Cathode material, cathode containing the same, and lithium secondary battery

Abstract

The present invention relates to a first positive electrode active material in the form of single particles, and a secondary particle in the form of a material with an average particle size (D) greater than that of the first positive electrode active material. 50 The positive electrode material contains a large second positive electrode active material and a positive electrode material with a load of 6,500 kgf / cm². 2 The present invention relates to a positive electrode material in which, when a certain pressure is applied, the volume of particles with a particle size of 1 μm or less relative to the total volume of particles present in the positive electrode material is 10% or less, and to a positive electrode for a lithium secondary battery and a lithium secondary battery containing the same.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2023-0047003 dated April 10, 2023, and all content disclosed in the said Korean Patent Application is incorporated herein by reference. This invention relates to a positive electrode material for lithium secondary batteries, a positive electrode containing the same, and a lithium secondary battery. [Background technology]

[0002] As technological development and demand for mobile devices increase, the demand for rechargeable batteries as an energy source is rapidly growing. Among these rechargeable batteries, lithium-ion batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0003] Lithium-complex transition metal oxides are used as the positive electrode active material in lithium-ion secondary batteries, and among them, lithium-cobalt-complex metal oxides such as LiCoO2, which have a high operating voltage and excellent capacity characteristics, are mainly used. However, LiCoO2 has poor thermal properties due to the destabilization of its crystal structure by delithiation. In addition, LiCoO2 is expensive, which limits its use in large quantities as a power source in fields such as electric vehicles.

[0004] As alternatives to LiCoO2, materials such as lithium manganese composite metal oxides (LiMnO2 or LiMn2O4, etc.), lithium iron phosphate compounds (LiFePO4, etc.), and lithium nickel composite metal oxides (LiNiO2, etc.) have been developed. Among these, research and development on lithium nickel composite metal oxides, which have a high reversible capacity of approximately 200 mAh / g and facilitate the realization of high-capacity batteries, has been particularly active. However, compared to LiCoO2, LiNiO2 has inferior thermal stability, and if an internal short circuit occurs due to external pressure while charged, the positive electrode active material itself decomposes, causing the battery to rupture and ignite. Therefore, as a method to maintain the excellent reversible capacity of LiNiO2 and improve its low thermal stability, lithium transition metal oxides in which some of the Ni is substituted with Co, Mn, or Al have been developed.

[0005] In lithium-ion batteries, where lithium-complex transition metal oxides, particularly those containing high levels of nickel (Ni-rich), are used as positive electrode active materials, the battery capacity, the presence or absence of high power output, and the presence or absence of gas generation at high temperatures are influenced 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 the surface, but also by physical properties such as the size, surface area, density, and shape of the positive electrode active material particles.

[0006] Generally, to maximize the volumetric energy density of a battery, a method is used in which large-particle positive electrode active material and small-particle positive electrode active material are mixed. The small-particle positive electrode active material fills the gaps between the large-particle positive electrode active material particles, thereby improving the volumetric energy density of the battery. To produce a more dense positive electrode active material layer, a method of rolling the positive electrode active material layer using a roll press is employed. However, in this case, due to the difference in particle strength between the large-particle and small-particle positive electrode active materials, excessive cracking occurs in the particles with relatively weaker particle strength during rolling. This not only causes the particles to lose their original shape but also increases the contact area with the electrolyte excessively, resulting in a problem of reduced battery life when applied to a battery. Therefore, there is a need to develop cathode materials that can improve volumetric energy density and suppress particle cracking during rolling for cathode manufacturing, thereby improving lifetime characteristics. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Korean Published Patent Publication No. 2021-0117212 [Overview of the project] [Problems that the invention aims to solve]

[0008] The object of the present invention is to provide a cathode material that has improved volumetric energy density and reduced particle cracking during rolling for cathode manufacturing. Another object of the present invention is to provide a positive electrode that includes the positive electrode material, in which cracking of the included positive electrode active material particles is mitigated, and which exhibits excellent electrochemical performance. Another object of the present invention is to provide a lithium secondary battery including the positive electrode. [Means for solving the problem]

[0009] To solve the above problems, the present invention provides a positive electrode material, a positive electrode for a lithium secondary battery including the positive electrode material, and a lithium secondary battery. (1) The present invention relates to a first positive electrode active material in the form of single particles, and a secondary particle in the form of a first positive electrode active material with an average particle size (D) greater than that of the first positive electrode active material. 50 The positive electrode material contains a large second positive electrode active material and a positive electrode material with a load of 6,500 kgf / cm². 2 The present invention provides a positive electrode material in which, when a certain pressure is applied, the volume of particles with a particle size of 1 μm or less is 10% or less of the total volume of particles present in the positive electrode material.

[0010] (2) The present invention provides the cathode material described in (1) above, having a bimodal particle size distribution.

[0011] (3) In the present invention, the average particle size (D) of the first positive electrode active material 50 ) is the average particle size (D) of the second positive electrode active material. 50 The present invention provides a positive electrode material according to (1) or (2) above, which is 50% or less of the standard.

[0012] (4) The present invention provides a cathode material according to any one of the above (1) to (3), wherein the single particulate material is single crystalline.

[0013] (5) The present invention provides a positive electrode material according to any one of the above (1) to (4), wherein the weight ratio of the first positive electrode active material to the second positive electrode active material is 1:0.1 to 10.

[0014] (6) The present invention relates to the average particle size (D) of the first positive electrode active material. 50 The present invention provides a positive electrode material according to any one of the above (1) to (5), wherein the thickness of the ) is 1 μm or more and 10 μm or less.

[0015] (7) The present invention relates to the average particle size (D) of the second positive electrode active material. 50 The present invention provides a positive electrode material according to any one of the above items (1) to (6), wherein the thickness of the ) is 6 μm or more and 25 μm or less.

[0016] (8) In the present invention, the first positive electrode active material provides the positive electrode material according to any one of (1) to (7) above, which has a composition represented by the following Chemical Formula 1.

[0017] [Chemical Formula 1] Li 1+a1 Ni x1 Co y1 M 1 z1 M 2 w1 O2

[0018] In Chemical Formula 1 above, M 1 is one or more selected from the group consisting of Mn and Al, and M 2 is one or more selected from the group consisting 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.

[0019] (9) In the present invention, the second positive electrode active material provides the positive electrode material according to any one of (1) to (8) above, which has a composition represented by the following Chemical Formula 2.

[0020] [Chemical Formula 2] Li 1+a2 Ni x2 Co y2 M 3 z2 M 4 w2 O2

[0021] In Chemical Formula 2 above, M 3 is one or more selected from the group consisting of Mn and Al, and M 4 is one or more selected from the group consisting 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.

[0022] (10) The present invention provides a positive electrode comprising a positive electrode active material layer containing the positive electrode material described in any one of the above (1) to (9).

[0023] (11) The present invention provides a lithium secondary battery including the positive electrode described in (10) above. [Effects of the Invention]

[0024] The positive electrode material according to the present invention comprises a first positive electrode active material in the form of single particles, and a secondary particle in the form of a second particle with an average particle size (D) greater than that of the first positive electrode active material. 50 The positive electrode material contains a large second positive electrode active material and a positive electrode material with a load of 6,500 kgf / cm². 2 When pressure is applied, the volume of particles with a particle size of 1 μm or less relative to the total volume of particles present in the positive electrode material is 10% or less, which has the effect of reducing particle cracking of the positive electrode material during rolling for manufacturing the positive electrode. As a result, when using the positive electrode material according to the present invention, the occurrence of side reactions with the electrolyte caused by particle cracking of the positive electrode material can be minimized, and excellent capacity characteristics and life characteristics can be achieved. [Brief explanation of the drawing]

[0025] [Figure 1] This is an SEM image of the first cathode active material produced in manufacturing example 2. [Figure 2] This is an SEM image of the second cathode active material produced in Production Example 1. [Figure 3] This is an SEM image of the small-particle size secondary particulate cathode active material produced in Comparative Manufacturing Example 1. [Figure 4] This is an SEM image of the small-particle, single-particle positive electrode active material produced in Comparative Manufacturing Example 2. [Figure 5] This is a particle size distribution curve measured by PSA before and after applying a pressure of 6,500 kgf / cm2 to the cathode material manufactured in Example 1. [Figure 6] This is a particle size distribution curve measured by PSA before and after applying a pressure of 6,500 kgf / cm2 to the cathode material manufactured in Example 2. [Figure 7] This is the particle size distribution curve measured by PSA before and after applying a pressure of 6,500 kgf / cm2 to the cathode material manufactured in Comparative Example 1. [Figure 8] This is the particle size distribution curve measured by PSA before and after applying a pressure of 6,500 kgf / cm2 to the cathode material manufactured in Comparative Example 2. [Figure 9] This is the particle size distribution curve measured by PSA before and after applying a pressure of 6,500 kgf / cm2 to the cathode material manufactured in Comparative Example 3. [Figure 10] This is an EBSD-IPF map for the first cathode active material produced in Production Example 2. [Figure 11] This data concerns the battery characteristics (capacity retention rate) of lithium secondary batteries containing the cathode materials manufactured in Example 1 and Comparative Example 1. [Figure 12] This data concerns the evaluation of battery characteristics (volume change rate) of lithium secondary batteries containing the cathode materials manufactured in Example 1 and Comparative Example 1. [Modes for carrying out the invention]

[0026] The present invention will be described in more detail below. The terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0027] In this specification, terms such as “include,” “provide,” or “have” indicate the presence of implemented features, figures, steps, components, or combinations thereof, and should be understood not to preemptively exclude the possibility of the presence or addition of one or more other features, figures, steps, components, or combinations thereof.

[0028] In this invention, the term "primary particle" refers to the smallest particle unit recognized 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.

[0029] In this invention, the term "secondary particulate matter" refers to a spherical shape formed by the aggregation of tens to hundreds of primary particles manufactured by conventional methods, and specifically means a form consisting of more than 50 primary particles. More precisely, the secondary particulate matter in this invention is a form formed by the aggregation of more than 50 primary particles, and may also be a form formed by the aggregation of hundreds or thousands of particles.

[0030] In this invention, the term "single-particle form" is a concept in contrast to the spherical secondary particle form, which is formed by the aggregation of tens to hundreds of primary particles manufactured by conventional methods. Instead, it refers to a form consisting of 50 or fewer primary particles. Specifically, the single-particle form in this invention may be a single particle consisting of one primary particle, or it may be a secondary particle form formed by the aggregation of 2 or more, or 5 or fewer, 10 or fewer, 15 or fewer, 20 or fewer, 25 or fewer, 30 or fewer, 35 or fewer, 40 or fewer, 45 or fewer, or 50 or fewer primary particles.

[0031] In this invention, the term "single crystal" can be replaced with the term "single-crystallized," and refers to a positive electrode active material or lithium composite transition metal oxide containing 1 to 50 crystal grains. Typically, a single-crystal particle refers to a particle in which the entire sample consists of a single crystal grain or crystal grain region. In this invention, a single-crystal positive electrode active material or single-crystal positive electrode active material consists of 1 to 50 single-crystal particles. Specifically, in this invention, it may be a single crystal particle consisting of one crystal grain, or it may be an aggregate of 2 or more, and 5 or fewer, 10 or fewer, 15 or fewer, 20 or fewer, 25 or fewer, 30 or fewer, 35 or fewer, 40 or fewer, 45 or fewer, or 50 or fewer single-crystal particles, and may exhibit properties similar to a single single-crystal particle by containing a small number of single-crystal particles. The term "crystal grain" or "crystal grain region" refers to a region in which atoms in the sample are arranged continuously and periodically in one direction. The aforementioned crystal grains can be analyzed using an electron backscatter diffraction (ESBD) analyzer.

[0032] In this invention, the term "average particle size (D 50 "Average particle size" refers to the particle size at the 50% point of the volume cumulative distribution corresponding to the particle size. The average particle size is calculated by dispersing the powder to be measured in a dispersion medium, introducing it into a commercially available laser diffraction particle size analyzer (for example, Microtrac's S3500), measuring the difference in diffraction patterns according to the particle size as the particles pass through the laser beam, calculating the particle size distribution, and then calculating the diameter of the particles at the point where the volume cumulative distribution corresponding to the particle size in the measuring device reaches 50%. 50 It can be measured.

[0033] In this invention, the term "fine powder" refers to particles with a particle size of 1 μm or less, obtained by dispersing the pressurized powder to be measured in a dispersion medium, introducing it into a commercially available laser diffraction particle size analyzer (for example, Microtrac's S3500), and calculating the particle size distribution by measuring the difference in diffraction patterns according to the particle size as the particles pass through the laser beam.

[0034] Cathode material The cathode material according to the present invention will be described below. The positive electrode material of the present invention comprises a first positive electrode active material in the form of single particles, and a secondary particle in the form of a second particle with an average particle size (D) greater than that of the first positive electrode active material. 50 The positive electrode material contains a large second positive electrode active material and a positive electrode material with a load of 6,500 kgf / cm². 2 When the pressure is applied, the volume of particles with a particle size of 1 μm or less relative to the total volume of particles present in the positive electrode material is 10% or less.

[0035] High-Ni (Ni) cathode active materials in secondary particulate form have the advantage of excellent energy density, but as the charge-discharge process is repeated, structural distortion and the generation of fine particles due to internal cracks inevitably lead to instability in the crystal structure. The higher the degree of single-particle formation of the cathode active material, the less particle cracking or disintegration occurs during rolling, and the lower the rate of fine particle generation during rolling, but this has the disadvantage of lower energy density.

[0036] Therefore, the present inventors have developed a first positive electrode active material in the form of single particles, and a secondary particle in the form of a first positive electrode active material with an average particle size (D) greater than that of the first positive electrode active material. 50 The positive electrode material contains a large second positive electrode active material and a positive electrode material with a load of 6,500 kgf / cm². 2 We have discovered that when a certain pressure is applied, if the volume of particles with a particle size of 1 μm or less relative to the total volume of particles present in the positive electrode material is 10% or less, particle collapse during rolling can be suppressed, the generation of fine powder can be reduced, the rollability of the electrode can be improved, and the energy density characteristics can be enhanced, thus completing the present invention.

[0037] The positive electrode material according to the present invention includes a single-particulate first positive electrode active material. That is, the first positive electrode active material is a single particle, or a single-particulate material formed by the aggregation of 2 to 50 primary particles. Specifically, it may be a single particle consisting of one primary particle, or it may be a secondary-particulate material formed by the aggregation of 2 to 5 primary particles, or 10 or fewer primary particles. The single-particulate material is distinguished from secondary particles formed by the aggregation of more than 50 primary particles. When the first positive electrode active material is in a single-particulate form, it has excellent stability, so even if the positive electrode material containing it is rolled, cracks and fissures do not occur in the positive electrode material, and side reactions between the positive electrode material and the electrolyte can be reduced. As a result, durability against volume changes during battery charging and discharging can be improved, and the lifespan characteristics can be improved. When the first positive electrode active material is in a secondary-particulate form, cracks and fissures occur in the positive electrode material containing it, and there is a problem that the lifespan characteristics are inferior due to side reactions between the positive electrode material and the electrolyte.

[0038] According to one embodiment of the present invention, the single-particulate form may be single-crystalline. Specifically, the single-particulate form may be a single particle consisting of one primary particle. In this case, the single-particulate form may be a primary particle consisting of one single-crystal particle, or it may be a primary particle consisting of two or more, and five or fewer, or ten or fewer single-crystal particles. Alternatively, the single-particulate form may be a secondary particle form in which two or more, and five or fewer, or ten or fewer primary particles are aggregated. In this case, the single-particulate form may be a form in which primary particles consisting of one single-crystal particle are aggregated, or it may be a form in which primary particles consisting of two or more, and five or fewer, or ten or fewer single-crystal particles are aggregated. When the single-particulate form is single-crystalline, the number of crystal grain interfaces is reduced, and side reactions between the positive electrode material and the electrolyte can be reduced.

[0039] The positive electrode material according to the present invention includes a second positive electrode active material in the form of secondary particulate matter. That is, the second positive electrode active material is in the form of secondary particulate matter formed by the aggregation of more than 50 primary particles. This secondary particulate matter is distinguished from a single particle or a single-particle form formed by the aggregation of 2 to 50 primary particles. When the second positive electrode active material is in the form of secondary particulate matter, the voids in the positive electrode material are reduced, and the energy density can be improved. This can improve the capacity characteristics of the battery. When the second positive electrode active material is in the form of single particulate matter, the energy density of the positive electrode material containing it decreases, resulting in the problem of inferior capacity characteristics.

[0040] The second positive electrode active material has a lower average particle size (D) than the first positive electrode active material. 50 The size of the particle size (D) is large. The higher the degree of single-particle formation of the cathode material, the less particle cracking or disintegration occurs during rolling, and the lower the rate of fine powder generation during rolling. Therefore, when a cathode is manufactured using this material, it can exhibit excellent electrochemical performance. It is in single-particle form, with an average particle size (D). 50 The first positive electrode active material has a smaller size, and is in the form of secondary particles, with an average particle size (D 50 By including a second positive electrode active material with a larger size, it is possible to maintain energy density and increase the degree of single-particle formation of the positive electrode material. This improves the battery characteristics of the battery containing the positive electrode material.

[0041] The cathode material according to the present invention has a cathode material with a load of 6,500 kgf / cm². 2 When the pressure is applied, the volume of particles with a particle size of 1 μm or less relative to the total volume of particles present in the positive electrode material is 10% or less. Specifically, 6,500 kgf / cm² is applied to the positive electrode material. 2 When the pressure is applied, the volume of particles with a particle size of 1 μm or less relative to the total volume of particles present in the positive electrode material is 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, or 5% or less, and may be 0.01% or more.

[0042] The volume of particles with a particle size of 1 μm or less relative to the total volume of particles present in the positive electrode material, i.e., the fine particle generation rate, is determined by filling 3 g of positive electrode material into a circular mold with a diameter of 1.3 cm and then pressing it with a 9-ton press at 6,500 kgf / cm². 2This value is defined as the fine particle generation rate, obtained by measuring the particle distribution of the positive electrode material after applying pressure and determining the proportion of fine particles with a particle size of 1 μm or less. Since the first and second positive electrode active materials contained in the positive electrode material before pressurization do not contain fine particles with a particle size of 1 μm or less, or only contain trace amounts of such particles, the content of fine particles with a particle size of 1 μm or less contained in the positive electrode material after pressurization can be measured and defined as the fine particle generation rate.

[0043] According to one embodiment of the present invention, the positive electrode material of the present invention may contain both a first positive electrode active material and a second positive electrode active material having different average particle sizes, and may have a bimodal particle size distribution. When there is a bimodal particle size distribution, the energy density can be maintained and the degree of single-particle formation of the positive electrode material can be increased. This makes it possible to improve the battery characteristics of a battery containing the positive electrode material.

[0044] According to one embodiment of the present invention, the first positive electrode active material has a relatively average particle size (D 50 The particles are small, and the second positive electrode active material has a relatively small average particle size (D 50 ) are large particles, specifically the average particle size (D) of the first positive electrode active material. 50 ) is the average particle size (D) of the second positive electrode active material. 50 ) is used as the standard and the average particle size (D) is 50% or less. 50 ) may have, specifically 50% or less, 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%, and more specifically 20% to 40%. The average particle size (D) of the second positive electrode active material. 50 Based on the average particle size (D) of the first positive electrode active material, 50 If the above range is met, particle cracking of the positive electrode material including these can be effectively reduced.

[0045] 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 may be 1:0.1 to 10. Specifically, the weight ratio of the first positive electrode active material to the second positive electrode active material may be 1:1 to 8, or 1:1 to 5, or more specifically, 1:1 to 4. When the first positive electrode active material and the second positive electrode active material are included in the above weight ratio, particle cracking of the positive electrode material containing them can be effectively reduced, the positive electrode material can exhibit excellent electrochemical performance, and the effect of improving rolling density can be obtained.

[0046] According to one embodiment of the present invention, the first positive electrode active material exhibits a particle strength at least twice that of the second positive electrode active material, specifically 2 to 10 times, or 2 to 8 times, or more specifically 2.2 to 6 times. When the first positive electrode active material exhibits a particle strength within the above range relative to the particle strength of the second positive electrode active material, particle cracking of the positive electrode material containing them can be effectively reduced.

[0047] According to one embodiment of the present invention, the cathode material contains both a first cathode active material and a second cathode active material, and the first cathode active material and the second cathode active material satisfy the ratio of particle sizes within the range and the weight ratio, thereby effectively reducing particle cracking of the cathode material containing both, and thereby enabling it to exhibit excellent life characteristics.

[0048] According to one embodiment of the present invention, the average particle size (D) of the first positive electrode active material 50 The average particle size (D) of the first positive electrode active material may be 1 μm or more and 10 μm or less. Specifically, it may be 1 μm or more, 2 μm or more, 3 μm or more, or 4 μm or more, and may be 5 μm or less, 6 μm or less, 7 μm or less, 8 μm or less, 9 μm or less, or 10 μm or less. 50 When the coefficient of variation () is within the aforementioned range, it exhibits excellent stability, so even if the positive electrode material containing it is rolled, cracks or fissures do not occur in the positive electrode material, and side reactions between the positive electrode material and the electrolyte can be reduced. As a result, the durability against volume changes during charging and discharging of the battery can be improved, and the lifespan characteristics can be improved.

[0049] According to one embodiment of the present invention, the average particle size (D) of the preceding second positive electrode active material 50 The average particle size (D) of the second positive electrode active material may be 6 μm or more and 25 μm or less. Specifically, it may be 6 μm or more, 7 μm or more, 8 μm or more, 9 μm or more, or 10 μm or more, and may be 11 μm or less, 12 μm or less, 13 μm or less, 14 μm or less, 15 μm or less, 16 μm or less, 17 μm or less, 18 μm or less, 19 μm or less, 20 μm or less, 21 μm or less, 22 μm or less, 23 μm or less, 24 μm or less, or 25 μm or less. 50 If the value is within the aforementioned range, it has the effect of improving energy density.

[0050] 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 satisfied, particle cracking of the positive electrode material containing these is mitigated, and the first positive electrode active material particles fill the spaces between the second positive electrode active material particles, thereby improving the tap density of the positive electrode material containing it. The higher the tap density, the higher the packing density of the electrode. Therefore, when an electrode is manufactured using it, a slurry containing the positive electrode material having the above tap density can be thinly applied to the surface of the positive electrode current collector, resulting in a thinner electrode thickness after coating. This reduces particle cracking of the single-particle first positive electrode active material during the rolling process, and the pressure required to reach the electrode thickness necessary to match the rolling density is reduced, thus improving cracking of the positive electrode material due to rolling. Furthermore, the gaps between particles are reduced, improving the volumetric energy density, which further improves the capacitance characteristics.

[0051] On the other hand, the particle strength of the positive electrode active material varies depending on the composition and properties of the raw material precursor for the positive electrode active material (such as transition metal hydroxides and transition metal oxyhydroxides) and the firing conditions. Therefore, by appropriately adjusting the firing conditions (temperature and time) according to the composition and / or properties (surface area, density, shape, etc.) of the precursor for the positive electrode active material, a positive electrode active material having the desired particle strength can be produced.

[0052] The first positive electrode active material and the second positive electrode active material may each independently contain a lithium composite transition metal oxide in which the molar ratio of nickel among the transition metals is 60% or more. Because the high-content nickel-containing lithium transition metal oxide has a large capacity per unit volume, when applied to a battery, it can achieve excellent capacity characteristics.

[0053] According to one embodiment of the present invention, the first positive electrode active material may have a composition represented by the following chemical formula 1.

[0054] [Chemical formula 1] Li 1+a1 Ni x1 Co y1 M 1 z1 M 2 w1 O2

[0055] In the aforementioned chemical formula 1, M 1 is one or more selected from the group consisting of Mn and Al, M 2 is one or more elements selected from the group consisting 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. -0.1≦a1≦0.3, 0.6≦x1<1.0, 0 <y1<0.4、0<z1<0.4、0≦w1≦0.1である。

[0056] The above a1 represents the molar ratio of lithium in the lithium composite transition metal oxide, and -0.1 ≦ a1 ≦ 0.3, specifically 0 ≦ a1 ≦ 0.25, and more specifically 0 ≦ a1 ≦ 0.10 may be applicable.

[0057] The above x1 represents the molar ratio of nickel among all the transition metals in the lithium composite transition metal oxide, and 0.6 ≦ x1 < 1.0, specifically 0.6 ≦ x1 ≦ 0.99, or 0.7 ≦ x1 ≦ 0.99, and more specifically 0.8 ≦ x1 ≦ 0.95 may be applicable. When the nickel content satisfies the above range, excellent capacity characteristics can be realized.

[0058] The above y1 represents the molar ratio of cobalt among all the transition metals in the lithium composite transition metal oxide, and 0 < y1 < 0.4, specifically 0 < y1 ≦ 0.35, and more specifically 0.01 ≦ y1 ≦ 0.3 may be applicable.

[0059] The above z1 represents the molar ratio of element M 1 among all the transition metals in the lithium composite transition metal oxide, and 0 < z1 ≦ 0.4, specifically 0 < z1 < 0.35, and more specifically 0.01 ≦ z1 ≦ 0.30 may be applicable.

[0060] The above w1 represents the molar ratio of M 2 among all the transition metals, and 0 ≦ w1 ≦ 0.1, specifically 0 ≦ w1 ≦ 0.08, and more specifically 0 ≦ w1 ≦ 0.05 may be applicable. The above x1, y1, z1, w1 may satisfy x1 + y1 + z1 + w1 = 1.

[0061] According to one embodiment of the present invention, the second positive electrode active material may have a composition represented by the following Chemical Formula 2.

[0062] [Chemical Formula 2] Li 1+a2 Ni x2 Co y2 M 3 z2 M 4 w2 O2

[0063] In the chemical formula 2, M 3 is one or more selected from the group consisting of Mn and Al, M 4 is one or more selected from the group consisting 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, -0.1 ≦ a2 ≦ 0.3, 0.6 ≦ x2 < 1.0, 0 < y2 < 0.4, 0 < z2 < 0.4, 0 ≦ w2 ≦ 0.1.

[0064] The a2 represents the molar ratio of lithium in the lithium composite transition metal oxide, and -0.1 ≦ a2 ≦ 0.3, specifically 0 ≦ a2 ≦ 0.25, and more specifically 0 ≦ a2 ≦ 0.10 may be applicable.

[0065] The x2 represents the molar ratio of nickel among all the transition metals in the lithium composite transition metal oxide, and 0.6 ≦ x2 < 1.0, specifically 0.6 ≦ x2 ≦ 0.99, or 0.7 ≦ x2 ≦ 0.99, and more specifically 0.8 ≦ x2 ≦ 0.95 may be applicable. When the nickel content satisfies the above range, excellent capacity characteristics can be achieved.

[0066] The y2 represents the molar ratio of cobalt among all the transition metals in the lithium composite transition metal oxide, and 0 < y2 < 0.4, specifically 0 < y2 ≦ 0.35, and more specifically 0.01 ≦ y2 ≦ 0.3 may be applicable.

[0067] The z2 represents the molar ratio of the element M 3 among all the transition metals in the lithium composite transition metal oxide, and 0 < z2 ≦ 0.40, specifically 0 < z2 < 0.35, and more specifically 0.01 ≦ z2 ≦ 0.30 may be applicable.

[0068] The w2 represents M among all the transition metals 4This represents the molar ratio, and may be 0 ≤ w2 ≤ 0.1, specifically 0 ≤ w2 ≤ 0.08, or more specifically 0 ≤ w2 ≤ 0.05. The aforementioned x2, y2, z2, and w2 may also be x2 + y2 + z2 + w2 = 1.

[0069] The compositions of the first positive electrode active material and the second positive electrode active material may be the same or different. For example, the first positive electrode active material may be a lithium composite transition metal oxide in which the molar ratio of nickel among the transition metals is 88 mol% or more, and the second positive electrode active material may be a lithium composite transition metal oxide in which the molar ratio of nickel among the transition metals is 86 mol%.

[0070] On the other hand, the first positive electrode active material and the second positive electrode active material may further include a coating layer on the surface of the lithium transition metal oxide, if necessary, which contains one or more elements selected from the group consisting of 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 (hereinafter referred to as "coating elements"). When such a coating layer is included, contact between the lithium transition metal oxide and the electrolyte is blocked, and the generation of gases due to side reactions with the electrolyte and the elution of transition metals can be effectively suppressed.

[0071] The coating layer may be formed by mixing a lithium transition metal oxide and a raw material containing the coating element, followed by heat treatment at a temperature of 200°C to 800°C.

[0072] positive electrode Furthermore, the present invention provides a positive electrode for a lithium secondary battery, comprising a positive electrode active material layer containing the positive electrode material. Specifically, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer containing the positive electrode material located on at least one side of the positive electrode current collector.

[0073] According to one embodiment of the present invention, the positive electrode active material layer may have a porosity of 10 to 30 volumes, specifically 15 to 30 volumes, and more specifically 18 to 27 volumes.

[0074] According to one embodiment of the present invention, if the positive electrode active material layer has the porosity, the positive electrode may contain 50% or less of particles with a particle size of less than 1 μm, based on the total volume of particles in the positive electrode active material layer, when measured using PSD (Particle Size Distribution).

[0075] The positive electrode may contain particles with a particle size of less than 1 μm, based on the total volume of positive electrode active material particles, specifically in amounts of 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%.

[0076] Because particle cracking of the positive electrode material is mitigated, even when the positive electrode active material layer is rolled to have a porosity within the aforementioned range during manufacturing, the positive electrode can contain only a small amount of fine powder with a particle size of less than 1 μm within that range.

[0077] The volume of particles with a particle size of less than 1 μm may be determined by forming a positive electrode active material layer containing the positive electrode material, rolling it to a volume of 10% to 30% by volume, specifically 15% to 30% by volume, or more specifically 18% to 24% by volume, and then heat-treating it in an air atmosphere at 500°C for 2 hours, at which point the volume of particles located in the positive electrode active material layer may be measured.

[0078] The volume of particles with a particle size of less than 1 μm may be the ratio of the volume when the total volume of positive electrode active material particles contained in the positive electrode active material layer is taken as 100%. Specifically, after measuring the PSD using "MICROTRAC S3500" from MICROTRAC, "CILAS920, France" from CILAS, and "Mastersizer2000, USA" from MALVERN, the volume can be determined by dividing the area of ​​particles with a particle size of less than 1 μm by the total area in the PSD graph.

[0079] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesion of the positive electrode material. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0080] The positive electrode active material layer may also include a conductive material and a binder, along with the positive electrode material according to the present invention as described above. The positive electrode material may be included in an amount of 80 to 99% by weight, more specifically 85 to 98% by weight, relative to the total weight of the positive electrode active material layer. When included within this content range, excellent capacitance characteristics can be observed.

[0081] The conductive material is used to impart conductivity to the electrodes and can be used in any battery without particular limitations as long as it has electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these may be used alone or in mixtures of two or more. The conductive material may be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0082] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The binder may be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0083] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except that the positive electrode material according to the present invention is used. Specifically, the positive electrode can be manufactured by coating a composition for forming a positive electrode active material layer, which is prepared by dissolving or dispersing the positive electrode material, a binder, a conductive material, and additives as needed in a solvent, onto a positive electrode current collector, followed by drying and rolling. In this case, the types and contents of the positive electrode material, binder, and conductive material are as described above.

[0084] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of solvent used should be sufficient to dissolve or disperse the cathode material, conductive material, and binder, and to have a viscosity that allows for excellent thickness uniformity when applied for cathode manufacturing, taking into consideration the coating thickness of the slurry and the manufacturing yield.

[0085] Alternatively, the positive electrode can be manufactured by casting the positive electrode active material layer forming composition onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0086] Lithium-ion battery Furthermore, the present invention can be used to manufacture an electrochemical element including the positive electrode. Specifically, the electrochemical element may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0087] The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Since the positive electrode is the same as described above, a detailed explanation will be omitted, and only the remaining components will be described in detail below.

[0088] The lithium secondary battery may further optionally include a battery container for housing the electrode assembly comprising the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0089] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector. The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector may also have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0090] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material. As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. As for the carbon material, either low-crystallinity carbon or high-crystallinity carbon may be used. Examples of low-crystalline carbon include soft carbon and hard carbon, while examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes. The negative electrode active material may be present in an amount of 80 to 99 parts by weight per 100 parts by weight of the total weight of the negative electrode active material layer.

[0091] The binder is a component that assists in bonding between the conductive material, active material, and current collector, and is usually added in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0092] The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 parts by weight or less, preferably 5 parts by weight or less, per 100 parts by weight of the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, and may be used, for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives.

[0093] For example, the negative electrode active material layer can be manufactured by coating a negative electrode composite material, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode composite material onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0094] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Generally, any separator commonly used in lithium secondary batteries can be used without particular limitations, and it is especially preferable that the separator has low resistance to ion movement of the electrolyte and excellent electrolyte impregnation ability. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric substances may be used, and they may be selectively used as single-layer or multi-layer structures.

[0095] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0096] Specifically, the electrolyte may include an organic solvent and a lithium salt. The organic solvent can be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move, without any particular limitations. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a hydrocarbon group with 2 to 20 carbon atoms in a linear, branched, or cyclic structure, and may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery (e.g., ethylene carbonate or propylene carbonate) and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the cyclic carbonate and linear carbonate can be mixed in a volume ratio of about 1:1 to about 1:9 to produce an electrolyte with excellent performance.

[0097] The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, without any particular limitations. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte has suitable conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0098] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for purposes such as improving battery life characteristics, suppressing the decrease in battery capacity, and improving battery discharge capacity. These additives may include, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexalic acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the total weight of the electrolyte.

[0099] As described above, lithium secondary batteries containing the positive electrode material according to the present invention stably exhibit excellent discharge capacity, output characteristics, and life characteristics, making them useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0100] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided. The battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0101] The external shape of the lithium secondary battery according to the present invention is not particularly limited, but may be cylindrical, rectangular, pouch-type, or coin-type, using a can.

[0102] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also preferably as a unit battery in medium- and large-sized battery modules containing multiple battery cells. [Examples]

[0103] The present invention will be described in detail below with reference to examples. However, the examples of the present invention can be modified into various different forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to give a more complete explanation of the present invention to a person of average knowledge in the industry.

[0104] Manufacturing example Manufacturing Example 1 - Manufacturing of the Second Cathode Active Material NiSO4, CoSO4, and MnSO4 were dissolved in water in a nickel:cobalt:manganese molar ratio of 88:5:7 to prepare a 2M transition metal-containing solution.

[0105] The containers containing the transition metal-containing solution, along with containers containing a 25% by weight NaOH solution and a 15% by weight NH4OH aqueous solution, were respectively connected to a 200L batch reactor set to 55°C.

[0106] Next, deionized water was added to the batch reactor, and then nitrogen gas was purged to remove dissolved oxygen from the water, creating a non-oxidizing atmosphere inside the reactor. After that, NaOH was added, and the mixture was stirred at a stirring speed of 250 rpm to maintain the pH inside the reactor at 11.7.

[0107] Subsequently, the transition metal-containing solution was added to the reactor at a rate of 250 mL / hr, an NH4OH aqueous solution was added at a rate of 40 mL / hr, and an NaOH aqueous solution was added at a rate that maintained the pH of the reaction solution at 11.7. After 6 hours of reaction, stirring was stopped, and the upper layer was removed to concentrate the solution. This process was repeated 4 to 5 times to obtain the average particle size (D 50 The particles were grown until they reached a size of approximately 10 μm.

[0108] The particles produced in this way are filtered using a filter press, then dried at 130°C for 24 hours, and Ni 0.885 Co 0.035 Mn 0.080 A precursor for the second positive electrode active material with an (OH)2 composition was obtained.

[0109] Next, LiOH·H2O is added to the second cathode active material precursor in an amount of 1.06 equivalents, Al(OH)3 is added, and the mixture is calcined in an oxygen atmosphere at 640°C for 5 hours, followed by recalcination at 775°C for 5 hours, resulting in a nickel:cobalt:manganese:aluminum molar ratio of 86:5:7:2 and an average particle size (D 50 A secondary particulate second cathode active material with a diameter of approximately 10 μm was manufactured.

[0110] Manufacturing Example 2 - Manufacturing of the First Cathode Active Material Cathode active material precursor [Composition: Ni 0.885 Co 0.035 Mn 0.08 (OH)2, average particle size (D 50)4 μm] and anhydrous LiOH as a lithium raw material were mixed at a molar ratio of 1:1, and after primary firing at 850 °C for 6 hours in an oxygen atmosphere to produce a calcined product, the calcined product was pulverized, and then further mixed with anhydrous LiOH at a molar ratio of 1:0.03, and secondary fired at 800 °C for 10 hours in an oxygen atmosphere, with an average particle size (D 50 ) being 4 μm to produce a single-particle first positive electrode active material.

[0111] Comparative Production Example 1 - Production of a positive electrode active material in the form of small-sized secondary particles In Production Example 1, except that the concentration process was repeated 2 to 3 times and the particles were grown until the average particle size (D 50 ) became about 4 μm, a precursor for a positive electrode active material in the form of secondary particles was produced in the same manner as in Production Example 1.

[0112] Next, except that the precursor for the positive electrode active material in the form of secondary particles was used, a positive electrode active material in the form of small-sized secondary particles with an average particle size (D 50 ) of 4 μm was produced in the same manner as in Production Example 1.

[0113] Comparative Production Example 2 - Production of a positive electrode active material in the form of small-sized single particles Positive electrode active material precursor [composition: Ni 0.885 Co 0.035 Mn 0.08 (OH)2, average particle size (D 50 ) 4 μm] and anhydrous LiOH as a lithium raw material were mixed at a molar ratio of 1:1.03, and primary fired at 850 °C for 16 hours in an oxygen atmosphere to produce a positive electrode active material in the form of small-sized single particles with an average particle size (D 50 ) of 4 μm.

[0114] Examples and Comparative Examples Example 1 A positive electrode material was produced by mixing the first positive electrode active material produced in Production Example 2 and the second positive electrode active material produced in Production Example 1 at a weight ratio of 1:4.

[0115] Example 2 A positive electrode material was produced by mixing the first positive electrode active material produced in Production Example 2 and the second positive electrode active material produced in Production Example 1 at a weight ratio of 1:1.

[0116] Comparative Example 1 A cathode material was manufactured by mixing the small-particle secondary particulate cathode active material produced in Comparative Manufacturing Example 1 with the second cathode active material produced in Manufacturing Example 1 in a weight ratio of 1:4.

[0117] Comparative Example 2 A cathode material was manufactured by mixing the small-particle secondary particulate cathode active material produced in Comparative Manufacturing Example 1 with the second cathode active material produced in Manufacturing Example 1 in a 1:1 weight ratio.

[0118] Comparative Example 3 A cathode material was manufactured by mixing the small-particle, single-particle cathode active material produced in Comparative Manufacturing Example 2 with the second cathode active material produced in Manufacturing Example 1 in a weight ratio of 1:4.

[0119] Experimental Example 1 Scanning electron microscope (SEM) images were obtained for each of the cathode active materials produced in Production Example 2, Production Example 1, Comparative Production Example 1, and Comparative Production Example 2 using a Quanta (FEI Corporation). These are shown in Figures 1 to 4.

[0120] Figure 1 is an SEM image of the first cathode active material produced in Production Example 2. Figure 2 is an SEM image of the second cathode active material produced in Production Example 1. Figure 3 is an SEM image of the small-particle size secondary particulate cathode active material produced in Comparative Manufacturing Example 1. Figure 4 is an SEM image of the small-particle, single-particle positive electrode active material produced in Comparative Manufacturing Example 2.

[0121] Figure 1 confirms that the first positive electrode active material is in the form of single particles. Specifically, we confirmed that the first positive electrode active material is in the form of secondary particles, which are aggregates of 1 to 10 primary particles, or more specifically, 1 to 5 primary particles. Figure 2 confirms that the second positive electrode active material is in the form of secondary particles, which are aggregates of more than 50 primary particles.

[0122] Experimental Example 2 The particle size distribution of the cathode materials manufactured in the above examples and comparative examples was measured before and after pressurization using a PSA (MICROTRAC S3500 manufactured by MICROTRAC).

[0123] Specifically, the particle size distribution before pressurization was measured by uniformly mixing 50 mg each of the cathode materials produced in the above examples and comparative examples with 40 ml of distilled water and 500 μL of dispersant, and then injecting the mixture into PSA.

[0124] The particle size distribution after pressurization was determined by placing 3g each of the positive electrode materials produced in the above examples and comparative examples into a circular mold with a diameter of 1.3cm, and then pressing the positive electrode material in the mold with a 9-ton press at 6,500 kgf / cm². 2 After pressurizing with the specified pressure, the pressurized cathode material was crushed in a mortar. Then, using PSA (MICROTRAC S3500 manufactured by MICROTRAC), 50 mg of each crushed cathode material was uniformly mixed with 40 ml of distilled water and 500 μL of dispersant, and the mixture was injected into the PSA for measurement.

[0125] The cathode materials produced in the examples and comparative examples were subjected to a load of 6,500 kgf / cm². 2 Figures 5 to 9 show the particle size distribution curves measured by PSA before and after applying pressure. Using the particle size distribution curves measured by PSA, the volume of particles with a particle size of 1 μm or less relative to the total volume of particles present in the cathode material after pressurization (fine particle generation rate (%)) was measured and is shown in Table 1 below.

[0126] Figure 5 shows the cathode material manufactured in Example 1 subjected to 6,500 kgf / cm². 2 These are particle size distribution curves measured with PSA before and after applying pressure. Figure 6 shows the cathode material manufactured in Example 2 subjected to 6,500 kgf / cm². 2 These are particle size distribution curves measured with PSA before and after applying pressure. Figure 7 shows the cathode material manufactured in Comparative Example 1 subjected to 6,500 kgf / cm². 2 These are particle size distribution curves measured with PSA before and after applying pressure.

[0127] Figure 8 is a particle size distribution curve measured by PSA before and after applying a pressure of 6,500 kgf / cm to the positive electrode material manufactured in Comparative Example 2. 2 Figure 9 is a particle size distribution curve measured by PSA before and after applying a pressure of 6,500 kgf / cm to the positive electrode material manufactured in Comparative Example 3. 2

[0128] From FIGS. 5 and 7, it was confirmed that the positive electrode materials of Example 1 and Comparative Example 1 contain two types of positive electrode active materials at the same mixing ratio, and each of the two types of positive electrode active materials has the same particle size. However, the change in particle size after pressurization in Example 1 is significantly less than that in Comparative Example 1.

[0129] From FIGS. 6 and 8, it was similarly confirmed that the positive electrode materials of Example 2 and Comparative Example 2 contain two types of positive electrode active materials at the same mixing ratio, and each of the two types of positive electrode active materials has the same particle size. However, the change in particle size after pressurization in Example 2 is significantly less than that in Comparative Example 2.

[0130] From FIGS. 5 and 9, it was confirmed that the positive electrode materials of Example 1 and Comparative Example 3 are different only in the manufacturing method of the first positive electrode active material, specifically, only the firing step. However, the change in particle size after pressurization in Example 1 is significantly less than that in Comparative Example 3.

[0131]

Table 1

[0132] From Table 1 above, it was confirmed that the positive electrode materials manufactured in Examples 1 and 2 have a fine powder generation rate, that is, when a pressure of 6,500 kgf / cm is applied to the positive electrode material, the volume of particles with a particle size of 1 μm or less is 10% or less with respect to the total volume of particles present in the positive electrode material. 2 On the other hand, it was confirmed that the positive electrode materials manufactured in Comparative Examples 1 to 3 have a fine powder generation rate exceeding 10%.

[0133] Experimental Example 3 Using an ion milling system (JBOL, IB19520CCP) (acceleration voltage: 6kV), the first cathode active material produced in Production Example 2 was subjected to Ar ion milling for 2 hours to prepare a cross-sectional sample.

[0134] A cross-sectional sample of the first cathode active material was measured and analyzed using a field emission scanning electron microscope (SEM, JEOL JSM-7900F w / Oxford symmetry EBSD detector) (acceleration voltage: 20kV). An EBSD IPF map was created using AztecCrystal, an image processing and EBSD quantification analysis software from Oxford Instruments.

[0135] Figure 10 shows the EBSD-IPF map for the first cathode active material produced in Production Example 2. Figure 10 confirms that the first positive electrode active material of manufacturing example 2 is single-crystalline. Specifically, it was confirmed that the first positive electrode active material is composed of one primary particle consisting of one to ten, more specifically one to five, single-crystal particles, or in an aggregated form of the primary particles.

[0136] Experimental Example 4 - Manufacturing of coin-type half-cells A cathode slurry was prepared by mixing 97.5% by weight of the cathode material produced in Example 1 and Comparative Example 1, 1.0% by weight of carbon black as a conductive material, and 1.5% by weight of polyvinylidene fluoride (PVDF) as a binder (specifically, 1.4% by weight of KF9709 and 0.1% by weight of BM740H) in an N-methylpyrrolidone (NMP) solvent. The cathode slurry prepared above was applied to one side of an aluminum current collector, dried at 130°C, and then rolled to a porosity of 24% to produce a cathode.

[0137] An electrode assembly was manufactured using a lithium metal electrode as the negative electrode, with a porous polyethylene separator interposed between the positive and negative electrodes. This assembly was placed inside a battery case, and a coin-type half-cell was manufactured by injecting an electrolyte solution prepared by dissolving 1.0 M LiPF6 in an organic solvent mixture of ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) in a volume ratio of 3:3:4.

[0138] - Battery characteristics evaluation The battery was charged to 4.25V at 25°C using the CC-CV method (0.1C, cut-off current: 0.05C), and then discharged to 3.0V using the CC method (0.1C). The charge / discharge capacity (mAh / g) was measured during this process. The measured charge / discharge capacity (mAh / g) and the percentage of discharge capacity relative to charge capacity (efficiency (%)) were calculated, and the results are shown in Table 2 below.

[0139] [Table 2] Table 2 confirms that the secondary battery using the positive electrode material according to the present invention exhibits excellent discharge capacity and efficiency at room temperature.

[0140] Experimental Example 5 - Manufacturing of pouch-type monocell batteries A cathode slurry was prepared by mixing 97.5% by weight of the cathode material produced in Example 1 and Comparative Example 1, 1.0% by weight of carbon black as a conductive material, and 1.5% by weight of polyvinylidene fluoride (PVDF) as a binder (specifically, 1.4% by weight of KF9709 and 0.1% by weight of BM740H) in an N-methylpyrrolidone (NMP) solvent. The cathode slurry prepared above was applied to one side of an aluminum current collector, dried at 130°C, and then rolled to a porosity of 24% to produce a cathode.

[0141] A negative electrode slurry was prepared by mixing a negative electrode active material consisting of natural graphite and artificial graphite in a 5:5 weight ratio, Super C conductive material, additives (Daicel, DAIEL2200), and a binder (ZEON, BML302) in water in a weight ratio of 95.6:1.0:2.3:1.1. After applying the negative electrode slurry to one side of a copper current collector, the negative electrode was manufactured by drying at 130°C and rolling.

[0142] An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive and negative electrodes. This assembly was then placed inside a battery case, and an electrolyte solution was injected by dissolving 1.0 M LiPF6 in an organic solvent mixture of ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) in a volume ratio of 3:3:4 to produce a pouch-type monocell.

[0143] -Battery characteristics evaluation 1 Using the pouch-type monocell manufactured as described above, one cycle consists of charging to 4.25V at 45°C using the CC-CV method (0.33C) and discharging to 3.0V using the CC method (0.33C). A total of 400 charge-discharge cycles are repeated, and the discharge capacity is measured in the first cycle, the 100th cycle, and the 400th cycle. The percentage of the discharge capacity at the 100th cycle relative to the discharge capacity at the first cycle (capacity retention rate) is then calculated. 100 (%) and the percentage of the discharge capacity at the 400th cycle relative to the discharge capacity at the first cycle (capacity retention rate) 400 The percentages (%) are shown in Table 3 and Figure 11 below. Figure 11 shows data regarding the battery characteristics evaluation (capacity retention rate) of lithium secondary batteries containing the cathode materials manufactured in Example 1 and Comparative Example 1.

[0144] [Table 3] Table 3 confirms that the secondary battery using the positive electrode material according to the present invention exhibits excellent lifespan characteristics.

[0145] -Battery characteristics evaluation 2 As described above, a pouch-type monocell was manufactured and charged to 4.25V at 25°C using the CC-CV method (0.33C), after which the positive electrode was separated. The separated positive electrode was placed in a cell pouch, electrolyte was added, and the pouch was sealed to prepare the sample. The sample was stored at 60°C for 12 weeks, and the degree of volume change was measured. The percentage of the sample volume at week 12 relative to the sample volume at week 0 (volume change rate (%)) is shown in Table 4 and Figure 12 below. Figure 12 shows data regarding the evaluation of battery characteristics (volume change rate) of lithium secondary batteries containing the cathode materials manufactured in Example 1 and Comparative Example 1.

[0146] [Table 4] Table 4 confirms that the secondary battery using the positive electrode material according to the present invention is excellent in reducing gas generation.

Claims

1. A single-particle first positive electrode active material, It is in the form of secondary particles, and has an average particle size (D) greater than that of the first positive electrode active material. ５０ The second positive electrode active material has a large size, Includes, 6,500 kgf / cm² applied to the positive electrode material. ２ A positive electrode material in which, when pressure is applied, the volume of particles with a particle size of 1 μm or less is 10% or less of the total volume of particles present in the positive electrode material.

2. The cathode material according to claim 1, having a bimodal particle size distribution.

3. The average particle size (D) of the first positive electrode active material ５０ ) is the average particle size (D) of the second positive electrode active material. ５０ The positive electrode material according to claim 1, wherein the value is 50% or less based on the standard.

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

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 1:0.1 to 10.

6. The average particle size (D) of the first positive electrode active material ５０ The positive electrode material according to claim 1, wherein the thickness is 1 μm or more and 10 μm or less.

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

8. The cathode material according to claim 1, wherein the first cathode active material has a composition represented by the following chemical formula 1. [Chemical formula 1] Li １＋ａ１ Ni ｘ１ Co ｙ１ M １ ｚ１ M ２ ｗ１ O ２ In the aforementioned chemical formula 1, M １ is one or more selected from the group consisting of Mn and Al, M ２ is one or more selected from the group consisting 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. -0.1 ≤ a1 ≤ 0.3, 0.6 ≤ x1 < 1.0, 0 < y1 < 0.4, 0 < z1 < 0.4, 0 ≤ w1 ≤ 0.

1.

9. The cathode material according to claim 1, wherein the second cathode active material has a composition represented by the following chemical formula 2. [Chemical formula 2] Li １＋ａ２ Ni ｘ２ Co ｙ２ M ３ ｚ２ M ４ ｗ２ O ２ In the aforementioned chemical formula 2, M ３ is one or more selected from the group consisting of Mn and Al, M ４ is one or more selected from the group consisting 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. -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 containing the positive electrode material described in any one of claims 1 to 9.

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

Images