Cathode active material, cathode comprising same, and lithium secondary battery

Abstract

The present invention relates to a cathode active material and, to a bimodal cathode active material, a cathode comprising same, and a lithium secondary battery, the cathode active material comprising: a first lithium-rich manganese-based oxide in the form of a discrete particle; and a second lithium-rich manganese-based layered oxide in the form of a secondary particle, wherein the first lithium-rich manganese-based layered oxide and the second lithium-rich manganese-based layered oxide comprise both a Li2MnO3 phase and a LiMO2 (where M is an element including at least one selected from Ni, Co and Mn) phase, the first lithium-rich manganese-based layered oxide has an average diameter (D50), which is smaller than that of the second lithium-rich manganese-based layered oxide, and the weight ratio of the first lithium-rich manganese-based layered oxide to the second lithium-rich manganese-based layered oxide is 1:1.5 to 8.

Description

Cathode active material, cathode and lithium secondary battery containing same

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2023-0097407, filed July 26, 2023, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a bimodal positive electrode active material, a positive electrode including the same, and a lithium secondary battery, and more particularly, to a bimodal positive electrode active material including a lithium-excess manganese oxide, a positive electrode including the same, and a lithium secondary battery.

[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=at least one of Ni, Mn, and 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] Meanwhile, lithium-excess oxides in the form of secondary particles manufactured using conventional co-precipitation methods suffer from low pellet density and high porosity when applied to electrodes, resulting in low volumetric energy density. Furthermore, mechanical stress during rolling for electrode manufacture is not distributed, leading to particle breakage and increased gas generation during battery operation.

[0009] Accordingly, there is a need to develop lithium-excess oxides with high pellet density and low particle breakage rate during rolling.

[0010]

[0011] The problem to be solved in the present invention is to improve the energy density and stability of a positive electrode active material, thereby improving the performance of a battery including the same.

[0012] In addition, the present invention aims to provide a positive electrode and a lithium secondary battery including the positive electrode active material.

[0013]

[0014] To solve the above problem, the present invention provides a positive electrode active material, a positive electrode, and a lithium secondary battery.

[0015] (1) The present invention comprises a first lithium-excess manganese oxide in the form of a single particle; and a second lithium-excess manganese oxide in the form of a secondary particle; wherein the first lithium-excess manganese oxide and the second lithium-excess manganese oxide simultaneously comprise a Li2MnO3 phase and a LiMO2 (wherein M is an element including at least one selected from Ni, Co, and Mn) phase, and the first lithium-excess manganese oxide has an average particle diameter (D) larger than that of the second lithium-excess manganese oxide. 50 ) is small, and the weight ratio of the first lithium-excess manganese oxide and the second lithium-excess manganese oxide is 1:1.5 to 8, and a bimodal positive electrode active material is provided.

[0016] (2) The present invention provides a bimodal positive electrode active material in the above (1), wherein the first lithium-excess manganese oxide has a single crystallinity (χ) of 0.4 or more according to the following formula 1.

[0017] [Formula 1]

[0018]

[0019] In the above equation 1,

[0020] a i When a single particle is composed of i crystal grains, the cross-sectional area of ​​the i-th crystal grain (A) is the cross-sectional area of ​​the single particle (A). i ) value (A i / A) means.

[0021] (3) In the present invention, in the above (1) or (2), the first lithium-excess manganese oxide has an average particle diameter (D 50 ) provides a bimodal positive electrode active material having a diameter of 0.5 μm to 3.5 μm.

[0022] (4) In any one of (1) to (3), the second lithium-excess manganese oxide has an average particle diameter (D 50 ) provides a bimodal positive electrode active material having a diameter of 5.0㎛ to 10.0㎛.

[0023] (5) The present invention provides a bimodal positive electrode active material in any one of the above (1) to (4), wherein the first lithium-excess manganese oxide has a composition represented by the following chemical formula 1.

[0024] [Chemical Formula 1]

[0025] Li 1+x1 Ni a1 Mn b1 M 1 c1 O y1

[0026] In the above chemical formula 1,

[0027] M 1is at least one selected from Co, Mo, W, V, Zr, Al and Nb,

[0028] 0.1≤x1≤0.2, 0 <a1≤0.5, 0.5≤b1≤0.75, 0≤c1≤0.1, 0≤y1≤2.0이고,

[0029] x1+a1+b1+c1=1.0.

[0030] (6) The present invention provides a bimodal positive electrode active material in any one of the above (1) to (5), wherein the second lithium-excess manganese oxide has a composition represented by the following chemical formula 2.

[0031] [Chemical Formula 2]

[0032] Li 1+x2 Ni a2 Mn b2 M 2 c2 O y2

[0033] In the above chemical formula 2,

[0034] M 2 is at least one selected from Co, Mo, W, V, Zr, Al, and Nb,

[0035] 0.1≤x2≤0.2, 0 <a2≤0.5, 0.5≤b2≤0.75, 0≤c2≤0.1, 0≤y2≤2.0이고,

[0036] x2+a2+b2+c2=1.0.

[0037] (7) The present invention is characterized in that the pellet density is 2.20 g / cm in any one of the above (1) to (6). 3 2.70g / cm 3 A bimodal positive electrode active material is provided.

[0038] (8) The present invention provides a positive electrode comprising a positive electrode active material according to any one of (1) to (7).

[0039] (9) The present invention provides a lithium secondary battery including a positive electrode according to (8).

[0040]

[0041] The cathode active material of the present invention simultaneously contains a lithium-excess manganese oxide in the form of a single particle and a lithium-excess manganese oxide in the form of a secondary particle at a specific weight ratio, thereby having excellent energy density and stability, and as a result, the performance of a battery containing the cathode active material, for example, capacity characteristics, energy density, etc., can be improved, and the cathode active material particles can be prevented from breaking during battery manufacturing or operation.

[0042]

[0043] Figure 1 is an SEM image of lithium-excess manganese oxides manufactured in Manufacturing Examples 1 and 2. Specifically, Figure 1(A) is an SEM image of lithium-excess manganese oxide (A1) manufactured in Manufacturing Example 1, and Figure 1(B) is an SEM image of lithium-excess manganese oxide (A2) manufactured in Manufacturing Example 2.

[0044] Fig. 2 is a cross-sectional SEM image of a positive electrode including the positive electrode active material of Example 1 and Comparative Example 1. Specifically, Fig. 2(A) is a cross-sectional SEM image of a positive electrode including the positive electrode active material of Example 1, and Fig. 2(B) is a cross-sectional SEM image of a positive electrode including the positive electrode active material of Example 2.

[0045]

[0046] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0047] 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.

[0048] In this specification, it should be understood that terms such as “include,” “have,” or “have” 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.

[0049] In this specification, the term "single particle form" refers to a form composed of 10 or fewer primary particles, in contrast to the spherical secondary particle form formed by the agglomeration of tens to hundreds of primary particles. Specifically, the "single particle form" may be a single particle form composed of one primary particle, or a secondary particle form in which several primary particles are agglomerated.

[0050] In this specification, 'primary particle' means the smallest unit of particle recognized when observing a positive electrode active material using a scanning electron microscope (SEM), and may be composed of multiple crystal grains, and 'secondary particle' means a secondary structure formed by the aggregation of multiple primary particles.

[0051] In this specification, 'single crystal' means a crystal that does not contain grain boundaries inside the particles.

[0052] In this specification, "crystal grain" refers to a particle unit having substantially the same crystal orientation, which can be measured by Electron Backscatter Diffraction (EBSD). Specifically, it refers to the smallest particle unit displayed in the same color in an IPF map obtained by EBSD analysis of a cross-section of a cathode active material cut through ion milling.

[0053] In this specification, the average particle diameter (D 50 ) can be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve. The average particle size (D 50) can be measured, for example, using a laser diffraction method, and more specifically, after dispersing a lithium composite transition metal oxide in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac Mt 3000) and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and then the average particle diameter (D) corresponding to 50% of the particle size distribution in the measuring device is measured. 50 ) can be produced.

[0054] In this specification, the pellet density is a value calculated by Equation 2 below when a force equivalent to 2,000 kgf is applied to form a pellet using an automatic pellet press. Specifically, the pellet density is a value obtained according to (1) to (3) below.

[0055] (1) Using a universal testing machine (UTM: Universal Testing Machine, Instron, Model 5966), adjust the zero point for thickness using a cylindrical mold for a circular pellet holder.

[0056] (2) Place the positive electrode active material in the above circular pellet holder, apply force until a force equivalent to 2,000 kgf is reached, and measure the thickness of the formed pellet.

[0057] (3) Calculate the pellet volume using the following equation 2, and calculate the pellet density using the following equation 3.

[0058] [Formula 2]

[0059] Pellet volume (cm) 3 ) = π(radius of the circular pellet holder) 2 × Pellet thickness

[0060] [Formula 3]

[0061] Pellet density (g / cm) 3 ) = Positive active material weight (g) / Pellet volume (cm 3 )]]

[0062]

[0063] The present inventors have found that when a positive electrode active material simultaneously includes a small particle lithium-excess manganese oxide in the form of a single particle and a large particle lithium-excess manganese oxide in the form of a secondary particle, when the positive electrode active material is applied to a positive electrode for a secondary battery, the electrode density can be improved, particle breakage can be minimized, when the positive electrode active material is applied to a secondary battery, the capacity characteristics, energy density, etc. of the battery can be improved, and when the positive electrode active material is applied to a secondary battery, breakage of the positive electrode active material particles can be prevented during battery manufacturing or operation, thereby suppressing gas generation, and thus completing the present invention.

[0064]

[0065] Bimodal positive electrode active material

[0066] The cathode active material according to the present invention includes a first lithium-excess manganese oxide in the form of a single particle (hereinafter, small-particle lithium-excess manganese oxide); and a second lithium-excess manganese oxide in the form of a secondary particle (hereinafter, large-particle lithium-excess manganese oxide); wherein the first lithium-excess manganese oxide and the second lithium-excess manganese oxide simultaneously include a Li2MnO3 phase and a LiMO2 (wherein M is an element including at least one selected from Ni, Co, and Mn) phase, and the first lithium-excess manganese oxide has an average particle diameter (D) larger than that of the second lithium-excess manganese oxide. 50 ) is a bimodal positive electrode active material in which the weight ratio of the first lithium-excess manganese oxide and the second lithium-excess manganese oxide is 1:1.5 to 8.

[0067]

[0068] The above bimodal positive electrode active material includes a small particle lithium-excess manganese oxide and an opposing lithium-excess manganese oxide simultaneously including a Li2MnO3 phase and a LiMO2 (wherein M is an element including at least one selected from Ni, Co, and Mn) phase at a specific weight ratio, so that the small particle lithium-excess manganese oxide is filled between the opposing lithium-excess manganese oxide, so that the pellet density is high, and the stress applied to the opposing lithium-excess manganese oxide is distributed, so that particle breakage can be prevented during rolling for electrode manufacture.

[0069]

[0070] The above first lithium-excess manganese oxide and the above second lithium-excess manganese oxide simultaneously include a Li2MnO3 phase and a LiMO2 phase (wherein M is an element including at least one selected from Ni, Co, and Mn), and include a monoclinic structure and a rhombohedral structure.

[0071]

[0072] The above-mentioned small-particle lithium-excess manganese oxide can be manufactured through a process (solid-state synthesis) of dry mixing lithium raw materials and transition metal raw materials, followed by calcination. Specifically, the lithium raw materials and transition metal raw materials can be manufactured by placing them in a crushing device, dry mixing and crushing (high-energy ball mill crushing), then calcining the crushed raw materials, and then crushing the calcined product. However, the present invention is not limited thereto.

[0073] The above lithium-excess manganese oxide can be obtained by preparing a precursor through co-precipitation in the same manner as in the prior art, mixing it with a lithium raw material, and calcining it, but is not limited thereto.

[0074]

[0075] According to the present invention, the first lithium-excess manganese oxide may have a single crystallinity (χ) of 0.4 or more according to the following formula 1.

[0076] [Formula 1]

[0077]

[0078] In the above equation 1,

[0079] a i When a single particle is composed of i crystal grains, the cross-sectional area of ​​the i-th crystal grain (A) is the cross-sectional area of ​​the single particle (A). i ) value (A i / A) means.

[0080] In the present invention, the degree of single crystallinity is evaluated and expressed as a parameter represented by the above formula 1. The degree of single crystallinity as referred to in the present invention is a value that is adjusted according to the number of crystal grains forming one single particle and the area of ​​each crystal grain, and the higher the area of ​​a specific crystal grain with the largest area within one single particle is close to the area of ​​the entire single particle, the higher the degree of single crystallinity.

[0081] That is, the degree of single crystallinity shown in the present invention can be higher as the number of crystal grains forming a single particle is smaller, and if the number of crystal grains is the same, the degree of single crystallinity is higher when a specific crystal grain has a larger area than other crystal grains rather than when the areas of the crystal grains are similar, and the difference between the areas of the entire single particle is small.

[0082] For example, the maximum value of the single crystallinity is 1, which means that one single particle is made up of one crystal grain (single crystal single particle). In addition, when one single particle is made up of N crystal grains, the single crystallinity varies depending on the area of ​​each crystal grain, but the minimum value of the single crystallinity that can be had when there are N crystal grains is 1 / N, which is when all N crystal grains have the same area. Even if one single particle is made up of N crystal grains, if a specific crystal grain has a larger area than the other crystal grains, the single crystallinity is higher than 1 / N, because the shape is closer to a single crystal when a specific crystal grain has the largest area than when N crystal grains have the same area.

[0083] From this point of view, the smaller the area of ​​the added crystal grains, the smaller the degree of single crystallinity decreases. This is because the small-sized crystal grains have a small area compared to the total particle area, so their effect on the decrease in the degree of single crystallinity is small.

[0084]

[0085] The single crystallinity of the first lithium-excess manganese oxide may be specifically 0.4, 0.45, 0.5, 0.55, 0.6 or more, and 0.65, 0.7, 0.75, 0.8 or less. When the single crystallinity of the first lithium-excess manganese oxide is within the above range, one single particle is composed of 10 or fewer crystal grains, which has the advantage of less particle breakage. Accordingly, particle breakage due to grain boundaries is suppressed during electrode rolling and battery operation, thereby suppressing gas generation, and the grain boundary area in contact with the electrolyte is reduced, thereby reducing side reactions with the electrolyte, thereby significantly improving the lifespan of the secondary battery.

[0086]

[0087] According to the present invention, the first lithium-excess manganese oxide has an average particle diameter (D 50) may be 0.5㎛ to 3.5㎛. Specifically, the average particle diameter (D of the first lithium-excess manganese oxide 50 ) can be 0.5㎛, 0.7㎛, 0.9㎛ or more, 1.1㎛, 1.5㎛, 2.0㎛, or 3.5㎛ or less.

[0088] According to the present invention, the second lithium-excess manganese oxide has an average particle diameter (D 50 ) may be 5.0㎛ to 10.0㎛. Specifically, the average particle diameter (D of the second lithium-excess manganese oxide 50 ) may be 5.0㎛, 5.5㎛, 6.0㎛, 6.5㎛ or more, 7.5㎛, 8.0㎛, 9.0㎛, or 10.0㎛ or less.

[0089] The average particle diameter (D) of the first lithium transition metal oxide and the second lithium transition metal oxide 50 ) is within the above range, the second lithium transition metal oxide may be appropriately distributed between the first lithium transition metal oxide, so that the filling rate may be excellent.

[0090] The ratio of the average particle size of the first lithium-excess manganese oxide to the average particle size of the second lithium-excess manganese oxide may be 1:3 to 1:5. When the ratio of the average particle size of the first lithium-excess manganese oxide to the average particle size of the second lithium-excess manganese oxide is within the above range, not only is the filling rate excellent, but there is also the advantage of improved pellet density.

[0091]

[0092] According to the present invention, the first lithium-excess manganese oxide may have a composition represented by the following chemical formula 1.

[0093] [Chemical Formula 1]

[0094] Li 1+x1 Ni a1 Mn b1 M 1 c1 O y1

[0095] In the above chemical formula 1,

[0096] M 1 is at least one selected from Co, Mo, W, V, Zr, Al and Nb,

[0097] 0.1≤x1≤0.2, 0 <a1≤0.5, 0.5≤b1≤0.75, 0≤c1≤0.1, 0≤y1≤2.0이고,

[0098] x1+a1+b1+c1=1.0.

[0099] Above M 1 is a doping element, specifically the above M 1 M may be at least one selected from Co, Mo, W, V, Zr, Al and Nb. 1 Although not necessarily included, when included in an appropriate amount, the particle shape of the first lithium-excess manganese oxide can be improved and the stability of the crystal structure can be enhanced.

[0100] The above x1 may be 0.10, 0.11, 0.12, 0.13, 0.14 or more, and may be 0.16, 0.17, 0.18, 0.19, 0.20 or less. When x1 satisfies the above range, high capacity characteristics and high energy density per unit volume can be realized.

[0101] The above a1 may be greater than 0, 0.1, 0.2, or greater, and may be 0.3, 0.4, or 0.5 or less. When a1 satisfies the above range, the first lithium-excess manganese oxide exhibits a high energy density, thereby realizing high-capacity characteristics.

[0102] The above b1 may be 0.50, 0.51, 0.52, 0.53, 0.54, 0.55 or more, and may be 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75 or less. When b1 satisfies the above range, high-capacity characteristics can be implemented. In addition, the high-temperature stability of the first lithium-excess manganese oxide can increase, and the decomposition reaction of the electrolyte can be relatively reduced.

[0103] The above c1 may be 0 or greater, and may be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.10 or less. When c1 satisfies the above range, the stability of the first lithium-excess manganese oxide crystal structure may be improved and the grain shape may be improved.

[0104] Meanwhile, the first lithium-excess manganese oxide may not contain expensive cobalt, and may improve the performance of a lithium secondary battery without containing cobalt.

[0105]

[0106] According to the present invention, the second lithium-excess manganese oxide may have a composition represented by the following chemical formula 2.

[0107] [Chemical Formula 2]

[0108] Li 1+x2 Ni a2 Mn b2 M 2 c2 O y2

[0109] In the above chemical formula 2,

[0110] M 2 is at least one selected from Co, Mo, W, V, Zr, Al, and Nb,

[0111] 0.1≤x2≤0.2, 0 <a2≤0.5, 0.5≤b2≤0.75, 0≤c2≤0.1, 0≤y2≤2.0이고,

[0112] x2+a2+b2+c2=1.0.

[0113] Above M 2 is a doping element, specifically the above M 2 M may be at least one selected from Co, Mo, W, V, Zr, Al and Nb. 2 Although not necessarily included, when included in an appropriate amount, the particle shape of the second lithium-excess manganese oxide can be improved and the stability of the crystal structure can be enhanced.

[0114] The above x2 may be 0.10, 0.11, 0.12, 0.13, 0.14 or more, and may be 0.16, 0.17, 0.18, 0.19, 0.20 or less. When x2 satisfies the above range, high capacity characteristics and high energy density per unit volume can be realized.

[0115] The above a2 may be greater than 0, 0.1, 0.2, or more, and may be 0.3, 0.4, or 0.5 or less. When a2 satisfies the above range, the second lithium-excess manganese oxide exhibits a high energy density, thereby realizing high-capacity characteristics.

[0116] The above b2 may be 0.50, 0.51, 0.52, 0.53, 0.54, 0.55 or more, and may be 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75 or less. When B2 satisfies the above range, high-capacity characteristics can be implemented. In addition, the high-temperature stability of the second lithium-excess manganese oxide can increase, and the decomposition reaction of the electrolyte can be relatively reduced.

[0117] The above c2 may be 0 or greater, and may be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.10 or less. When C2 satisfies the above range, the stability of the second lithium-excess manganese oxide crystal structure may be improved and the grain shape may be improved.

[0118] Meanwhile, the second lithium-excess manganese oxide may not contain expensive cobalt, and may improve the performance of a lithium secondary battery without containing cobalt.

[0119]

[0120] According to the present invention, the weight ratio of the first lithium-excess manganese oxide and the second lithium-excess manganese oxide may be 1:1.5 to 8. Specifically, the weight ratio of the first lithium-excess manganese oxide and the second lithium-excess manganese oxide may be 1:1.5 to 8, 1:1.5 to 7, 1:1.5 to 6, 1:1.5 to 5, 1:1.5 to 4, 1:1.5 to 3, or 1:1.5 to 2. When the weight ratio of the first lithium-excess manganese oxide and the second lithium-excess manganese oxide is within the above range, the packing density of the particles can be increased, and as a result, when applied to a battery, the capacity, energy density, etc. of the battery can be increased.

[0121]

[0122] According to the present invention, the bimodal positive electrode active material has a pellet density of 2.20 g / cm 3 2.70g / cm 3 It can be. Specifically, the pellet density of the bimodal positive electrode active material is 2.20 g / cm 3 , 2.40g / cm 3 , 2.50g / cm 3 , 2.60g / cm 3 Above, 2.65g / cm 3 , 2.70g / cm 3It may be as follows. When the pellet density of the bimodal positive electrode active material is within the above range, capacity characteristics, energy density, etc. can be improved, and the positive electrode active material particles can be prevented from breaking during battery manufacturing or operation.

[0123]

[0124] anode

[0125] The present invention provides a positive electrode comprising the positive electrode active material. That is, a positive electrode comprising the bimodal positive electrode active material is provided.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133]

[0134] lithium secondary battery

[0135] The present invention provides a lithium secondary battery including the positive electrode.

[0136]

[0137] 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.

[0138] 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.

[0139] 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.

[0140] The above negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150]

[0151] 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).

[0152] 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.

[0153] 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.

[0154] Accordingly, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0155] 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.

[0156]

[0157] 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.

[0158]

[0159] Manufacturing example

[0160] Manufacturing Example 1

[0161] Li2CO3, NiCO3, MnO2 were dry mixed in an amount such that the molar ratio of lithium, nickel, and manganese was 1.143:0.286:0.571, and pulverized using a High Energy Ball milling equipment (Zoz) at 1600 rpm for 30 minutes, and then sintered at 1000°C in an air atmosphere to produce a sintered product. The sintered product was pulverized using a Jet mill equipment under 3.5 bar conditions, and Li 1.143 Ni 0.286 Mn 0.571 It has a composition represented by O2 and an average particle size (D 50 ) was prepared as a single particle of lithium-excess manganese oxide (A1) having a particle size of 1 μm. The SEM image of the lithium-excess manganese oxide (A1) measured using SEM (JEOL, JSM7610F) is shown in Fig. 1(A).

[0162]

[0163] Manufacturing Example 2

[0164] Li2CO3, NiCO3, MnO2 were dry mixed in an amount such that the molar ratio of lithium, nickel, and manganese was 1.16:0.24:0.60, and the same method as in Manufacturing Example 1 was used. 1.16 Ni 0.24 Mn 0.60 It has a composition represented by O2 and an average particle size (D 50 ) was prepared as a single particle of lithium-excess manganese oxide (A2) having a particle size of 1 μm. The SEM image of the lithium-excess manganese oxide (A2) measured using SEM (JEOL, JSM7610F) is shown in Fig. 1(B).

[0165]

[0166] Example

[0167] Example 1

[0168] Li 1.14 Ni 0.28 Mn 0.58 It has a composition represented by O2 and an average particle size (D 50 ) was prepared as a secondary particle of lithium-excess manganese oxide (B1) with a particle size of 6.97 μm.

[0169] A bimodal positive electrode active material was manufactured by mixing the lithium-excess manganese oxide (A1) in the single particle form manufactured in Manufacturing Example 1 and the lithium-excess manganese oxide (B1) in the secondary form at a weight ratio of 1:4.

[0170]

[0171] Example 2

[0172] A bimodal positive electrode active material was manufactured in the same manner as Example 1, except that the lithium-excess manganese oxide (A2) in the form of a single particle manufactured in Manufacturing Example 2 was used instead of the lithium-excess manganese oxide (A1) in the form of a single particle manufactured in Manufacturing Example 1.

[0173]

[0174] Example 3

[0175] The lithium-excess manganese oxide (A1) in the form of a single particle manufactured in Manufacturing Example 1 and the lithium-excess manganese oxide (B1) in the form of a secondary particle were mixed in a weight ratio of 35:65 (=1:1.86) to manufacture a bimodal positive electrode active material.

[0176]

[0177] Comparative Example 1

[0178] The secondary form of lithium-excess manganese oxide (B1) used in Example 1 was used as the positive electrode active material of Comparative Example 1.

[0179]

[0180] Comparative Example 2

[0181] The lithium-excess manganese oxide (A1) in the form of a single particle manufactured in the above Manufacturing Example 1 was used as the positive electrode active material of Comparative Example 2.

[0182]

[0183] Comparative Example 3

[0184] A bimodal positive electrode active material was manufactured by mixing the lithium-excess manganese oxide (A1) in the form of a single particle manufactured in Manufacturing Example 1 and the lithium-excess manganese oxide (B1) in the form of a secondary particle at a weight ratio of 1:1.

[0185]

[0186] Comparative Example 4

[0187] A bimodal positive electrode active material was manufactured by mixing the lithium-excess manganese oxide (A1) in the form of a single particle manufactured in Manufacturing Example 1 and the lithium-excess manganese oxide (B1) in the form of a secondary particle at a weight ratio of 9:1 (=1:0.11).

[0188]

[0189] Comparative Example 5

[0190] A bimodal positive electrode active material was manufactured by mixing the lithium-excess manganese oxide (A1) in the form of a single particle manufactured in Manufacturing Example 1 and the lithium-excess manganese oxide (B1) in the form of a secondary particle at a weight ratio of 1:9.

[0191]

[0192] Experimental example

[0193] Experimental Example 1: Pellet Density Evaluation

[0194] Using an automatic pellet press (Auto Pellet Press, Carver, 3887.4), a cylindrical mold was used to adjust the zero point for thickness on a circular pellet holder having a diameter of 13 mm. Then, 3 g each of the positive electrode active materials manufactured in Examples 1 to 3 and Comparative Examples 1 to 5 was placed into the circular pellet holder, and a force was applied until a force corresponding to 2,000 kgf was reached, and the thickness of the formed pellet was measured. Then, the pellet volume was calculated using the following Equation 2, and the pellet density was calculated using the following Equation 3, and the results are shown in Table 1.

[0195] [Formula 2]

[0196] Pellet volume (cm) 3 ) = π(radius of the circular pellet holder) 2 × Pellet thickness

[0197] [Formula 3]

[0198] Pellet density (g / cm) 3 ) = Positive active material weight (g) / Pellet volume (cm 3 )

[0199]

[0200] Experimental Example 2: Analysis of particle breakage after rolling

[0201] For each of the above examples and comparative examples, the positive electrode active material, Super P as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in a weight ratio of 92:4:4 in an N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. 5 g of the prepared 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. Meanwhile, in the case of the positive electrodes including the positive electrode active materials of Examples 1 to 3 and Comparative Example 2, the rolling was performed so that the electrode porosity became 22%, and in the case of the positive electrodes including the positive electrode active materials of Comparative Examples 1, 3, and 4, the height did not decrease beyond a certain level no matter how much rolling was performed, so the rolling was performed so that the electrode porosity became 30%.

[0202] The above-mentioned rolled positive electrode was cut using a FIB (Focused Ion Beam) method to obtain a cross-section of the positive electrode active material layer. An SEM image of the cross-section of the positive electrode active material layer was measured using an SEM (JEOL, JSM7610F), and the image is shown in Fig. 2. Fig. 2(A) is a cross-sectional SEM image of the positive electrode including the positive electrode active material of Example 1, and Fig. 2(B) is a cross-sectional SEM image of the positive electrode including the positive electrode active material of Example 2.

[0203]

[0204] Experimental Example 3: Electrode porosity evaluation

[0205] For each of the above examples and comparative examples, the positive electrode active material, Super P as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were mixed in a weight ratio of 92:4:4 in an N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. 5 g of the prepared positive electrode slurry was applied to one surface of an aluminum current collector and then dried at 130°C to prepare a positive electrode. After the positive electrode was rolled using a rolling mill (roller rolling mill, Welcose), the height of the rolled positive electrode was measured to calculate the volume, and the empty space was converted into a porosity by reflecting the positive electrode active material content. Specifically, the porosity (%) was obtained using the following Equation 4, and is shown in Table 1 below.

[0206] [Formula 4]

[0207] Height after rolling (mm) = [{(weight of positive electrode active material (mg) - weight of aluminum current collector (mg)) / (area of ​​positive electrode (cm) 2 ) × (1-porosity (%)) × true density (g / cm 3 ))}+0.02]×1000

[0208]

[0209] Experimental Example 4: Single Crystallinity Analysis

[0210] The above first lithium-excess manganese oxide (A1), carbon black conductive agent, and PVDF binder were mixed in a weight ratio of 95:2:3 in an NMP solvent to prepare a cathode slurry. The cathode slurry was applied to one surface of an aluminum current collector, dried, and then rolled to prepare a cathode. The prepared cathode was cut using a FIB method to obtain a cross-section of the cathode, and SEM and EBSD images of the same part were measured to obtain the shape and area of ​​the particles (obtained from the SEM image) and the cross-section of the crystal grains (obtained from the EBSD image) within the map. Then, a clustering algorithm was applied to distinguish the crystal grains within the particles, and the single crystallinity of the cathode active material was analyzed through Equation 1 of the present invention.

[0211] [Formula 1]

[0212]

[0213] In the above equation 1,

[0214] a i When a single particle is composed of i crystal grains, the cross-sectional area of ​​the i-th crystal grain (A) is the cross-sectional area of ​​the single particle (A). i ) value (A i / A) means.

[0215]

[0216] As a result of the analysis, the first lithium-excess manganese oxide (A1) had a single crystallinity (χ) of 0.64 according to the following equation 1.

[0217]

[0218] Experimental Example 5: Battery Characteristics Evaluation

[0219] For each of the above examples and comparative examples, the positive electrode active material, Super P as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were mixed in a weight ratio of 92:4:4 in an N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. The prepared 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. Meanwhile, in the case of the positive electrodes including the positive electrode active materials of Examples 1 to 3 and Comparative Example 2, the rolling was performed so that the electrode porosity became 22%, and in the case of the positive electrodes including the positive electrode active materials of Comparative Examples 1, 3, and 4, the height did not decrease beyond a certain level no matter how much rolling was performed, so the rolling was performed so that the electrode porosity became 30%.

[0220] 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. This was placed inside a battery case, and a coin-type half-cell was manufactured by injecting an electrolyte solution containing 1 M LiPF6 dissolved in an organic solvent containing ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) in a volume ratio of 3:4:3.

[0221] Coin-type half-cells containing the positive electrode active materials of each of the above examples and comparative examples were charged to 4.65 V in CC (0.1 C)-CV (Cut-off current: 0.05 C) mode at 45°C, and then discharged to 2.0 V at 0.1 C to perform an activation process (formation). Subsequently, they were charged to 4.25 V in CC (0.1 C)-CV (Cut-off current: 0.05 C) mode at 25°C, and then discharged to 2.5 V at 0.1 C to measure the initial discharge capacity, which is shown in Table 1 below.

[0222] Next, after charging to 4.25 V in CC (0.33 C)-CV (Cut-off current: 0.05 C) mode at 25°C, a cycle of discharging to 2.5 V at 0.33 C was considered one cycle, and a total of 30 cycles of charging and discharging were repeated. After measuring the discharge capacity at 30 cycles, the percentage of the discharge capacity at 30 cycles to the initial discharge capacity was defined as the capacity retention rate and is shown in Table 1 below.

[0223] Separation Pellet Density (g / cm) 3 ) Electrode Porosity (%) Discharge Capacity (mAh / g) Capacity Retention Rate (%) Example 12.6 29 22 196.99 7.8 Example 22.60 122 198.79 7.2 Example 32.60 022 193.39 7.2 Comparative Example 12.23 030 198.198.1 Comparative Example 22.40 022 180.99 6.2 Comparative Example 32.59 430 184.397.0 Comparative Example 42.43 030 182.09 6.0 Comparative Example 52.48 022 197.29 3.4

[0224] Referring to Table 1 above, it can be confirmed that the bimodal positive electrode active materials of Examples 1 to 3 according to the present invention have high energy densities, significantly higher pellet densities and electrode porosities than the positive electrode active material of Comparative Example 1, and that the discharge capacity and capacity retention rate are at equivalent levels. In addition, it can be confirmed that the bimodal positive electrode active materials of Examples 1 to 3 according to the present invention have significantly higher pellet densities than the positive electrode active material of Comparative Example 2, and that both the discharge capacity and capacity retention rate are significantly superior.

[0225] In addition, it can be confirmed that the bimodal positive electrode active materials of Examples 1 to 3 according to the present invention have a significantly higher pellet density and a significantly superior discharge capacity compared to the positive electrode active materials of Comparative Examples 3 and 4. In addition, it can be confirmed that the bimodal positive electrode active materials of Examples 1 to 3 according to the present invention have a significantly higher pellet density and a significantly superior capacity retention rate compared to the positive electrode active material of Comparative Example 5.

[0226] In conclusion, it can be seen that the cathode active material of the present invention simultaneously contains a lithium-excess manganese oxide in the form of a single particle and a lithium-excess manganese oxide in the form of a secondary particle at a specific weight ratio, thereby having excellent energy density and stability, and consequently improving the performance of a battery containing the same, for example, capacity characteristics, energy density, etc., and preventing the cathode active material particles from breaking during battery manufacturing or operation.

Claims

1. A first lithium-excess manganese oxide in the form of a single particle; and a second lithium-excess manganese oxide in the form of a secondary particle; The first lithium-excess manganese oxide and the second lithium-excess manganese oxide simultaneously include a Li2MnO3 phase and a LiMO2 phase (wherein M is an element including at least one selected from Ni, Co, and Mn), The above first lithium-excess manganese oxide has a larger average particle diameter (D) than the above second lithium-excess manganese oxide. 50 ) is small, A bimodal positive electrode active material in which the weight ratio of the first lithium-excess manganese oxide and the second lithium-excess manganese oxide is 1:1.5 to 8.

2. In claim 1, The above first lithium-excess manganese oxide is a bimodal positive electrode active material having a single crystallinity (χ) of 0.4 or more according to the following formula 1: [Formula 1] In the above equation 1, a i When a single particle is composed of i crystal grains, the cross-sectional area of ​​the i-th crystal grain (A) is the cross-sectional area of ​​the single particle (A). i ) value (A i / A) means.

3. In claim 1, The above first lithium-excess manganese oxide has an average particle diameter (D 50 ) is a bimodal positive electrode active material having a diameter of 0.5㎛ to 3.5㎛.

4. In claim 1, The above second lithium-excess manganese oxide has an average particle diameter (D 50 ) is a bimodal positive electrode active material having a diameter of 5.0㎛ to 10.0㎛.

5. In claim 1, The above first lithium-excess manganese oxide is a bimodal positive electrode active material having a composition represented by the following chemical formula 1: [Chemical Formula 1] Li 1+x1 Ni a1 Mr b1 M 1 c1 O y1 In the above chemical formula 1, M 1 is at least one selected from Co, Mo, W, V, Zr, Al and Nb, 0.1≤x1≤0.2, 0 <a1≤0.5, 0.5≤b1≤0.75, 0≤c1≤0.1, 0≤y1≤2.0이고, x1+a1+b1+c1=1.

0.

6. In claim 1, The above second lithium-excess manganese oxide is a bimodal positive electrode active material having a composition represented by the following chemical formula 2: [Chemical Formula 2] Li 1+x2 Ni a2 Mr b2 M 2 c2 O y2 In the above chemical formula 2, M 2 is at least one selected from Co, Mo, W, V, Zr, Al, and Nb, 0.1≤x2≤0.2, 0 <a2≤0.5, 0.5≤b2≤0.75, 0≤c2≤0.1, 0≤y2≤2.0이고, x2+a2+b2+c2=1.

0.

7. In claim 1, Pellet density is 2.20g / cm 3 2.70g / cm 3 Bimodal positive electrode active material.

8. A positive electrode comprising a bimodal positive electrode active material according to any one of claims 1 to 7.

9. A lithium secondary battery comprising a positive electrode according to claim 8.

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