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

Abstract

The present invention relates to a positive electrode material, a positive electrode for a lithium secondary battery comprising the same, and a lithium secondary battery, the positive electrode material comprising: a first positive electrode active material in the form of a single particle; and a second positive electrode active material in the form of secondary particles and having an average particle diameter (D50) larger than the average particle diameter (D50) of the first positive electrode active material, in which the volume of particles having a particle diameter of 1 [mu] m or less is 10% or less relative to the total volume of particles present in the positive electrode material when a pressure of 6,500 kgf / cm2 is applied to the positive electrode material.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2023-0047003, filed on April 10, 2023, the disclosure of which is incorporated herein by reference. Technical Field

[0003] This invention relates to a positive electrode material for lithium secondary batteries, as well as a positive electrode containing the same and a lithium secondary battery. Background Technology

[0004] With the development of mobile device technology and increasing demand, the demand for secondary batteries as an energy source has increased significantly. Among these secondary batteries, lithium secondary batteries, which have high energy density, high voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0005] Lithium-based composite transition metal oxides have been used as positive electrode active materials for lithium-ion secondary batteries. Among these oxides, lithium-cobalt composite metal oxides, such as LiCoO2, are mainly used due to their high operating voltage and excellent capacity characteristics. However, LiCoO2 exhibits poor thermal properties because its crystal structure is unstable due to delithiation. Furthermore, the high cost of LiCoO2 limits its use in large quantities as a power source for applications such as electric vehicles.

[0006] As alternatives to LiCoO2, lithium manganese composite metal oxides (LiMnO2 or LiMn2O4), lithium iron phosphate compounds (LiFePO4, etc.), or lithium nickel composite metal oxides (LiNiO2, etc.) have been developed. Among these materials, lithium nickel composite metal oxides, which can easily realize large-capacity batteries due to their high reversible capacity of about 200 mAh / g, have been more actively researched and developed. However, the limitation of LiNiO2 is that its thermal stability is worse than that of LiCoO2, and when an internal short circuit occurs due to external pressure during charging, the positive electrode active material itself decomposes, leading to battery rupture and fire. Therefore, as a method to improve the low thermal stability while maintaining the excellent reversible capacity of LiNiO2, lithium transition metal oxides in which a portion of the nickel (Ni) is replaced by cobalt (Co), manganese (Mn), or aluminum (Al) have been developed.

[0007] For lithium-ion batteries that use lithium composite transition metal oxides, especially lithium composite transition metal oxides with high nickel content (Ni-rich), as positive electrode active materials, battery capacity, high output, and gas generation at high temperatures are affected not only by chemical properties such as the composition of the positive electrode active material, the content of impurities, and the content of lithium by-products present on its surface, but also by physical properties such as the size, surface area, density, and shape of the positive electrode active material particles.

[0008] Typically, to maximize the volumetric energy density of a battery, methods have been employed to improve the volumetric energy density by using a mixture of large-particle-size and small-particle-size positive electrode active materials, thereby filling the voids between the large-particle-size positive electrode active material particles with the small-particle-size material. Furthermore, methods using a roll calender to calender the positive electrode active material layer have been used to prepare a positive electrode active material layer with a denser structure. However, in this case, due to the difference in particle strength between the large-particle-size and small-particle-size positive electrode active materials, particles with relatively weak particle strength undergo excessive fragmentation during calendering. Consequently, the particles not only lose their original shape but also excessively increase their contact area with the electrolyte. Therefore, when this positive electrode active material layer is used in a battery, a reduction in battery life characteristics occurs.

[0009] Therefore, there is a need to develop a cathode material that can improve volumetric energy density and improve lifetime characteristics by suppressing particle breakage during compression delay in cathode preparation.

[0010] [Existing technical documents]

[0011] [Patent Literature]

[0012] (Patent Document 1) Korean Patent Application Publication No. 2021-0117212 Summary of the Invention

[0013] Technical issues

[0014] One aspect of the present invention provides a cathode material in which particle breakage during compression delay in cathode fabrication is reduced, while improving volumetric energy density.

[0015] Another aspect of the present invention provides a positive electrode comprising a positive electrode material and exhibiting excellent electrochemical performance by mitigating the breakage of the contained positive electrode active material particles.

[0016] Another aspect of the present invention provides a lithium secondary battery comprising the positive electrode.

[0017] Technical solution

[0018] To address the aforementioned problems, the present invention provides a positive electrode material, a positive electrode for a lithium secondary battery comprising the positive electrode material, and a lithium secondary battery.

[0019] (1) The present invention provides a positive electrode material, the positive electrode material comprising:

[0020] A first positive electrode active material, wherein the first positive electrode active material is in single-particle form; and

[0021] The second positive electrode active material is in the form of secondary particles and has an average particle size (D). 50 ) compared to the average particle size (D) of the first positive electrode active material 50 Larger

[0022] Among them, when a cathode material is subjected to 6,500 kgf / cm 2 Under pressure, the volume of particles with a diameter of less than 1 μm is less than 10% of the total volume of particles present in the cathode material.

[0023] (2) The present invention provides the cathode material of (1) above, wherein the cathode material has a bimodal particle size distribution.

[0024] (3) The present invention provides the positive electrode material of (1) or (2) above, wherein the average particle size (D) of the second positive electrode active material is used as the basis for the positive electrode material. 50 The average particle size (D) of the first positive electrode active material 50 The percentage is below 50%.

[0025] (4) The present invention provides a cathode material of any one of (1) to (3) above, wherein the single-particle form has single crystallinity.

[0026] (5) The present invention provides a positive electrode material of any one of (1) to (4) above, wherein the weight ratio of the first positive electrode active material to the second positive electrode active material is in the range of 1:0.1 to 1:10.

[0027] (6) The present invention provides a positive electrode material according to any one of (1) to (5) above, wherein the average particle size (D) of the first positive electrode active material is... 50 The range is from 1 μm to 10 μm.

[0028] (7) The present invention provides a positive electrode material according to any one of (1) to (6) above, wherein the average particle size (D) of the second positive electrode active material is... 50 The thickness ranges from 6 μm to 25 μm.

[0029] (8) The present invention provides a positive electrode material of any one of (1) to (7) above, wherein the composition of the first positive electrode active material is represented by chemical formula 1.

[0030] [Chemical Formula 1]

[0031] Li 1+a1 Ni x1 Co y1 M 1 z1 M 2 w1 O2

[0032] In chemical formula 1,

[0033] M 1 It is selected from at least one of manganese (Mn) and aluminum (Al).

[0034] M 2 It is selected from at least one of boron (B), barium (Ba), cerium (Ce), chromium (Cr), fluorine (F), magnesium (Mg), vanadium (V), titanium (Ti), iron (Fe), zirconium (Zr), zinc (Zn), silicon (Si), yttrium (Y), niobium (Nb), gallium (Ga), tin (Sn), molybdenum (Mo), tungsten (W), phosphorus (P), sulfur (S), strontium (Sr), tantalum (Ta), lanthanum (La), and hafnium (Hf), and

[0035] -0.1≤a1≤0.3,0.6≤x1<1.0,0 <y1<0.4,0<z1<0.4,0≤w1≤0.1。

[0036] (9) The present invention provides a positive electrode material of any one of (1) to (8) above, wherein the composition of the second positive electrode active material is represented by chemical formula 2.

[0037] [Chemical Formula 2]

[0038] Li 1+a2 Ni x2 Co y2 M 3 z2 M 4 w2 O2

[0039] In chemical formula 2,

[0040] M 3 It is selected from at least one of Mn and Al.

[0041] M 4 It is selected from at least one of B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf, and

[0042] -0.1≤a²≤0.3, 0.6≤x²<1.0, 0 <y2<0.4,0<z2<0.4,0≤w2≤0.1。

[0043] (10) The present invention provides a positive electrode comprising a positive electrode active material layer comprising any one of the positive electrode materials in (1) to (9) above.

[0044] (11) The present invention provides a lithium secondary battery, the lithium secondary battery comprising the positive electrode of (10) above.

[0045] Beneficial effects

[0046] Since the cathode material according to the present invention comprises: a first cathode active material, the first cathode active material being in single-particle form; and a second cathode active material, the second cathode active material being in secondary-particle form and having an average particle size (D) 50 ) compared to the average particle size (D) of the first positive electrode active material 50 The effect is even greater, especially when a cathode material is subjected to an application of 6,500 kgf / cm². 2 At the specified pressure, the volume of particles with a diameter of 1 μm or less in the cathode material is less than 10% of the total volume of particles present in the cathode material. Therefore, this cathode material has the effect of reducing particle breakage during the pressure delay of cathode preparation. Thus, when using the cathode material according to the present invention, side reactions with the electrolyte caused by particle breakage of the cathode material can be minimized, and excellent capacity and lifetime characteristics can be achieved. Attached Figure Description

[0047] Figure 1 The image is a scanning electron microscope (SEM) image of the first positive electrode active material prepared in Example 2.

[0048] Figure 2 The image shows a SEM image of the second positive electrode active material prepared in Example 1.

[0049] Figure 3 To compare the SEM images of the small-particle secondary particle positive electrode active material prepared in Preparation Example 1.

[0050] Figure 4 To compare the SEM images of the small-particle single-particle positive electrode active material prepared in Preparation Example 2.

[0051] Figure 5 To apply a 6,500 kgf / cm² pressure to the cathode material prepared in Example 1 2 The particle size distribution curves were measured by a particle size analyzer (PSA) before and after the pressure.

[0052] Figure 6 To apply a 6,500 kgf / cm² pressure to the cathode material prepared in Example 2 2 Particle size distribution curves measured by PSA before and after pressure.

[0053] Figure 7 To apply a 6,500 kgf / cm² pressure to the cathode material prepared in Comparative Example 1 2 Particle size distribution curves measured by PSA before and after pressure.

[0054] Figure 8 To apply a 6,500 kgf / cm² pressure to the cathode material prepared in Comparative Example 2 2 Particle size distribution curves measured by PSA before and after pressure.

[0055] Figure 9 To apply a 6,500 kgf / cm² pressure to the cathode material prepared in Comparative Example 3 2 Particle size distribution curves measured by PSA before and after pressure.

[0056] Figure 10 The image shows the electron backscatter diffraction-inverse pole figure (EBSD-IPF) of the first positive electrode active material prepared in Example 2.

[0057] Figure 11 Data related to the evaluation of battery characteristics (capacity retention) of lithium secondary batteries containing the cathode materials prepared in Example 1 and Comparative Example 1, respectively.

[0058] Figure 12 Data related to the evaluation of battery characteristics (volume change rate) of lithium secondary batteries containing the cathode materials prepared in Example 1 and Comparative Example 1, respectively. Detailed Implementation

[0059] The invention will be described in more detail below.

[0060] It should be understood that the words or terms used in this specification and claims should not be interpreted as having the meaning defined in a common dictionary. Rather, it should be understood that, based on the principle that the inventors may appropriately define the meaning of words or terms to best interpret the invention, the words or terms should be interpreted as having a meaning consistent with their meaning in the context of the relevant field and technical spirit of the invention.

[0061] It should also be understood that the terms “comprising,” “including,” or “having” in this specification specify the presence of a feature, number, step, constituent element, or combination thereof, but do not exclude the presence or addition of more than one other feature, number, step, constituent element, or combination thereof.

[0062] In this invention, the term "primary particle" refers to the smallest particle unit identified when observing a positive electrode active material using a scanning electron microscope (SEM), and the term "secondary particle" refers to a secondary structure formed by the aggregation of multiple primary particles.

[0063] In this invention, the term "secondary particle form" refers to a spherical form formed by the aggregation of tens to hundreds of primary particles, prepared by conventional methods, wherein it indicates a form consisting of more than 50 primary particles. Specifically, in this invention, a secondary particle form is a form in which more than 50 primary particles are aggregated, and can also be a form in which hundreds or thousands of particles are aggregated.

[0064] In this invention, the term "single-particle form" is a concept contrasted with the spherical secondary particle form, which is formed by the aggregation of tens to hundreds of primary particles and prepared by conventional methods. Specifically, it refers to a form consisting of 50 or fewer primary particles. More specifically, the single-particle form in this invention can be a single particle consisting of one primary particle, or a secondary particle form in which 2 or more but less than 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50 primary particles are aggregated.

[0065] In this invention, the term "single crystal" can be used interchangeably with "single crystallinity," and refers to a cathode active material or lithium composite transition metal oxide containing 1 to 50 grains. Generally, a single crystal particle refers to a particle in which the entire sample consists of only one grain or grain region. The single-crystal cathode active material or single-crystalline cathode active material in this invention can be 1 to 50 single crystal particles, specifically a single crystal particle consisting of one grain, or it can be a material containing agglomerated 2 to 5, 10 to 15, 20 to 25, 30 to 35, 40 to 45, or 50 single crystal particles, wherein by containing a small number of single crystal particles, it can exhibit properties similar to those of a single crystal particle. A "grain" or "grain region" refers to a region in a sample where atoms are arranged continuously and periodically in one direction. Grains can be analyzed using electron backscatter diffraction (EBSD) analysis.

[0066] The term "average particle size (D)" in this specification is used to describe the particle size distribution. 50")" indicates the particle size at 50% of the volumetric cumulative distribution based on particle size. After dispersing the target powder in a dispersion medium, the dispersion medium is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the difference in diffraction patterns caused by particle size as particles pass through the laser beam. The D can be measured using this analyzer by calculating the particle size at 50% of the volumetric cumulative distribution based on particle size. 50 .

[0067] In this invention, "fine powder" refers to particles with a diameter of less than 1 μm when the pressurized target powder is dispersed in a dispersion medium, the dispersion medium is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500), and the particle size distribution is calculated by measuring the difference in diffraction patterns caused by particle size when the particles pass through the laser beam.

[0068] cathode materials

[0069] The cathode material according to the present invention will be described below.

[0070] The positive electrode material of the present invention comprises:

[0071] A first positive electrode active material, wherein the first positive electrode active material is in single-particle form; and

[0072] The second positive electrode active material is in the form of secondary particles and has an average particle size (D). 50 ) compared to the average particle size (D) of the first positive electrode active material 50 Larger

[0073] Among them, when a cathode material is subjected to 6,500 kgf / cm 2 Under pressure, the volume of particles with a diameter of less than 1 μm is less than 10% of the total volume of particles present in the cathode material.

[0074] High-nickel (high-Ni) cathode active materials in the form of secondary particles have the advantage of excellent energy density, but their limitation lies in the inevitable instability of the crystal structure due to the generation of fine powder caused by structural deformation and internal cracks during repeated charge and discharge processes. The advantage of other cathode active materials is that the higher the degree of single-particle formation, the less particle breakage or collapse during rolling, and the lower the fine powder generation rate during rolling, but they suffer from poor energy density.

[0075] Therefore, the inventors have discovered that, under the following conditions: the positive electrode material comprises: a first positive electrode active material, wherein the first positive electrode active material is in the form of a single particle; and a second positive electrode active material, wherein the second positive electrode active material is in the form of a secondary particle and has an average particle size (D...50 ) compared to the average particle size (D) of the first positive electrode active material 50 The effect is even greater, especially when a cathode material is subjected to an application of 6,500 kgf / cm². 2 Under pressure, the volume of particles with a diameter of less than 1 μm is less than 10% of the total volume of particles present in the cathode material. This can reduce the generation of fine powder and improve the rolling performance of the electrode by suppressing particle collapse during the rolling period, and can also improve the energy density characteristics, thereby completing the present invention.

[0076] The cathode material according to the present invention comprises a first cathode active material in the form of a single particle. That is, the first cathode active material is a single particle or a single particle in which 2 to 50 primary particles are aggregated. Specifically, the first cathode active material can be a single particle consisting of one primary particle, or it can be a secondary particle in which 2 or more but less than 5 or less, or less than 10 primary particles are aggregated. The single particle form is different from the secondary particle in which more than 50 primary particles are aggregated. When the first cathode active material is in the form of a single particle, due to its excellent stability, the cathode material containing the first cathode active material will not break or fracture even when the cathode material is rolled, thus reducing side reactions between the cathode material and the electrolyte. As a result, the lifespan characteristics can be improved due to the improved durability against volume changes during battery charge and discharge. When the first cathode active material is in the form of a secondary particle, since the cathode material containing the first cathode active material breaks or fractures, there is a problem of poor lifespan characteristics due to side reactions between the cathode material and the electrolyte.

[0077] According to one embodiment of the present invention, the single-particle form can possess single crystallinity. Specifically, the single-particle form can be a single particle composed of a single primary particle. In this case, the single-particle form can be a primary particle composed of a single crystal particle, or a primary particle composed of two or more but five or fewer, or ten or fewer, single crystal particles. Furthermore, the single-particle form can be a secondary particle form in which two or more but five or fewer, or ten or fewer, primary particles are aggregated. In this case, the single-particle form can be a form in which a primary particle composed of a single crystal particle is aggregated, or a form in which a primary particle composed of two or more but five or fewer, or ten or fewer, single crystal particles are aggregated. When the single-particle form possesses single crystallinity, since the grain interface can be reduced, side reactions between the cathode material and the electrolyte can be reduced.

[0078] The cathode material according to the present invention comprises a second cathode active material in the form of secondary particles. That is, the second cathode active material is in the form of secondary particles in which more than 50 primary particles are aggregated. The secondary particle form differs from a single particle form or a single particle form in which 2 to 50 primary particles are aggregated. When the second cathode active material is in the form of secondary particles, the energy density can be improved due to the reduction in pores in the cathode material. As a result, the capacity characteristics of the battery can be improved. When the second cathode active material is in the form of single particles, the capacity characteristics may be poor because the energy density of the cathode material containing the second cathode active material is reduced.

[0079] The average particle size (D) of the second positive electrode active material 50 ) compared to the average particle size (D) of the first positive electrode active material 50 The cathode material has a higher single-particle formation degree, resulting in less particle breakage or collapse during calendering and a lower fine powder generation rate during the calendering period. Therefore, when preparing a cathode using this cathode material, excellent electrochemical performance can be obtained. The cathode material comprises: a first cathode active material, which is in single-particle form and has an average particle size (D...). 50 The second positive electrode active material is relatively small; and the second positive electrode active material is in the form of secondary particles and has an average particle size (D) 50 The cathode material has a relatively large particle formation rate, which allows for increased single-particle formation while maintaining energy density. As a result, the battery characteristics of batteries containing cathode materials can be improved.

[0080] In the cathode material according to the present invention, when a cathode material is subjected to 6,500 kgf / cm 2 When subjected to pressure of 6,500 kgf / cm², the volume of particles with a diameter of less than 1 μm is less than 10% of the total volume of particles present in the cathode material. Specifically, when the cathode material is subjected to pressure of 6,500 kgf / cm², the volume of particles with a diameter of less than 1 μm is less than 10%. 2 Under pressure, the volume of particles with a diameter of less than 1 μm is less than 10%, less than 9%, less than 8%, less than 7%, less than 6%, or less than 5% of the total volume of particles present in the cathode material, and may be more than 0.01%.

[0081] The volume of particles smaller than 1 μm relative to the total volume of particles present in the cathode material, i.e., the fine powder generation rate, is determined by filling 3 g of cathode material into a circular mold with a diameter of 1.3 cm and applying 6,500 kgf / cm² using a 9-ton press. 2The pressure was applied, and then the particle distribution of the cathode material was measured to obtain the proportion of fine powder with a particle size of less than 1 μm. Since the first and second cathode active materials contained in the cathode material before pressurization do not contain or contain very small amounts of fine powder with a particle size of less than 1 μm, the amount of fine powder with a particle size of less than 1 μm contained in the cathode material after pressurization was measured and can be defined as the fine powder generation rate.

[0082] According to one embodiment of the present invention, the cathode material of the present invention simultaneously comprises a first cathode active material and a second cathode active material, which have different average particle sizes from each other, wherein the cathode material may have a bimodal particle size distribution. When the cathode material has a bimodal particle size distribution, the single-particle formation degree of the cathode material can be increased while maintaining energy density. As a result, the battery characteristics of a battery containing the cathode material can be improved.

[0083] According to one embodiment of the present invention, the first positive electrode active material has an average particle size (D) 50 The particles are relatively small, and the second positive electrode active material has an average particle size (D). 50 Relatively large particles, specifically, based on the average particle size (D) of the second positive electrode active material. 50 The average particle size (D) of the first positive electrode active material 50 The content can be below 50%, specifically within the ranges of below 50%, 10% to 50%, 10% to 45%, 10% to 42%, 12% to 50%, 12% to 45%, 12% to 42%, 15% to 50%, 15% to 45%, or 15% to 42%, more specifically within the range of 20% to 40%. The average particle size (D) of the first positive electrode active material... 50 Based on the average particle size (D) of the second positive electrode active material 50 If the above range is met, particle breakage of the cathode material containing them can be effectively reduced.

[0084] According to one embodiment of the present invention, the weight ratio of the first positive electrode active material to the second positive electrode active material can be in the range of 1:0.1 to 1:10. Specifically, the weight ratio of the first positive electrode active material to the second positive electrode active material can be in the range of 1:1 to 1:8 or 1:1 to 1:5, more specifically in the range of 1:1 to 1:4. When the first and second positive electrode active materials are included in the above weight ratio, particle breakage of the positive electrode material containing them can be effectively reduced, and the effect of improving the rolling density of the positive electrode material can be obtained while the positive electrode material exhibits excellent electrochemical performance.

[0085] According to one embodiment of the present invention, the particle strength of the first positive electrode active material is more than twice that of the particle strength of the second positive electrode active material, wherein the particle strength of the first positive electrode active material can specifically be 2 to 10 times or 2 to 8 times that of the second positive electrode active material, more specifically 2.2 to 6 times. When the particle strength of the first positive electrode active material is within the above-mentioned range based on the particle strength of the second positive electrode active material, particle breakage of the positive electrode material containing them can be effectively reduced.

[0086] According to one embodiment of the present invention, since the first positive electrode active material and the second positive electrode active material satisfy the above-mentioned particle size ratio range and the above-mentioned weight ratio, and the positive electrode material simultaneously contains the first positive electrode active material and the second positive electrode active material, particle breakage of the positive electrode material simultaneously containing them can be effectively reduced, and correspondingly, excellent lifetime characteristics can be exhibited.

[0087] According to one embodiment of the present invention, the average particle size (D) of the first positive electrode active material 50 The particle size can range from 1 μm to 10 μm. Specifically, the average particle size (D) of the first positive electrode active material... 50 The particle size can be greater than 1 μm, greater than 2 μm, greater than 3 μm, or greater than 4 μm, and can be less than 5 μm, less than 6 μm, less than 7 μm, less than 8 μm, less than 9 μm, or less than 10 μm. The average particle size (D) of the first positive electrode active material... 50 Within the aforementioned range, due to its excellent stability, the cathode material containing it will not break or crack even when the cathode material is rolled, thus reducing side reactions between the cathode material and the electrolyte. As a result, lifespan characteristics can be improved due to the enhanced durability against volume changes during battery charge and discharge.

[0088] According to one embodiment of the present invention, the average particle size (D) of the second positive electrode active material 50 The average particle size (D) of the second positive electrode active material can range from 6 μm to 25 μm. Specifically, the average particle size (D) of the second positive electrode active material can range from 6 μm to 25 μm. 50 The particle size can be 6 μm or larger, 7 μm or larger, 8 μm or larger, 9 μm or larger, or 10 μm or larger, and can be less than 11 μm, less than 12 μm, less than 13 μm, less than 14 μm, less than 15 μm, less than 16 μm, less than 17 μm, less than 18 μm, less than 19 μm, less than 20 μm, less than 21 μm, less than 22 μm, less than 23 μm, less than 24 μm, or less than 25 μm. The average particle size (D) of the second positive electrode active material... 50 Within the aforementioned range, there is an effect of improving energy density.

[0089] The average particle size (D) of the first positive electrode active material and the second positive electrode active material 50 When the above range is met, particle breakage of the cathode material containing them is mitigated, and since the first cathode active material particles fill the spaces between the second cathode active material particles, the tap density of the cathode material containing them can be improved. Since a higher tap density results in a higher electrode packing density, when preparing an electrode using the cathode material, a slurry containing the cathode material having the above-mentioned tap density can be thinly coated onto the surface of the cathode current collector. Therefore, the coated electrode thickness is improved to be thinner, and during the calendering of the coated cathode current collector, there is less breakage of the first cathode active material particles in single-particle form. Furthermore, the pressure required to achieve an electrode thickness matching the calendering density can be reduced, thus improving cathode material breakage due to calendering. In addition, the volumetric energy density is improved due to the reduced interparticle voids, thereby further improving capacity characteristics.

[0090] Since the particle strength of the positive electrode active material depends on the composition and properties of the precursor (transition metal hydroxide, transition metal hydroxyl oxide, etc.) used as raw material and the sintering conditions, the positive electrode active material with the desired particle strength can be prepared by appropriately adjusting the sintering conditions (temperature and time) according to the composition and / or properties (surface area, density, shape, etc.) of the precursor.

[0091] The first and second positive electrode active materials can each independently contain lithium composite transition metal oxides, wherein the molar ratio of nickel in the transition metal is greater than 60%. Because nickel-rich lithium transition metal oxides have a high capacity per unit volume, they can achieve excellent capacity characteristics when used in batteries.

[0092] According to one embodiment of the present invention, the composition of the first positive electrode active material can be represented by the following chemical formula 1.

[0093] [Chemical Formula 1]

[0094] Li 1+a1 Ni x1 Co y1 M 1 z1 M 2 w1 O2

[0095] In chemical formula 1,

[0096] M 1 It is selected from at least one of manganese (Mn) and aluminum (Al).

[0097] M 2is at least one selected from boron (B), barium (Ba), cerium (Ce), chromium (Cr), fluorine (F), magnesium (Mg), vanadium (V), titanium (Ti), iron (Fe), zirconium (Zr), zinc (Zn), silicon (Si), yttrium (Y), niobium (Nb), gallium (Ga), tin (Sn), molybdenum (Mo), tungsten (W), phosphorus (P), sulfur (S), strontium (Sr), tantalum (Ta), lanthanum (La), and hafnium (Hf), and

[0098] -0.1 ≤ a1 ≤ 0.3, 0.6 ≤ x1 < 1.0, 0 < y1 < 0.4, 0 < z1 < 0.4, 0 ≤ w1 ≤ 0.1.

[0099] a1 represents the molar ratio of lithium in the lithium composite transition metal oxide, where a1 can satisfy -0.1 ≤ a1 ≤ 0.3, particularly 0 ≤ a1 ≤ 0.25, and more particularly 0 ≤ a1 ≤ 0.10.

[0100] x1 represents the molar ratio of nickel in all transition metals in the lithium composite transition metal oxide, where x1 can satisfy 0.6 ≤ x1 < 1.0, particularly 0.6 ≤ x1 ≤ 0.99 or 0.7 ≤ x1 ≤ 0.99, and more particularly 0.8 ≤ x1 ≤ 0.95. When the nickel content satisfies the above range, excellent capacity characteristics can be achieved.

[0101] y1 represents the molar ratio of cobalt in all transition metals in the lithium composite transition metal oxide, where y1 can satisfy 0 < y1 < 0.4, particularly 0 < y1 ≤ 0.35, and more particularly 0.01 ≤ y1 ≤ 0.3.

[0102] z1 represents the element M in the lithium composite transition metal oxide 1 in the molar ratio of all transition metals, where z1 can satisfy 0 < z1 ≤ 0.4, particularly 0 < z1 < 0.35, and more particularly 0.01 ≤ z1 ≤ 0.30.

[0103] w1 represents M 2 in the molar ratio of all transition metals, where w1 can satisfy 0 ≤ w1 ≤ 0.1, particularly 0 ≤ w1 ≤ 0.08, and more particularly 0 ≤ w1 ≤ 0.05.

[0104] x1, y1, z1, and w1 can satisfy x1 + y1 + z1 + w1 = 1.

[0105] According to an embodiment of the present invention, the composition of the second positive electrode active material can be represented by the following Chemical Formula 2.

[0106] [Chemical Formula 2]

[0107] Li 1+a2 Ni x2 Co y2M 3 z2 M 4 w2 O2

[0108] In Chemical Formula 2,

[0109] M 3 is at least one selected from Mn and Al,

[0110] M 4 is at least one selected from B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf, and

[0111] -0.1 ≤ a2 ≤ 0.3, 0.6 ≤ x2 < 1.0, 0 < y2 < 0.4, 0 < z2 < 0.4, 0 ≤ w2 ≤ 0.1.

[0112] a2 represents the molar ratio of lithium in the lithium composite transition metal oxide, where a2 can satisfy -0.1 ≤ a2 ≤ 0.3, particularly 0 ≤ a2 ≤ 0.25, more particularly 0 ≤ a2 ≤ 0.10.

[0113] x2 represents the molar ratio of nickel in all transition metals in the lithium composite transition metal oxide, where x2 can satisfy 0.6 ≤ x2 < 1.0, particularly 0.6 ≤ x2 ≤ 0.99 or 0.7 ≤ x2 ≤ 0.99, more particularly 0.8 ≤ x2 ≤ 0.95. When the nickel content satisfies the above range, excellent capacity characteristics can be achieved.

[0114] y2 represents the molar ratio of cobalt in all transition metals in the lithium composite transition metal oxide, where y2 can satisfy 0 < y2 < 0.4, particularly 0 < y2 ≤ 0.35, more particularly 0.01 ≤ y2 ≤ 0.3.

[0115] z2 represents element M in the lithium composite transition metal oxide 3 in the molar ratio of all transition metals, where z2 can satisfy 0 < z2 ≤ 0.40, particularly 0 < z2 < 0.35, more particularly 0.01 ≤ z2 ≤ 0.30.

[0116] w2 represents M 4 in the molar ratio of all transition metals, where w2 can satisfy 0 ≤ w2 ≤ 0.1, particularly 0 ≤ w2 ≤ 0.08, more particularly 0 ≤ w2 ≤ 0.05.

[0117] x2, y2, z2, and w2 can satisfy x2 + y2 + z2 + w2 = 1.

[0118] The compositions of the first positive electrode active material and the second positive electrode active material can be the same or different from each other. For example, the first positive electrode active material can be a lithium composite transition metal oxide with a nickel molar ratio of more than 88 mol% in the transition metal, and the second positive electrode active material can be a lithium composite transition metal oxide with a nickel molar ratio of more than 86 mol% in the transition metal.

[0119] As needed, the first and second positive electrode active materials may further comprise a coating on the surface of the lithium transition metal oxide, said coating comprising at least one element selected from the following (hereinafter referred to as "coating element"): cobalt (Co), Al, B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf. With the coating as described above, since the contact between the lithium transition metal oxide and the electrolyte is blocked, gas generation due to side reactions with the electrolyte and the dissolution of the transition metal can be effectively suppressed.

[0120] The coating can be formed by mixing lithium transition metal oxide with a raw material containing coating elements and then heat-treating the mixture at a temperature of 200°C to 800°C.

[0121] positive electrode

[0122] Furthermore, the present invention provides a positive electrode for a lithium secondary battery, the positive electrode for a lithium secondary battery comprising a positive electrode active material layer containing the aforementioned positive electrode material. Specifically, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector and comprising the positive electrode material.

[0123] According to one embodiment of the present invention, the porosity of the positive electrode active material layer can be from 10 vol% to 30 vol%, particularly from 15 vol% to 30 vol%, and even more particularly from 18 vol% to 27 vol%.

[0124] According to one embodiment of the present invention, when the positive electrode active material layer has the above-mentioned porosity, during the measurement of particle size distribution (PSD), the positive electrode may contain particles with a particle size of less than 1 μm, based on an amount of less than 50% of the total volume of particles in the positive electrode active material layer.

[0125] The positive electrode may specifically contain the following amounts of particles with a diameter of less than 1 μm: based on the total volume of the positive electrode active material particles being 0.01% to 50%, 0.05% to 30%, 0.1% to 28%, 0.05% to 27.5%, 0.1% to 27.5%, 0.05% to 15%, or 0.1% to 15%.

[0126] Because the particle breakage of the cathode material is mitigated, even when the cathode active material is laminated to have a porosity within the above range, the cathode can contain only a small amount of fine powder with a particle size of less than 1 μm within the above range.

[0127] After forming a positive electrode active material layer containing positive electrode material and then rolling it to a porosity of 10 vol% to 30 vol%, particularly 15 vol% to 30 vol%, and even more particularly 18 vol% to 24 vol%, when the positive electrode active material layer is heat-treated at 500°C in an air atmosphere for 2 hours, the volume of particles with a particle size of less than 1 μm can be obtained by measuring the volume of particles located in the positive electrode active material layer.

[0128] When the total volume of positive electrode active material particles contained in the positive electrode active material layer is defined as 100%, the volume of particles with a diameter of less than 1 μm can be a proportion of the volume. Specifically, it can be obtained by measuring the PSD using a MICROTRAC MRB “MICROTRACS3500”, a CILAS “CILAS920 (France)”, or a MALVERN Panalytical Ltd. “Mastersizer2000 (USA)”, and then dividing the area of ​​particles with a diameter of less than 1 μm by the total area in the PSD plot.

[0129] There are no particular restrictions on the positive electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery. For example, it can be made of stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. Furthermore, the thickness of the positive electrode current collector can typically range from 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. The positive electrode current collector can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0130] In addition to the cathode material described above according to the present invention, the cathode active material layer may also include conductive materials and adhesives.

[0131] Based on the total weight of the positive electrode active material layer, the content of the positive electrode material can be from 80% to 99% by weight, more specifically from 85% to 98% by weight. When the content of the positive electrode material is within the above range, excellent capacity characteristics can be obtained.

[0132] Conductive materials are used to provide conductivity to the electrodes. Any conductive material can be used without particular restriction, as long as it has suitable electronic conductivity and will not cause adverse chemical changes in the battery. Specific examples of conductive materials include: graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, and carbon fibers; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more thereof can be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material can typically range from 1% to 30% by weight.

[0133] The adhesive improves the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples of adhesives can be: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof can be used. Based on the total weight of the positive electrode active material layer, the adhesive content can be from 1% by weight to 30% by weight.

[0134] Besides using the cathode material according to the invention, the cathode can be prepared according to typical cathode preparation methods. Specifically, a cathode active material layer forming composition prepared by dissolving or dispersing the above-described cathode material, along with optional binders, conductive materials, and additives in a solvent as needed, is coated onto a cathode current collector. The cathode can then be prepared by drying and calendering the coated cathode current collector. In this case, the types and amounts of cathode material, binder, and conductive material are the same as those described above.

[0135] The solvent can be any solvent commonly used in the art. Solvents may include dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water, and any one or a mixture of two or more thereof may be used. If the amount of solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to allow for a viscosity that provides excellent thickness uniformity during subsequent coating of the positive electrode, taking into account the coating thickness and manufacturing yield of the slurry, then the amount of solvent used may be adequate.

[0136] Alternatively, as another method, the positive electrode can be prepared by casting a composition for forming the positive electrode active material layer on a separate carrier, and then stacking the film layer separated from the carrier onto the positive electrode current collector.

[0137] Lithium secondary batteries

[0138] Furthermore, in this invention, an electrochemical device comprising the aforementioned positive electrode can be prepared. Specifically, the electrochemical device can be a battery or a capacitor, and more specifically, a lithium secondary battery.

[0139] A lithium secondary battery specifically includes: a positive electrode, a negative electrode facing the positive electrode, a separator between the positive and negative electrodes, and an electrolyte. Since the positive electrode is the same as described above, its detailed description will be omitted. Only the remaining components will be described in detail below.

[0140] The lithium secondary battery may also optionally include: a battery container housing an electrode assembly containing a positive electrode, a negative electrode, and a separator, and a sealing member for sealing the battery container.

[0141] In a lithium secondary battery, the negative electrode comprises a negative electrode current collector and a layer of negative electrode active material disposed on the negative electrode current collector.

[0142] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and will not cause adverse chemical changes in the battery. For example, materials such as copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. Furthermore, the thickness of the negative electrode current collector can typically range from 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 improve the adhesion of the negative electrode active material. The negative electrode current collector can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0143] In addition to the negative electrode active material, the negative electrode active material layer may optionally include a binder and a conductive material.

[0144] Compounds capable of reversibly inserting and de-intercalating lithium can be used as anode active materials. Specific examples of anode active materials include: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; (semi-)metallic materials that can form alloys with lithium, such as silicon (Si), aluminum (Al), tin (Sn), lead (Pb), zinc (Zn), bismuth (Bi), indium (In), magnesium (Mg), gallium (Ga), cadmium (Cd), Si alloys, Sn alloys, or Al alloys; and (semi-)metal oxides that can be doped and de-doped with lithium, such as SiO2. β(0 < β < 2), SnO2, vanadium oxides, and lithium vanadium oxides; or composite materials containing (semi-)metallic materials and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more thereof may be used. Furthermore, lithium metal films can be used as negative electrode active materials. Additionally, both low-crystallinity carbon and high-crystallinity carbon can be used as carbon materials. Typical examples of low-crystallinity carbon can be soft carbon and hard carbon, and typical examples of high-crystallinity carbon can be irregular, planar, sheet-like, spherical, or fibrous natural or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and high-temperature sintered carbon such as coke derived from petroleum or coal tar pitch.

[0145] Based on a negative electrode active material layer with a total weight of 100 parts by weight, the content of the negative electrode active material can be from 80 parts by weight to 99 parts by weight.

[0146] The adhesive is a component that assists in the bonding between the conductive material, the active material, and the current collector. Based on a total weight of 100 parts by weight of the negative electrode active material layer, the amount of adhesive added is typically from 0.1 parts by weight to 10 parts by weight. Examples of adhesives include: polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0147] The conductive material is a component used to further improve the conductivity of the negative electrode active material. Based on a total negative electrode active material layer of 100 parts by weight, the amount of conductive material added can be less than 10 parts by weight, preferably less than 5 parts by weight. There are no particular limitations on the conductive material, as long as it is conductive and will not cause adverse chemical changes in the battery. For example, conductive materials such as: graphite (e.g., natural or artificial graphite); carbon black (e.g., acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black); conductive fibers (e.g., carbon fiber or metal fiber); fluorocarbons; metal powders (e.g., aluminum and nickel powder); conductive whiskers (e.g., zinc oxide whiskers and potassium titanate whiskers); conductive metal oxides (e.g., titanium oxide); or polyphenylene derivatives can be used.

[0148] For example, the negative electrode active material layer can be prepared by coating a mixture of negative electrode materials, prepared by dissolving or dispersing an optional binder and conductive material and the negative electrode active material in a solvent, onto a negative electrode current collector and drying the coated negative electrode current collector; or it can be prepared by casting the negative electrode material mixture on a separate carrier and then laminating the film separated from the carrier onto the negative electrode current collector.

[0149] In lithium-ion secondary batteries, the separator separates the negative and positive electrodes and provides a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is commonly used in lithium-ion secondary batteries. Specifically, separators with high electrolyte retention capacity and low resistance to electrolyte ion transfer can be used. In particular, porous polymer films can be used, such as porous polymer films 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. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Additionally, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can optionally be used.

[0150] Furthermore, the electrolyte used in this invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used to prepare lithium secondary batteries, but this invention is not limited thereto.

[0151] Specifically, electrolytes can contain organic solvents and lithium salts.

[0152] Any organic solvent can be used without particular limitation, as long as it serves as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, the following organic solvents can be used: 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; or carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitriles, such as R-CN (where R is a linear, branched, or cyclic C2 to C20 hydrocarbon group and may contain double bonds, aromatic rings, or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents are preferred, and even more preferred are mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, which can improve the charge / discharge performance of the battery, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate). In this case, when cyclic carbonates and linear carbonates are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte can be excellent.

[0153] Lithium salts can be used without particular restrictions, as long as they are compounds capable of providing lithium ions for use in lithium secondary batteries. Specifically, the following lithium salts can be used: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. Lithium salts can be used in concentrations ranging from 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, excellent electrolyte performance can be obtained because the electrolyte can have suitable conductivity and viscosity, and lithium ions can move efficiently.

[0154] To improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, in addition to the electrolyte component, the electrolyte may also contain at least one additive, such as alkylene carbonate halide compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (condensed) glycol dimethyl ethers, hexamethylphosphoric triamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted sulfadiazine ketones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, based on 100 parts by weight of electrolyte, the additive content can be from 0.1 parts by weight to 5 parts by weight.

[0155] As described above, lithium secondary batteries containing the cathode material according to the present invention stably exhibit excellent discharge capacity, output characteristics and lifespan characteristics, making them suitable for portable devices such as mobile phones, laptops and digital cameras; and electric vehicles such as hybrid electric vehicles (HEVs).

[0156] Therefore, according to another embodiment of the present invention, a battery module comprising the lithium secondary battery as a unit battery and a battery pack comprising the battery module are provided.

[0157] Battery modules or battery packs can be used as a power source for at least one medium to large-sized device, including: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0158] There are no particular limitations on the shape of the lithium secondary battery of the present invention, but cylindrical, prismatic, bag-shaped or coin-shaped batteries made from cans can be used.

[0159] The lithium secondary battery according to the present invention can be used not only in battery cells used as power sources for small devices, but also as unit batteries in medium and large battery modules comprising multiple battery cells.

[0160] Preferred implementation scheme

[0161] The invention will now be described in detail with reference to specific examples. However, the invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these exemplary embodiments are provided so that this specification will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0162] Preparation Example

[0163] Preparation Example 1 – Preparation of Second Positive Electrode Active Material

[0164] NiSO4, CoSO4, and MnSO4 were dissolved in water to make a nickel:cobalt:manganese molar ratio of 88:5:7 to prepare a 2 M solution containing transition metals.

[0165] A container containing a solution of transition metals, a container containing an additional 25% by weight of NaOH solution, and a container containing 15% by weight of NH4OH aqueous solution were respectively connected to a 200 L batch reactor set at 55°C.

[0166] Subsequently, deionized water was introduced into a batch reactor, and dissolved oxygen in the water was removed by purging with nitrogen to establish a non-oxidizing atmosphere in the reactor. Afterward, NaOH was added, and the pH in the reactor was maintained at 11.7 while the mixture was stirred at 250 rpm.

[0167] Subsequently, a solution containing transition metals was added to the reactor at a rate of 250 mL / hr, followed by an aqueous solution of NH4OH at a rate of 40 mL / hr, and then an aqueous solution of NaOH at a rate that maintained the pH of the reaction solution at 11.7. After reacting for 6 hours, stirring was stopped and the supernatant was removed to concentrate the reaction solution. This process was repeated 4 to 5 times to allow particle growth until the average particle size (D) reached the target value. 50 It reaches approximately 10 μm.

[0168] The particles prepared therefrom were filtered using a filter press and then dried at 130°C for 24 hours to obtain a Ni composition. 0.885 Co 0.035 Mn 0.080 (OH)2 is used as a precursor for the second positive electrode active material.

[0169] Subsequently, LiOH·H2O was added to make the equivalent ratio of LiOH·H2O to the precursor of the second positive electrode active material 1.06. Al(OH)3 was added, and the nickel:cobalt:manganese:aluminum molar ratio of 86:5:7:2 and the average particle size (D) were prepared by sintering at 640℃ for 5 hours in an oxygen atmosphere and then at 775℃ for another 5 hours. 50 The second positive electrode active material is in the form of secondary particles of approximately 10 μm.

[0170] Preparation Example 2 – Preparation of the First Positive Electrode Active Material

[0171] The positive electrode active material precursor [composition: Ni] 0.885 Co 0.035 Mn 0.08 (OH)2, average particle size (D) 50 A pre-sintered product was prepared by mixing anhydrous LiOH (4 μm) with lithium raw material at a molar ratio of 1:1 and sintering it once at 850°C for 6 hours in an oxygen atmosphere. The pre-sintered product was then ground and mixed with anhydrous LiOH at a molar ratio of 1:0.03, followed by a second sintering at 800°C for 10 hours in an oxygen atmosphere to obtain a product with an average particle size (D). 50 The first positive electrode active material is in the form of a single particle with a size of 4 μm.

[0172] Comparative Preparation Example 1 – Preparation of Small-Density Secondary Particle Positive Electrode Active Materials

[0173] The precursor for the secondary particle positive electrode active material was prepared in the same manner as in Preparation Example 1, except that in Preparation Example 1, the concentration process was repeated 2 to 3 times to allow particle growth until the average particle size (D) was reached. 50 The diameter is approximately 4 μm.

[0174] Subsequently, the average particle size (D) was prepared in the same manner as in Preparation Example 1. 50 The difference is that it uses a small-particle secondary particle positive electrode active material with a particle size of 4 μm.

[0175] Comparative Preparation Example 2 – Preparation of Small-Particle Single-Particle Positive Electrode Active Materials

[0176] The positive electrode active material precursor [composition: Ni] 0.885 Co 0.035 Mn 0.08 (OH)2, average particle size (D) 50 The average particle size (D) was prepared by mixing anhydrous LiOH (as a lithium raw material) with a particle size of 4 μm at a molar ratio of 1:1.03 and sintering at 850 °C for 16 hours in an oxygen atmosphere. 50It is a small-particle single-particle positive electrode active material with a particle size of 4 μm.

[0177] Examples and Comparative Examples

[0178] Example 1

[0179] The cathode material was prepared by mixing the first cathode active material prepared in Preparation Example 2 with the second cathode active material prepared in Preparation Example 1 at a weight ratio of 1:4.

[0180] Example 2

[0181] The cathode material was prepared by mixing the first cathode active material prepared in Preparation Example 2 with the second cathode active material prepared in Preparation Example 1 at a weight ratio of 1:1.

[0182] Comparative Example 1

[0183] The cathode material was prepared by mixing the small-particle secondary particle cathode active material prepared in Comparative Preparation Example 1 with the second cathode active material prepared in Preparation Example 1 at a weight ratio of 1:4.

[0184] Comparative Example 2

[0185] The cathode material was prepared by mixing the small-particle secondary particle cathode active material prepared in Comparative Preparation Example 1 with the second cathode active material prepared in Preparation Example 1 at a weight ratio of 1:1.

[0186] Comparative Example 3

[0187] The cathode material was prepared by mixing the small-particle single-particle cathode active material prepared in Comparative Preparation Example 2 with the second cathode active material prepared in Preparation Example 1 at a weight ratio of 1:4.

[0188] Experimental Example 1

[0189] For each positive electrode active material prepared in Preparation Example 2, Preparation Example 1, Comparative Preparation Example 1, and Comparative Preparation Example 2, SEM images were obtained using a scanning electron microscope (SEM) (FEI Corporation, Quanta) and are shown below. Figures 1 to 4 middle.

[0190] Figure 1 The image shows a SEM image of the first positive electrode active material prepared in Example 2.

[0191] Figure 2 The image shows a SEM image of the second positive electrode active material prepared in Example 1.

[0192] Figure 3 To compare the SEM images of the small-particle secondary particle positive electrode active material prepared in Preparation Example 1.

[0193] Figure 4 To compare the SEM images of the small-particle single-particle positive electrode active material prepared in Preparation Example 2.

[0194] according to Figure 1 It has been confirmed that the first positive electrode active material is in single-particle form.

[0195] Specifically, it was confirmed that the first positive electrode active material is in the form of a secondary particle containing 1 to 10, more specifically 1 to 5, primary particles aggregated therein.

[0196] according to Figure 2 It has been confirmed that the second positive electrode active material is in the form of secondary particles in which more than 50 primary particles are aggregated.

[0197] Experiment Example 2

[0198] The particle size distribution of each cathode material prepared in the examples and comparative examples before and after pressurization was measured using a particle size analyzer (PSA) (MICROTRAC S3500 of MICROTRAC MRB).

[0199] Specifically, the particle size distribution before pressurization was measured by uniformly mixing 50 mg of the cathode material prepared in each example and comparative example with 40 ml of distilled water and 500 μL of dispersant and injecting the mixture into a PSA.

[0200] Three g of the cathode material prepared in each example and comparative example was placed into a circular mold with a diameter of 1.3 cm and pressed using a 9-ton press at 6,500 kgf / cm². 2 After pressurizing the positive electrode material placed in the mold, the pressurized positive electrode material is crushed with a mortar and pestle, and then the particle size distribution after pressurization is measured by using a PSA (MICROTRAC S3500 of MICROTRAC MRB) as follows: 50 mg of each crushed positive electrode material is uniformly mixed with 40 ml of distilled water and 500 μL of dispersant, and the mixture is injected into the PSA.

[0201] The cathode materials prepared in the examples and comparative examples were subjected to a pressure of 6,500 kgf / cm². 2 The particle size distribution curves measured by PSA before and after pressure are shown below. Figures 5 to 9 In addition, using the particle size distribution curve measured by PSA, the volume of particles with a diameter of less than 1 μm after pressurization was measured relative to the total volume of particles present in the cathode material (fine powder generation rate (%)) and is shown in Table 1 below.

[0202] Figure 5 To apply a 6,500 kgf / cm² pressure to the cathode material prepared in Example 12 Particle size distribution curves measured by PSA before and after pressure.

[0203] Figure 6 To apply a 6,500 kgf / cm² pressure to the cathode material prepared in Example 2 2 Particle size distribution curves measured by PSA before and after pressure.

[0204] Figure 7 To apply a 6,500 kgf / cm² pressure to the cathode material prepared in Comparative Example 1 2 Particle size distribution curves measured by PSA before and after pressure.

[0205] Figure 8 To apply a 6,500 kgf / cm² pressure to the cathode material prepared in Comparative Example 2 2 Particle size distribution curves measured by PSA before and after pressure.

[0206] Figure 9 To apply a 6,500 kgf / cm² pressure to the cathode material prepared in Comparative Example 3 2 Particle size distribution curves measured by PSA before and after pressure.

[0207] according to Figure 5 and 7 The cathode materials of Example 1 and Comparative Example 1 contain two cathode active materials with the same mixing ratio, and each of the two cathode active materials has the same particle size. However, it was confirmed that the particle size change of Example 1 after pressurization was significantly smaller compared with Comparative Example 1.

[0208] according to Figure 6 and 8 The cathode materials of Example 2 and Comparative Example 2 also contained two cathode active materials with the same mixing ratio, and each of the two cathode active materials had the same particle size. However, it was confirmed that the particle size change of Example 2 after pressurization was significantly smaller compared with Comparative Example 2.

[0209] according to Figure 5 and 9 Although the cathode materials of Example 1 and Comparative Example 3 differ only in the preparation method of the first cathode active material (specifically sintering), it was confirmed that the particle size change of Example 1 after pressurization was significantly smaller compared to Comparative Example 3.

[0210]

[0211] Table 1 confirms the fine powder production rate of the cathode materials prepared in Examples 1 and 2 (i.e., when 6,500 kgf / cm² is applied to the cathode material). 2Under pressure, the volume of particles with a diameter of less than 1 μm (relative to the total volume of particles present in the cathode material) is less than 10%.

[0212] In contrast, it was confirmed that the fine powder production rate of the cathode materials prepared in Comparative Examples 1 to 3 was greater than 10%.

[0213] Experimental Example 3

[0214] A cross-sectional sample was prepared by argon (Ar) ion milling for 2 hours on the first positive electrode active material prepared in Preparation Example 2 using an ion milling system (JBOL, IB19520CCP) (accelerating voltage: 6 kV).

[0215] Cross-sectional samples of the first positive electrode active material were measured and analyzed using field emission scanning electron microscopy (SEM, JEOL JSM-7900F w / Oxford symmetric EBSD detector) (accelerating voltage: 20 kV). Electron backscatter diffraction (EBSD) inverse pole figure (IPF) was created using AztecCrystal from OXFORD Instruments as the image processing EBSD quantitative analysis software.

[0216] Figure 10 The image shows the EBSD-IPF diagram of the first positive electrode active material prepared in Example 2.

[0217] according to Figure 10 It was confirmed that the first positive electrode active material in Preparation Example 2 has single crystallinity. Specifically, it was confirmed that the first positive electrode active material is composed of a primary particle containing 1 to 10, more specifically 1 to 5, single crystal particles, or is in the form of aggregates of the aforementioned primary particles.

[0218] Experiment Example 4

[0219] – Preparation of coin-type half-cells

[0220] A positive electrode slurry was prepared by mixing 97.5 wt% of the positive electrode materials prepared in Example 1 and Comparative Example 1, 1.0 wt% of carbon black as a conductive material, and 1.5 wt% of polyvinylidene fluoride (PVDF) as a binder (specifically 1.4 wt% of KF9709 and 0.1 wt% of BM740H) in an N-methylpyrrolidone (NMP) solvent. The positive electrode slurry was coated onto one surface of an aluminum current collector, dried at 130°C, and then calendered to a porosity of 24%.

[0221] A lithium metal electrode was used as the negative electrode, and an electrode assembly was prepared by placing a porous polyethylene membrane between the positive and negative electrodes. The electrode assembly was placed in a battery case, and an electrolyte solution of 1.0 M LiPF6 dissolved in an organic solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) in a volume ratio of 3:3:4 was injected to prepare a coin-type half-cell.

[0222] – Battery performance evaluation

[0223] A coin-type half-cell was charged at 25°C in constant current-constant voltage (CC-CV) mode (0.1 C, cutoff current: 0.05 C) to 4.25 V, and then discharged in CC mode (0.1 C) to 3.0 V to measure the charging and discharging capacities (mAh / g) under these conditions. The percentage of discharge capacity relative to charge capacity (efficiency (%)) was calculated, and the measured charging and discharging capacities (mAh / g) and their results are shown in Table 2 below.

[0224]

[0225] Table 2 confirms that the secondary battery using the cathode material according to the present invention has excellent discharge capacity and efficiency at room temperature.

[0226] Experimental Example 5

[0227] - Fabrication of pouch-type single-cell batteries

[0228] A positive electrode slurry was prepared by mixing 97.5 wt% of the positive electrode materials prepared in Example 1 and Comparative Example 1, 1.0 wt% of carbon black as a conductive material, and 1.5 wt% of polyvinylidene fluoride (PVDF) as a binder (specifically 1.4 wt% of KF9709 and 0.1 wt% of BM740H) in an N-methylpyrrolidone (NMP) solvent. The positive electrode slurry was coated onto one surface of an aluminum current collector, dried at 130°C, and then calendered to a porosity of 24%.

[0229] A negative electrode slurry was prepared by mixing natural graphite and artificial graphite (in a 5:5 weight ratio), Super C conductive material, additives (Daicel Corporation, DAICEL2200), and binder (ZEON CORPORATION, BML302) in water at a weight ratio of 95.6:1.0:2.3:1.1. The negative electrode slurry was then coated onto one surface of a copper current collector, dried at 130°C, and subsequently calendered to prepare the negative electrode.

[0230] An electrode assembly was prepared by placing a porous polyethylene membrane between the positive and negative electrodes. The electrode assembly was placed in a battery case, and an electrolyte solution of 1.0 M LiPF6 dissolved in an organic solvent containing ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) in a volume ratio of 3:3:4 was injected to prepare a pouch cell.

[0231] – Battery Characteristic Evaluation 1

[0232] Using the pouch cell prepared as described above, a cycle was defined as charging the pouch cell in CC-CV mode (0.33C) to 4.25 V and discharging it in CC mode (0.33C) to 3.0 V at 45°C. This cycle was repeated for a total of 400 charge-discharge cycles. After measuring the discharge capacity at the first, 100th, and 400th cycles, the percentage of the discharge capacity in the 100th cycle relative to the discharge capacity in the first cycle (capacity retention) was calculated. 100 (%) and the percentage of discharge capacity in the 400th cycle relative to the discharge capacity in the 1st cycle (capacity retention). 400 (%) is shown in Table 3 below and Figure 11 middle.

[0233] Figure 11 Data related to the evaluation of battery characteristics (capacity retention) of lithium secondary batteries containing the cathode materials prepared in Example 1 and Comparative Example 1, respectively.

[0234]

[0235] Table 3 confirms that the secondary battery using the cathode material according to the present invention has excellent lifespan characteristics.

[0236] – Battery Characteristic Evaluation 2

[0237] The pouch cell prepared as described above was charged to 4.25 V at 25°C using CC-CV mode (0.33 C), and then the positive electrode was separated. The separated positive electrode was placed in a battery pouch, electrolyte was injected, and the pouch was then sealed to prepare the sample. The volume change was measured while the sample was stored at 60°C for 12 weeks, and the percentage of sample volume at 12 weeks relative to the sample volume at 0 weeks (volume change rate (%)) is shown in Table 4 below. Figure 12 middle.

[0238] Figure 12 Data related to the evaluation of battery characteristics (volume change rate) of lithium secondary batteries containing the cathode materials prepared in Example 1 and Comparative Example 1, respectively.

[0239]

[0240] Table 4 confirms that secondary batteries using the cathode material according to the present invention have excellent effects in reducing gas generation.

Claims

1. A positive electrode material, said positive electrode material comprising: A first positive electrode active material, wherein the first positive electrode active material is in single-particle form; and The second positive electrode active material is in the form of secondary particles and has an average particle size (D). 50 The average particle size (D) of the first positive electrode active material is higher than that of the first positive electrode active material. 50 Larger in, When the cathode material is subjected to an application of 6,500 kgf / cm 2 Under pressure, the volume of particles with a diameter of less than 1 μm is less than 10% of the total volume of particles present in the cathode material.

2. The cathode material according to claim 1, wherein the cathode material has a bimodal particle size distribution.

3. The cathode material according to claim 1, wherein the average particle size (D) of the second cathode active material is used as the reference. 50 The average particle size (D) of the first positive electrode active material 50 The percentage is below 50%.

4. The cathode material according to claim 1, wherein the single-particle form has single crystallinity.

5. The positive electrode material according to claim 1, wherein the weight ratio of the first positive electrode active material to the second positive electrode active material is in the range of 1:0.1 to 1:

10.

6. The cathode material according to claim 1, wherein the average particle size (D) of the first cathode active material is... 50 The range is from 1 μm to 10 μm.

7. The positive electrode material according to claim 1, wherein the average particle size (D) of the second positive electrode active material is... 50 The thickness ranges from 6 μm to 25 μm.

8. The positive electrode material according to claim 1, wherein the composition of the first positive electrode active material is represented by chemical formula 1: [Chemical Formula 1] Li 1+a1 Ni x1 Co y1 M 1 z1 M 2 w1 O2 in, In chemical formula 1, M 1 It is selected from at least one of Mn and Al. M 2 It is selected from at least one of B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf, and -0.1≤a1≤0.3,0.6≤x1<1.0,0 <y1<0.4,0<z1<0.4,0≤w1≤0.1。 9. The positive electrode material according to claim 1, wherein the composition of the second positive electrode active material is represented by chemical formula 2: [Chemical Formula 2] Li 1+a2 Ni x2 Co y2 M 3 z2 M 4 w2 O2 in, In chemical formula 2, M 3 It is selected from at least one of Mn and Al. M 4 It is selected from at least one of B, Ba, Ce, Cr, F, Mg, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, S, Sr, Ta, La, and Hf, and -0.1≤a²≤0.3, 0.6≤x²<1.0, 0 <y2<0.4,0<z2<0.4,0≤w2≤0.1。 10. A positive electrode comprising a positive electrode active material layer, the positive electrode active material layer comprising the positive electrode material according to any one of claims 1 to 9.

11. A lithium secondary battery, the lithium secondary battery comprising the positive electrode as described in claim 10.

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