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

Abstract

The present invention relates to a secondary particle precursor for a positive electrode active material, a positive electrode active material prepared therefrom, a method for preparing the same, and a lithium secondary battery comprising the same; the secondary particle precursor includes a core and a shell, the particle diameter (D50) of the secondary particle precursor is 6 µm ± 2 µm, the particle diameter (D50) of the core is 1 µm to 5 µm, and the porosity of the core is higher than the porosity of the shell. According to one embodiment of the present invention, the positive electrode active material prepared using the above-described secondary particle precursor for a positive electrode active material has an increased tap density and a reduced breakage.

Description

Technical Field

[0001] This invention relates to precursors for preparing novel cathode active materials, cathode active materials, and lithium secondary batteries containing the same.

[0002] This application claims priority to Korean Patent Application No. 10-2020-0170277, filed in Korea on December 8, 2020, the disclosure of which is incorporated herein by reference. Background Technology

[0003] Recently, with the widespread use of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for small, lightweight, and relatively high-capacity rechargeable batteries has grown rapidly. In particular, lithium-ion batteries, as power sources for mobile devices, have attracted attention due to their advantages of light weight and high energy density. Therefore, many efforts have been made to improve the performance of lithium-ion batteries.

[0004] Lithium-ion batteries include organic or polymer electrolytes that are filled between positive and negative electrodes made of active materials that enable lithium ions to be inserted and extracted, and generate electrical energy through oxidation and reduction reactions of lithium ions during the insertion / extraction process at the positive and negative electrodes.

[0005] The positive electrode active materials for lithium-ion secondary batteries include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4), and lithium iron phosphate compounds (LiFePO4). Among these, lithium cobalt oxide (LiCoO2) is widely used due to its high operating voltage and large capacity, and is often used as a positive electrode active material for high-voltage applications. However, due to rising cobalt (Co) prices and unstable supply, the large-scale use of cobalt (Co) as a power source in electric vehicles is limited, thus necessitating the development of alternative positive electrode active materials.

[0006] Therefore, nickel-cobalt-manganese-based lithium composite transition metal oxides (hereinafter referred to as "NCM-based lithium composite transition metal oxides") were developed, in which nickel (Ni) and manganese (Mn) partially replace cobalt (Co).

[0007] Meanwhile, conventionally developed NCM-based lithium composite transition metal oxides are secondary particles formed from the aggregation of primary microparticles, resulting in a large specific surface area and low particle strength. Furthermore, when cathode active materials containing secondary particles aggregated from primary microparticles are used to manufacture electrodes, followed by roll forming, severe particle breakage occurs, generating a large amount of gas during battery operation, leading to low stability. In particular, high-nickel NCM-based lithium composite transition metal oxides, which have higher nickel (Ni) content to ensure high capacity, exhibit low structural and chemical stability, and are even more difficult to ensure thermal stability. Summary of the Invention

[0008] [Technical Issues]

[0009] The present invention aims to solve the problems described above, and therefore aims to provide a precursor for providing a positive electrode active material, the positive electrode active material comprising an average particle size D having the same or similar level as conventional technology. 50 The secondary particles, unlike conventional techniques, contain primary macro particles to minimize particle breakage in the positive electrode active material during rolling.

[0010] Therefore, the present invention aims to provide a nickel-based cathode active material with long life and improved gas properties.

[0011] [Technical Solution]

[0012] One aspect of the present invention provides a secondary particulate precursor according to the following embodiments.

[0013] Specifically, a secondary particle precursor for positive electrode active materials is provided, comprising a core and a shell, wherein the particle size D of the secondary particle precursor is... 50 The core particle size D is 6μm ± 2μm. 50 The porosity is 1μm to 5μm, and the porosity of the core is higher than that of the shell.

[0014] The porosity of the core, measured by tap density, can be less than 2.0 g / cc. More specifically, the porosity of the core, measured by tap density, can be below 1.9 g / cc.

[0015] Core particle size D 50 It can be 1μm to 3μm.

[0016] The porosity of the shell, measured by tap density, can be above 2.0 g / cc. More specifically, the porosity of the shell, measured by tap density, can be above 2.1 g / cc.

[0017] The secondary particle precursor can be composed of Li a Ni 1-x-y Co x M1 y M2 w (OH)2 (1.0≤a≤1.5, 0≤x≤0.2, 0≤y≤0.2, 0≤w≤0.1, 0≤x+y≤0.2, M1 is at least one selected from the group consisting of Mn and Al, and M2 is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo) represents a nickel-based lithium transition metal hydroxide.

[0018] One aspect of the present invention provides a positive electrode active material for lithium secondary batteries, which is an oxide prepared by sintering the precursor of the aforementioned positive electrode active material.

[0019] The oxide can be composed of particles with a diameter D. 50 Particle size D is formed by the aggregation of large primary particles larger than 1 μm. 50 Secondary particles ranging from 3μm to 5μm.

[0020] The average grain size of a single large particle can be over 200 nm.

[0021] The average particle size D of the secondary particles 50 / Average particle size D of primary large particles 50 The ratio can be 2 to 4 times.

[0022] The above oxides can be made from Li a Ni 1-x-y Co x M1 y M2 w O2 (1.0≤a≤1.5, 0≤x≤0.2, 0≤y≤0.2, 0≤w≤0.1, 0≤x+y≤0.2, M1 is at least one selected from the group consisting of Mn and Al, and M2 is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo) represents a nickel-based lithium transition metal oxide.

[0023] Another aspect of the present invention provides a lithium secondary battery comprising the above-described positive electrode active material.

[0024] Another aspect of the present invention provides the following preparation method.

[0025] Specifically, a method for preparing a secondary particle precursor for a positive electrode active material is provided. The method includes: (S1) a first stirring step of stirring a transition metal solution containing nickel-containing raw materials, cobalt-containing raw materials, manganese-containing raw materials, a nitrogen-containing chelating agent, and an alkaline compound; and (S2) a second stirring step of stirring the product obtained in step (S1), wherein the first stirring speed in the first stirring step is slower than the second stirring speed in the second stirring step, and the concentration of the nitrogen-containing chelating agent in the first stirring step is higher than the concentration of the nitrogen-containing chelating agent in the second stirring step. Specifically, the concentration of the nitrogen-containing chelating agent in the first stirring step can be above 5000 ppm, and the concentration of the nitrogen-containing chelating agent in the second stirring step can be below 4000 ppm.

[0026] The concentration of the nitrogen-containing chelating agent in the first stirring step can be above 5000 ppm, while the concentration of the nitrogen-containing chelating agent in the second stirring step can be below 5000 ppm.

[0027] More specifically, the first stirring speed can be below 800 rpm, and the second stirring speed can be above 1000 rpm.

[0028] [Beneficial Effects]

[0029] According to embodiments of the present invention, a precursor for a positive electrode active material comprising secondary particles can be provided, wherein the secondary particles have an average particle size D of larger primary particles. 50 It has improved resistance by growing simultaneously with grain size.

[0030] According to embodiments of the present invention, a precursor that enables nickel-based cathode active materials to have increased compaction density, longer lifespan, and improved gas properties can be provided. Attached Figure Description

[0031] The accompanying drawings illustrate preferred embodiments of the invention and, together with the foregoing description, are used to aid in a further understanding of the technical aspects of the invention. Therefore, the invention should not be construed as being limited to the drawings. Furthermore, the shape, size, extent, or scale of elements in the drawings may be exaggerated for clearer illustration.

[0032] Figure 1 This is a scanning electron microscope (SEM) image of the positive electrode active material of the comparative example disclosed herein.

[0033] Figure 2 This is a SEM image of the positive electrode active material according to one embodiment of the present invention.

[0034] Figure 3 This is a schematic diagram of the positive electrode active material particles after the existing secondary particle precursor is sintered once.

[0035] Figure 4 This is a schematic diagram of positive electrode active material particles after a secondary particle precursor is sintered once, according to one embodiment of the present invention.

[0036] Figure 5 This is a graph showing the compaction density of embodiments and comparative examples of the present invention.

[0037] Figure 6 This is a graph showing the charge-discharge curves of embodiments and comparative examples of the present invention.

[0038] Figure 7 This is a graph illustrating the high-temperature life characteristics of embodiments and comparative examples of the present invention.

[0039] Figure 8 This is a graph showing the measured quantities of the generated gases in embodiments and comparative examples of the present invention. Detailed Implementation

[0040] Embodiments of the present invention will be described in detail below. Before description, it should be understood that the terms or words in the specification and appended claims should not be construed as limited to their general and dictionary meanings, but should be interpreted according to their meanings and concepts corresponding to the technical aspects of the invention, based on the principle that the inventors are allowed to appropriately define terms for the best interpretation. Therefore, the disclosure of the embodiments described herein is only the most preferred embodiment of the invention and is not intended to completely describe all technical aspects of the invention. Thus, it should be understood that at the time of filing this application, the invention may have many other equivalent forms and modifications.

[0041] Unless the context clearly indicates otherwise, it should be understood that the use of the term "comprising" in this specification specifies the presence of the stated element, but does not preclude the presence or addition of one or more other elements.

[0042] In the specification and appended claims, "comprising multiple grains" refers to a crystal structure formed by two or more grains having an average grain size within a specific range. In this case, the grain size can be quantitatively analyzed using X-ray diffraction (XRD) analysis based on Cu Kα X-rays (Xrα). Specifically, the average grain size can be quantitatively analyzed by placing the prepared particles in a support and analyzing the diffraction grating of the X-rays irradiated onto the particles.

[0043] In the specification and appended claims, D 50 It can be defined as the particle size at 50% of the particle size distribution and can be measured using laser diffraction. For example, the average particle size D of a positive electrode active material. 50 The determination method may include: dispersing particles of the positive electrode active material in a dispersion medium, introducing them into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT3000), irradiating them with ultrasound at approximately 28 kHz with an output power of 60 W, and calculating the average particle size D corresponding to 50% of the cumulative volume in the analyzer. 50 .

[0044] In this invention, "primary particles" refers to particles that appear to have no grain boundaries when observed with a scanning electron microscope at a magnification of 5000 to 20000.

[0045] In this invention, "secondary particles" refers to particles formed by the aggregation of primary particles.

[0046] In this invention, "monolith" refers to a particle that exists independently of secondary particles and appears to be free of grain boundaries, for example, a particle with a diameter of 0.5 μm or larger.

[0047] In this invention, "particles" may include any one or all of single-piece particles, secondary particles, and primary particles.

[0048] One aspect of the present invention provides a precursor for providing a positive electrode active material, the precursor being in the form of secondary particles of a different type from conventional techniques.

[0049] Precursors for positive electrode active materials

[0050] like Figure 1 As shown, conventional secondary particles do not exhibit uniform grain growth in the positive electrode active material. Under these circumstances, it is impossible to prepare secondary particles uniformly, resulting in poor electrochemical performance.

[0051] In attempting to solve this problem, the inventors achieved uniform particle growth in the positive electrode active material by altering the density in the precursor. For example... Figure 2 As shown, when secondary particles are prepared using the precursor of one aspect of the present invention, the grains of the positive electrode active material can grow uniformly.

[0052] Specifically, in one aspect of the present invention, a secondary particle precursor for a positive electrode active material comprises a core and a shell, wherein the particle size D of the secondary particle precursor is... 50 It is 6μm±2μm.

[0053] Core particle size D 50 The size is 1μm to 5μm, and

[0054] The porosity of the core is higher than that of the shell.

[0055] Typically, nickel-based lithium transition metal oxides are secondary particles. These secondary particles can be aggregates of primary particles.

[0056] Specifically, dense nickel-based lithium transition metal hydroxide secondary particles prepared by co-precipitation are used as a precursor. This precursor is mixed with a lithium precursor and sintered at a temperature below 960°C to obtain nickel-based lithium transition metal oxide secondary particles. This series of processes is illustrated in... Figure 3 . refer to Figure 3 When a conventional dense precursor undergoes a single sintering process, the average particle size of the primary particles on the surface increases due to grain growth from the surface of the secondary particles, while the average particle size of the primary particles inside decreases. When the positive electrode active material containing these conventional secondary particles is coated onto a current collector and subsequently rolled, the particles themselves fracture, leading to an increase in specific surface area. As the specific surface area increases, rock salt forms on the surface, reducing electrical resistance.

[0057] In contrast, in one aspect of the invention, in order to solve the problems described above, instead of the conventional method using the aforementioned dense nickel-based lithium transition metal hydroxide secondary particles as precursors, a porous precursor is used instead of the conventional precursor. In this case, monolithic nickel-based lithium transition metal oxides that are no longer in the form of secondary particles can be synthesized at a lower sintering temperature compared to the same nickel content.

[0058] Secondary particle precursors can be derived from Li a Ni 1-x-y Co x M1 y M2 w (OH)2 (1.0≤a≤1.5, 0≤x≤0.2, 0≤y≤0.2, 0≤w≤0.1, 0≤x+y≤0.2, M1 is at least one selected from the group consisting of Mn and Al, and M2 is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo) represents a nickel-based lithium transition metal hydroxide.

[0059] like Figure 4 As shown, in one aspect of the present invention, the core of the secondary particle precursor has a higher porosity than the shell. Therefore, large primary particles with large diameters can be grown without increasing the sintering temperature; in contrast, fewer secondary particles can be grown compared to conventional techniques. Furthermore, secondary particles with uniform grain growth can be provided. As a result, inwardly uniform particle growth can be achieved, thereby providing good electrical and chemical properties, minimizing particle breakage, and improving lifetime and gas performance.

[0060] In one specific embodiment of the present invention, the particle size of the secondary particle precursor is 6 μm ± 2 μm. That is, the secondary particle precursor of one aspect of the present invention can have an average particle size D that is the same as or similar to that of conventional technology. 50 .

[0061] In one specific embodiment of the present invention, the core particle size D 50 The core diameter ranges from 1 μm to 5 μm. More specifically, the core particle size D... 50 It can be 1μm to 3μm.

[0062] Meanwhile, in one specific embodiment of the invention, the shell refers to the remaining portion of the monolithic precursor excluding the core. The shell is defined as the outer portion of the boundary where the porosity begins to decrease from the core.

[0063] The thickness of the shell refers to the diameter D of the entire precursor. 50 Subtract the core particle size D 50The thickness of the remaining portion is calculated. The shell thickness can be 0.1 μm to 5 μm, specifically 0.5 μm to 4 μm, and more specifically 1 μm to 3 μm.

[0064] In a secondary particle precursor of one aspect of the invention, the porosity of the core is higher than that of the shell.

[0065] In this case, the porosity can be determined by the tap density, and in a specific embodiment of the invention, the core porosity, measured by tap density, can be less than 2.0 g / cc. More specifically, the core porosity can be less than 1.9 g / cc, less than 1.8 g / cc, 1.7 g / cc, or less than 1.5 g / cc. In a specific embodiment of the invention, the shell porosity, measured by tap density, can be 2.0 g / cc or more. More specifically, the shell porosity can be 2.0 g / cc or more, 2.1 g / cc or more, 2.2 g / cc or more, or 2.5 g / cc or more. As described above, when using precursors with different tap densities, large primary particles with large grain sizes can be grown without increasing the sintering temperature, while fewer secondary particles can be grown compared to conventional techniques. Furthermore, secondary particles with uniform grain growth can be provided.

[0066] One aspect of the present invention provides a positive electrode active material for lithium secondary batteries, which is an oxide prepared by sintering the precursor of the aforementioned positive electrode active material.

[0067] Therefore, the secondary particles of the oxide constituting one aspect of the present invention have an average particle size D that is the same as or similar to that of conventional technology. 50 And it has a large average particle size D 50 The primary particles. That is, in contrast to the typical composition of conventional positive electrode active materials (i.e., secondary particles formed by the aggregation of primary particles with small average particle size), secondary particles are provided, which are formed by the aggregation of primary large particles (i.e., primary particles with increased size).

[0068] In one specific embodiment of the present invention, the secondary particle can be an aggregate of 1 to 10 primary large particles. More specifically, the secondary particle can be an aggregate of 1 or more, 2 or more, 3 or more, or 4 or more primary large particles within the range described above, and can also be an aggregate of 10 or fewer, 9 or fewer, 8 or fewer, or 7 or fewer primary large particles within the range described above.

[0069] In this invention, the average particle size D of the "primary large particles" 50 It can be larger than 1μm.

[0070] In one specific embodiment of the present invention, the average particle size of the primary large particles can be 1 μm or more, 2 μm or more, 2.5 μm or more, 3 μm or more, or 3.5 μm or more, and can be less than 5 μm, 4.5 μm or less, or 4 μm or less. When the average particle size of the primary large particles is less than 1 μm, corresponding to conventional secondary particles, particle breakage may occur during the rolling process.

[0071] Meanwhile, in this invention, the average particle size D of the "primary large particles" 50 The ratio of the average grain size to the average grain size can be 10 or higher. That is, compared with the primary microparticles that form conventional secondary particles, the average particle size of the primary large particles and the average grain size of the primary particles increase simultaneously.

[0072] From a fracture perspective, it is advantageous to have a large average grain size and an appearance of no grain boundaries, similar to monoliths. Therefore, to achieve a relatively large average grain size D of primary particles... 50 The inventors have made many efforts to increase the average particle size D of the particles. In their research, they discovered that if the average particle size D is increased only once through over-sintering... 50 This results in the formation of rock salt on the surface of the primary particles, increasing electrical resistance. Furthermore, the inventors discovered that increasing the average grain size of the primary particles together helps reduce electrical resistance.

[0073] Therefore, in this invention, a primary large particle can be a particle with a large average particle size and a large average grain size and which appears to have no grain boundaries.

[0074] As mentioned above, compared to monoliths with increased resistance due to the presence of rock salt on the surface caused by high-temperature sintering, the simultaneous growth of primary particles with both average particle size and average grain size reduces resistance and provides a longer lifespan advantage.

[0075] As described above, compared to monoliths, the "secondary particles formed by the aggregation of primary large particles" used in one aspect of the invention is advantageous in terms of increasing the size of the primary particles themselves, reducing the formation of rock salt, and consequently reducing electrical resistance.

[0076] In this context, the average grain size of primary large particles can be quantitatively analyzed using Cu Kα X-ray-based X-ray diffraction (XRD). Specifically, the average grain size of primary large particles can be quantitatively analyzed by placing the prepared particles in a support and analyzing the diffraction grating of the X-rays irradiated onto the particles.

[0077] In one specific embodiment of the present invention, the average particle size D 50 The ratio of / to average grain size can be 4 or higher, 7 or higher, or 10 or higher, and can be 30 or lower, or 20 or lower.

[0078] In addition, the average grain size of a single large particle can be above 200nm or above 250nm, and can be below 450nm or below 400nm.

[0079] In one aspect of the invention, the secondary particles have an average particle size D that is the same as or similar to that of conventional techniques. 50 And has an average particle size D 50 Larger primary particles. That is, in contrast to the typical composition of conventional positive electrode active materials (i.e., secondary particles formed by the aggregation of primary particles with small average particle size), secondary particles are provided, which are aggregated from large primary particles (i.e., primary particles with increased size).

[0080] The average particle size D of the secondary particles in one aspect of the present invention 50 The particle size is 3μm to 5μm. More specifically, the average particle size D 50 It can be 3μm or larger, 3.5μm or larger, 4μm or larger, or 4.5μm or larger, and it can also be 5μm or smaller, 4.5μm or smaller, or 4μm or smaller, or 3.5μm or smaller.

[0081] Generally, regardless of particle type, with the same composition, the particle size and average grain size increase with increasing sintering temperature. Conversely, compared to conventional techniques, the primary particles of one aspect of the present invention can grow into large primary particles with large particle sizes without increasing the sintering temperature, while the growth of secondary particles can be smaller than in conventional techniques.

[0082] Therefore, the secondary particles of one aspect of the present invention have the same or similar average particle size D as conventional secondary particles. 50 It also contains primary large particles with a larger average particle size and a larger average grain size than conventional primary microparticles.

[0083] In one specific embodiment of the present invention, the average particle size D of the secondary particles is... 50 / Average particle size D of primary large particles 50 The ratio can be 2 to 4 times.

[0084] Secondary particles can be nickel-based lithium transition metal oxides.

[0085] In this case, nickel-based lithium transition metal oxides may include Li a Ni 1-x-y Co x M1 y M2 wO2 (1.0≤a≤1.5, 0≤x≤0.2, 0≤y≤0.2, 0≤w≤0.1, 0≤x+y≤0.2, M1 is at least one selected from the group consisting of Mn and Al, and M2 is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo).

[0086] In the above formula, a, x, y, and w represent the molar proportions of each element in the nickel-based lithium transition metal oxide.

[0087] In this case, the doped metals M1 and M2 in the lattice of the secondary particles can be disposed on only a portion of the surface of the particle according to the positional preference of M1 and / or M2, or can be disposed with a decreasing concentration gradient from the particle surface to the particle center, or can be disposed uniformly throughout the entire particle.

[0088] In particular, when secondary particles are doped or coated with and doped with metals M1 and M2, the long lifespan characteristics of the active material can be further improved through surface structure stabilization.

[0089] Preparation method of secondary particle precursors for positive electrode active materials

[0090] The precursor of one aspect of the present invention can be prepared by the following method. However, the present invention is not limited thereto.

[0091] Specifically, the precursor is prepared by adding a nitrogen-containing chelating agent and an alkaline compound to a transition metal solution containing nickel-containing, cobalt-containing, and manganese-containing raw materials, stirring, and inducing a co-precipitation reaction.

[0092] Nickel-containing raw materials may include, for example, nickel-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides or hydroxyoxides. Specifically, they may include at least one of Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel salts of fatty acids or nickel halides, but are not limited thereto.

[0093] Cobalt-containing raw materials may include cobalt-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides or hydroxy oxides. Specifically, they may include at least one of Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4 or Co(SO4)2·7H2O, but are not limited thereto.

[0094] Manganese-containing raw materials may include at least one of manganese-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or hydroxyoxides. Specifically, they may include, but are not limited to, at least one of the following: manganese oxides, such as Mn2O3, MnO2, and Mn3O4; manganese salts, such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylate, manganese citrate, and manganese fatty acid salts; manganese hydroxyoxides or manganese chloride.

[0095] Transition metal solutions can be prepared by adding nickel-containing, cobalt-containing, and manganese-containing raw materials to a solvent, specifically water, or a mixture of water and an organic solvent (such as an alcohol) that forms a homogeneous mixture with water, or by mixing an aqueous solution of nickel-containing raw material, an aqueous solution of cobalt-containing raw material, and a manganese-containing raw material.

[0096] Chelating agents containing ammonium cations may include, but are not limited to, at least one of, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, or (NH4)2CO3. Furthermore, chelating agents containing ammonium cations may be used in the form of an aqueous solution, and in this case, the solvent may include water, or a mixture of water and an organic solvent (specifically, an alcohol, etc.) that is mixed with water to form a homogeneous mixture.

[0097] The basic compound may include at least one hydroxide or hydrate of an alkali metal or alkaline earth metal, such as NaOH, KOH, or Ca(OH)₂. The basic compound may be used in the form of an aqueous solution, and in this case, the solvent may include water, or a mixture of water and an organic solvent (specifically, an alcohol, etc.) that is mixed with water to form a homogeneous mixture.

[0098] Alkaline compounds can be added to control the pH of the reaction solution, and the amount added can make the pH of the metal solution 11 to 13.

[0099] In this case, the concentration of the nitrogen-containing chelating agent and the reaction rate of the stirrer can be controlled during the stirring step to prepare core-shell type secondary particle precursors.

[0100] Specifically, the stirring step includes a first stirring step and a second stirring step, wherein the concentration of the nitrogen-containing chelating agent in the first stirring step is higher than the concentration of the nitrogen-containing chelating agent in the second stirring step, and the first stirring speed in the first stirring step is lower than the second stirring speed in the second stirring step.

[0101] For example, the concentration of the nitrogen-containing chelating agent in the first stirring step can be above 5000 ppm, above 6000 ppm, above 7000 ppm, above 8000 ppm, above 9000 ppm, or above 10000 ppm, while the concentration of the nitrogen-containing chelating agent in the second stirring step can be below 5000 ppm, below 4000 ppm, or below 3000 ppm. More specifically, the concentration of the nitrogen-containing chelating agent in the first stirring step can be above 5000 ppm, while the concentration of the nitrogen-containing chelating agent in the second stirring step can be below 4000 ppm.

[0102] For example, the first stirring speed can be below 800 rpm, below 700 rpm, or below 600 rpm, and the second stirring speed can be above 1000 rpm, above 1100 rpm, or above 1200 rpm.

[0103] Meanwhile, the coprecipitation reaction can be carried out in an inert atmosphere of nitrogen or argon at 40℃ to 70℃. That is, sintering can be performed in one step.

[0104] Secondary particle precursors for positive electrode active materials containing a core and a shell with the above characteristics can be prepared by the above method.

[0105] Subsequently, the aforementioned precursor was mixed with lithium raw materials and subjected to secondary sintering.

[0106] Lithium raw materials can include, but are not limited to, any type of water-soluble material, and can include, for example, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or hydroxyoxides. Specifically, lithium raw materials can include at least one of Li₂CO₃, LiNO₃, LiNO₂, LiOH, LiOH·H₂O, LiH, LiF, LiCl, LiBr, LiI, CH₃COOLi, Li₂O, Li₂SO₄, CH₃COOLi, or Li₃C₆H₅O₇.

[0107] In the case of high-nickel NCM-based lithium composite transition metal oxides with a nickel (Ni) content of 60 mol% or more, secondary sintering can be carried out at 700°C to 1000°C, more preferably at 780°C to 980°C, and even more preferably at 780°C to 900°C. Primary sintering can be carried out in an air or oxygen atmosphere for 10 to 35 hours.

[0108] Through the above process, positive electrode active materials containing secondary particle aggregates with large primary particles can be prepared.

[0109] Positive electrode and lithium secondary battery

[0110] According to another embodiment of the present invention, a positive electrode for a lithium secondary battery and a lithium secondary battery are provided, wherein the positive electrode for the lithium secondary battery comprises the above-mentioned positive electrode active material.

[0111] Specifically, the positive electrode includes a positive current collector and a layer of positive active material containing positive active material formed on the positive current collector.

[0112] In the positive electrode, the positive electrode current collector is not limited to a specific type and can include any type of material that is conductive and will not cause any chemical changes to the battery, such as stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, or silver. Furthermore, the thickness of the positive electrode current collector is typically from 3 μm to 500 μm, and it can have a fine texture on its surface to improve the adhesion strength of the positive electrode active material. For example, the positive electrode current collector can take many forms, such as films, sheets, foils, meshes, porous materials, foams, and nonwoven fabrics.

[0113] In addition to the aforementioned positive electrode active material, the positive electrode active material layer may also include conductive materials and adhesives.

[0114] In this context, conductive materials are used to impart conductivity to the electrodes and can include, but are not limited to, any type of conductive material capable of conducting electrons without causing any chemical changes to the battery. Specific examples of conductive materials may include at least one of the following: graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, and carbon fibers; 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; and conductive polymers, such as polyphenylene derivatives. Typically, the content of conductive material can be from 1% to 30% by weight, based on the total weight of the positive electrode active material layer.

[0115] In addition, the adhesive is used to improve the bonding between the positive electrode active material particles and the adhesion strength between the positive electrode active material and the positive electrode current collector. Specific examples of the adhesive may include at least one of 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 polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or a variety of copolymers thereof. Based on the total weight of the positive electrode active material layer, the adhesive content can be from 1% to 30% by weight.

[0116] Besides using the aforementioned positive electrode active material, the positive electrode can be manufactured using common positive electrode manufacturing methods. Specifically, the positive electrode can be manufactured by coating a composition comprising the aforementioned positive electrode active material and optionally a binder and a conductive agent for forming a positive electrode active material layer onto a positive electrode current collector, drying, and rolling. In this case, the types and amounts of the positive electrode active material, binder, and conductive material can be the same as described above.

[0117] The solvent may include solvents commonly used in the relevant technical field, such as at least one of dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water. Considering the slurry coating thickness and yield, the amount of solvent used should be such that it has sufficient viscosity to achieve good thickness uniformity when dissolving or dispersing the positive electrode active material, conductive material, and binder and coating them to manufacture the positive electrode.

[0118] Alternatively, the positive electrode can be manufactured by casting a composition for forming the positive electrode active material layer onto a support, peeling the membrane from the support, and laminating the membrane onto the positive electrode current collector.

[0119] According to another embodiment of the present invention, an electrochemical device comprising the aforementioned positive electrode is provided. Specifically, the electrochemical device may include a battery or a capacitor, and more specifically, may include a lithium secondary battery.

[0120] Specifically, a lithium secondary battery includes a positive electrode, a negative electrode opposite to the positive electrode, a separator disposed between the positive and negative electrodes, and an electrolyte, wherein the positive electrode is the same as described above. Additionally, the lithium secondary battery may optionally include a battery case housing an electrode assembly comprising the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery case.

[0121] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material disposed on the negative electrode current collector.

[0122] The negative electrode current collector can include any type of material with high conductivity that will not cause any chemical changes in the battery, such as copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, or silver, and aluminum-cadmium alloys, but is not limited to these. Furthermore, the thickness of the negative electrode current collector is generally 3μm to 500μm, and its surface, like the positive electrode current collector, can have fine textures to improve the bonding strength of the negative electrode active material. For example, the negative electrode current collector can take various forms, such as films, sheets, foils, meshes, porous materials, foams, and nonwoven fabrics.

[0123] In addition to the negative electrode active material, the negative electrode active material layer may optionally include a binder and a conductive material. For example, the negative electrode active material layer may be manufactured by coating a negative electrode forming composition comprising the negative electrode active material and optionally a binder and a conductive material onto a negative electrode current collector and drying it, or by casting the negative electrode forming composition onto a support, peeling the film off the support, and laminating the film onto the negative electrode current collector.

[0124] Negative electrode active materials may include compounds capable of reversibly inserting and de-intercalating lithium. Specific examples of negative electrode active materials may include at least one of the following: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metallic substances capable of forming alloys with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and metal oxides capable of doping and de-doping lithium, such as SiO₂. β (0<β<2), SnO2, vanadium oxide or lithium vanadium oxide; or a composite containing the aforementioned metallic substance and carbonaceous material, such as a Si-C composite or a Sn-C composite. Alternatively, a thin film of metallic lithium can be used as the negative electrode active material. Furthermore, the carbonaceous material can include low-crystallinity carbon and high-crystallinity carbon. Low-crystallinity carbon typically includes soft carbon and hard carbon, while high-crystallinity carbon typically includes high-temperature sintered carbon, such as amorphous, planar, sheet-like, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and coke derived from petroleum or coal tar pitch.

[0125] In addition, the adhesive and conductive materials can be the same as those in the positive electrode described above.

[0126] Meanwhile, in lithium-ion secondary batteries, the separator separates the negative electrode from the positive electrode and provides a channel for the movement of lithium ions. It can be any separator commonly used in lithium-ion secondary batteries, including but not limited to. Particularly preferred is that the separator has low resistance to the movement of electrolyte ions and good electrolyte wettability. Specifically, the separator can include, for example, a porous polymer membrane made of polyolefin polymers, such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminate of two or more porous polymer membranes. Alternatively, the separator can include common porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers and polyethylene terephthalate fibers. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic or polymer materials can be used, and single-layer or multi-layer structures can be selectively used.

[0127] Furthermore, the electrolytes used in this invention may include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used to manufacture lithium secondary batteries.

[0128] Specifically, electrolytes can include organic solvents and lithium salts.

[0129] Organic solvents can include, but are not limited to, any type of organic solvent that acts as a medium through which ions participating in the electrochemical reaction of the battery move. Specifically, organic solvents can include: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic solvents, such as benzene, fluorobenzene; carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC); alcohol solvents, such as ethanol, isopropanol; R-CN nitriles (R is a C2-C20 straight-chain, branched, or cyclic hydrocarbon, and may contain exocyclic double bonds or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Preferably, carbonate solvents are used. More preferably, cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, which help improve the charge-discharge performance of the battery, can be mixed with low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate). In this case, cyclic carbonates and linear carbonates can be mixed in a volume ratio of about 1:1 to about 1:9 to improve the performance of the electrolyte.

[0130] Lithium salts can include, but are not limited to, any compound capable of providing lithium ions for use in lithium-ion secondary batteries. Specifically, lithium salts can include 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 can be in the range of 0.1M to 2.0M. When the concentration of the lithium salt is within this range, the electrolyte exhibits optimal conductivity and viscosity, resulting in good electrolyte performance and efficient lithium ion movement.

[0131] In addition to the constituent substances of the electrolyte described above, the electrolyte may also contain, for example, at least one of the following additives to improve battery life characteristics, prevent battery capacity decay, and increase battery discharge capacity: halogenated alkyl carbonate compounds, such as ethylene difluorocarbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the content of the additives may be from 0.1% to 5% by weight, based on the total weight of the electrolyte.

[0132] Lithium secondary batteries incorporating the positive electrode active material of the present invention can be used in fields including mobile devices such as mobile phones, laptops and digital cameras, as well as electric vehicles including hybrid electric vehicles (HEVs).

[0133] Therefore, 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 battery module are provided.

[0134] The battery module or battery pack can be used as a power source for at least one of the following medium to large-sized devices: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles and plug-in hybrid electric vehicles (PHEVs); or energy storage systems.

[0135] In the following description, embodiments of the present invention will be fully and thoroughly described to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments set forth herein.

[0136] Example 1

[0137] [Preparation of secondary particle precursors for positive electrode active materials]

[0138] NiSO4, CoSO4, and MnSO4 were mixed in a metallic acid at a molar ratio of 83:11:6 using a continuous stirred tank reactor (CSTR). Ammonia was used as a chelating agent for co-precipitation, and NaOH, which provides oxide ions (OH), was used as the coprecipitant to generate the coprecipitate. The coprecipitate was then washed and dried in a desiccator at 120°C for approximately 12 hours to prepare Ni. 0.83 Co 0.11 Mn 0.06(OH)₂ precursor powder. In this process, the ammonia concentration in the reactant solution within the reactor is increased to above 10,000 ppm and stirred at 600 rpm, thereby forming a porous core. Subsequently, the ammonia concentration is reduced to 3,000 ppm and stirred at 1200 rpm, thereby forming a dense shell, thus preparing a core-shell type secondary particle precursor for positive electrode active materials. In this case, the internal conditions of the reactor are used to maintain the temperature of the reactant solution at 60°C and the pH at 10.5–12.0.

[0139] [Preparation of positive electrode active materials]

[0140] The prepared positive electrode active material precursor is in the form of particles with a porous core and a dense shell. The synthesized Ni... 0.83 Co 0.11 Mn 0.06 The (OH)₂ precursor was mixed with lithium feedstock LiOH to achieve a final Li / Me molar ratio of 1.03. The mixture was then heat-treated at 800℃ for 10 hours to synthesize Li(Ni)₂. 0.83 Co 0.11 Mn 0.06 O2 positive electrode active material.

[0141] Example 2

[0142] The positive electrode active material was synthesized using the same method as in Example 1, except that the stirring speed for forming the porous core was changed to 1000 rpm and the stirring speed for forming the shell was changed to 2000 rpm when preparing the secondary particle precursor for the positive electrode active material.

[0143] Comparative example

[0144] [Preparation of precursors for positive electrode active materials]

[0145] In the comparative example, the mixture was stirred at 1500 rpm while maintaining the ammonia concentration in the reactant solution within the reactor at 3000 ppm during co-precipitation, thereby preparing a dense precursor without a core or shell. Except as described above, the precursor was prepared using the same method as in the examples.

[0146] [Preparation of positive electrode active materials]

[0147] Other conditions were the same as in the example, but Li(Ni) was synthesized by heat treatment at a sintering temperature of 850°C for 10 hours. 0.83 Co 0.11 Mn 0.06 O2 positive electrode active material.

[0148] Table 1

[0149]

[0150] As can be seen from the examples and comparative examples, one aspect of the present invention can prepare a precursor comprising a porous core and a dense shell by controlling the concentration of ammonia in the reactant solution and the stirring speed. When the prepared secondary particle precursor is used to prepare a positive electrode active material, positive electrode active materials with high compaction density and improved electrochemical performance, as shown in Table 1, can be obtained. In particular, due to the different compositions of the positive electrode active materials, absolute comparisons are difficult, but it can be seen that the positive electrode active materials exhibit similar efficiencies of 88.9% and 88.6%, while the absolute values ​​of charge and discharge in the examples are found to be higher.

[0151] [Experiment Example 1: Observation of Positive Electrode Active Materials]

[0152] Figure 1 and Figure 2 Images of the positive electrode active materials prepared in the comparative examples and the examples, observed under magnification using a scanning electron microscope (SEM), are shown respectively.

[0153] [Experimental Example 2: Compacted Density]

[0154] The compaction density was measured using an HPRM-1000. Specifically, 5g of the positive electrode active material from each example and comparative example was placed into a cylindrical mold, and the mold containing the positive electrode active material was compressed to 63.694MPa. Subsequently, the height of the compressed mold was measured using vernier calipers, and the compaction density was determined. The results are shown in Table 1.

[0155] [Experimental Example 3: Average Particle Size]

[0156] D 50 It can be defined as the particle size at 50% of the particle size distribution and determined using laser diffraction.

[0157] [Experimental Example 4: Average Grain Size of Primary Particles]

[0158] Using the Bruker D8 Endeavor equipped with a LynxEye XE-T position-sensitive sensor The sample was measured with a step size of 0.02° and a scanning range of 90°FDS 0.5°, 2-θ15°, resulting in a total scanning time of 20 minutes.

[0159] The measurement data were Rietveld refined, taking into account the charge at each site (metal +3 for transition metal sites, nickel +2 for Li sites) and cation mixing. In grain size analysis, instrument broadening was considered using the fundamental parametric method (FPA) performed in the Bruker TOPAS program, and all peaks within the measurement range were used during fitting. Of the peak types available in TOPAS, only the Lorentz contribution was used as the first principle (FP) for peak shape fitting, and strain was not considered in this case. The grain size results are shown in Table 1 above.

[0160] [Experimental Example 5: Tap Density]

[0161] The tap density of the precursor was determined using TAP-2S (manufacturer: LOGAN) according to ASTM B527-06.

Claims

1. A method for preparing a positive electrode active material for lithium secondary batteries, the method comprising: The secondary particle precursor for positive electrode active materials is prepared by a process including the following steps: (S1) A first stirring step of stirring a transition metal solution, wherein the transition metal solution contains nickel-containing raw materials, cobalt-containing raw materials and manganese-containing raw materials, as well as nitrogen-containing chelating agents and alkaline compounds; (S2) A second stirring step in which the product obtained in step (S1) is stirred. In this process, the first stirring speed in the first stirring step is slower than the second stirring speed in the second stirring step. Furthermore, the concentration of the nitrogen-containing chelating agent in the first stirring step is higher than the concentration of the nitrogen-containing chelating agent in the second stirring step; and The positive electrode active material is prepared by sintering a secondary particle precursor to obtain an oxide as the positive electrode active material. The secondary particle precursor includes a core and a shell. Wherein, the particle size D of the secondary particle precursor 50 It is 6μm±2μm. The core particle size D 50 It is 1μm to 5μm, and The porosity of the core is higher than that of the shell; The oxide is composed of particles with a diameter D 50 Secondary particles are formed by the aggregation of primary large particles larger than 1 μm, and the average grain size of the primary large particles is greater than 200 nm.

2. The method as described in claim 1, wherein, The porosity of the core is less than 2.0 g / cc, measured by tap density.

3. The method as described in claim 1, wherein, The porosity of the core is less than 1.9 g / cc, measured by tap density.

4. The method of claim 1, wherein, The core particle size D 50 The size ranges from 1μm to 3μm.

5. The method of claim 1, wherein, The porosity of the shell, measured by tap density, is above 2.0 g / cc.

6. The method of claim 1, wherein, The porosity of the shell, measured by tap density, is above 2.1 g / cc.

7. The method of claim 1, wherein, The secondary particle precursor is composed of Li a Ni 1-x-y Co x M1 y M2 w (OH)2 represents a nickel-based lithium transition metal hydroxide, wherein 1.0≤a≤1.5, 0≤x≤0.2, 0≤y≤0.2, 0≤w≤0.1, 0≤x+y≤0.2, M1 is at least one selected from the group consisting of Mn and Al, and M2 is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo.

8. The method of claim 1, wherein, The oxide is a secondary particle formed by the aggregation of 1 to 10 of the primary large particles.

9. The method of claim 1, wherein, The oxide has a particle size D 50 Secondary particles ranging from 3μm to 5μm.

10. The method of claim 1, wherein, The average grain size of the primary large particles is 250 nm to 450 nm.

11. The method of claim 1, wherein, The average particle size D of the secondary particles of the oxide 50 / The average particle size D of the primary large particles 50 The ratio is 2 to 4 times.

12. The method of claim 1, wherein, The oxide is composed of Li a Ni 1-x-y Co x M1 y M2 w O2 represents a nickel-based lithium transition metal oxide, wherein 1.0≤a≤1.5, 0≤x≤0.2, 0≤y≤0.2, 0≤w≤0.1, 0≤x+y≤0.2, M1 is at least one selected from the group consisting of Mn and Al, and M2 is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo.

13. The method of claim 1, wherein, The concentration of the nitrogen-containing chelating agent in the first stirring step is above 5000 ppm, and The concentration of the nitrogen-containing chelating agent in the second stirring step is below 5000 ppm.

14. The method of claim 1, wherein, The first stirring speed is below 800 rpm, and the second stirring speed is above 1000 rpm.

15. The method of claim 1, wherein, The concentration of the nitrogen-containing chelating agent in the first stirring step is above 5000 ppm, and The concentration of the nitrogen-containing chelating agent in the second stirring step is below 4000 ppm.

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