocell and its weight in water was measured, the volume change within the monocell was calculated, and the amount of gas generated per 1 g of the positive electrode active material was calculated by dividing the volume change (ml) by the weight (g) of the positive electrode active material.

[0262] Gas generation amount (ml / g) during 50 cycles Increase rate (%) compared to Comparative Example 1 in 50 cycles Example 10.342-40.1 Example 20.298-48.5 Example 30.137-76.3 Example 40.130-77.5 Example 50.033-94.3 Comparative Example 10.579-Comparative Example 20.411-29.0 Reference Example 10.104-82.0

[0263]

[0264] 2) Evaluation of gas generation during high-temperature storage

[0265] The above monocell was charged to 4.65 V under CC (0.1 C)-CV (Cut off current: 0.05 C) conditions at 45°C, discharged to 2.0 V at 0.1 C, and charged to 4.4 V under CC (0.1 C)-CV (Cut off current: 0.05 C) conditions at 25°C. Afterwards, the generated gas was removed by degassing, recovered, and stored in a chamber at 60°C. After two weeks of storage, the monocell was taken out from the chamber at weekly intervals, and the difference between the original weight of the monocell and its weight in water was measured using a hydrometer (MATSUHAKU, TWD-150DM), and the volume change within the monocell was calculated. The volume change (ml) was divided by the weight (g) of the positive electrode active material to calculate the amount of gas generated per 1 g of the positive electrode active material, and the results are shown in Table 2 and FIG. 14 below.

[0266] Gas generation during storage (ml / g) Increase rate (%) compared to Comparative Example 1 2 weeks 3 weeks 4 weeks Example 10.0 5 5 0.1 5 6 0.1 4 2-77.1 Example 20.0 9 4 0.1 9 20.2 0 3-67.3 Example 30 0.0 9 8-84.2 Example 40.0 1 1 0.0 9 6 0.1 6 7-73.1 Example 50 0.0 4 9 0.1 0 9 2-82.4 Comparative Example 10.2 8 9 0.5 8 5 0.6 2-1 Comparative Example 20.1 5 20.3 8 9 0.4 9 1-20.1 Reference Example 10.0 8 4 0.0 9 8 0.0 9 1-85.3

[0267] Referring to Table 1, Table 2, and FIGS. 13 and 14 above, in the case of the battery including the positive electrode active material manufactured in Examples 1 and 2, since there are uniform first and second layers formed continuously, it can be confirmed that the amount of gas generated is less during repeated charge and discharge cycles at high temperatures, and the amount of gas generated is also less when stored at high temperatures for a long period of time, compared to the battery including the positive electrode active material manufactured in Comparative Example 1.

[0268] That is, it can be seen that the positive electrode active material according to the present invention has uniform first and second layers, and thus, when applied to a battery, the stability of the battery can be improved.

[0269]

[0270] - Electrochemical performance evaluation

[0271] A positive electrode slurry was prepared by mixing 92.5 wt% of each of the positive electrode active materials manufactured in the above examples and comparative examples, 3 wt% of carbon black as a conductive agent, and 4.5 wt% of polyvinylidene fluoride (PVDF) as a binder in an N-methylpyrrolidone (NMP) solvent. The positive electrode slurry was applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to manufacture a positive electrode.

[0272] An electrode assembly was manufactured using a lithium metal electrode as the negative electrode and a porous polyethylene separator interposed between the positive and negative electrodes. The electrode assembly was placed inside a battery case, and an electrolyte solution (additives: LiBF 42%, FEC 5%) in which 1 M LiPF6 was dissolved in an organic solvent mixed with ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 was injected to manufacture a half-cell.

[0273]

[0274] The above half-cell was charged to 4.65 V under CC (0.1 C)-CV (Cut off current: 0.05 C) conditions at 45°C, and then discharged to 2.0 V at 0.1 C (hereinafter, Formation cycle) to perform an activation process (formation). The half-cell that went through the activation process was charged to 4.4 V under CC (0.1 C)-CV (Cut off current: 0.05 C) conditions at 25°C, and then discharged to 2.5 V at 0.1 C (hereinafter, 0 thAfter cycling, it was charged to 4.4 V under CC (0.33 C)-CV (Cut off current: 0.05 C) conditions at 25°C, and then discharged to 2.5 V at 0.33 C, repeating 50 cycles (1 cycle) st Cycle ~ 50 th (cycle) was done.

[0275] At this time, the charge / discharge profile graph (Fig. 15), specific capacity graph (Fig. 16), average discharge voltage graph (Fig. 17), and energy density graph (Fig. 18) according to the repetition of the cycle are shown in Figs. 15 to 18, and the charge / discharge capacity of the Formation cycle, 0 th Charge / discharge capacity of a cycle, 1 st The discharge capacity and de-rating of the cycle were confirmed and are shown in Table 3 below. In addition, the resistance increase rate at 10, 30, and 50 cycles was confirmed and is shown in Table 4 below. For reference, the de-rating is 0. th 1 for the discharge capacity of the cycle st This is a value that represents the percentage of the discharge capacity of the cycle.

[0276] Formation Cycle 0 th Cycle (0.1C, 45℃)1 st Cycle discharge capacity (0.33C, 25℃) (mAh / g) De-rating (%) Charge capacity (mAh / g) Discharge capacity (mAh / g) Charge capacity (mAh / g) Discharge capacity (mAh / g) Example 1 30 1 2 7 5 2 2 9 2 1 6 2 0 3 9 3.9 Example 2 30 4 2 7 8 2 3 0 2 1 9 2 0 8 9 4.9 Example 3 30 3 2 7 6 2 2 9 2 1 8 2 0 7 9 5.0 Example 4 2 9 8 2 7 0 2 3 2 1 0 2 0 9 5.2 Example 5 30 5 2 8 0 2 3 2 2 1 8 2 0 7 9 5.0 Comparative example 1 30 4 2 7 6 2 6 2 0 9 1 9 1.3 Comparative example 2 30 5 2 7 8 2 3 1 2 1 4 1 9 8 9 2.5

[0277] Increase in resistance (%) 10 th Cycle 30 th Cycle 50 thCycle Example 194.7104.8116.2 Example 293.4102.7110.8 Example 386.887.890.5 Example 475.374.178.4 Example 578.574.475.8 Comparative Example 195.4106.9117.9 Comparative Example 293.8103.2112.6

[0278] Referring to Table 3, Table 4 and FIGS. 15 to 18, it can be confirmed that the batteries including the positive electrode active materials manufactured in Examples 1 and 4 have superior discharge capacity after formation, higher de-rating, and lower resistance increase rate compared to the battery including the positive electrode active material manufactured in Comparative Example 1. In addition, it can be confirmed that the batteries including the positive electrode active materials manufactured in Examples 2, 3, and 5 have superior discharge capacity after formation, higher de-rating, and lower resistance increase rate compared to the battery including the positive electrode active material manufactured in Comparative Example 2.

[0279] From this, it can be seen that the positive electrode active material according to the present invention has a uniform first layer and second layer, and thus, when applied to a battery, can improve various performances of the battery.

Claims

1. A core portion comprising a lithium-excess manganese oxide having a layered structure simultaneously including a Li2MnO3 phase and a LiMO2 (wherein M is an element including at least one selected from Ni, Co, and Mn) phase; A first layer formed continuously on the core portion and including a crystal structure belonging to the R-3m space group; and A cathode active material comprising a second layer formed continuously on the first layer and including a rock salt crystal structure belonging to the Fm-3m space group.

2. In claim 1, The above lithium-excess manganese oxide is a cathode active material comprising at least one doping element selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr.

3. In claim 1, The above lithium-excess manganese oxide is a cathode active material having a crystal structure belonging to the C2 / m space group and the R-3m space group.

4. In claim 1, The above lithium-excess manganese oxide is a cathode active material having a manganese (Mn) content of 50 mol% or more among all metals excluding lithium.

5. In claim 1, The above lithium-excess manganese oxide is a positive electrode active material having 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 the above chemical formula 1, Me is one or more selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr, 1.09≤a≤1.20, 0≤b≤0.50, 0≤c≤0.10, 0.50≤d≤1.0, 0 <e≤0.10이다.

6. In claim 1, The above lithium-excess manganese oxide is a cathode active material in the form of secondary particles.

7. In claim 1, The above lithium-excess manganese oxide has an average particle diameter (D 50 ) A positive electrode active material having a diameter of 5㎛ to 15㎛.

8. In claim 1, A positive electrode active material, wherein the positive electrode active material is formed on the second layer and further includes a coating layer including at least one selected from carbon and sulfur.

9. In claim 8, The above coating layer is a positive electrode active material further containing boron.

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

11. In claim 1, The above first layer is a positive electrode active material having a thickness of 0.5 nm to 20 nm.

12. In claim 1, The second layer is a positive electrode active material having a thickness of 0.5 nm to 20 nm. 13.(A) A step of producing a lithium-excess manganese oxide by dry mixing a composite transition metal hydroxide and a lithium-containing raw material, then first calcining at 400°C to 500°C, and second calcining at 800°C to 1000°C; and (B) A method for producing a cathode active material according to claim 1, comprising the step of dry mixing at least one selected from urea and thiourea and the lithium-excess manganese oxide using a mechanofusion method, and then heat-treating the mixture at a temperature of 300°C to 550°C.

14. In claim 13, A method for producing a cathode active material, wherein, when dry mixing a composite transition metal hydroxide and a lithium-containing raw material in the above 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 is further mixed.

15. In claim 13, A method for producing a positive electrode active material, wherein the above complex 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 the above chemical formula 2, Me is one or more selected from Mo, Nb, K, Cl, Na, Ti, Mg, Ru, Ta, and Zr, 0≤b'≤0.50, 0≤c'≤0.10, 0.50≤d'≤1.0, 0≤e'≤0.10, b'+c'+d'+e'=1.

16. In claim 13, A method for manufacturing a positive electrode active material, wherein the first firing and the second firing are each independently performed under an air atmosphere or an oxygen atmosphere.

17. In claim 13, A method for producing a positive electrode active material, wherein in the step (B), at least one selected from urea and thiourea is mixed in an amount of 0.3 to 3 parts by weight per 100 parts by weight of the lithium-excess manganese oxide.

18. In claim 13, A method for manufacturing a positive electrode active material, wherein the above heat treatment is performed under an N2 atmosphere.

19. In claim 13, A method for producing a positive electrode active material, wherein, in step (B), when dry mixing at least one selected from urea and thiourea and the lithium-excess manganese oxide, a boron-containing raw material is further mixed.

20. In claim 19, A method for producing a positive electrode active material, wherein the boron-containing raw material is mixed in an amount of 0.2 to 2 parts by weight relative to 100 parts by weight of the lithium-excess manganese oxide.

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