Positive electrode active material, positive electrode comprising same, and lithium secondary battery

Abstract

The present invention relates to a positive electrode active material, which is a bimodal positive electrode active material, comprising: a first Li-rich layered manganese-based oxide in the form of a single particle; and a second Li-rich layered manganese-based oxide in the form of secondary particles, in which the first Li-rich layered manganese-based oxide and the second Li-rich layered manganese-based oxide simultaneously comprise a Li2MnO3 phase and a LiMO2 (wherein M is an element comprising one or more selected from the group consisting of Ni, Co and Mn) phase, the average particle diameter (D50) of the first Li-rich layered manganese-based oxide is smaller than the average particle diameter (D50) of the second Li-rich layered manganese-based oxide, and the weight ratio of the first Li-rich layered manganese-based oxide to the second Li-rich layered manganese-based oxide is 1: 1.5-8, and a positive electrode and a lithium secondary battery comprising the positive electrode active material.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2023-0097407, filed on July 26, 2023, the disclosure of which is incorporated herein by reference. Technical Field

[0003] The present invention relates to a bimodal cathode active material and a cathode and a lithium secondary battery comprising the bimodal cathode active material, and more specifically, to a bimodal cathode active material comprising a Li-rich layered manganese-based oxide and a cathode and a lithium secondary battery comprising the bimodal cathode active material. Background Technology

[0004] Lithium-ion batteries consist of four main components: a positive electrode, a negative electrode, a separator, and an electrolyte. Among these, the positive electrode active material plays a crucial role in determining the battery's capacity, output, and lifespan. To achieve high energy density, output, and lifespan in lithium-ion batteries, it is necessary to improve the performance of the positive electrode active material; therefore, research into developing high-performance positive electrode active materials has been actively pursued recently.

[0005] Li-rich layered oxides, as a type of positive electrode active material, exhibit high operating voltage (relative to Li / Li) in a mixed phase of Li₂MnO₃ and LiMO₂ (M being one or more of Ni, Mn, and Co). + It possesses the characteristic of providing a very large capacity of 250 mAh / g at >3.5 V. Therefore, Li-rich layered oxides have attracted attention as inexpensive, high-capacity cathode active materials.

[0006] Meanwhile, conventional Li-rich layered oxides in secondary particle form prepared by co-precipitation have low sheet density and high porosity when applied to electrodes, resulting in low energy density per unit volume. Furthermore, during the rolling process for electrode fabrication, undispersed mechanical stress causes particle breakage, leading to the generation of large amounts of gas during battery operation.

[0007] Therefore, there is a need to develop Li-rich layered oxides with high tablet density and low particle breakage rate during rolling. Summary of the Invention

[0008] Technical issues

[0009] The present invention seeks to improve the energy density and stability of positive electrode active materials, and thus improve the performance of batteries containing such positive electrode active materials.

[0010] In addition, the present invention aims to provide a positive electrode and a lithium secondary battery comprising the positive electrode active material.

[0011] Technical solution

[0012] To address the aforementioned technical problems, this invention provides a positive electrode active material, a positive electrode, and a lithium secondary battery.

[0013] (1) This invention provides a bimodal cathode active material comprising: a first Li-rich layered manganese oxide in the form of single particles; and a second Li-rich layered manganese oxide in the form of secondary particles, wherein the first Li-rich layered manganese oxide and the second Li-rich layered manganese oxide simultaneously comprise a Li2MnO3 phase and a LiMO2 phase (wherein M is an element selected from one or more of Ni, Co, and Mn), and the average particle size (D) of the first Li-rich layered manganese oxide is... 50 The average particle size (D) of the second Li-rich layered manganese-based oxide is smaller than that of the second Li-rich layered manganese-based oxide. 50 The weight ratio of the first Li-rich layered manganese oxide to the second Li-rich layered manganese oxide is 1:1.5 to 8.

[0014] (2) The present invention provides the bimodal positive electrode active material of (1) above, wherein, according to the following equation 1, the first Li-rich layered manganese-based oxide has a single crystallinity (χ) of 0.4 or more:

[0015] [Equation 1]

[0016]

[0017] In equation 1 above,

[0018] When a single particle is formed from i grains, a i It refers to the cross-sectional area (A) of the i-th grain. i The ratio of the cross-sectional area (A) of a single particle to the cross-sectional area (A) of a single particle. i / A).

[0019] (3) The present invention provides the bimodal positive electrode active material described in (1) or (2) above, wherein the average particle size (D) of the first Li-rich layered manganese-based oxide is... 50 The thickness ranges from 0.5 μm to 3.5 μm.

[0020] (4) The present invention provides a bimodal positive electrode active material according to any one of (1) to (3) above, wherein the average particle size (D) of the second Li-rich layered manganese-based oxide is... 50 The thickness ranges from 5.0 μm to 10.0 μm.

[0021] (5) The present invention provides a bimodal positive electrode active material according to any one of (1) to (4) above, wherein the first Li-rich layered manganese-based oxide has a composition represented by the following chemical formula 1:

[0022] [Chemical Formula 1]

[0023] Li 1+x1 Ni a1 Mn b1 M 1 c1 O y1

[0024] Among them, in the above Chemical Formula 1,

[0025] M 1 is one or more selected from Co, Mo, W, V, Zr, Al, and Nb,

[0026] 0.1 ≤ x1 ≤ 0.2, 0 < a1 ≤ 0.5, 0.5 ≤ b1 ≤ 0.75, 0 ≤ c1 ≤ 0.1 and 0 ≤ y1 ≤ 2.0, and

[0027] x1 + a1 + b1 + c1 = 1.0.

[0028] (6) The present invention provides the bimodal cathode active material described in any one of the above (1) to (5), wherein the second Li-rich layered manganese-based oxide has a composition represented by the following Chemical Formula 2:

[0029] [Chemical Formula 2]

[0030] Li 1+x2 Ni a2 Mn b2 M 2 c2 O y2

[0031] Among them, in the above Chemical Formula 2,

[0032] M 2 is one or more selected from Co, Mo, W, V, Zr, Al, and Nb,

[0033] 0.1 ≤ x2 ≤ 0.2, 0 < a2 ≤ 0.5, 0.5 ≤ b2 ≤ 0.75, 0 ≤ c2 ≤ 0.1 and 0 ≤ y2 ≤ 2.0, and

[0034] x2 + a2 + b2 + c2 = 1.0.

[0035] (7) The present invention provides the bimodal cathode active material described in any one of the above (1) to (6), wherein the tablet density is 2.20 g / cm 3 to 2.70 g / cm 3 .

[0036] (8) The present invention provides a positive electrode comprising any one of the positive electrode active materials described in (1) to (7) above.

[0037] (9) The present invention provides a lithium secondary battery having the positive electrode described in (8) above.

[0038] Beneficial effects

[0039] The positive electrode active material of the present invention contains, in a specific weight ratio, small Li-rich layered manganese oxide particles in the form of single particles and large Li-rich layered manganese oxide particles in the form of secondary particles. Therefore, it has excellent energy density and stability. Thus, batteries containing this positive electrode active material can have improved performance, such as improved capacity characteristics and energy density, and can prevent particle breakage of the positive electrode active material during battery preparation or operation. Attached Figure Description

[0040] Figure 1 SEM images of the Li-rich layered manganese-based oxides prepared according to Preparation Examples 1 and 2 are shown. Specifically, Figure 1 (A) is a SEM image of the Li-rich layered manganese-based oxide (Al) prepared according to Preparation Example 1. Figure 1 (B) is a SEM image of the Li-rich layered manganese-based oxide (A2) prepared according to Preparation Example 2.

[0041] Figure 2 Cross-sectional SEM images of the positive electrodes comprising the positive electrode active materials of Example 1 and Comparative Example 1 are shown. Specifically, Figure 2 (A) is a cross-sectional SEM image of the positive electrode containing the positive electrode active material of Example 1. Figure 2 (B) is a cross-sectional SEM image of the positive electrode containing the positive electrode active material of Example 2. Detailed Implementation

[0042] In the following description, the invention will be presented in more detail to aid in understanding.

[0043] It should be understood that the terms or words used in the specification and claims of this invention should not be interpreted as having the meaning defined in a common dictionary, and should be further understood that, based on the inventor's ability to appropriately define the meaning of terms or words to best explain the principles of the invention, the terms or words should be interpreted as having a meaning consistent with their meaning in the relevant field and in the technical concept of the invention.

[0044] It should also be understood that the terms “comprising,” “including,” “having,” etc., as used in this specification specify the presence of the stated features, integers, steps, elements, or combinations thereof, but do not exclude the presence or addition of one or more other features, integers, steps, elements, or combinations thereof.

[0045] In this specification, "single-particle form" is the opposite of the spherical secondary particle form formed by the aggregation of tens to hundreds of primary particles, and refers to a form consisting of ten or fewer primary particles. In particular, "single-particle form" can also refer to a single-particle form made from a single primary particle, or a secondary particle form in which several primary particles are aggregated.

[0046] In this specification, "primary particle" refers to the smallest unit of particle identified when observing positive electrode active material using a scanning electron microscope (SEM), which can be formed by multiple grains, while "secondary particle" refers to a secondary structure formed by the aggregation of multiple primary particles.

[0047] In this specification, "single crystal" refers to a crystal in which the particles do not contain grain boundaries.

[0048] In this specification, "grain" refers to a particle unit having substantially the same crystal orientation and which can be measured using electron backscatter diffraction (EBSD). Specifically, a grain is the smallest particle unit marked with the same color on an IPF map obtained by EBSD analysis on a cross-section of the positive electrode active material cut by ion milling.

[0049] 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 The particle size distribution can be measured using, for example, laser diffraction. More specifically, lithium composite transition metal oxides can be dispersed in a dispersion medium, which is then introduced into a commercial laser diffraction particle size analyzer (e.g., Microtrac MT 3000) and irradiated with ultrasound at approximately 28 kHz at a 60 W output. The average particle size (D) corresponding to 50% of the particle size distribution in the analyzer can then be calculated. 50 ).

[0050] In this specification, the tablet density is the value calculated by the following equation 2 when granules are formed by applying force using an automatic granulator until it becomes a force equal to 2000 kgf. In particular, the tablet density is the value obtained according to (1) to (3) below.

[0051] (1) The thickness zero point of the circular particle holder is adjusted by using a cylindrical mold with a Universal Testing Machine (UTM) (Instron, model 5966).

[0052] (2) Place the positive electrode active material in a circular particle holder, apply force until it reaches a force equal to 2000 kgf to form particles, and measure the thickness of the particles.

[0053] (3) The particle volume is calculated by Equation 2 below, and the tablet density is calculated by Equation 3 below.

[0054] [Equation 2]

[0055] Particle volume (cm) 3 ) = π (radius of the circular particle holder) 2 ×particle thickness

[0056] [Equation 3]

[0057] Tablet density (g / cm³) 3 = Weight of positive electrode active material (g) / Particle volume (cm³) 3 )]]

[0058] The inventors have discovered that when the positive electrode active material simultaneously comprises small Li-rich layered manganese oxide particles in single-particle form and large Li-rich layered manganese oxide particles in secondary-particle form, the electrode density can be increased and particle breakage minimized when the positive electrode active material is coated onto the positive electrode of a secondary battery. Furthermore, when the positive electrode active material is applied to a secondary battery, the battery's capacity characteristics and energy density can be improved. During battery preparation or operation, particle breakage of the positive electrode active material can be prevented, thereby suppressing gas generation. Thus, this invention is complete.

[0059] Bimodal cathode active material

[0060] The positive electrode active material of the present invention is a bimodal positive electrode active material, comprising: a first Li-rich layered manganese oxide in single-particle form (hereinafter referred to as small-particle Li-rich layered manganese oxide); and a second Li-rich layered manganese oxide in secondary-particle form (hereinafter referred to as large-particle Li-rich layered manganese oxide), wherein the first Li-rich layered manganese oxide and the second Li-rich layered manganese oxide simultaneously contain Li2MnO3 phase and LiMO2 phase (where M is an element selected from one or more of Ni, Co and Mn), and the average particle size (D) of the first Li-rich layered manganese oxide is... 50 The average particle size (D) of the second Li-rich layered manganese-based oxide is smaller than that of the second Li-rich layered manganese-based oxide. 50 The weight ratio of the first Li-rich layered manganese oxide to the second Li-rich layered manganese oxide is 1:1.5~8.

[0061] Because the bimodal cathode active material comprises small-particle Li-rich layered manganese oxide and large-particle Li-rich layered manganese oxide in a specific weight ratio, and thus the small-particle Li-rich layered manganese oxide fills the spaces between the large-particle Li-rich layered manganese oxide, the pellet density is high, and the stress applied to the large-particle Li-rich layered manganese oxide can be dispersed, thereby preventing particle breakage during rolling for electrode preparation.

[0062] The first and second Li-rich layered manganese-based oxides simultaneously include the Li2MnO3 phase and the LiMO2 phase (where M is an element selected from one or more of Ni, Co and Mn), and include monoclinic and rhombohedral crystal structures.

[0063] Small-particle, Li-rich, layered manganese-based oxides can be prepared by a solid-state synthesis process involving dry mixing and calcination of lithium and transition metal feedstocks. Specifically, the lithium and transition metal feedstocks are placed in a grinding apparatus for dry mixing and grinding (high-energy ball mill grinding), followed by calcination of the ground material. The calcined product is then pulverized to prepare small-particle, Li-rich, layered manganese-based oxides. However, the preparation method is not limited to this.

[0064] Large-particle Li-rich layered manganese-based oxides can be obtained by the same method as conventional methods, in which the precursor is prepared by co-precipitation, then mixed with lithium feedstock and the mixture is calcined, but the preparation is not limited to this.

[0065] According to the present invention, the first Li-rich layered manganese-based oxide may have a single crystallinity (χ) of 0.4 or more according to the following Equation 1.

[0066] [Equation 1]

[0067]

[0068] In equation 1 above,

[0069] When a single particle is formed from i grains, ai refers to the ratio (Ai / A) of the cross-sectional area (A) of the i-th grain to the cross-sectional area (A) of the single particle.

[0070] In this invention, single crystallinity is evaluated and expressed as a parameter represented by Equation 1 above. In this invention, single crystallinity refers to a value adjusted based on the number of grains constituting a single particle and the area of ​​each grain, wherein the single crystallinity becomes higher when a specific grain having the largest area in a single particle has a larger area that is closer to the area of ​​the entire single particle.

[0071] That is, the fewer the number of crystals constituting a single particle, the higher the degree of monocrystallization in this invention. If the number of crystals is the same, compared with the case where the area of ​​the crystals is the same, the higher the degree of monocrystallization is when the area of ​​a particular crystal is larger than that of other crystals, such that the area difference between the particular crystal and the entire single particle is small.

[0072] For example, the maximum crystallinity is 1, meaning a single particle is formed from a single grain (monocrystalline single particle). Furthermore, when a single particle is formed from N grains, the crystallinity varies depending on the area of ​​each grain, but the minimum possible degree of crystallinity for N grains is 1 / N, and this occurs when all N grains have the same area. Even if a single particle is formed from N grains, if a particular grain has a larger area than the others, the crystallinity becomes higher than 1 / N. This is because the shape is closer to a single crystal when a particular grain has the largest area compared to when all N grains have the same area.

[0073] From this perspective, as the area of ​​the added grains decreases, the degree of single crystallinity decreases to a smaller extent. This means that because the area of ​​small-sized grains is smaller than the area of ​​the entire particle, the effect on reducing the degree of single crystallinity is relatively small.

[0074] The crystallinity of the first Li-rich layered manganese-based oxide can be specifically 0.4 or higher, 0.45 or higher, 0.5 or higher, 0.55 or higher, 0.6 or higher, and 0.65 or lower, 0.7 or lower, 0.75 or lower, or 0.8 or lower. When the crystallinity of the first Li-rich layered manganese-based oxide falls within the above range, a single particle is formed by 10 or fewer grains, thus having the advantage of less grain breakage. Therefore, since grain breakage caused by grain boundaries during electrode rolling and battery operation is suppressed, gas generation can be suppressed, and since the contact area between the grain boundaries and the electrolyte solution is reduced, side reactions with the electrolyte solution can be reduced, thereby significantly improving the life of the secondary battery.

[0075] According to the present invention, the average particle size (D) of the first Li-rich layered manganese-based oxide 50 The average particle size (D) ranges from 0.5 μm to 3.5 μm. Specifically, the average particle size of the first Li-rich layered manganese-based oxide is... 50 The size can be above 0.5 μm, above 0.7 μm, above 0.9 μm, below 1.1 μm, below 1.5 μm, below 2.0 μm, or below 3.5 μm.

[0076] According to the present invention, the average particle size (D) of the second Li-rich layered manganese-based oxide 50 The average particle size (D) can range from 5.0 μm to 10.0 μm. In particular, the average particle size (D) of the second Li-rich layered manganese-based oxide is... 50) can be 5.0 μm or more, 5.5 μm or more, 6.0 μm or more, 6.5 μm or more, 7.5 μm or less, 8.0 μm or less, 9.0 μm or less, 10.0 μm or less.

[0077] When the average particle diameters (D 50 ) of the first lithium transition metal oxide and the second lithium transition metal oxide each fall within the above range, the first lithium transition metal oxide can be appropriately distributed among the second lithium transition metal oxides, thereby showing an excellent filling rate.

[0078] The ratio of the average particle diameter of the first Li-rich layered manganese-based oxide to the average particle diameter of the second Li-rich layered manganese-based oxide can be 1:3 to 5. When the ratio of the average particle diameter of the first Li-rich layered manganese-based oxide to the average particle diameter of the second Li-rich layered manganese-based oxide is within the above range, in addition to having an excellent filling rate, it also has the advantage of increased pellet density.

[0079] According to the present invention, the first Li-rich layered manganese-based oxide can have a composition represented by the following Chemical Formula 1.

[0080] [Chemical Formula 1]

[0081] Li 1+x1 Ni a1 Mn b1 M 1 c1 O y1

[0082] In the above Chemical Formula 1,

[0083] M 1 is one or more selected from Co, Mo, W, V, Zr, Al, and Nb,

[0084] 0.1 ≤ x1 ≤ 0.2, 0 < a1 ≤ 0.5, 0.5 ≤ b1 ≤ 0.75, 0 ≤ c1 ≤ 0.1 and 0 ≤ y1 ≤ 2.0, and [[ID=四十]]

[0085] x1 + a1 + b1 + c1 = 1.0.

[0086] The above M 1 is a doping element. In particular, the above M 1 can be one or more selected from Co, Mo, W, V, Zr, Al, and Nb. It does not necessarily have to contain the above M 1 , but if it is contained in an appropriate amount, it can improve the particle shape of the first Li-rich layered manganese-based oxide and can improve the stability of the crystal structure.

[0087] The x1 mentioned above can be 0.10 or higher, 0.11 or higher, 0.12 or higher, 0.13 or higher, 0.14 or higher, and 0.16 or lower, 0.17 or lower, 0.18 or lower, 0.19 or lower, 0.20 or lower. When x1 falls within the above range, high capacity characteristics and high energy density per unit volume can be achieved.

[0088] The value of a1 can be greater than 0, greater than 0.1, greater than 0.2, or less than 0.3, less than 0.4, or less than 0.5. When a1 is within the above range, the first Li-rich layered manganese-based oxide can exhibit high energy density, thereby achieving high capacity characteristics.

[0089] The aforementioned b1 can be 0.50 or higher, 0.51 or higher, 0.52 or higher, 0.53 or higher, 0.54 or higher, 0.55 or higher, and 0.60 or lower, 0.61 or lower, 0.62 or lower, 0.63 or lower, 0.64 or lower, 0.65 or lower, 0.66 or lower, 0.67 or lower, 0.68 or lower, 0.69 or lower, 0.70 or lower, 0.71 or lower, 0.72 or lower, 0.73 or lower, 0.74 or lower, and 0.75 or lower. When b1 falls within the above range, high capacity characteristics can be achieved. Furthermore, the high-temperature stability of the first Li-rich layered manganese-based oxide can be improved, and the decomposition reaction of the electrolyte solution can be relatively reduced.

[0090] The value of c1 can be greater than or equal to 0, less than or equal to 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.10. When c1 is within the above range, the stability of the crystal structure of the first Li-rich layered manganese-based oxide is improved, and the particle shape is enhanced.

[0091] Meanwhile, the first Li-rich layered manganese-based oxide may not contain expensive cobalt, and can improve the performance of lithium secondary batteries even without cobalt.

[0092] According to the present invention, the second Li-rich layered manganese-based oxide may have a composition represented by the following chemical formula 2.

[0093] [Chemical Formula 2]

[0094] Li 1+x2 Ni a2 Mn b2 M 2 c2 O y2

[0095] In the above chemical formula 2,

[0096] M 2is one or more selected from Co, Mo, W, V, Zr, Al, and Nb,

[0097] 0.1 ≤ x2 ≤ 0.2, 0 < a2 ≤ 0.5, 0.5 ≤ b2 ≤ 0.75, 0 ≤ c2 ≤ 0.1, and 0 ≤ y2 ≤ 2.0, and

[0098] x2 + a2 + b2 + c2 = 1.0.

[0099] The above M 2 is a doping element. In particular, the above M 2 can be one or more selected from Co, Mo, W, V, Zr, Al, and Nb. It does not necessarily have to contain the above M 2 , but if it is contained in an appropriate amount, it can improve the particle shape of the second Li-rich layered manganese-based oxide and can enhance the stability of the crystal structure.

[0100] The above x2 can be 0.10 or more, 0.11 or more, 0.12 or more, 0.13 or more, 0.14 or more, and 0.16 or less, 0.17 or less, 0.18 or less, 0.19 or less, 0.20 or less. When x2 falls within the above range, high-capacity characteristics and high energy density per unit volume can be achieved.

[0101] The above a2 can be greater than 0, 0.1 or more, 0.2 or more, and 0.3 or less, 0.4 or less, 0.5 or less. When a2 falls within the above range, the second Li-rich layered manganese-based oxide can exhibit high energy density, thus achieving high-capacity characteristics.

[0102] The above b2 can be 0.50 or more, 0.51 or more, 0.52 or more, 0.53 or more, 0.54 or more, 0.55 or more, and 0.60 or less, 0.61 or less, 0.62 or less, 0.63 or less, 0.64 or less, 0.65 or less, 0.66 or less, 0.67 or less, 0.68 or less, 0.69 or less, 0.70 or less, 0.71 or less, 0.72 or less, 0.73 or less, 0.74 or less, 0.75 or less. When B2 falls within the above range, high-capacity characteristics can be achieved. In addition, the high-temperature stability of the second Li-rich layered manganese-based oxide can be enhanced, and the decomposition reaction of the electrolyte solution can be relatively reduced.

[0103] The above c2 can be 0 or more, 0.01 or less, 0.02 or less, 0.03 or less, 0.04 or less, 0.05 or less, 0.06 or less, 0.07 or less, 0.08 or less, 0.09 or less, 0.10 or less. When C2 is within the above range, the stability of the crystal structure of the second Li-rich layered manganese-based oxide is enhanced, and the particle shape is improved.

[0104] Meanwhile, the second Li-rich layered manganese-based oxide may not contain expensive cobalt, and can improve the performance of lithium secondary batteries even without cobalt.

[0105] According to the present invention, the weight ratio of the first Li-rich layered manganese oxide and the second Li-rich layered manganese oxide can be from 1:1.5 to 8. Specifically, the weight ratio of the first Li-rich layered manganese oxide to the second Li-rich layered manganese oxide can be from 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 Li-rich layered manganese oxide to the second Li-rich layered manganese oxide falls within the above ranges, the particle packing density can be increased; therefore, when applied to a battery, the battery capacity, energy density, etc., can be increased.

[0106] According to the present invention, the bimodal positive electrode active material can have a concentration of 2.20 g / cm³. 3 Up to 2.70 g / cm 3 The tableting density. Specifically, the tableting density of the bimodal cathode active material can be 2.20 g / cm³. 3 Above, 2.40 g / cm 3 Above, 2.50 g / cm 3 Above, 2.60 g / cm 3 Above, 2.65 g / cm 3 Below or 2.70 g / cm 3 The following applies. When the pressing density of the bimodal cathode active material falls within the above range, it can improve capacity characteristics, energy density, etc., and can prevent particle breakage of the cathode active material during battery preparation or operation.

[0107] positive electrode

[0108] This invention provides a positive electrode comprising the aforementioned positive electrode active material. Specifically, it provides a positive electrode comprising a bimodal positive electrode active material.

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

[0110] The positive electrode current collector can contain a highly conductive metal, as long as it is a non-reactive metal that easily adheres to the positive electrode active material layer and is within the battery's voltage range. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum and stainless steel surface-treated with carbon, nickel, titanium, silver, etc., can be used as positive electrode current collectors. Furthermore, positive electrode current collectors typically have a thickness ranging from 3 μm to 500 μm, and minute irregularities can be formed on their surface to improve the adhesion of the positive electrode active material. For example, positive electrode current collectors can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

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

[0112] Conductive materials can be used to provide conductivity to electrodes, and any material can be used in the battery without particular restrictions, as long as it does not cause chemical changes and conducts electrons. Specific examples can be graphite, such as natural or artificial graphite; carbon-based materials, including carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, etc.; metal powders or fibers including copper, nickel, aluminum, silver, etc.; conductive tubes including carbon nanotubes, etc.; conductive whiskers containing zinc oxide, potassium titanate, etc.; conductive metal oxides including titanium oxide, etc.; or conductive polymers including polyphenylene derivatives, etc., and any one or a mixture of two or more can be used alone. Based on the total weight of the positive electrode active material layer, the content of conductive material can be from 0.1% by weight to 15% by weight.

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

[0114] In addition to using the aforementioned positive electrode active material, a positive electrode can be prepared according to general methods for preparing a positive electrode. Specifically, a positive electrode active material and, if necessary, a binder, conductive material, and dispersant are dissolved or dispersed in a solvent to prepare a composition for forming a positive electrode active material layer. This composition is then applied to a positive electrode current collector, followed by drying and pressing to prepare a positive electrode. Alternatively, the composition for forming the positive electrode active material layer can be cast onto a separate carrier, and the film layer separated from the carrier can be pressed onto the positive electrode current collector to prepare a positive electrode.

[0115] The solvent can be one commonly used in the art, including dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, water, etc., and any one or a mixture of two or more can be used alone. The amount of solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into account the thickness of the coating slurry and the manufacturing yield, and provides a viscosity during coating that allows for excellent thickness uniformity for subsequent positive electrode preparation.

[0116] Lithium secondary batteries

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

[0118] A lithium secondary battery may include: a positive electrode; a negative electrode; a separator introduced between the positive electrode and the negative electrode; and an electrolyte. Alternatively, the lithium secondary battery may optionally further include a battery casing housing an electrode assembly containing the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery casing.

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

[0120] As a negative electrode current collector, there are no particular limitations as long as it does not cause chemical changes to the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and copper or stainless steel, aluminum-cadmium alloys with surface treatments using carbon, nickel, titanium, silver, etc., can be used. Furthermore, negative electrode current collectors typically have a thickness from 3 μm to 500 μm, and like positive electrode current collectors, minute irregularities can be formed on the surface of the current collector to enhance the adhesion of the negative electrode active material. For example, negative electrode current collectors can be used in various forms, including films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0121] The negative electrode active material layer may selectively include adhesives, conductive materials, and negative electrode active materials as needed.

[0122] As anode active materials, compounds capable of reversibly inserting and deintercalating lithium can be used. Specific examples include carbon-based materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; and metal-based compounds capable of alloying with lithium, including Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; such as SiO₂. β Metal oxides capable of doping or dedoping lithium, such as (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; composites containing metal-based compounds and carbon-based materials, such as Si-C composites and Sn-C composites, can also be used, as well as mixtures of one or more of them. Additionally, lithium metal films can be used as the negative electrode active material. Furthermore, low-crystallinity carbon or high-crystallinity carbon can be used as the carbon material. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include non-shaped, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived coke. The negative electrode active material can be contained in an amount of 80% to 99% by weight based on the total weight of the negative electrode active material layer.

[0123] The binder of the negative electrode active material layer is a component that facilitates the bonding between the conductive material, the active material, and the current collector, and its content is typically 0.1% to 10% by weight relative to the total weight of the negative electrode active material layer. Examples of such binders may 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 rubber, fluororubber, and various copolymers thereof.

[0124] The conductive material in the negative electrode active material layer is a component that further improves the conductivity of the negative electrode active material. Its content relative to the total weight of the negative electrode active material layer can be less than 10% by weight, preferably less than 5% by weight. As a conductive material, there are no particular limitations as long as it does not cause chemical changes to the battery and has conductivity. Examples include natural graphite, artificial graphite, etc.; carbon black including acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc.; conductive fibers, including carbon fibers, metal fibers, etc.; fluorocarbons; metal powders including aluminum powder, nickel powder, etc.; conductive whiskers containing zinc oxide, potassium titanate, etc.; conductive metal oxides including titanium oxide, etc.; and conductive materials including polyphenylene derivatives, etc., can be used.

[0125] A composition for forming a negative electrode active material layer is prepared by dissolving or dispersing the negative electrode active material, as well as selectively binders and conductive materials in a solvent, as needed. The composition is then applied to a negative electrode current collector and dried to prepare a negative electrode. Alternatively, the composition for forming a negative electrode active material layer is cast onto a separate carrier, and the film layer separated from the carrier is then pressed onto a negative electrode current collector to prepare a negative electrode.

[0126] The separator separates the negative and positive electrodes and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitation, but separators with low resistance to ion movement in the electrolyte and excellent hygroscopic capacity of the electrolyte solution are particularly preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes prepared from polyolefin polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures having two or more layers. Alternatively, general porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, to ensure heat resistance or mechanical strength, coated separators including ceramic components or polymer materials can be used, and they can be selectively used in single-layer or multi-layer structures.

[0127] Electrolytes can include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used to prepare lithium secondary batteries. Specific examples of electrolytes can include organic solvents and lithium salts.

[0128] As for organic solvents, there are no particular restrictions as long as they serve as a medium through which ions can move in the electrochemical reactions of the battery; any organic solvent can be used. Specifically, as organic solvents, ester solvents, including methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone, etc.; ether solvents, including dibutyl ether, tetrahydrofuran, etc.; ketone solvents, including cyclohexanone, etc.; aromatic hydrocarbon solvents, including benzene, fluorobenzene, etc.; carbonate solvents, including dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), etc.; alcohol solvents, including ethanol, isopropanol, etc.; nitriles, including R-CN (where R is a straight-chain, branched, or cyclic C2-C20 hydrocarbon group, and may include double-bonded aromatic rings or ether bonds), etc.; amides, including dimethylformamide, etc.; dioxolane, including 1,3-dioxolane, etc.; or sulfolane. Preferably, carbonate solvents are used, and more preferably, a mixture of cyclic carbonates (such as ethylene carbonate, propylene carbonate, etc.) with high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery and low viscosity linear carbonate compounds (such as ethyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) is used.

[0129] Lithium salts can be any compound capable of providing lithium ions used in lithium secondary batteries, without particular limitations. Specifically, the negative ions of the lithium salt can be selected from 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 of the following groups can be used as a lithium salt: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. The lithium salt can be used in a concentration range from 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can have suitable conductivity and viscosity, thus exhibiting excellent electrolyte performance and allowing for efficient lithium ion movement.

[0130] In addition to the electrolyte component, to improve battery life characteristics, suppress battery capacity reduction, and increase battery discharge capacity, at least one additive can be included in the electrolyte. Examples of additives include halogenated alkyl carbonate compounds such as ethylene difluorocarbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, N-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinyl ethers, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride. In this case, based on the total weight of the electrolyte, the additive content can be from 0.1% to 5% by weight.

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

[0132] The shape of the lithium secondary battery of the present invention is not particularly limited, and may include cylindrical, prismatic, bag-shaped, coin-shaped, etc.

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

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

[0135] Battery modules or battery packs can be used as a power source for any one or more medium and large-sized devices in power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or systems for energy storage. Detailed Implementation

[0136] Embodiments of the present invention will be described in detail below to enable those skilled in the art to readily implement the invention. However, the invention may be implemented in several different forms and is not limited to the embodiments described herein.

[0137] Preparation Example

[0138] Preparation Example 1

[0139] Li₂CO₃, NiCO₃, and MnO₂ were dry-mixed at a lithium, nickel, and manganese molar ratio of 1.143:0.286:0.571. The mixture was then ground at 1600 rpm for 30 minutes using a high-energy ball mill (Zoz). The resulting product was calcined at 1000°C in air. The calcined product was then ground using a jet mill instrument at 3.5 bar to prepare a product with Li₂CO₃ content. 1.143 Ni 0.286 Mn 0.571 O2 represents the composition and average particle size (D) 50 Li-rich layered manganese oxide (Al) is a single-particle morphology with a particle size of 1 μm. SEM images of the Li-rich layered manganese oxide (Al), measured using a SEM (JEOL product, JSM7610F), are shown below. Figure 1 (A) in.

[0140] Preparation Example 2

[0141] Li₂CO₃, NiCO₃, and MnO₂ were dry-mixed in a lithium, nickel, and manganese molar ratio of 1.16:0.24:0.60. Otherwise, a Li₂CO₃-containing compound was prepared in the same manner as in Preparation Example 1. 1.16 Ni 0.24 Mn 0.60 O2 represents the composition and average particle size (D) 50 SEM images of Li-rich layered manganese oxide (A2) with a single particle morphology of 1 μm are shown below, measured using a SEM (JEOL product, JSM7610F). Figure 1 (B)

[0142] Example

[0143] Example 1

[0144] Prepare Li-rich layered manganese-based oxide (B1) with secondary particle morphology, its composition being Li 1.14 Ni 0.28 Mn 0.58 O2, and average particle size (D 50 The value is 6.97 μm.

[0145] The single-particle form of Li-rich layered manganese oxide (A1) and the secondary-particle form of Li-rich layered manganese oxide (B1) prepared in Example 1 were mixed at a weight ratio of 1:4 to prepare a bimodal cathode active material.

[0146] Example 2

[0147] The bimodal cathode active material was prepared in the same manner as in Example 1, except that the single-particle form of Li-rich layered manganese oxide (A2) prepared in Preparation Example 2 was used instead of the single-particle form of Li-rich layered manganese oxide (A1) prepared in Preparation Example 1.

[0148] Example 3

[0149] The single-particle form of Li-rich layered manganese oxide (A1) and the secondary-particle form of Li-rich layered manganese oxide (B1) prepared in Example 1 were mixed at a weight ratio of 35:65 (=1:1.86) to prepare a bimodal cathode active material.

[0150] Comparative Example 1

[0151] The Li-rich layered manganese oxide (B1) in the form of secondary particles used in Example 1 above was used as the positive electrode active material in Comparative Example 1.

[0152] Comparative Example 2

[0153] The single-particle form of Li-rich layered manganese oxide (Al) prepared in Preparation Example 1 was used as the positive electrode active material in Comparative Example 2.

[0154] Comparative Example 3

[0155] The single-particle form of Li-rich layered manganese oxide (A1) and the secondary-particle form of Li-rich layered manganese oxide (B1) prepared in Example 1 were mixed in a weight ratio of 1:1 to prepare a bimodal cathode active material.

[0156] Comparative Example 4

[0157] The single-particle form of Li-rich layered manganese oxide (A1) and the secondary-particle form of Li-rich layered manganese oxide (B1) prepared in Example 1 were mixed at a weight ratio of 9:1 (=1:0.11) to prepare a bimodal cathode active material.

[0158] Comparative Example 5

[0159] The single-particle form of Li-rich layered manganese oxide (A1) and the secondary-particle form of Li-rich layered manganese oxide (B1) prepared in Example 1 were mixed at a weight ratio of 1:9 to prepare a bimodal cathode active material.

[0160] Experimental Example

[0161] Experimental Example 1: Evaluation of tablet density

[0162] Using an automatic granulator (Carver, 3887.4), the zero point of thickness was adjusted using a cylindrical die for a circular granule holder with a diameter of 13 mm. Next, 3 g of each of the positive electrode active material prepared according to Examples 1-3 and Comparative Examples 1-5 was placed into the circular granule holder, and a force was applied until a force equivalent to 2000 kgf was reached to form granules. The thickness of the granules was then measured. The granule volume was calculated using Equation 2 below, and the tablet density was calculated using Equation 3 below. The values ​​are listed in Table 1 below.

[0163] [Equation 2]

[0164] Particle volume (cm) 3 =π (radius of the circular particle holder) 2 ×particle thickness

[0165] [Formula 3]

[0166] Tablet density (g / cm³) 3 = Weight of positive electrode active material (g) / Particle volume (cm³) 3 )

[0167] Experimental Example 2: Evaluation of Particle Fracture After Rolling

[0168] A positive electrode slurry was prepared by mixing the positive electrode active materials of each example and comparative example, Super P as a conductive material, and polyvinylidene fluoride (PVDF) as a binder in an N-methylpyrrolidone (NMP) solvent at a weight ratio of 92:4:4. 5g of the prepared positive electrode slurry was coated onto one side of an aluminum current collector, dried at 130°C, and then pressed to prepare the positive electrode. Meanwhile, in the case of the positive electrode containing the positive electrode active materials of Examples 1-3 and Comparative Example 2, rolling was performed to reduce the electrode porosity to 22%, and in the case of the positive electrode containing the positive electrode active materials of Comparative Examples 1, 3, and 4, rolling was performed to reduce the electrode porosity to 30%. This is because no matter how many times rolling is performed, the height will not decrease below a certain level.

[0169] The pressed positive electrode was cut using focused ion beam (FIB) to obtain the cut surface of the positive electrode active material layer. SEM images of the cut surface of the positive electrode active material layer were obtained using a SEM (JEOL, JSM7610F), and the results are shown below. Figure 2 . Figure 2 (A) is a SEM image of a cross-section of the positive electrode containing the positive electrode active material of Example 1. Figure 2 (B) is a SEM image of a cross-section of the positive electrode containing the positive electrode active material of Example 2.

[0170] Experimental Example 3: Evaluation of Electrode Porosity

[0171] A positive electrode slurry was prepared by mixing the positive electrode active material of each embodiment and comparative example, Super P as a conductive material, and polyvinylidene fluoride (PVDF) as a binder in an N-methylpyrrolidone (NMP) solvent at a weight ratio of 92:4:4. 5 g of the prepared positive electrode slurry was coated onto one side of an aluminum current collector and dried at 130°C to prepare the positive electrode. The positive electrode was rolled using a rolling mill (a product of Welcose Corporation), and the height of the pressed positive electrode was measured to calculate the volume. The amount of positive electrode active material was used to convert the voids into porosity. Specifically, the porosity (%) was calculated using the following Equation 4, and its values ​​are listed in Table 1 below.

[0172] [Formula 4]

[0173] Rolled height (mm) = [{(weight of positive electrode active material (mg) - weight of aluminum current collector (mg)) / (positive electrode area (cm²)] 2 )×(1-porosity (%)×true density (g / cm³) 3 ))}+0.02]× 1000

[0174] Experimental Example 4: Evaluation of Single Crystallinity

[0175] A positive electrode slurry was prepared by mixing a first Li-rich layered manganese-based oxide (Al), carbon black conductive material, and PVDF binder in an NMP solvent at a weight ratio of 95:2:3. The positive electrode slurry was coated onto one side of an aluminum current collector, dried, and then pressed to prepare the positive electrode. The prepared positive electrode was cut using the FIB method to obtain its cross-section. SEM and EBSD images of the same location were measured to obtain the shape and area of ​​the particles (obtained from the SEM image) and the cross-section of the grains (obtained from the EBSD image). Then, a clustering algorithm was applied to distinguish the grains within the particles, and the degree of monocrystallization of the positive electrode active material was evaluated using Equation 1 of this invention.

[0176] [Formula 1]

[0177]

[0178] In equation 1 above,

[0179] When a single particle is formed from i grains, ai refers to the ratio (Ai / A) of the cross-sectional area (A) of the i-th grain to the cross-sectional area (A) of the single particle.

[0180] As an evaluation result, according to Equation 1 above, the single crystallinity (χ) of the first Li-rich layered manganese-based oxide (Al) is 0.64.

[0181] Experimental Example 5: Evaluation of Battery Characteristics

[0182] A positive electrode slurry was prepared by mixing the positive electrode active materials of each example and comparative example, Super P as a conductive material, and polyvinylidene fluoride (PVDF) as a binder in an N-methylpyrrolidone (NMP) solvent at a weight ratio of 92:4:4. The prepared positive electrode slurry was coated onto one side of an aluminum current collector, dried at 130°C, and then pressed to prepare a positive electrode. In the case of positive electrodes containing the positive electrode active materials of Examples 1-3 and Comparative Example 2, rolling was performed to reduce the electrode porosity to 22%. In the case of positive electrodes containing the positive electrode active materials of Comparative Examples 1, 3, and 4, rolling was performed to reduce the electrode porosity to 30%, because the height would not decrease below a certain level regardless of the number of rolling operations.

[0183] An electrode assembly was prepared by using a lithium metal electrode as the negative electrode and introducing a porous polyethylene membrane between the positive and negative electrodes. The electrode assembly was placed inside the battery casing, and an electrolyte solution was injected. The electrolyte solution contained 1M LiPF6 dissolved in an organic solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) mixed in a volume ratio of 3:4:3 to prepare a coin-shaped half-cell.

[0184] The coin-shaped half-cells containing the positive electrode active materials of each embodiment and comparative example were charged to 4.65 V at 45°C in a CC(0.1C)-CV (cutoff current: 0.05 C) mode, and then discharged to 2.0 V at 0.1 C for formation. Then, the coin-shaped half-cells were charged to 4.25 V at 25°C in a CC(0.1 C)-CV (cutoff current: 0.05 C) mode, and then discharged to 2.5 V at 0.1 C. The initial discharge capacity was measured, and the results are listed in Table 1 below.

[0185] Subsequently, the charge-discharge cycle was repeated a total of 30 times. One cycle refers to charging to 4.25 V at 25°C using CC (0.33 C) - CV (cutoff current: 0.05 C) and then discharging to 2.5 V at 0.33 C. After measuring the discharge capacity of 30 cycles, the capacity retention rate was calculated as the percentage of the discharge capacity of 30 cycles relative to the initial discharge capacity, and the values ​​are listed in Table 1 below.

[0186] [Table 1]

[0187]

[0188] Referring to Table 1 above, it can be seen that, compared with the positive electrode active material of Comparative Example 1, the bimodal positive electrode active materials of Examples 1 to 3 of the present invention have high energy density, and therefore significantly higher pressing density and electrode porosity, while the discharge capacity and capacity retention are at the same level. Furthermore, it can be seen that, compared with the positive electrode active material of Comparative Example 2, the bimodal positive electrode active materials of Examples 1 to 3 of the present invention have significantly higher pressing density and significantly better discharge capacity and capacity retention.

[0189] Furthermore, it can be seen that, compared with the positive electrode active materials of Comparative Examples 3 and 4, the bimodal positive electrode active materials of Examples 1 to 3 according to the present invention have significantly higher pressing density and significantly better discharge capacity. Furthermore, it can be seen that, compared with the positive electrode active material of Comparative Example 5, the bimodal positive electrode active materials of Examples 1 to 3 according to the present invention have significantly higher pressing density and significantly better capacity retention.

[0190] It can be seen that the positive electrode active material of the present invention contains both small Li-rich layered manganese oxide particles in the form of single particles and large Li-rich layered manganese oxide particles in the form of secondary particles in a specific weight ratio. Therefore, it has excellent energy density and stability. Thus, batteries containing the positive electrode active material can have improved performance, such as improved capacity characteristics and energy density, and can prevent particle breakage of the positive electrode active material during battery preparation or operation.

Claims

1. A bimodal cathode active material, comprising: A first Li-rich layered manganese-based oxide in the form of single particles; and A second Li-rich layered manganese-based oxide in the form of secondary particles, in, The first Li-rich layered manganese-based oxide and the second Li-rich layered manganese-based oxide simultaneously contain a Li2MnO3 phase and a LiMO2 phase, wherein M is an element containing one or more selected from Ni, Co, and Mn, The average particle size (D) of the first Li-rich layered manganese-based oxide 50 The average particle size (D) of the second Li-rich layered manganese-based oxide is smaller than that of the second Li-rich layered manganese-based oxide. 50 ),and The weight ratio of the first Li-rich layered manganese-based oxide to the second Li-rich layered manganese-based oxide is 1:1.5 to 8.

2. The bimodal positive electrode active material according to claim 1, wherein, According to the following Equation 1, the first Li-rich layered manganese-based oxide has a crystallinity (χ) of 0.4 or more: [Equation 1] Wherein, in the above Equation 1, When a single particle is formed from i grains, a i It refers to the cross-sectional area (A) of the i-th grain. i The ratio of the cross-sectional area (A) of the single particle to the cross-sectional area (A) i / A).

3. The bimodal positive electrode active material according to claim 1, wherein, The average particle size (D) of the first Li-rich layered manganese-based oxide 50 The thickness ranges from 0.5 μm to 3.5 μm.

4. The bimodal positive electrode active material according to claim 1, wherein, The average particle size (D) of the second Li-rich layered manganese-based oxide 50 The thickness ranges from 5.0 μm to 10.0 μm.

5. The bimodal positive electrode active material according to claim 1, wherein, The first Li-rich layered manganese-based oxide has a composition represented by the following Chemical Formula 1: [Chemical Formula 1] Li 1+x1 Ni a1 Mr b1 M 1 c1 O y1 Wherein, in the above Chemical Formula 1, M 1 It is selected from one or more of 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 and 0 ≤ y1 ≤ 2.0, and x1 + a1 + b1 + c1 = 1.

0.

6. The bimodal positive electrode active material according to claim 1, wherein, The second Li-rich layered manganese-based oxide has a composition represented by the following Chemical Formula 2: [Chemical Formula 2] Li 1+x2 Ni a2 Mr b2 M 2 c2 O y2 Wherein, in the above Chemical Formula 2, M 2 It is selected from one or more of 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 and 0 ≤ y2 ≤ 2.0, and x2 + a2 + b2 + c2 = 1.

0.

7. The bimodal positive electrode active material according to claim 1, wherein, The tablet density is 2.20 g / cm³. 3 Up to 2.70 g / cm 3 .

8. A cathode comprising the bimodal cathode active material according to any one of claims 1 to 7.

9. A lithium secondary battery comprising the cathode according to claim 8.

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