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

Abstract

The present invention relates to a positive electrode active material and comprises a first lithium-excess manganese oxide in single-particle form and a second lithium-excess manganese oxide in secondary-particle form, wherein the first lithium-excess manganese oxide and the second lithium-excess manganese oxide simultaneously contain a Li2MnO3 phase and a LiMO2 phase (where M is an element comprising one or more elements selected from Ni, Co, and Mn), and the first lithium-excess manganese oxide has a larger average particle size (D) than the second lithium-excess manganese oxide. 50 The present invention relates to a bimodal type positive electrode active material having a small ) and a weight ratio of 1:1.5 to 8 between the first lithium-excess manganese oxide and the second lithium-excess manganese oxide, a positive electrode containing the same, and a lithium secondary battery.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2023-0097407 dated July 26, 2023, and all content disclosed in the documents of the said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to a bimodal positive electrode active material, a positive electrode containing the same, and a lithium secondary battery, and more specifically, to a bimodal positive electrode active material containing a lithium-excess manganese oxide, a positive electrode containing the same, and a lithium secondary battery. [Background technology]

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

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

[0005] On the other hand, lithium-excess oxide in secondary particle form produced by conventional coprecipitation methods has problems such as low pellet density, high porosity, and low energy density per unit volume when applied to electrodes. Furthermore, during rolling for electrode production, mechanical stress is not dispersed, leading to particle cracking and problems such as the generation of large amounts of gas when the battery is powered.

[0006] Therefore, there is a need to develop lithium-excess oxides that have high pellet density and a low rate of particle cracking during rolling. [Overview of the project] [Problems that the invention aims to solve]

[0007] The problem that this invention aims to solve is to improve the energy density and stability of the positive electrode active material, and as a result improve the performance of a battery containing it.

[0008] Furthermore, the present invention aims to provide a positive electrode containing the positive electrode active material and a lithium secondary battery. [Means for solving the problem]

[0009] To solve the above problems, the present invention provides a positive electrode active material, a positive electrode, and a lithium secondary battery.

[0010] (1) The present invention comprises a first lithium-excess manganese oxide in single-particle form and a second lithium-excess manganese oxide in secondary-particle form, wherein the first lithium-excess manganese oxide and the second lithium-excess manganese oxide simultaneously contain a Li2MnO3 phase and a LiMO2 phase (where M is an element comprising one or more elements selected from Ni, Co and Mn), and the first lithium-excess manganese oxide has a larger average particle size (D) than the second lithium-excess manganese oxide. 50 The present invention provides a bimodal cathode active material in which the ) is small and the weight ratio of the first lithium-excess manganese oxide to the second lithium-excess manganese oxide is 1:1.5 to 8.

[0011] (2) The present invention provides a bimodal positive electrode active material in which the first lithium-excess manganese oxide has a single crystallinity (χ) of 0.4 or more according to the following formula 1.

number

[0012] (3) The present invention provides a bimodal type cathode active material in the above (1) or (2), wherein the first lithium-excess manganese-based oxide has an average particle size (D 50 ) of 0.5 μm to 3.5 μm.

[0013] (4) The present invention provides a bimodal type cathode active material in any one of the above (1) to (3), wherein the second lithium-excess manganese-based oxide has an average particle size (D 50 ) of 5.0 μm to 10.0 μm.

[0014] (5) The present invention provides a bimodal type cathode active material in any one of the above (1) to (4), wherein the first lithium-excess manganese-based oxide has a composition represented by the following Chemical Formula 1. [Chemical Formula 1] Li 1+x1 Ni a1 Mn b1 M 1 c1 O y1 In the above Chemical Formula 1, M 1 is one or more 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 ≦ 2.0, and x1 + a1 + b1 + c1 = 1.0.

[0015] (6) The present invention provides a bimodal type cathode active material in any one of the above (1) to (5), wherein the second lithium-excess manganese-based oxide has a composition represented by the following Chemical Formula 2. [Chemical Formula 2] Li 1+x2 Nia2 Mn b2 M 2 c2 O y2 In the aforementioned chemical formula 2, M 2 is one or more 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≦2.0であり、 x² + a² + b² + c² = 1.0.

[0016] (7) In any one of (1) to (6) above, the present invention provides a pellet density of 2.20 g / cm³. 3 ~2.70g / cm 3 The present invention provides a bimodal type cathode active material.

[0017] (8) The present invention provides a positive electrode comprising a positive electrode active material according to any one of (1) to (7) above.

[0018] (9) The present invention provides a lithium secondary battery including the positive electrode according to (8) above. [Effects of the Invention]

[0019] The positive electrode active material of the present invention contains small lithium-excess manganese oxide particles in single particle form and large lithium-excess manganese oxide particles in secondary particle form in a specific weight ratio, resulting in excellent energy density and stability. Consequently, it can improve the performance of batteries containing it, such as capacity characteristics and energy density, and can prevent the positive electrode active material particles from cracking during battery manufacturing or operation. [Brief explanation of the drawing]

[0020] [Figure 1]These are SEM images of lithium-excess manganese oxides produced in Production Examples 1 and 2. Specifically, Figure 1(A) is an SEM image of lithium-excess manganese oxide (A1) produced in Production Example 1, and Figure 1(B) is an SEM image of lithium-excess manganese oxide (A2) produced in Production Example 2. [Figure 2] These are cross-sectional SEM images of the positive electrodes containing the positive electrode active material of Example 1 and Comparative Example 1. Specifically, Figure 2(A) is a cross-sectional SEM image of the positive electrode containing the positive electrode active material of Example 1, and Figure 2(B) is a cross-sectional SEM image of the positive electrode containing the positive electrode active material of Example 2. [Modes for carrying out the invention]

[0021] The present invention will be described in more detail below to facilitate understanding of it.

[0022] The terms and words used in the description and claims of this invention should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​this invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0023] In this specification, terms such as “includes,” “equip,” or “have” specify the presence of an implemented feature, figure, step, component, or combination thereof, and should be understood not to preclude the existence or possibility of adding one or more other features, figures, steps, components, or combinations thereof.

[0024] In this specification, "single-particle form" is a concept contrasted with the spherical secondary particle form formed by the aggregation of tens to hundreds of primary particles, and refers to a form consisting of 10 or fewer primary particles. Specifically, "single-particle form" may be a single-particle form consisting of one primary particle, or it may be a secondary particle form formed by the aggregation of several primary particles.

[0025] In this specification, "primary particle" refers to the smallest particle unit recognized when observing the positive electrode active material using a scanning electron microscope (SEM), and may consist of multiple crystal grains, while "secondary particle" refers to a secondary structure formed by the aggregation of multiple primary particles.

[0026] In this specification, "single crystal" means a crystal in which no grain boundaries are present within the particles.

[0027] In this specification, "crystal grain" refers to a particle unit having substantially the same crystal orientation, and can be measured by EBSD (Electron Backscatter Diffraction). Specifically, it refers to the smallest particle unit represented by the same hue in the IPF map obtained by EBSD analysis of a cross-section of a positive electrode active material cut by ion milling.

[0028] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 ) can be measured, for example, using the laser diffraction method. More specifically, lithium composite transition metal oxide is dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac Mt 3000), and after irradiating with ultrasound at approximately 28 kHz with an output of 60 W, the average particle size (D) corresponding to 50% of the particle size distribution in the measuring device is measured. 50 It is possible to calculate ).

[0029] In this specification, the pellet density is the value calculated by the following formula 2 when pellets are formed by applying force to an automatic pellet press until a force equivalent to 2,000 kgf is reached. Specifically, the pellet density is the value obtained by the following (1) to (3).

[0030] (1) Using a Universal Testing Machine (UTM, Instron, Model 5966), adjust the zero point relative to the thickness of a circular pellet holder using a cylindrical mold.

[0031] (2) Place the positive electrode active material into the circular pellet holder and apply force until a force equivalent to 2,000 kgf is applied, and measure the thickness of the formed pellet.

[0032] (3) Calculate the pellet volume using formula 2 below, and calculate the pellet density using formula 3 below.

[0033] [Formula 2] Pellet volume (cm³) 3 ) = π (radius of the circular pellet holder) 2 × Pellet thickness

[0034] [Formula 3] Pellet density (g / cm³) 3 ) = Weight of positive electrode active material (g) / Pellet volume (cm³) 3 )

[0035] The present inventors have discovered that when a positive electrode active material simultaneously contains small lithium-excess manganese oxide in single-particle form and large lithium-excess manganese oxide in secondary-particle form, the electrode density can be improved and particle cracking can be minimized when the positive electrode active material is applied to the positive electrode of a secondary battery. Furthermore, when the positive electrode active material is applied to a secondary battery, the capacity characteristics and energy density of the battery can be improved. Additionally, cracking of the positive electrode active material particles can be prevented during battery manufacturing or operation, and gas generation can be suppressed. Based on these findings, the present invention has been completed.

[0036] Bimodal type cathode active material The positive electrode active material according to the present invention comprises a first lithium-excess manganese oxide in single-particle form (hereinafter referred to as small-particle lithium-excess manganese oxide) and a second lithium-excess manganese oxide in secondary-particle form (hereinafter referred to as large-particle lithium-excess manganese oxide), wherein the first lithium-excess manganese oxide and the second lithium-excess manganese oxide simultaneously contain a Li2MnO3 phase and a LiMO2 phase (where M is an element containing one or more selected from Ni, Co, and Mn), and the first lithium-excess manganese oxide has a larger average particle size (D) than the second lithium-excess manganese oxide. 50 The bimodal cathode active material has a small ) and the weight ratio of the first lithium-excess manganese oxide to the second lithium-excess manganese oxide is 1:1.5 to 8.

[0037] The bimodal positive electrode active material contains small-particle lithium-excess manganese oxide and large-particle lithium-excess manganese oxide in a specific weight ratio, with the small-particle lithium-excess manganese oxide filling the spaces between the large-particle lithium-excess manganese oxide. This results in a high pellet density, which disperses the stress applied to the large-particle lithium-excess manganese oxide and prevents particle cracking during rolling for electrode manufacturing.

[0038] The first lithium-excess manganese oxide and the second lithium-excess manganese oxide simultaneously contain a Li2MnO3 phase and a LiMO2 phase (where M is an element containing one or more selected from Ni, Co, and Mn), and include monoclinic and rhombohedral structures.

[0039] The aforementioned small-particle lithium-excess manganese oxide can be produced by a process (solid-phase synthesis method) in which lithium raw material and transition metal raw material are dry-mixed and then calcined. Specifically, the lithium raw material and transition metal raw material are put into a pulverizer, dry-mixed and pulverized (high-energy ball mill pulverization) is performed, the pulverized raw material is calcined, and the calcined product is crushed. However, it is not limited to this.

[0040] The aforementioned large-particle lithium-excess manganese oxide can be obtained by producing a precursor by coprecipitation using the same method as in the past, mixing it with a lithium raw material, and then calcining it, but is not limited to this method.

[0041] According to the present invention, the first lithium-excess manganese oxide may have a single crystallinity degree (χ) of 0.4 or higher according to the following formula 1.

[0042]

number

[0043] In the above formula 1, a i When a single particle consists of i crystal grains, the cross-sectional area of ​​the i-th crystal grain (A) is given by the cross-sectional area of ​​the single particle (A). i ) value (A i This means / A).

[0044] In this invention, the degree of single crystallinity is evaluated and expressed by the parameter represented by Formula 1 above. The degree of single crystallinity as defined in this invention is a value that is adjusted according to the number of crystal grains that make up a single particle and the area of ​​each crystal grain. A higher degree of single crystallinity is indicated when the specific crystal grain with the largest area within a single particle has an area close to the total area of ​​the single particle.

[0045] In other words, the degree of single crystallinity shown in this invention can be higher the fewer the number of crystal grains that make up a single particle. If the number of crystal grains is the same, a higher degree of single crystallinity is observed when a particular 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 that and the total area of ​​the single particle is small.

[0046] For example, the maximum value of the single crystallinity is 1, which means that one single particle consists of one crystal grain (single crystal single particle). Also, when one single particle consists of N crystal grains, the single crystallinity differs 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 when one single particle consists of N crystal grains, if a particular crystal grain has a larger area than the other crystal grains, the single crystallinity will be higher than 1 / N, because the form is closer to a single crystal when a particular crystal grain has the largest area than when all N crystal grains have the same area.

[0047] From this perspective, the smaller the area of ​​the added crystal grains, the smaller the degree of single crystallinity decreases. This is because small crystal grains have a small area relative to the total grain area, and therefore have a low impact on the decrease in the degree of single crystallinity.

[0048] The single crystallinity of the first lithium-excess manganese oxide may be, specifically, 0.4, 0.45, 0.5, 0.55, 0.6 or higher, 0.65, 0.7, 0.75, or 0.8 or lower. When the single crystallinity of the first lithium-excess manganese oxide is within the above range, each single particle consists of 10 or fewer crystal grains, which has the advantage of reducing particle cracking. As a result, during electrode rolling and battery operation, particle cracking due to grain boundaries is suppressed, gas generation is suppressed, the area of ​​grain boundaries in contact with the electrolyte is reduced, side reactions with the electrolyte are reduced, and the lifespan of the secondary battery can be significantly improved.

[0049] According to the present invention, the first lithium-excess manganese oxide has an average particle size (D 50The average particle size (D) of the first lithium-excess manganese oxide may be 0.5 μm to 3.5 μm. Specifically, the average particle size (D) of the first lithium-excess manganese oxide 50 The particle size may be 0.5 μm, 0.7 μm, 0.9 μm or larger, 1.1 μm, 1.5 μm, 2.0 μm, or 3.5 μm or smaller.

[0050] According to the present invention, the second lithium-excess manganese oxide has an average particle size (D 50 The average particle size (D) of the second lithium-excess manganese oxide may be 5.0 μm to 10.0 μm. Specifically, the average particle size (D) of the second lithium-excess manganese oxide 50 The particle size may be 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm or larger, 7.5 μm, 8.0 μm, 9.0 μm, or 10.0 μm or smaller.

[0051] The average particle size (D) of the first lithium transition metal oxide and the second lithium transition metal oxide. 50 When the range is within the above range, the second lithium transition metal oxide is appropriately distributed among the first lithium transition metal oxides, and excellent packing efficiency can be achieved.

[0052] 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 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, there is the advantage of not only excellent packing efficiency but also improved pellet density.

[0053] According to the present invention, the first lithium-excess manganese oxide may have a composition represented by the following chemical formula 1.

[0054] [Chemical formula 1] Li 1+x1 Ni a1 Mn b1 M 1 c1 O y1

[0055] In the above chemical formula 1, M 1is one or more 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≦2.0であり、 x1 + a1 + b1 + c1 = 1.0.

[0056] Said M 1 This is a doping element, specifically, the aforementioned M 1 The M may be one or more selected from Co, Mo, W, V, Zr, Al, and Nb. 1 Although not an essential component, when present in appropriate amounts, it can improve the particle shape of the first lithium-excess manganese oxide and enhance the stability of its crystal structure.

[0057] The value of x1 may be 0.10, 0.11, 0.12, 0.13, 0.14 or greater, or 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 achieved.

[0058] The value of a1 may be greater than 0, 0.1, 0.2 or greater, or 0.3, 0.4, 0.5 or less. When a1 satisfies the above range, the first lithium-excess manganese oxide exhibits a high energy density, enabling high capacity characteristics.

[0059] The value of b1 may be 0.50, 0.51, 0.52, 0.53, 0.54, 0.55 or higher, or 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 lower. When b1 satisfies the above range, high capacity characteristics can be achieved. In addition, the high-temperature stability of the first lithium-excess manganese oxide is increased, and the decomposition reaction of the electrolyte can be relatively reduced.

[0060] The value of c1 may be 0 or greater, or it 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 is improved, and the grain shape can be improved.

[0061] On the other hand, the first lithium-excess manganese oxide does not need to contain expensive cobalt, and can improve the performance of lithium secondary batteries while being cobalt-free.

[0062] According to the present invention, the second lithium-excess manganese oxide may have a composition represented by the following chemical formula 2.

[0063] [Chemical formula 2] Li 1+x2 Ni a2 Mn b2 M 2 c2 O y2

[0064] In the aforementioned chemical formula 2, M 2 is one or more 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≦2.0であり、 x² + a² + b² + c² = 1.0.

[0065] Said M 2 This is a doping element, specifically, the aforementioned M 2 The M may be one or more selected from Co, Mo, W, V, Zr, Al, and Nb. 2 Although not an essential component, when included in an appropriate amount, it can improve the particle shape of the second lithium-excess manganese oxide and enhance the stability of the crystal structure.

[0066] The aforementioned x2 may be 0.10, 0.11, 0.12, 0.13, 0.14 or greater, 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 achieved.

[0067] The value of a2 may be greater than 0, 0.1, 0.2 or greater, or 0.3, 0.4, 0.5 or less. When a2 satisfies the above range, the second lithium-excess manganese oxide exhibits a high energy density, enabling high capacity characteristics.

[0068] The value of b2 may be 0.50, 0.51, 0.52, 0.53, 0.54, 0.55 or higher, or 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 lower. When b2 satisfies the above range, high capacity characteristics can be achieved. In addition, the high-temperature stability of the second lithium-excess manganese oxide is increased, and the decomposition reaction of the electrolyte can be relatively reduced.

[0069] The value of c2 may be 0 or greater, or it 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 is improved, and the grain shape can be improved.

[0070] On the other hand, the second lithium-excess manganese oxide does not need to contain expensive cobalt, and can improve the performance of lithium secondary batteries while being cobalt-free.

[0071] According to the present invention, the weight ratio of the first lithium-excess manganese oxide to the second lithium-excess manganese oxide may be 1:1.5 to 8. Specifically, the weight ratio of the first lithium-excess manganese oxide to 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 to the second lithium-excess manganese oxide is within the above range, the particle packing density can be increased, and as a result, when applied to a battery, the battery capacity, energy density, etc. can be increased.

[0072] According to the present invention, the bimodal positive electrode active material has a pellet density of 2.20 g / cm³. 3 ~2.70g / cm 3 This may also be the case. Specifically, the pellet density of the bimodal positive electrode active material is 2.20 g / cm³. 3 2.40 g / cm³ 3 2.50 g / cm³ 3 2.60 g / cm³ 3 More than 2.65g / cm 3 2.70 g / cm³ 3 The following is also possible: 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 cracking of the positive electrode active material particles can be prevented during battery manufacturing or operation.

[0073] positive electrode The present invention provides a positive electrode containing the positive electrode active material. That is, it provides a positive electrode containing the bimodal type positive electrode active material.

[0074] 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.

[0075] The positive electrode current collector is not particularly limited as long as it contains a highly conductive metal, allows for easy adhesion of the positive electrode active material layer, and is unreactive within the battery voltage range. Examples of materials that can be used for the positive electrode current collector include stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, or silver. Furthermore, the positive electrode current collector can typically have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous materials, foams, and nonwoven fabrics.

[0076] The positive electrode active material layer may optionally contain a conductive material and a binder along with the positive electrode active material. Here, the positive electrode active material can be included in an amount of 80% to 99% by weight, more specifically 85% to 98.5% by weight, relative to the total weight of the positive electrode active material layer, and within this range, excellent capacitance characteristics can be observed.

[0077] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations in the battery it is configured in, as long as it does not cause chemical changes and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Of these, one or more can be used. The conductive material can be included in an amount of 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0078] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which the hydrogen atoms of these materials are substituted with Li, Na, or Ca, or various copolymers thereof. One of these materials alone or a mixture of two or more materials can be used. The binder can be present in an amount of 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0079] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except that the positive electrode active material is used. Specifically, the positive electrode can be manufactured by coating a positive electrode active material layer-forming composition, which is prepared by dissolving or dispersing the positive electrode active material and, if necessary, selectively, a binder, a conductive material, and a dispersant in a solvent, onto a positive electrode current collector, followed by drying and rolling; or by casting the positive electrode active material layer-forming composition onto another support, peeling it off the support, and laminating the resulting film onto the positive electrode current collector.

[0080] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and one or more of these can be used individually or in mixtures of two or more. The amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode.

[0081] Lithium-ion rechargeable battery The present invention provides a lithium secondary battery including the positive electrode.

[0082] The lithium secondary battery may include a positive electrode, a negative electrode, a separator interposed between the positive and negative electrodes, and an electrolyte. The lithium secondary battery may also selectively further include a battery container for housing the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0083] The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0084] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. The negative electrode current collector can usually have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0085] The negative electrode active material layer may selectively include a binder and a conductive material together with the negative electrode active material.

[0086] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. βExamples include metallic oxides that can be doped and dedoped with lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more mixtures thereof can be used. A metallic lithium thin film can also be used as the negative electrode active material. Furthermore, both low-crystallinity carbon and high-crystallinity carbon can be used as the carbon material. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbons such as petroleum or coal tar pitch-derived cokes. The anode active material can be present in an amount of 80% to 99% by weight relative to the total weight of the anode active material layer.

[0087] The binder in the negative electrode active material layer is a component that helps to bond the conductive material, active material, and current collector, and is usually added in an amount of 0.1% to 10% by weight relative to the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0088] The conductive material in the negative electrode active material layer is a component for further improving the conductivity of the negative electrode active material, and can be added in an amount of 10% by weight or less, preferably 5% by weight or less, relative to the total weight of the negative electrode active material layer. Such conductive materials are not particularly limited as long as they do not cause chemical changes in the battery and are conductive, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used.

[0089] The negative electrode can be manufactured by coating a negative electrode active material layer-forming composition, which is prepared by dissolving or dispersing a negative electrode active material and, selectively, a binder and a conductive material in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode active material layer-forming composition onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0090] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a separator typically used in lithium secondary batteries. Particularly preferred is one that exhibits low resistance to ion movement of the electrolyte and has excellent electrolyte impregnation ability. Specifically, porous polymer films, such as polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof, can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used in single-layer or multi-layer structures.

[0091] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries. Specifically, the electrolyte may contain an organic solvent and a lithium salt.

[0092] The aforementioned organic solvent can be used without particular limitations, as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the aforementioned organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0093] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the anion of the lithium salt is F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - The lithium salt may be selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably in the range of 0.1M to 2.0M. When the concentration of the lithium salt falls within this range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0094] In addition to the components of the electrolyte, the electrolyte may also contain one or more additives, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethyl alcoholamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethyl alcohol, or aluminum trichloride, for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. Here, the additive may be present in an amount of 0.1% to 5% by weight relative to the total weight of the electrolyte.

[0095] The lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent capacity characteristics, output characteristics, and life characteristics in a stable manner, making it useful in fields such as portable devices like mobile phones, notebook computers, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs).

[0096] The external shape of the lithium secondary battery of the present invention is not particularly limited, but it may be cylindrical, rectangular, pouch-type, or coin-type, using a can.

[0097] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also preferably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0098] This provides a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

[0099] The battery module or battery pack can be used as a power source for one or more medium to large-sized devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0100] Hereinafter, embodiments of the present invention will be described in detail so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement them. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0101] Manufacturing example Production Example 1 Li2CO3, NiCO3, and MnO2 were dry-mixed in amounts such that the molar ratio of lithium, nickel, and manganese was 1.143:0.286:0.571, pulverized at 1600 rpm for 30 minutes using a High Energy Ball milling device (manufactured by Zoz), and then fired at 10,000 °C in an air atmosphere to produce a fired product. The fired product was pulverized using a Jet mill device under the condition of 3.5 bar, and lithium-excess manganese-based oxide (A1) in the form of single particles having a composition represented by Li 1.143 Ni 0.286 Mn 0.571 O2 and an average particle size (D 50 ) of 1 μm was produced. The SEM image of the lithium-excess manganese-based oxide (A1) measured using SEM (JSM7610F, manufactured by JEOL) is shown in (A) of FIG. 1.

[0102] Production Example 2 Li2CO3, NiCO3, and MnO2 were dry-mixed in amounts such that the molar ratio of lithium, nickel, and manganese was 1.16:0.24:0.60, and then, in the same manner as in Production Example 1, Li 1.16 Ni 0.24 Mn 0.60 O2 and having an average particle size (D 50A lithium-excess manganese-based oxide (A2) in the form of single particles with a size of 1 μm was produced. The SEM image of the lithium-excess manganese-based oxide (A2) measured using SEM (JSM7610F manufactured by JEOL) is shown in (B) of FIG. 1.

[0103] Examples Example 1 Li 1.14 Ni 0.28 Mn 0.58 A lithium-excess manganese-based oxide (B1) in the form of secondary particles having a composition represented by O2 and an average particle size (D 50 ) of 6.97 μm was prepared.

[0104] The single-particle lithium-excess manganese-based oxide (A1) produced in Production Example 1 and the secondary-form lithium-excess manganese-based oxide (B1) were mixed at a weight ratio of 1:4 to produce a bimodal-type positive electrode active material.

[0105] Example 2 A bimodal-type positive electrode active material was produced in the same manner as in Example 1, except that the single-particle lithium-excess manganese-based oxide (A2) produced in Production Example 2 was used instead of the single-particle lithium-excess manganese-based oxide (A1) produced in Production Example 1.

[0106] Example 3 The single-particle lithium-excess manganese-based oxide (A1) produced in Production Example 1 and the secondary-particle lithium-excess manganese-based oxide (B1) were mixed at a weight ratio of 35:65 (= 1:1.86) to produce a bimodal-type positive electrode active material.

[0107] Comparative Example 1 The secondary-form lithium-excess manganese-based oxide (B1) used in Example 1 was used as the positive electrode active material in Comparative Example 1.

[0108] Comparative Example 2 The single-particle lithium-excess manganese-based oxide (A1) produced in Production Example 1 was used as the positive electrode active material in Comparative Example 2.

[0109] Comparative Example 3 A bimodal cathode active material was produced by mixing the lithium-excess manganese oxide (A1) in single-particle form and the lithium-excess manganese oxide (B1) in secondary-particle form, as manufactured in Manufacturing Example 1, in a 1:1 weight ratio.

[0110] Comparative Example 4 A bimodal cathode active material was produced by mixing the lithium-excess manganese oxide (A1) in single-particle form and the lithium-excess manganese oxide (B1) in secondary-particle form, as manufactured in Manufacturing Example 1, in a weight ratio of 9:1 (=1:0.11).

[0111] Comparative Example 5 A bimodal cathode active material was produced by mixing the single-particle lithium-excess manganese oxide (A1) and the secondary-particle lithium-excess manganese oxide (B1) manufactured in Manufacturing Example 1 in a weight ratio of 1:9.

[0112] Experimental example Experimental Example 1: Evaluation of Pellet Density Using an automatic pellet press (Carver, 3887.4), a cylindrical mold was used to adjust the zero point relative to the thickness of a circular pellet holder with a diameter of 13 mm. Next, 3 g each of the positive electrode active material produced in Examples 1-3 and Comparative Examples 1-5 was placed into the circular pellet holder, and a force equivalent to 2,000 kgf was applied to measure the thickness of the formed pellets. Then, the pellet volume was calculated using Equation 2 below, and the pellet density was calculated using Equation 3 below, as shown in Table 1.

[0113] [Formula 2] Pellet volume (cm³) 3 ) = π (radius of the circular pellet holder) 2 × Pellet thickness

[0114] [Formula 3] Pellet density (g / cm³)3 ) = Weight of positive electrode active material (g) / Pellet volume (cm³) 3 )

[0115] Experimental Example 2: Particle cracking analysis after rolling For each of the above examples and comparative examples, Super P was used as the positive electrode active material and polyvinylidene fluoride (PVDF) as the binder, and these were mixed in N-methylpyrrolidone (NMP) solvent in a weight ratio of 92:4:4 to produce a positive electrode slurry. 5 g of the produced positive electrode slurry was applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to produce a positive electrode. On the other hand, for the positive electrodes containing the positive electrode active materials of Examples 1-3 and Comparative Example 2, the electrodes were rolled to achieve an electrode porosity of 22%, while for the positive electrodes containing the positive electrode active materials of Comparative Examples 1, 3, and 4, the electrodes were rolled so that the height did not decrease below a certain level regardless of the amount of rolling, and the electrode porosity was 30%.

[0116] The rolled positive electrode was cut using the FIB (Focused Ion Beam) method to obtain a cross-section of the positive electrode active material layer. An SEM (JSM7610F, JEOL) was used to measure the SEM image of the cross-section of the positive electrode active material layer, which is shown in Figure 2. Figure 2(A) is a cross-sectional SEM image of the positive electrode containing the positive electrode active material of Example 1, and Figure 2(B) is a cross-sectional SEM image of the positive electrode containing the positive electrode active material of Example 2.

[0117] Experimental Example 3: Evaluation of Electrode Porosity For each of the above examples and comparative examples, Super P was used as the positive electrode active material and polyvinylidene fluoride (PVDF) as the binder, and these were mixed in N-methylpyrrolidone (NMP) solvent in a weight ratio of 92:4:4 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 dried at 130°C to prepare the positive electrode. The positive electrode was rolled in a rolling mill (roller mill, manufactured by Welcose), and the height of the rolled positive electrode was measured to calculate its volume. The voids were converted to a porosity, reflecting the content of the positive electrode active material. Specifically, the porosity (%) was calculated using the following formula 4 and is shown in Table 1 below.

[0118] [Formula 4] Height after rolling (mm) = [{(Weight of positive electrode active material (mg) - Weight of aluminum current collector (mg)) / (Area of ​​positive electrode (cm²) 2 ) × (1-porosity (%)) × true density (g / cm 3 ))}+0.02]×1000

[0119] Experimental Example 4: Analysis of Single Crystallinity The first lithium-excess manganese oxide (A1), carbon black conductive material, and PVDF binder were mixed in an NMP solvent in a weight ratio of 95:2:3 to produce a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector, dried, and then rolled to produce a positive electrode. The produced positive electrode was cut using the FIB method to obtain a cross-section, and SEM and EBSD images of the same portion were measured to obtain the particle morphology and region (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 separate the crystal grains within the particles, and the degree of single crystallinity of the positive electrode active material was analyzed using Equation 1 of the present invention.

[0120]

number

[0121] In the above formula 1, a iWhen a single particle consists of i crystal grains, the cross-sectional area of ​​the i-th crystal grain (A) is given by the cross-sectional area of ​​the single particle (A). i ) value (A i This means / A).

[0122] Analysis results show that the first lithium-excess manganese oxide (A1) has a single crystallinity degree (χ) of 0.64 according to the following formula 1.

[0123] Experimental Example 5: Evaluation of Battery Characteristics For each of the above examples and comparative examples, Super P was used as the positive electrode active material and polyvinylidene fluoride (PVDF) as the binder, and these were mixed in N-methylpyrrolidone (NMP) solvent in a weight ratio of 92:4:4 to produce a positive electrode slurry. The produced positive electrode slurry was applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to produce a positive electrode. On the other hand, in the case of the positive electrodes containing the positive electrode active materials of Examples 1 to 3 and Comparative Example 2, the electrodes were rolled to have an electrode porosity of 22%, while in the case of the positive electrodes containing the positive electrode active materials of Comparative Examples 1, 3, and 4, the height did not decrease below a certain level no matter how much rolling was performed, and the electrodes were rolled to have an electrode porosity of 30%.

[0124] An electrode assembly was manufactured using a lithium metal electrode as the negative electrode, with a porous polyethylene separator interposed between the positive and negative electrodes. This assembly was placed inside a battery case, and an electrolyte solution prepared by dissolving 1M LiPF6 in an organic solvent mixture of ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) in a volume ratio of 3:4:3 was injected to manufacture a coin-type half-cell.

[0125] Using coin-type half-cells containing the positive electrode active materials of the above-described examples and comparative examples, the activation process (formation) was performed by charging to 4.65V at 45°C in CC(0.1C)-CV(Cut-off current:0.05C) mode, and then discharging to 2.0V at 0.1C. Next, the initial discharge capacity was measured and is shown in Table 1 below, after charging to 4.25V at 25°C in CC(0.1C)-CV(Cut-off current:0.05C) mode, and then discharging to 2.5V at 0.1C.

[0126] Next, the battery was charged to 4.25V in CC (0.33C)-CV (Cut-off current: 0.05C) mode at 25°C, and then discharged to 2.5V at 0.33C. This cycle was defined as one cycle, and a total of 30 charge-discharge cycles were repeated. After measuring the discharge capacity over 30 cycles, the capacity retention rate was defined as the percentage of the discharge capacity over 30 cycles relative to the initial discharge capacity, and is shown in Table 1 below.

[0127] [Table 1]

[0128] 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 density, significantly higher pellet density and electrode porosity compared to the positive electrode active material of Comparative Example 1, and that their discharge capacity and capacity retention rate are at a comparable level. Furthermore, 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 density and significantly superior discharge capacity and capacity retention rate compared to the positive electrode active material of Comparative Example 2.

[0129] Furthermore, 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 density and 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 significantly higher pellet density and significantly superior capacity retention compared to the positive electrode active material of Comparative Example 5.

[0130] In other words, the positive electrode active material of the present invention simultaneously contains small lithium-excess manganese oxide particles in single particle form and large lithium-excess manganese oxide particles in secondary particle form in a specific weight ratio, exhibiting excellent energy density and stability. As a result, it is possible to improve the performance of batteries containing this material, such as capacity characteristics and energy density, and to prevent the positive electrode active material particles from cracking during battery manufacturing or operation.

Claims

1. It comprises a first lithium-excess manganese oxide in single-particle form and a second lithium-excess manganese oxide in secondary-particle form, The first lithium-excess manganese oxide and the second lithium-excess manganese oxide are Li ２ MnO ３ Ai and LiMO ２ (Here, M is an element containing one or more elements selected from Ni, Co, and Mn) The phase simultaneously contains, The first lithium-excess manganese oxide has a lower average particle size (D) than the second lithium-excess manganese oxide. ５０ A bimodal cathode active material having a small ) and a weight ratio of 1:1.5 to 8 between the first lithium-excess manganese oxide and the second lithium-excess manganese oxide.

2. The first lithium-excess manganese oxide has a single crystallinity degree (χ) of 0.4 or higher according to the following formula 1, the bimodal type cathode active material according to claim 1. [Math 1] In the above formula 1, a ｉ When a single particle consists of i crystal grains, the cross-sectional area of ​​the i-th crystal grain (A) is relative to the cross-sectional area of ​​the single particle (A). ｉ The value of (A ｉ It means / A).

3. The first lithium-excess manganese oxide has an average particle size (D ５０ The bimodal positive electrode active material according to claim 1, wherein the diameter is 0.5 μm to 3.5 μm.

4. The second lithium-excess manganese-based oxide has an average particle size (D ５０ ), which is 5.0 µm to 10.0 µm, and is the bimodal-type cathode active material according to claim 1.

5. The first lithium-excess manganese oxide has a composition represented by the following chemical formula 1, the bimodal cathode active material according to claim 1. [Chemical formula 1] Li １＋ｘ１ Ni ａ１ Mn ｂ１ M １ ｃ１ O ｙ１ In the aforementioned chemical formula 1, M １ is one or more 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 ≤ 2.0, x1 + a1 + b1 + c1 = 1.

0.

6. The bimodal cathode active material according to claim 1, wherein the second lithium-excess manganese oxide has a composition represented by the following chemical formula 2. [Chemical formula 2] Li １＋ｘ２ Ni ａ２ Mn ｂ２ M ２ ｃ２ O ｙ２ In the aforementioned chemical formula 2, M ２ is one or more 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 ≤ 2.0, x² + a² + b² + c² = 1.

0.

7. The pellet density is 2.20 g / cm³. ３ ~2.70 g / cm ３ The bimodal type cathode active material according to claim 1.

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 the positive electrode described in claim 8.

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