Positive active material for lithium secondary battery, method for preparing the same, and lithium secondary battery comprising the same

Abstract

This invention relates to cathode active materials, methods for preparing the same, and lithium secondary batteries comprising the same, wherein the cathode active material comprises at least one secondary particle, the secondary particle comprising an aggregate of primary macroparticles. According to embodiments of the invention, a cathode active material comprising secondary particles that simultaneously increase the average particle size D50 and crystal size of the primary macroparticles, thereby improving resistivity, can be provided. According to embodiments of the invention, a cathode active material with high crystal density can be provided. Therefore, by ensuring the movement path of lithium ions and minimizing defects in the crystal structure of the cathode active material, nickel-based cathode active materials with improved lifetime and resistivity characteristics can be obtained.

Description

Technical Field

[0001] This disclosure relates to positive electrode active materials for lithium secondary batteries containing large primary particles and methods for preparing the same.

[0002] This application claims priority to Korean Patent Application No. 10-2020-0159518, filed in the Republic of Korea on November 25, 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 rechargeable batteries with small size, light weight, and relatively high capacity has grown rapidly. In particular, lithium-ion batteries are attracting attention as a power source for mobile devices 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] A lithium secondary battery comprises an organic electrolyte solution or a polymer electrolyte solution filled between a positive electrode and a negative electrode made of an active material capable of inserting and deintercalating lithium ions, and generates electrical energy through oxidation and reduction reactions during the insertion / deintercalation of lithium ions 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 therefore used as a high-voltage positive electrode active material. However, the widespread use of cobalt (Co) as a power source in electric vehicles is limited due to its rising price and unstable supply, 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, conventional NCM-based lithium composite transition metal oxides are formed from secondary particles through the aggregation of primary microparticles. They possess a large specific surface area and low particle rigidity. Furthermore, during electrode fabrication and the rolling process, the breakage of these secondary particles generates a large amount of gas during battery operation, resulting in poor cycle performance and low stability. In particular, high-capacity, high-Ni NCM-based lithium composite transition metal oxides exhibit low structural and chemical stability, and are even more difficult to ensure thermal stability. Summary of the Invention

[0008] Technical issues

[0009] This disclosure relates to providing a positive electrode active material in the form of secondary particles having an average particle size D50 at the same or similar level as conventional technology, whereas, in contrast to conventional technology, the positive electrode active material comprises primary large particles, thereby minimizing particle breakage during the rolling process.

[0010] This disclosure also relates to providing positive electrode active materials with increased true density (crystal density).

[0011] Therefore, this disclosure also relates to providing positive electrode active materials with improved lifetime and resistivity characteristics.

[0012] Technical solution

[0013] One aspect of this disclosure provides a positive electrode active material according to the following embodiments.

[0014] Specifically, a positive electrode active material for lithium secondary batteries is provided, comprising at least one secondary particle comprising an agglomerate of primary macro particles, wherein the average particle size D50 of the primary macro particles is 2 μm or more, the ratio of the average particle size D50 of the primary macro particles to the average crystal size of the primary macro particles is 8 or more, the average particle size D50 of the secondary particles is 3 μm to 10 μm, and the crystal density of the secondary particles is 4.74 or more.

[0015] We can provide positive electrode active materials for lithium secondary batteries, in which the average crystal size of the primary large particles is above 200nm.

[0016] It can provide positive electrode active materials for lithium secondary batteries, wherein the ratio of the average particle size D50 of secondary particles to the average particle size D50 of primary large particles is 2 to 4 times.

[0017] We can provide positive electrode active materials for lithium secondary batteries, wherein the secondary particles contain nickel-based lithium transition metal oxides.

[0018] We can provide positive electrode active materials for lithium secondary batteries, wherein the nickel-based lithium transition metal oxide includes LiANi. 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 includes at least one selected from the group consisting of Mn and Al, and M2 includes at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo).

[0019] A positive electrode active material for lithium secondary batteries can be provided, wherein the positive electrode active material comprises a sintering additive, said sintering additive comprising at least one of zirconium, yttrium or strontium.

[0020] We can provide positive electrode active materials for lithium secondary batteries, wherein the positive electrode active materials are coated with boron-containing materials on their surface.

[0021] We can provide positive electrode active materials for lithium secondary batteries, wherein the positive electrode active materials are coated with cobalt-containing materials on their surface.

[0022] A positive electrode for a lithium secondary battery may be provided, comprising the positive electrode active material according to the above embodiments.

[0023] A lithium secondary battery comprising the positive electrode active material of the above embodiments can be provided.

[0024] Another aspect of the present invention provides a method for preparing a positive electrode active material.

[0025] Specifically, this disclosure relates to a method for preparing a positive electrode active material for lithium secondary batteries, comprising (S1) mixing a nickel-based transition metal oxide precursor having a tap density of less than 2.0 g / cc with a lithium precursor and performing a first sintering; and (S2) performing a second sintering on the product of the first sintering, wherein the positive electrode active material for lithium secondary batteries comprises at least one secondary particle, the secondary particle comprising an agglomeration of primary large particles formed by the first sintering and the second sintering, the primary large particle having an average particle size D50 of 2 μm or more, the ratio of the average particle size D50 of the primary large particle to the average crystal size of the primary large particle being 8 or more, and the secondary particle having an average particle size D50 of 3 μm to 10 μm, and the secondary particle having a crystal density of 4.74 or more.

[0026] A method for preparing positive electrode active materials for lithium secondary batteries can be provided, wherein the temperature of the first sintering is 780°C to 900°C.

[0027] Beneficial effects

[0028] According to embodiments of this disclosure, by simultaneously increasing the average particle size D50 of the primary large particles and the crystal size, a positive electrode active material containing secondary particles with improved resistance can be provided.

[0029] According to embodiments of this disclosure, nickel-based cathode active materials with increased true density (crystal density) can be provided. Therefore, by ensuring the movement path of lithium ions and minimizing defects in the crystal structure of the cathode active material, nickel-based cathode active materials with improved lifetime and resistivity characteristics can be provided. Attached Figure Description

[0030] The accompanying drawings illustrate preferred embodiments of the present disclosure and, together with the foregoing description, are used to aid in a further understanding of the technical aspects of the present disclosure; therefore, the present disclosure should not be construed as being limited to the drawings. Furthermore, the shape, size, dimensions, or scale of elements in the drawings may be exaggerated for emphasis and clearer description.

[0031] Figure 1 It is a graph showing the capacitance retention and resistance of embodiments and comparative examples according to the present disclosure.

[0032] Figure 2 It is a graph showing the resistance and state of charge (SOC) of embodiments and comparative examples according to the present disclosure. Detailed Implementation

[0033] The embodiments of this disclosure will be described in detail below. Before the description, it should be understood that the terms or words used in the specification and appended claims should not be construed as limited to their general or dictionary meanings, but rather are interpreted based on the principle of allowing the inventors to appropriately define the terms for the best interpretation, and based on their meaning and concepts corresponding to the technical aspects of this disclosure. Therefore, the disclosure of the embodiments described herein is merely the most preferred embodiment of this disclosure and is not intended to fully describe the technical aspects of this disclosure; thus, it should be understood that various other equivalents and modifications may be made thereto upon filing this application.

[0034] Unless the context clearly indicates otherwise, it should be understood that, when used in this specification, the term "comprising" specifies the presence of the stated element, but does not exclude the presence or addition of one or more other elements.

[0035] In the specification and appended claims, "comprising multiple grains" refers to a crystal structure formed by two or more crystal grains having an average crystal size within a specific range. In this case, the crystal size of the grains can be quantitatively analyzed using X-ray diffraction (XRD) via CuKα X-rays (Xrα). Specifically, the average crystal size of the grains can be quantitatively analyzed by placing the prepared particles in a holder and analyzing the X-rays irradiated onto the particles by a diffraction grating.

[0036] In the specification and appended claims, D50 can be defined as the particle size at 50% particle size distribution and can be measured using laser diffraction methods.

[0037] In this disclosure, "primary grain" refers to a grain that appears to have no grain boundaries when observed using a scanning electron microscope at a field of view of 5,000 to 20,000 magnifications.

[0038] In this disclosure, "secondary particles" are particles formed by the aggregation of primary particles.

[0039] In this disclosure, "monolithic" refers to a particle that exists independently of secondary particles and appears to be free of grain boundaries, and for example, it is a particle with a diameter of 1 μm or more.

[0040] In this disclosure, "particle" may include any or all of monoliths, secondary particles, and primary particles.

[0041] Positive electrode active material

[0042] One aspect of the present invention provides a positive electrode active material in the form of secondary particles, which differs from conventional technologies.

[0043] Specifically, a positive electrode active material for lithium secondary batteries is provided.

[0044] 1) Contains at least one secondary particle, said secondary particle comprising an aggregate of primary large particles.

[0045] 2) The average particle size D50 of the primary large particles is greater than 2 μm.

[0046] 3) The ratio of the average particle size D50 of the primary large particles to the average crystal size of the primary large particles is 8 or more.

[0047] 4) The average particle size D50 of the secondary particles is 3 μm to 10 μm, and

[0048] 5) The true density (crystal density) of the secondary particles is 4.74 or higher.

[0049] Primary and secondary particles with features 1) to 5) can provide nickel-based cathode active materials with improved lifetime and resistance properties.

[0050] The characteristics of primary and secondary particles will be described in detail below (1) to (5).

[0051] Particle morphology and primary large particles

[0052] Typically, nickel-based lithium transition metal oxides exist as secondary particles. These secondary particles can be aggregates of primary particles.

[0053] Specifically, nickel-based lithium transition metal oxide secondary particles can be obtained by using dense nickel-based lithium transition metal hydroxide secondary particles prepared by co-precipitation as a precursor, mixing this precursor with a lithium precursor, and sintering at a temperature below 960°C. However, when a positive electrode active material containing conventional secondary particles is coated onto a current collector and rolled, particle breakage occurs and the specific surface area increases. This increase in specific surface area leads to the formation of rock salt on the surface, resulting in low resistivity.

[0054] To address this issue, a monolithic form of the positive electrode active material was developed. Specifically, contrary to the conventional method described above which uses dense nickel-based lithium transition metal hydroxide secondary particles as precursors, a porous precursor was used instead of the conventional precursor. This allows for the synthesis of the same nickel content at a lower sintering temperature, yielding a monolithic form of nickel-based lithium transition metal oxide instead of secondary particles. However, when the monolithic positive electrode active material is coated onto the current collector and rolled, the monolith does not break, while the other active materials do.

[0055] One aspect of this disclosure is provided to address this problem.

[0056] When the dense precursor is sintered at a higher sintering temperature in the same manner as conventional techniques, the average particle size D50 of the primary particles increases, and the average particle size D50 of the secondary particles also increases.

[0057] In contrast, the secondary particles according to one aspect of this disclosure are different from the methods used to obtain conventional monoliths, as described below.

[0058] As described above, conventional monolithic sintering uses existing secondary particle precursors formed at relatively high primary sintering temperatures. In contrast, the secondary particles according to one aspect of this disclosure use porous precursors. Therefore, large primary particles with large particle sizes can be grown without increasing the sintering temperature, while the growth of secondary particles is smaller than in conventional techniques.

[0059] Therefore, according to one aspect of this disclosure, the secondary particles have an average particle size D50 that is the same as or similar to that of conventional technology, and a large average particle size D50 of the primary particles. That is, in contrast to the typical structure of conventional positive electrode active materials (i.e., secondary particles formed by the aggregation of primary particles with small average particle size), secondary particles formed by the aggregation of large primary particles (i.e., primary particles with larger particle size) are provided.

[0060] Specifically, according to one aspect of this disclosure, a secondary particle refers to an agglomeration of primary large particles. In a specific embodiment of this disclosure, a secondary particle can be an agglomeration of 1 to 10 primary large particles. More specifically, a secondary particle can be an agglomeration of 1 or more, 2 or more, 3 or more, or 4 or more primary large particles, and can also be an agglomeration of 10 or less, 9 or less, 8 or less, or 7 or less primary large particles.

[0061] In this disclosure, the "primary large particles" have an average particle size D50 of more than 2 μm.

[0062] In specific embodiments of this disclosure, the average particle size of the primary large particles can be 2 μm or more, 2.5 μm or more, 3 μm or more, or 3.5 μm or more, and can be 5 μm or less, 4.5 μm or less, or 4 μm or less. When the average particle size of the primary large particles is less than 2 μm, it corresponds to conventional secondary particles, and particle breakage may occur during the rolling process.

[0063] Furthermore, in this disclosure, the ratio of the average particle size D50 to the average crystal size of the "primary large particles" is 8 or more. That is, compared with primary micro particles that form conventional secondary particles, the primary large particles have both increased average particle size and average crystal size of the primary particles.

[0064] From a fracture perspective, the absence of grain boundaries and a large average grain size, similar to conventional monoliths, appear advantageous. Therefore, the inventors have devoted considerable effort to increasing the average grain size D50 of the primary particles. During their research, the inventors discovered that when only the average grain size D50 of the primary particles is increased through over-sintering, rock salt forms on the surface of the primary particles, and the initial resistivity increases. To address this problem, the inventors have invented a method to reduce resistivity. Furthermore, to reduce resistivity, it is also necessary to increase the crystal size of the primary particles.

[0065] Therefore, in this disclosure, a primary large particle refers to a particle having a large average grain size and a large average crystal size and appearing to have no grain boundaries.

[0066] Compared to conventional monoliths which have increased resistance due to the formation of rock salt on the surface by sintering at high temperatures, simultaneously increasing the average particle size and average crystal size of the primary particles is advantageous in terms of low resistance and long lifespan.

[0067] In this case, the average crystal size of the primary large particles can be quantitatively analyzed using X-ray diffraction (XRD) via CuKα X-rays. Specifically, the average crystal size of the primary large particles can be quantitatively analyzed by placing the prepared particles in a holder and analyzing the X-rays irradiated onto the particles by the diffraction grating.

[0068] In specific embodiments of this disclosure, the ratio of average particle size D50 to average crystal size is 8 or more, and preferably 10 or more.

[0069] In addition, the average crystal size of a single large particle can be above 200nm, above 250nm, or above 300nm.

[0070] Secondary particles

[0071] According to one aspect of this disclosure, the secondary particles have an average particle size D50 that is the same as or similar to that of conventional materials, and a large average particle size D50 of the primary particles. That is, in contrast to the typical structure of conventional positive electrode active materials (i.e., secondary particles formed by the aggregation of primary particles with small average particle size), secondary particles formed by the aggregation of large primary particles (i.e., primary particles with larger particle size) are provided.

[0072] According to one aspect of this disclosure, the secondary particles have an average particle size D50 of 3 μm to 10 μm. More specifically, the average particle size D50 of the secondary particles can be from 4 μm to 8 μm, and can be 4 μm or more, 4.5 μm or more, 5 μm or more, 5.5 μm or more, or 6 μm or more, and can be less than 8 μm, 7.5 μm or less, 7 μm or less, or 6.5 μm or less.

[0073] Generally, regardless of particle type, under the same composition, the particle size and average crystal size increase with increasing sintering temperature. Conversely, according to one aspect of this disclosure, primary particles are grown into large primary particles with a large particle size without increasing the sintering temperature compared to conventional techniques, and the growth of secondary particles is smaller than that of conventional techniques.

[0074] Therefore, the secondary particles according to one aspect of this disclosure have the same or similar average particle size D50 as conventional secondary particles, and include primary large particles having a larger average particle size and a larger average crystal size than conventional primary microparticles.

[0075] For example, according to one aspect of this disclosure, the secondary particles may comprise secondary particles having an average particle size D50 of about 5 μm, said secondary particles being formed by the aggregation of ten or fewer primary large particles having an average particle size D50 of about 2.5 μm. During the rolling process of the positive electrode active material, no breakage of the secondary particles occurs, and particle breakage is minimized when mixed with other particles and rolled.

[0076] More specifically, when at least one secondary particle is pressed down by 9 tons, the primary large particle is separated, and the secondary particle itself does not break.

[0077] Therefore, after applying 9 tons of pressure to the positive electrode active material according to one aspect of the present disclosure, the fine particles smaller than 1 μm are less than 10%.

[0078] In specific embodiments of this disclosure, the ratio of the average particle size D50 of the secondary particles to the average particle size D50 of the primary large particles can be 2 to 4 times.

[0079] Furthermore, the secondary particles according to this disclosure have a true density (crystal density) of 4.74 or higher.

[0080] The inventors investigated ways to simultaneously improve the lifetime and resistivity characteristics of positive electrode active materials. During the research, it was found that in some cases, even with an increase in the average particle size and crystal size of the primary large particles, differences in electrical and chemical properties still existed.

[0081] As a result of research aimed at solving this problem, the inventors unexpectedly discovered that when the average particle size and crystal size of the primary particles and the crystal density of the secondary particles are controlled simultaneously, a positive electrode active material with improved lifetime and resistivity characteristics can be provided.

[0082] In specific embodiments of this disclosure, the crystal density of the secondary particles can be 4.74 or higher, 4.77 or higher, or 4.78 or higher, and can be 4.80 or lower.

[0083] Composition

[0084] Secondary particles may contain nickel-based lithium transition metal oxides.

[0085] In this case, the nickel-based lithium transition metal oxide can contain LiaNi. 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).

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

[0087] In this case, depending on the positional preference of M1 and / or M2, the doped metals M1 and M2 in the lattice of the secondary particle may be located only on a portion of the surface of the particle and may be set with a concentration gradient that decreases in the direction from the particle surface to the particle center, or they may be located uniformly throughout the particle.

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

[0089] The positive electrode active material can be coated with a boron-containing material, such as lithium boron oxide, on its surface, and the coating can be applied such that the boron content is, for example, below 2000 ppm. Methods for coating boron-containing materials are well known in the relevant technical fields.

[0090] The positive electrode active material can be coated with a cobalt-containing material, such as lithium cobalt oxide, on its surface, and the coating can be applied such that the cobalt content is, for example, below 20,000 ppm. Coating methods for cobalt-containing materials are well known in the relevant technical fields.

[0091] Preparation method of positive electrode active material

[0092] The positive electrode active material according to one aspect of this disclosure can be prepared by the following method. However, this disclosure is not limited thereto.

[0093] Specifically, the method includes (S1) mixing a nickel-based transition metal oxide precursor and a lithium precursor with a tap density of less than 2.0 g / cc and performing a first sintering; and (S2) performing a second sintering on the product of the first sintering, wherein a positive electrode active material for lithium secondary batteries is prepared by the first sintering and the second sintering, the positive electrode active material comprising at least one secondary particle containing agglomerates of primary large particles.

[0094] The method for preparing the positive electrode active material will be described separately for each step.

[0095] First, a positive electrode active material precursor containing nickel (Ni), cobalt (Co), and manganese (Mn) with a tap density of less than 2.0 g / cc is prepared.

[0096] In this case, the precursor used to prepare the positive electrode active material can be a commercially available positive electrode active material precursor, or it can be prepared by a method known in the relevant technical field for preparing positive electrode active material precursors.

[0097] For example, the precursor can be prepared by adding an ammonium cation-containing complexing agent and a basic compound to a transition metal solution containing nickel-containing, cobalt-containing, and manganese-containing raw materials and inducing a co-precipitation reaction.

[0098] 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, aliphatic nickel salts or nickel halides, but are not limited thereto.

[0099] Cobalt-containing raw materials may include cobalt-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides or hydroxyoxides. 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.

[0100] Manganese-containing raw materials may include at least one of manganese-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or hydroxyoxides, and specifically may include at least one of the following: manganese oxides such as Mn2O3, MnO2, Mn3O4; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese salts of dicarboxylic acids, manganese citrate, and aliphatic manganese salts; manganese hydroxyoxides or manganese chloride, but are not limited thereto.

[0101] Transition metal solutions can be prepared by adding nickel-containing, cobalt-containing, and manganese-containing raw materials to a specific solvent (specifically water, or a mixed solvent of water and an organic solvent (e.g., alcohol) that forms a homogeneous mixture with water), or by mixing aqueous solutions of nickel-containing, cobalt-containing, and manganese-containing raw materials.

[0102] The complex forming agent containing ammonium cations may include, but is not limited to, at least one of, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, or (NH4)2CO3. Furthermore, the complex forming agent 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.) mixed with water to form a homogeneous mixture.

[0103] The basic compound may include at least one hydroxide or hydrate of an alkali metal or alkaline earth metal, such as sodium hydroxide, potassium hydroxide, 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.) mixed with water to form a homogeneous mixture.

[0104] An alkaline compound can be added to control the pH of the reaction solution, and it can be added in an amount that makes the pH of the metal solution between 9 and 11.

[0105] Meanwhile, the coprecipitation reaction can be carried out at 40°C to 70°C in an inert atmosphere of nitrogen or argon.

[0106] Nickel-cobalt-manganese hydroxide particles are produced using the above method and then precipitated in the reaction solution. A precursor with a nickel (Ni) content of over 60 mol% in the total metal content can be prepared by adjusting the concentrations of the nickel-containing, cobalt-containing, and manganese-containing raw materials. The precipitated nickel-cobalt-manganese hydroxide particles are separated and dried using conventional methods to obtain the nickel-cobalt-manganese precursor. The precursor can be secondary particles formed through the agglomeration of primary particles.

[0107] Subsequently, the aforementioned precursor was mixed with lithium raw materials and sintered once.

[0108] Lithium feedstocks can include, but are not limited to, any type of material dissolved in water, such as lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or hydroxyoxides. Specifically, lithium feedstocks may include at least one of Li₂CO₃, LiNO₃, LiNO₂, LiOH, LiOH·H₂O, LiH, LiF, LiCl, LiBr, LiI, CH₃COOLi, Li₂O, Li₂SO₄, CH₃COOLi, or Li₃C₆H₅O₇.

[0109] In the case of high-Ni NCM-based lithium composite transition metal oxides with a nickel (Ni) content of 60 mol% or more, a single sintering can be performed at 700°C to 1000°C, more preferably 780°C to 980°C, and even more preferably 780°C to 900°C. The single sintering can be carried out in an air or oxygen atmosphere and can last for 10 to 35 hours.

[0110] Subsequently, after the initial sintering, a second sintering can be carried out.

[0111] In the case of high-Ni NCM-based lithium composite transition metal oxides with a nickel (Ni) content of 60 mol% or more, secondary sintering can be performed at 650°C to 800°C, more preferably 700°C to 800°C, and even more preferably 700°C to 750°C. Secondary sintering can be performed in an air or oxygen atmosphere, and can be performed with the addition of cobalt oxide or cobalt hydroxide at a concentration of 0 to 20,000 ppm.

[0112] Meanwhile, the method does not include any washing process between steps (S1) and (S2).

[0113] Positive electrode active materials containing secondary particle agglomerates with large primary particles can be prepared by the above method.

[0114] Positive electrode and lithium secondary battery

[0115] According to another embodiment of this disclosure, a positive electrode for a lithium secondary battery and a lithium secondary battery are provided, wherein the positive electrode comprises a positive electrode active material.

[0116] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer containing positive electrode active material formed on the positive electrode current collector.

[0117] In the positive electrode, the positive electrode current collector is not limited to a specific type and can include any type of material with conductive properties that does not cause any chemical changes in the battery, such as stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel treated on the surface with carbon, nickel, titanium, or silver. Furthermore, the thickness of the positive electrode current collector can typically range from 3 μm to 500 μm, and it can have microstructures on its surface to improve the adhesion strength of the positive electrode active material. For example, the positive electrode current collector can be in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0118] In addition to the aforementioned positive electrode active material, the positive electrode active material layer may include conductive materials and adhesives.

[0119] In this context, the conductive material is used to impart conductivity to the electrode and can include, but is not limited to, any type of conductive material that has electronic conductivity without causing any chemical change in 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, thermal cracking 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; or conductive polymers, such as polyphenylene derivatives. Typically, the content of the conductive material can be from 1% by weight to 30% by weight, based on the total weight of the positive electrode active material layer.

[0120] Additionally, the adhesive is used to improve the bonding strength between the positive electrode active material particles and 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, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. Based on the total weight of the positive electrode active material layer, the adhesive content can be from 1% by weight to 30% by weight.

[0121] In addition to using the aforementioned positive electrode active materials, the positive electrode can be manufactured using conventional positive electrode manufacturing methods. Specifically, the positive electrode can be manufactured by coating a positive electrode active material layer forming composition comprising the positive electrode active material and optionally a binder and conductive material onto a positive electrode current collector, drying, and rolling. In this case, the type and amount of the positive electrode active material, binder, and conductive material can be the same as described above.

[0122] Solvents may include solvents commonly used in the art related to this disclosure, such as at least one of dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water. When dissolving or dispersing positive electrode active materials, conductive materials, binders, and coatings to manufacture a positive electrode, the solvent may be used in an amount with sufficient viscosity to achieve good thickness uniformity in terms of slurry coating thickness and productivity.

[0123] Alternatively, the positive electrode can be manufactured by casting a positive electrode active material layer forming composition onto a support, peeling the membrane off the support, and pressing the membrane onto the positive electrode current collector.

[0124] According to yet another embodiment of this disclosure, an electrochemical device comprising a positive electrode is provided. Specifically, the electrochemical device may include a battery or a capacitor, and more specifically, a lithium secondary battery.

[0125] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode disposed 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. Optionally, the lithium secondary battery may further include a battery casing and a sealing member, wherein the battery casing houses an electrode assembly including the positive electrode, negative electrode, and separator, and the sealing member is used to seal the battery casing.

[0126] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material located on the negative electrode current collector.

[0127] The negative electrode current collector can include any type of material with high conductivity that will not cause any chemical changes to the battery, such as copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel treated with carbon, nickel, titanium, or silver on the surface, and aluminum-cadmium alloys, but is not limited to these. Furthermore, the thickness of the negative electrode current collector can typically range from 3 μm to 500 μm, and similarly to the positive electrode current collector, the negative electrode current collector can have a microstructure on its surface to improve the adhesion strength of the negative electrode active material. For example, the negative electrode current collector can be in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0128] In addition to the negative electrode active material, the negative electrode active material layer optionally includes a binder and a conductive material. For example, the negative electrode active material layer can be prepared 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 carrier, peeling the film off the carrier, and pressing the film layer onto the negative electrode current collector.

[0129] Negative electrode active materials may include compounds capable of reversibly inserting and deintercalating 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 compounds 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 dedoping lithium, such as SiO₂. β (0<β<2), SnO2, vanadium oxide, lithium vanadium oxide; or composites containing metal compounds and carbonaceous materials, such as Si-C composites or Sn-C composites. Additionally, lithium metal films can be used as anode active materials. Furthermore, carbon materials 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, plate-like, sheet-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, carbon fibers based on mesophase pitch, mesophase carbon microspheres, mesophase pitch, and coke derived from petroleum or coal tar pitch.

[0130] In addition, the adhesive and conductive material can be the same as those used in the positive electrode described above.

[0131] Meanwhile, in lithium secondary batteries, the separator separates the negative electrode from the positive electrode and provides a channel for lithium ion movement. It can be any separator commonly used in lithium secondary batteries, including but not limited to those commonly found in lithium secondary batteries. In particular, preferably, the separator can have low resistance and good electrolyte solution wettability for ion movement in the electrolyte. Specifically, for example, porous polymer membranes or stacks of two or more porous polymer membranes made of polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers can be used. Alternatively, common porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers and polyethylene terephthalate fibers, can be used. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic or polymer materials can be used, and can be selectively used in single-layer or multi-layer structures.

[0132] In addition, the electrolytes used in this disclosure 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.

[0133] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0134] Organic solvents can include, but are not limited to, any type of organic solvent that serves as a medium for the movement of ions participating in the electrochemical reactions of the battery. 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 hydrocarbon 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. Ideally, carbonate solvents are used, and more preferably, cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, which contribute to improved 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 solution.

[0135] Lithium salts may include, but are not limited to, any compound that provides lithium ions for use in lithium secondary batteries. Specifically, lithium salts may 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 from 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte exhibits optimal conductivity and viscosity, resulting in good electrolyte performance and efficient lithium ion movement.

[0136] In addition to the constituent substances of the electrolyte, to improve battery life characteristics, prevent battery capacity decay, and increase battery discharge capacity, the electrolyte may also contain at least one type of additive, such as: halogenated alkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexaphosphoric triamine, 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 additive can be from 0.1% by weight to 5% by weight, based on the total weight of the electrolyte.

[0137] Lithium secondary batteries containing the positive electrode active material according to this disclosure can be used in portable devices (including mobile phones, laptops and digital cameras) and electric vehicles (including hybrid electric vehicles (HEVs)).

[0138] Therefore, according to another embodiment of this disclosure, a battery module including a lithium secondary battery as a unit cell and a battery pack including the battery module are provided.

[0139] The battery module or battery pack can be used as a power source for at least one medium to large unit of a power tool; an electric vehicle, including electric vehicles (EVs), hybrid electric vehicles and plug-in hybrid electric vehicles (PHEVs); or an energy storage system.

[0140] In the following description, embodiments of the present disclosure will be described in full detail to enable those skilled in the art to readily practice the disclosure. However, the present disclosure may be implemented in many different forms and is not limited to the disclosed embodiments.

[0141] Example 1

[0142] (Preparation of positive electrode active material)

[0143] A nickel-cobalt-manganese hydroxide (Ni) with a tap density of 1.8 g / cc was tested. 0.86 Co 0.07 Mn 0.07 The positive electrode active material precursor (OH)2) and lithium raw material LiOH were placed in a Henschel mixer (700L) to achieve a final Li / M (Ni,Co,Mn) molar ratio of 1.01, and mixed at 300 rpm for 20 minutes. The mixed powder was then placed in an alumina furnace with dimensions of 330 mm × 330 mm and sintered once at 900 °C for 10 hours under an oxygen (O2) atmosphere to form a primary sintered product.

[0144] Subsequently, the sintered product was ground once using a jet mill at a feed rate of 80 psi and a grinding rate of 60 psi.

[0145] The ground primary sintered product was placed in an alumina furnace with dimensions of 330mm×330mm, and a secondary sintering was carried out at 700℃ for 5 hours in an oxygen (O2) atmosphere with the addition of 10000ppm Co(OH)2 to prepare the positive electrode active material.

[0146] Example 2

[0147] The positive electrode active material was prepared by the same method as in Example 1, except that the tap density of the precursor was 1.5 g / cc, the primary sintering temperature was reduced by 20 °C, LiOH was introduced into a Henschel mixer (700 L) to make the final Li / M (Ni,Co,Mn) molar ratio 1.05, and Li was added at a rate of 0.02 mol% during the secondary sintering.

[0148] Comparative example

[0149] 10 L of distilled water was placed in a coprecipitation reactor (20 L capacity). While maintaining the temperature at 50 °C, 100 mL of a 28 wt% ammonia solution was added. A 3.2 mol / L transition metal solution (in which NiSO4, CoSO4, MnSO4, and Al3(SO4)2 were mixed in a nickel:cobalt:manganese:aluminum molar ratio of 82:5:11:2) and the 28 wt% ammonia solution were continuously added to the reactor at 300 mL / hr and 42 mL / hr, respectively. The mixture was stirred at an impeller speed of 400 rpm, and the pH was maintained at 11.0 using a 40 wt% sodium hydroxide solution. Precursor particles were formed through a 24-hour coprecipitation reaction. The precursor particles were separated, washed, and dried in an oven at 130 °C to prepare the precursor.

[0150] Ni synthesized via coprecipitation reaction 0.82 Co 0.05 Mn 0.11 Al 0.02 (OH)2 precursor and Li2CO3 were mixed at a Li / Me (Ni, Co, Mn, Al) molar ratio of 1.03 and heat-treated at 800°C for 10 hours under an oxygen atmosphere to prepare LiNi-containing precursor. 0.82 Co 0.05 Mn 0.11 Al 0.02 O2 lithium composite transition metal oxide positive electrode active material.

[0151] [Table 1]

[0152]

[0153] **a and c represent the unit cell size values ​​in the XRD analysis of the positive electrode active material.

[0154] Experimental Example 1: Average Particle Size

[0155] D50 can be defined as the particle size at 50% particle size distribution and is measured using laser diffraction.

[0156] Experimental Example 2: Crystal Size of Primary Particles

[0157] Using a Bruker Endeavor (Cu Kα) sensor equipped with a LynxEye XE-T position-sensitive detector. The sample was measured in steps of 0.02° within a scanning range of 90°FDS 0.5° and 2θ15°, with a total scanning time of 20 minutes.

[0158] Rietveld refinement of the measurement data was performed, taking into account the charge at each site (metal +3 at transition metal sites, Ni +2 at Li sites) and cation mixing. In crystal size analysis, instrumental broadening was accounted for using the fundamental parameter method (FPA) implemented in the Bruker TOPAS program, and all peaks within the measurement range were used in the fitting. Among the peak types available in TOPAS, peak shape fitting was performed using only the Lorentz contribution to the first principle (FP), and strain was not considered in this case. The crystal size results are shown in Table 1 above.

[0159] Experiment Example 3: Crystal Density Measurement

[0160] Using a Bruker Endeavor (Cu Kα) equipped with an X LynxEye XE-T position-sensitive detector, The sample was measured within a 90° FDS scan range of 0.5° and 2θ15° with a step size of 0.02°, for a total scan time of 20 minutes. Based on the measurement data, the crystal density was calculated as: (weight of elements in the unit cell, g) / (unit cell volume, cm³). 3 ).

[0161] Experimental Example 4: High-Temperature Lifetime Characteristics of Coin Cells

[0162] Lithium-ion secondary battery full cells manufactured using the positive electrode active materials prepared in Examples 1 to 2 and the Comparative Examples were charged to 4.25V in CC-CV mode at 0.7C and 45°C, and discharged to 2.5V at a constant current of 0.5C. Capacity retention was measured during 300 charge / discharge cycles to evaluate lifetime characteristics. The results are shown in... Figure 1 And in Table 2.

[0163] [Table 2]

[0164]

[0165] Experiment Example 5: Measurement of DCR resistance as a function of SOC

[0166] After fabricating a coin-type full cell and allowing it to stand for 10 hours, forming (0.2C / 0.2C) and charging / discharging, the resistance value of each SOC was calculated by applying a discharge pulse (1.0C pulse for 10 seconds) based on the SOC setting of the discharge capacity measured when formed after charging at 4.25V.

[0167] DC-IR is calculated as DCIR = (V0 - V1) / I

[0168] (V0 = voltage before pulse, V1 = voltage 10 seconds after pulse, I = applied current)

[0169] The results are shown in Figure 2 and in Tables 2 and 3.

[0170] [Table 3]

[0171] sample unit Comparative Example 1 Example 1 Example 2 SOC 10 Ω 30.92 23.19 19.71

Claims

1. A positive electrode active material for lithium secondary batteries, comprising: At least one secondary particle comprising an agglomerate of primary large particles. in, The secondary particles contain NCM-based lithium composite transition metal oxides with a nickel content of 60 mol% or more. The average particle size D50 of the primary large particles is greater than 2 μm. The ratio of the average particle size D50 of the primary large particle to the average crystal size of the primary large particle is 8 or more. The average particle size D50 of the secondary particles is 3 μm to less than 10 μm, and The secondary particles have a crystal density of 4.74 g / cc or higher; The average crystal size of the primary large particles is above 200 nm; The ratio of the average particle size D50 of the secondary particles to the average particle size D50 of the primary large particles is 2 to 4 times.

2. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The secondary particles are aggregates of 2 to 10 of the primary large particles.

3. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The crystal density of the secondary particles is 4.77 g / cc to 4.80 g / cc.

4. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The NCM-based lithium composite transition metal oxide contains Li a Ni 1-x-y Co x M1 y M2 w O2, where 1.0 ≤ a ≤ 1.5, 0 < x ≤ 0.2, 0 < y ≤ 0.2, 0 ≤ w ≤ 0.1, 0 < x + y ≤ 0.2, M1 includes Mn or includes Mn and Al, and M2 includes at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo.

5. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The positive electrode active material includes sintering additives, which include at least one of zirconium, yttrium, or strontium.

6. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The positive electrode active material is coated with a boron-containing material on its surface.

7. The positive electrode active material for lithium secondary batteries according to claim 1, wherein, The positive electrode active material is coated with a cobalt-containing material on its surface.

8. A positive electrode for a lithium secondary battery, comprising the positive electrode active material for a lithium secondary battery as described in claim 1.

9. A lithium secondary battery comprising the positive electrode active material for a lithium secondary battery as described in claim 1.

10. A method for preparing a positive electrode active material for lithium secondary batteries, the method comprising: (S1) A nickel-based transition metal oxide precursor with a tap density of less than 2.0 g / cc and a nickel content of more than 60 mol% in the total metal content is mixed with a lithium precursor and sintered once; and (S2) Perform a second sintering on the product from the first sintering. The positive electrode active material for lithium secondary batteries, as defined in claim 1, comprises at least one secondary particle, wherein the secondary particle comprises an agglomeration of large primary particles formed by the primary sintering and the secondary sintering. The average particle size D50 of the primary large particles is greater than 2 μm. The ratio of the average particle size D50 of the primary large particle to the average crystal size of the primary large particle is 8 or more, and The average particle size D50 of the secondary particles is 3 μm to less than 10 μm, and the crystal density of the secondary particles is 4.74 g / cc or more. The average crystal size of the primary large particles is above 200 nm; The ratio of the average particle size D50 of the secondary particles to the average particle size D50 of the primary large particles is 2 to 4 times.

11. The method for preparing a positive electrode active material for lithium secondary batteries according to claim 10, wherein, The temperature for the first sintering is between 780°C and 900°C.

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