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

Abstract

The present invention relates to a positive electrode active material comprising at least one secondary particle including agglomerates of primary large particles, a method for preparing the same, and a lithium secondary battery comprising the same. According to one embodiment of the present invention, the conductivity of the surface of the positive electrode active material can be improved by coating the surface of the secondary particle with a conductive carbon material. Accordingly, a nickel-based positive electrode active material can be provided, which improves the cycle life performance by minimizing the loss of the conductive network after cycling.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery containing primary large particles and a preparation method thereof.

[0002] This application claims priority to Korean Patent Application No. 10-2020-0163238 filed in Korea on November 27, 2020, the disclosure of which is hereby incorporated by reference. Background Art

[0003] Recently, with the widespread use of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for secondary batteries with small size, light weight, and relatively high capacity has been rapidly increasing. In particular, lithium secondary batteries are attracting increasing attention as power sources for mobile devices due to their advantages of light weight and high energy density. As a result, many efforts have been made to improve the performance of lithium secondary batteries.

[0004] A lithium secondary battery includes an organic electrolyte solution or a polymer electrolyte solution filled between a positive electrode and a negative electrode. The positive electrode and the negative electrode are made of active materials capable of intercalating and deintercalating lithium ions. During the intercalation / deintercalation of lithium ions in the positive electrode and the negative electrode, electrical energy is generated through oxidation and reduction reactions.

[0005] The positive electrode active materials of lithium secondary batteries include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4) and lithium iron phosphate compounds (LiFePO4). Among them, lithium cobalt oxide (LiCoO2) is widely used due to its advantages of high operating voltage and large capacity, and is used as a positive electrode active material for high voltage. However, due to the rising price and unstable supply of cobalt (Co), the large-scale use of cobalt as a power source in the field of electric vehicles has its limitations, so it is necessary to develop an alternative positive electrode active material. Therefore, a nickel-cobalt-manganese-based lithium composite transition metal oxide (hereinafter referred to as "NCM-based lithium composite transition metal oxide") was developed by partially replacing cobalt (Co) with nickel (Ni) and manganese (Mn).

[0006] At the same time, the NCM-based lithium composite transition metal oxides developed in the past are in the form of secondary particles formed by the agglomeration of primary microparticles, with a large specific surface area and low particle strength. In addition, when the positive electrode active material containing secondary particles formed by the agglomeration of primary microparticles is used to prepare the electrode, and then the roller pressing process is performed, the particles crack severely, and a large amount of gas is generated during the operation of the battery, resulting in low stability. In particular, high-nickel NCM-based lithium composite transition metal oxides have a high nickel (Ni) content to ensure high capacity, and are widely used in high energy density batteries due to their high capacity. However, as the nickel content increases, the thermal stability decreases and the electrochemical side reactions increase, resulting in higher resistance and a larger amount of gas generation.

[0007] To address these issues, monoliths have been researched and developed. Monoliths exist independently of secondary particles and appear to have no grain boundaries. Monoliths minimize unstable interfaces on the surface of the cathode active material, thereby improving thermal stability and reducing gas generation.

[0008] However, compared to secondary particles, the monolith has a smaller area involved in charge / discharge. Therefore, during the charge / discharge process, due to the larger amount of current flowing within the same area, the monolith undergoes more side reactions and forms a resistive layer on the particle surface. In addition, during the roller pressing process, when pressed under a predetermined pressure, the monolith cracks and produces fine particles. The fine particles increase the unstable interface, leading to side reactions with the electrolyte solution, resulting in a decrease in battery performance. Summary of the Invention

[0009] Technical issues

[0010] The present invention aims to solve the above-mentioned problems, and thus the present invention aims to provide a positive electrode active material including secondary particles of a new concept.

[0011] The present invention also aims to improve electrical and chemical properties by forming a coating layer comprising a carbon material on the surface of secondary particles.

[0012] Specifically, the cycle characteristics can be improved by minimizing the conductive network loss after charge and discharge.

[0013] Technical Solution

[0014] One aspect of the present invention provides a positive electrode active material according to the following embodiment.

[0015] Specifically, a positive electrode active material for a lithium secondary battery is provided, which positive electrode active material comprises: at least one secondary particle, which secondary particle comprises agglomerates of primary large particles; and a coating arranged on the surface of the secondary particle, which coating comprises a carbon material, wherein the average particle size D50 of the primary large particles is greater than 1.5 μm, the average particle size D50 of the secondary particles is 3 μm to 10 μm, and the positive electrode active material comprises a nickel-based lithium transition metal oxide.

[0016] The carbon material included in the coating layer may be present in an amount of 0.3 parts by weight to 5 parts by weight based on 100 parts by weight of the secondary particles.

[0017] The thickness of the coating may be from 10 nm to 50 nm.

[0018] The carbon material may include at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, carbon nanoribbons, carbon nanobelts, carbon nanorods, graphene, graphene oxide, reduced graphene oxide, carbon black, activated carbon, and mesoporous carbon.

[0019] Nickel-based lithium transition metal oxides can be Li a [Ni x Co y Mn 1-x-y ]O 2+b , where 0.9≤a≤1.5, -0.1≤b≤1.0, 0.5≤x≤0.95, 0<y≤0.5.

[0020] The ratio of the average particle diameter D50 of the primary large particles / the average crystal size of the primary large particles may be 2 or more.

[0021] The average crystal size of the primary large particles may be 130 nm or more.

[0022] The ratio of the average particle size D50 of the secondary particles / the average particle size D50 of the primary large particles may be 2 to 5 times.

[0023] During the roll-pressing process of the positive electrode active material, the primary large particles can be separated from the secondary particles without themselves cracking.

[0024] Rolling processing can be carried out under 1 ton conditions.

[0025] When the roll pressing process of the positive electrode active material is performed under 9-ton conditions, the presence ratio of fine particles smaller than 1 μm may be 1% or less.

[0026] One aspect of the present invention provides a positive electrode for a lithium secondary battery including the positive electrode active material.

[0027] One aspect of the present invention provides a lithium secondary battery including the above-mentioned positive electrode active material.

[0028] One aspect of the present invention provides the following preparation method. Specifically, the present invention relates to a method for preparing a positive electrode active material for a lithium secondary battery, the method comprising: (S1) mixing a precursor comprising nickel, cobalt and manganese with a hydroxide to prepare a porous nickel-based lithium transition metal hydroxide precursor; (S2) mixing the porous nickel-based lithium transition metal hydroxide precursor with a lithium raw material and heat-treating it to prepare secondary particles; and (S3) mixing the secondary particles with a carbon material to form a coating comprising a carbon material on the surface of the secondary particles, wherein the positive electrode active material comprises at least one secondary particle comprising an agglomerate of primary large particles and a coating provided on the surface of the secondary particles, the coating comprising a carbon material, the average particle size D50 of the primary large particles being 1.5 μm or more, the average particle size D50 of the secondary particles being 3 μm to 10 μm, and the positive electrode active material comprising a nickel-based lithium transition metal oxide.

[0029] The step (S1) may be performed at 35°C to 80°C, and the step (S2) may be performed at 700°C to 1000°C.

[0030] Step (S3) can be performed at room temperature.

[0031] Step (S1) can be performed at a pH value of 8 to 12.

[0032] The method may not include a cleaning process between step (S2) and step (S3).

[0033] The tap density of the porous nickel-based lithium transition metal hydroxide precursor in step (S2) may be 2.0 g / cc or less.

[0034] Beneficial effects

[0035] According to one embodiment of the present invention, a positive electrode active material can be provided, which includes secondary particles comprising primary large particles having an increased average particle size D50. Compared to conventional secondary particles, the use of the secondary particles can provide the positive electrode active material with lower resistance and increased thermal stability.

[0036] According to one embodiment of the present invention, a coating comprising a carbon material is formed on the surface of the secondary particles. This improves the conductivity of the surface of the positive electrode active material. Furthermore, the carbon material coating can smooth the surface of secondary particles with relatively high surface roughness, thereby increasing the compaction density and reducing the generation of fine particles during roller compaction.

[0037] Furthermore, the use of conductive carbon materials eliminates the need to add conductive materials when preparing electrodes containing positive active materials. Consequently, the amount of positive active material contained in the electrodes can be increased, thereby increasing energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings illustrate preferred embodiments of the present invention and, together with the foregoing description, are used to help further understand the technical features of the present invention. Therefore, the present invention should not be construed as being limited to the accompanying drawings. Furthermore, the shapes, sizes, scales, or proportions of elements in the accompanying drawings may be exaggerated to emphasize a clearer description.

[0039] Figure 1 is a scanning electron microscope (SEM) image of a positive electrode active material according to an embodiment of the present invention.

[0040] Figure 2 is a SEM image of the positive electrode active material of Comparative Example 1 of the present invention.

[0041] Figure 3 is a SEM image of the positive electrode active material of Comparative Example 2 of the present invention.

[0042] Figure 4 is a SEM image of the positive electrode active material of Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0043] Hereinafter, embodiments of the present invention will be described in detail. Before the description, it should be understood that the terms or words used in the specification and the appended claims should not be interpreted as limited to the general and dictionary meanings, but should be interpreted according to the meanings and concepts corresponding to the technical aspects of the present invention based on the principle of allowing the inventor to appropriately define the terms for the best interpretation. Therefore, the disclosure of the embodiments described herein is only the most preferred embodiment of the present invention and is not intended to fully describe the technical aspects of the present invention. Therefore, it should be understood that various other equivalents and modifications may be made when filing an application.

[0044] Unless the context clearly indicates otherwise, it should be understood that when the term "comprising" is used in this specification, it specifies the presence of stated elements but does not exclude the presence or addition of one or more other elements.

[0045] In the specification and the appended claims, "comprising a plurality of crystal grains" refers to a crystal structure formed by two or more crystal grains having a specific average crystal size range. In this case, the crystal size of the crystal grains can be quantitatively analyzed using X-ray diffraction analysis (XRD) using Cu Kα X-rays (Xrα). Specifically, the average crystal size of the crystal grains can be quantitatively analyzed by placing the prepared particles in a holder and analyzing the diffraction grating of the X-rays irradiated onto the particles.

[0046] In the specification and the appended claims, D50 may be defined as the particle size at 50% of the particle size distribution and may be measured using a laser diffraction method. For example, a method for measuring the average particle size D50 of a positive electrode active material may include dispersing particles of the positive electrode active material in a dispersion medium, introducing the particles into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating ultrasonic waves of approximately 28 kHz at an output power of 60 W, and calculating the average particle size D50 corresponding to 50% of the cumulative volume in the measuring device.

[0047] In the present invention, "primary particles" refer to particles having seemingly non-existent grain boundaries when observed using a scanning electron microscope at a field of view of 5000 to 20000 times. In the present invention, primary particles can be divided into primary fine particles and primary large particles based on the average particle size D50.

[0048] In the present invention, "secondary particles" are particles formed by agglomeration of primary particles.

[0049] In the present invention, the "monolith" refers to a particle that exists independently of the secondary particles and has a seemingly non-existent grain boundary, for example, it is a particle having a particle diameter of 0.5 μm or more.

[0050] In the present invention, "particles" may include any one or all of monoliths, secondary particles and primary particles.

[0051] positive electrode active material

[0052] One aspect of the present invention provides a positive electrode active material in the form of secondary particles that is different from conventional techniques.

[0053] Specifically, a positive electrode active material for a lithium secondary battery is provided, 1) comprising: at least one secondary particle comprising an agglomerate of primary large particles, 2) wherein the average particle size D50 of the primary large particles is 1.5 μm or more; and

[0054] 3) a coating disposed on the surface of the secondary particle, the coating comprising a carbon material;

[0055] 4) wherein the average particle size D50 of the secondary particles is 3 μm to 10 μm, and

[0056] 5) The positive electrode active material comprises a nickel-based lithium transition metal oxide.

[0057] The secondary particles having the above characteristics can provide a nickel-based positive active material with improved stability at high temperatures and high voltages.

[0058] Hereinafter, the above-mentioned characteristics 1) to 5) of the secondary particles will be described in detail.

[0059] Particle shape and primary large particles

[0060] Typically, the nickel-based lithium transition metal oxide is a secondary particle, which may be an aggregate of primary particles.

[0061] Specifically, dense secondary particles of nickel-based lithium transition metal hydroxide prepared by a coprecipitation method are used as a precursor. When this precursor is mixed with a lithium precursor and sintered at a temperature below 960°C, secondary particles of lithium transition metal oxide containing primary microparticles can be obtained. However, when the positive electrode active material containing conventional secondary particles is coated on the current collector and then rolled, the particles themselves crack and the specific surface area increases. When the specific surface area increases, rock salt forms on the surface, reducing the resistance.

[0062] In order to solve this problem, monolithic positive electrode active materials have also been developed. Specifically, in contrast to the conventional method of using the above-mentioned dense nickel-based lithium transition metal hydroxide secondary particles as precursors, a porous precursor is used instead of a conventional precursor, and a higher sintering temperature is used for the same nickel content, thereby obtaining a monolithic nickel-based lithium transition metal oxide, which no longer takes the form of secondary particles. However, during the synthesis of the monolith, the crystal structure of the monolith on the particle surface changes from a layered structure to a rock salt structure. The surface of the non-conductive rock salt structure hinders the movement of lithium ions during the charge / discharge process, resulting in a shortened battery life.

[0063] One aspect of the present invention is to solve this problem.

[0064] In the case of sintering using only a dense precursor at a higher sintering temperature as in the conventional art, the average particle size D50 of the primary particles increases, and simultaneously the average particle size D50 of the secondary particles also increases.

[0065] In contrast, the secondary particles of one aspect of the present invention differ from the method used to obtain conventional monoliths as described below.

[0066] As described above, conventional monoliths are formed at relatively high primary sintering temperatures, but still use conventional secondary particle precursors. In contrast, the secondary particles of one aspect of the present invention use porous precursors. Therefore, large primary particles with large particle sizes can be grown without increasing the sintering temperature, while fewer secondary particles are grown than with conventional techniques.

[0067] Therefore, the secondary particles of one aspect of the present invention have an average particle size D50 that is the same as or similar to that of conventional technology, and the primary particles have a large average particle size D50. That is, in contrast to the typical configuration of conventional positive electrode active materials (i.e., in the form of secondary particles formed by agglomeration of primary particles having a small average particle size), secondary particles formed by agglomeration of large primary particles (i.e., primary particles having increased size) are provided.

[0068] In the present invention, the average particle size D50 of the “primary large particles” is 1.5 μm or more.

[0069] In one embodiment of the present invention, the average particle size of the primary large particles may be 1.5 μm or more, 2 μm or more, 2.5 μm or more, 3 μm or more, or 3.5 μm or more, and may 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 1.5 μm, it corresponds to conventional secondary microparticles, and particle cracking may occur during the rolling process.

[0070] In the present invention, the average particle diameter D50 / average crystal size ratio of "primary large particles" is preferably greater than 2. That is, the average particle diameter and average crystal size of the primary particles of the primary large particles can be increased simultaneously when compared with the primary fine particles forming the conventional secondary particles.

[0071] From a cracking perspective, seemingly nonexistent grain boundaries and a large average particle size, as seen in conventional monoliths, are advantageous. Therefore, the present inventors focused on increasing the average particle size D50 of the primary particles. When the average particle size D50 of the primary particles is increased simply through oversintering, rock salt forms on the surface of the primary particles, increasing electrical resistance. To address this issue, the present inventors discovered that electrical resistance can be reduced by simultaneously increasing the crystal size of the large primary particles.

[0072] That is, in the present invention, the primary large particles are preferably particles having a large average particle diameter as well as a large average crystal size and seemingly no grain boundaries.

[0073] As described above, when the average particle diameter and the average crystal size of the primary particles are increased simultaneously, it is advantageous in terms of low resistance and long life compared to a conventional monolith having increased resistance due to formation of rock salt on the surface by high-temperature sintering.

[0074] As described above, the "secondary particles formed by agglomeration of large primary particles" used in one aspect of the present invention are advantageous in terms of low electrical resistance compared to conventional monoliths, which is brought about by the increase in size of the primary particles themselves and the reduction in the formation of rock salt.

[0075] In this case, the average crystal size of the primary large particles can be quantitatively analyzed using X-ray diffraction analysis (XRD) using Cu Kα 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 diffraction grating of the X-rays irradiated on the particles.

[0076] In one embodiment of the present invention, the ratio of average particle diameter D50 / average crystal size may be 2 or more, 2.5 or more, or 3 or more, and may be 50 or less, 40 or less, or 35 or less.

[0077] Furthermore, the average crystal size of the primary large particles may be 130 nm or more, 150 nm or more, 170 nm or more, or 200 nm or more, and may be 300 nm or less, 270 nm or less, or 250 nm or less.

[0078] Secondary particles

[0079] The secondary particles of one aspect of the present invention have an average particle size D50 that is the same as or similar to that of conventional technology, and the primary particles have a large average particle size D50. That is, in contrast to the typical configuration of conventional positive electrode active materials (i.e., in the form of secondary particles formed by agglomeration of primary particles having a small average particle size), secondary particles formed by agglomeration of large primary particles (i.e., primary particles having increased size) are provided.

[0080] In one embodiment of the present invention, the secondary particles may be agglomerates of 1 to 10 primary large particles. More specifically, the secondary particles may be agglomerates of 1 or more, 2 or more, 3 or more, or 4 or more primary large particles within this numerical range, and may be agglomerates of 10 or less, 9 or less, 8 or less, or 7 or less primary large particles within this numerical range.

[0081] The average particle size D50 of the secondary particles of one aspect of the present invention is 3 to 10 μm. More specifically, the average particle size D50 is 3 μm or more, 3.5 μm or more, 4 μm or more, or 4.5 μm or more, and 10 μm or less, 8 μm or less, or 7 μm or less.

[0082] Generally speaking, regardless of the particle type, under the same composition, the particle size and average crystal size in the particles increase with increasing sintering temperature. In contrast, in the secondary particles of one aspect of the present invention, large primary particles with large particle size can be grown using a porous precursor without increasing the sintering temperature, and the secondary particles grow less than conventional techniques.

[0083] Therefore, the secondary particles of one aspect of the present invention have an average particle diameter D50 that is the same as or similar to that of conventional secondary particles, and include primary large particles having a larger average particle diameter and a larger average crystal size than conventional primary microparticles.

[0084] In one embodiment of the present invention, the ratio of the average particle size D50 of the secondary particles / the average particle size D50 of the primary large particles may be 2 to 5 times.

[0085] In this case, during the roll pressing process of the secondary particles, the primary large particles separate but do not crack. In this case, the roll pressing condition can be a pressure of 1 ton to 9 tons. Specifically, the roll pressing condition can be a pressure of 1 ton.

[0086] The secondary particles contain nickel-based lithium transition metal oxide.

[0087] Specifically, the nickel-based lithium transition metal oxide contains Li a [Ni x Co y Mn 1-x-y O 2+b , where 0.9 ≤ a ≤ 1.5, -0.1 ≤ b ≤ 1.0, 0.5 ≤ x ≤ 0.95, 0 < y ≤ 0.5.

[0088] For example, the nickel-based lithium transition metal oxide can be selected from the group consisting of LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2 and LiNi 0.5 Co 0.3 Mn 0.2 O2.

[0089] Nickel (Ni) helps to increase the potential and capacity of the secondary battery and corresponds to x, and its amount can be included in 0 < x < 1. When the value of x is 0, the charge / discharge capacity characteristics will decrease, and when the value of x is greater than 1, the structure and thermal stability of the active material will decrease, and as a result, the life characteristics will decrease. When considering higher potential and higher capacity effects by controlling the nickel content, the content of nickel can be more specifically 0.5 ≤ x < 1, and even more specifically 0.5 ≤ x ≤ 0.8.

[0090] Cobalt (Co) helps to improve the charge / discharge cycle characteristics of the active material and corresponds to y, and its amount can be included in 0 < y ≤ 0.35. When y = 0, the structural stability and lithium ion conductivity will decrease, and as a result, the charge / discharge capacity will decrease, and when y is greater than 0.35, at a given upper voltage limit, the working voltage of the positive electrode active material will increase and the charge / discharge capacity will decrease. When considering the effect of improving the cycle characteristics of the active material by controlling the cobalt content, the content of cobalt can be more specifically 0.1 ≤ y < 0.35, and even more specifically 0.1 ≤ y ≤ 0.3.

[0091] Meanwhile, in the present invention, a part of the surface of the secondary particles includes a coating containing a carbon material. <{

[0092] The carbon material included in the coating layer may be present in an amount of 0.3 parts by weight to 5 parts by weight based on 100 parts by weight of the secondary particles.

[0093] The thickness of the coating may be from 10 nm to 50 nm.

[0094] The carbon material may include at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, carbon nanoribbons, carbon nanobelts, carbon nanorods, graphene, graphene oxide, reduced graphene oxide, carbon black, activated carbon, and mesoporous carbon.

[0095] The inclusion of a carbon coating can improve the surface conductivity of the positive electrode active material. Furthermore, the carbon coating can smooth the surface of secondary particles with relatively high surface roughness, thereby increasing the compaction density and reducing the generation of fine particles during roller compaction. Specifically, during roller compaction of the positive electrode active material under 9-ton conditions, the presence of fine particles smaller than 1 μm can be less than 1%, more specifically, less than 0.6%.

[0096] Furthermore, the use of conductive carbon materials eliminates the need to add conductive materials when preparing electrodes containing positive active materials. Consequently, the amount of positive active material contained in the electrodes can be increased, thereby increasing energy density.

[0097] Preparation method of positive electrode active material

[0098] The positive electrode active material of one aspect of the present invention can be prepared by the following method. However, the present invention is not limited thereto.

[0099] Specifically, the present invention relates to a method for preparing a positive electrode active material for a lithium secondary battery, the method comprising:

[0100] (S1) mixing a precursor containing nickel, cobalt and manganese with a hydroxide to prepare a porous nickel-based lithium transition metal hydroxide precursor;

[0101] (S2) mixing the porous nickel-based lithium transition metal hydroxide precursor with a lithium raw material and heat-treating the mixture to prepare secondary particles; and

[0102] (S3) mixing and grinding the secondary particles with the carbon material compound,

[0103] The positive electrode active material comprises at least one secondary particle comprising an aggregate of primary large particles, and a coating provided on the surface of the secondary particle, wherein the coating comprises a carbon material.

[0104] The average particle size D50 of the primary large particles is greater than 1.5 μm,

[0105] The average particle size D50 of the secondary particles is 3 μm to 10 μm, and

[0106] The positive electrode active material includes a nickel-based lithium transition metal oxide.

[0107] Each step of the method of preparing the positive electrode active material will be described in further detail.

[0108] First, a positive electrode active material precursor including nickel (Ni), cobalt (Co), and manganese (Mn) is prepared.

[0109] In this case, the precursor for preparing the positive electrode active material may be a commercially available positive electrode active material precursor, or may be prepared by a method for preparing a positive electrode active material precursor known in the corresponding technical field.

[0110] For example, the precursor can be prepared by adding a complex former containing ammonium cations and a basic compound to a transition metal solution containing a nickel-containing raw material, a cobalt-containing raw material, and a manganese-containing raw material, and causing a coprecipitation reaction.

[0111] The nickel-containing raw material may include, for example, nickel-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides or oxyhydroxides, specifically, 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 is not limited thereto.

[0112] The cobalt-containing raw material may include cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or hydroxide oxide, specifically, 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 is not limited thereto.

[0113] The manganese-containing raw material may include, for example, at least one of manganese-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides or oxyhydroxides. Specifically, it may include, for example, at least one of the following: manganese oxides, such as Mn2O3, MnO2, Mn3O4; manganese salts, such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, dicarboxylic manganese salts, manganese citrate and aliphatic manganese salts; manganese oxyhydroxide or manganese chloride; but is not limited thereto.

[0114] The transition metal solution can be prepared by adding a nickel-containing raw material, a cobalt-containing raw material and a manganese-containing raw material to a solvent, wherein the solvent is specifically water, or a mixed solvent of water and an organic solvent (e.g., alcohol, etc.) that is mixed with water to form a uniform mixture; or by mixing an aqueous solution of a nickel-containing raw material, an aqueous solution of a cobalt-containing raw material and an aqueous solution of a manganese-containing raw material.

[0115] The complex forming agent containing ammonium cations may include, for example, at least one of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, or NH4CO3, but is not limited thereto. Meanwhile, the complex forming agent containing ammonium cations may be used in the form of an aqueous solution. In this case, the solvent may include water, or a mixture of water and an organic solvent (specifically, an alcohol, etc.) that mixes with water to form a uniform mixture.

[0116] The alkaline compound may include at least one of a hydroxide or hydrate of an alkali metal or an alkaline earth metal, such as NaOH, KOH, or Ca(OH) 2. The alkaline compound may be used in the form of an aqueous solution, in which case the solvent may include water, or a mixture of water and an organic solvent (specifically, an alcohol, etc.) that mixes with water to form a uniform mixture.

[0117] The basic compound may be added to control the pH of the reaction solution, and may be added in such an amount that the pH of the metal solution is 8 to 12.

[0118] Subsequently, a precursor comprising nickel, cobalt, and manganese may be mixed with a hydroxide to prepare a porous nickel-based lithium transition metal hydroxide precursor.

[0119] In this case, the coprecipitation reaction may be performed at 35°C to 80°C in an inert atmosphere of nitrogen or argon.

[0120] Thus, a porous nickel-based lithium transition metal hydroxide precursor can be prepared by mixing a precursor containing nickel, cobalt, and manganese with hydroxide (S1).

[0121] Nickel-cobalt-manganese hydroxide particles are produced by the above method and precipitated in the reaction solution. By controlling the concentrations of the nickel-containing raw material, the cobalt-containing raw material, and the manganese-containing raw material, a precursor having a nickel (Ni) content of 60 mol% or more of the total metal content can be prepared. The precipitated nickel-cobalt-manganese hydroxide particles are separated by conventional methods and dried to obtain a nickel-cobalt-manganese precursor. The precursor may be a secondary particle formed by agglomeration of primary particles.

[0122] Subsequently, the above-mentioned precursor is mixed with a lithium raw material and subjected to heat treatment (primary sintering) ( S2 ).

[0123] The lithium raw material may include, but is not limited to, any type of material that is soluble in water, and may include, for example, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides. Specifically, the lithium raw material may include at least one of Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, or Li3C6H5O7.

[0124] In the case of a high-nickel NCM-based lithium composite transition metal oxide having a nickel (Ni) content of 60 mol % or more, the primary sintering may 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 primary sintering may be performed in air or an oxygen atmosphere and may be performed for 15 to 35 hours.

[0125] Subsequently, the secondary particles after the primary sintering may be mixed with a carbon material compound and ground ( S3 ).

[0126] In one aspect of the present invention, contrary to conventional techniques, the carbon material compound coating is performed by mechanical methods. For example, the carbon material compound can be coated on the surface of the secondary particles by mixing or grinding.

[0127] That is, step (S3) can be performed at room temperature.

[0128] In other words, step (S3) does not undergo any heat treatment. As described above, the positive electrode active material of one aspect of the present invention can be prepared by only simple processing without heat treatment. In addition, since no heat treatment is used, the oxidation number or structure of the transition metal compound does not change. Therefore, a positive electrode active material with fewer side reactions can be prepared.

[0129] At the same time, the method may not include any cleaning process between step (S2) and step (S3). In this case, based on the gross weight of the positive active material, the total amount of lithium remaining on the particle surface after primary sintering can be 0.5 wt % to 1.5 wt %. A cleaning process is carried out in the conventional art to wash away the lithium by-products present on the surface of the positive active material. The lithium by-products can react with the electrolyte solution in the battery and increase the amount of gas produced when stored at high temperatures. In contrast, the preparation method of one aspect of the present invention does not include any cleaning process. Therefore, lithium by-products are present on the particle surface, and when the lithium by-products are present in an amount of 0.5 wt % to 1.5 wt % based on the gross weight of the positive active material, a positive active material comprising secondary particle agglomerates (which contain primary large particles) of one aspect of the present invention can be prepared.

[0130] Positive electrode and lithium secondary battery

[0131] According to another embodiment of the present invention, a positive electrode for a lithium secondary battery including the positive electrode active material and a lithium secondary battery are provided.

[0132] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer including a positive electrode active material formed on the positive electrode current collector.

[0133] In the positive electrode, the positive electrode current collector is not limited to a specific type and can include any type of material that has conductivity without causing any chemical changes in the battery, for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. In addition, the thickness of the positive electrode current collector can generally be 3 μm to 500 μm, and can have a micro-texture on the 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 a film, sheet, foil, mesh, porous body, foam, non-woven fabric, etc.

[0134] The positive electrode active material layer may further include a binder and a conductive material in addition to the positive electrode active material described above.

[0135] In this case, a conductive material is used to impart conductivity to the electrode and can include any conductive material that has electronic conductivity without causing any chemical changes in the battery, without limitation. Specific examples of the conductive material may include at least one of the following: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives. Generally, the conductive material may be present in an amount of 1% to 30% by weight based on the total weight of the positive electrode active material layer.

[0136] In addition, the binder is used to improve the bonding between the positive active material particles and the adhesion strength between the positive active material and the positive current collector. Specific examples of the binder 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, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or its various copolymers. Based on the total weight of the positive active material layer, the content of the binder may be 1% to 30% by weight.

[0137] In addition to using the above-mentioned positive electrode active materials, the positive electrode can be manufactured by a commonly used positive electrode manufacturing method. Specifically, the positive electrode can be manufactured by coating a positive electrode active material layer-forming composition comprising a positive electrode active material and an optional binder and a conductive material on a positive electrode current collector, drying, and rolling. In this case, the types and contents of the positive electrode active material, binder, and conductive material can be the same as described above.

[0138] The solvent may include a solvent commonly used in the corresponding technical field, for example, at least one of dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or water. Considering the slurry coating thickness and yield, when dissolving or dispersing the positive electrode active material, the conductive material and the binder and coating to manufacture the positive electrode, the solvent may be used in an amount having sufficient viscosity to obtain good thickness uniformity.

[0139] Alternatively, the positive electrode may be manufactured by casting the positive electrode active material layer-forming composition on a support, peeling the film from the support, and laminating the film on a positive electrode current collector.

[0140] According to another embodiment of the present invention, an electrochemical device comprising the positive electrode is provided. Specifically, the electrochemical device may include a battery or a capacitor, and more specifically, may include a lithium secondary battery.

[0141] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode opposite to the positive electrode, a separator between the positive electrode and the negative electrode, and an electrolyte, and the positive electrode is as described above. In addition, optionally, the lithium secondary battery may also include a battery box for accommodating an electrode assembly (the electrode assembly includes a positive electrode, a negative electrode and a separator), and a sealing component for sealing the battery box.

[0142] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0143] The negative electrode current collector may comprise any material with high conductivity that does not cause any chemical changes in the battery, such as, but not limited to, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or copper or stainless steel surface-treated with carbon, nickel, titanium, or silver, and aluminum-cadmium alloys. Furthermore, the negative electrode current collector may typically have a thickness of 3 μm to 500 μm and, similar to the positive electrode current collector, may have a microtexture on its surface to enhance the bonding strength of the negative electrode active material. For example, the negative electrode current collector may be in various forms, such as a film, sheet, foil, mesh, porous body, foam, non-woven fabric, and the like.

[0144] In addition to the negative electrode active material, the negative electrode active material layer may optionally contain a binder and a conductive material. For example, the negative electrode active material layer may be formed by coating a negative electrode forming composition containing the negative electrode active material and optionally a binder and a conductive material on a negative electrode current collector and drying the coating, or by casting the negative electrode forming composition on a support, peeling the film from the support, and laminating the film on the negative electrode current collector.

[0145] The negative electrode active material may include a compound capable of reversibly intercalating and deintercalating lithium. Specific examples of the negative electrode active material may include at least one of the following: carbon materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metal materials capable of forming an alloy with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and dedoping lithium, such as SiO β (0<β<2), SnO2, vanadium oxide or lithium vanadium oxide; or a complex comprising a metal material and a carbon material, such as a Si-C complex or a Sn-C complex. In addition, a metallic lithium thin film can be used as a negative electrode active material. In addition, the carbon material can include low-crystalline carbon and high-crystalline carbon. Low-crystalline carbon typically includes soft carbon and hard carbon, while high-crystalline carbon typically includes high-temperature sintered carbon, such as amorphous, planar, flaky, spherical or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-type carbon fibers, mesophase carbon microbeads, mesophase pitch, and coke derived from petroleum or coal tar pitch.

[0146] In addition, the binder and the conductive material may be the same as those in the description of the positive electrode above.

[0147] Meanwhile, in lithium secondary batteries, the diaphragm separates the negative electrode from the positive electrode and provides a channel for the movement of lithium ions, and may include but is not limited to any diaphragm commonly used in lithium secondary batteries, and particularly preferably, the diaphragm may have low resistance to the movement of electrolyte ions and good wettability of electrolyte solution. Specifically, the diaphragm may include, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer, or a stack of two or more porous polymer films. In addition, the diaphragm may include a commonly used porous non-woven fabric, such as a non-woven fabric made of high melting point glass fiber and polyethylene terephthalate fiber. In addition, in order to ensure heat resistance or mechanical strength, a coated diaphragm comprising ceramic or polymer material may be used, and a single layer or multilayer structure may be selectively used.

[0148] Furthermore, the electrolyte used in the present invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries, but is not limited thereto.

[0149] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0150] The organic solvent may include any type of organic solvent that acts as a medium for the movement of ions involved in the electrochemical reaction of the battery, without any limitation. Specifically, the organic solvent may 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 and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; R-CN nitrile (R is a linear, branched or cyclic hydrocarbon of C2 to C20 and may contain an exocyclic double bond or an ether bond); and amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolane. Among them, carbonate solvents are ideal, and more preferably, cyclic carbonates with high dielectric constants (e.g., ethylene carbonate or propylene carbonate) that contribute to improving battery charge / discharge performance 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.

[0151] The lithium salt may include, but is not limited to, any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt 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 may be in the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has optimal conductivity and viscosity, resulting in good performance of the electrolyte and efficient movement of lithium ions.

[0152] In addition to the constituent materials of the above-mentioned electrolyte, the electrolyte may further include, for example, at least one type of additive: a halogenated alkylene carbonate compound (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum chloride to improve the life characteristics of the battery, prevent the capacity decay of the battery, and improve the discharge capacity of the battery. In this case, the content of the additive may be 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0153] The lithium secondary battery including the cathode active material of the present invention is useful in the fields of mobile devices including mobile phones, notebook computers, and digital cameras, and electric vehicles including hybrid electric vehicles (HEVs).

[0154] 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.

[0155] The battery module or battery pack can be used as a power source for at least one of the following medium to large devices: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0156] Hereinafter, the embodiments of the present invention will be described in sufficient detail so that those skilled in the art can easily practice the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described.

[0157] Comparative Example 1

[0158] 4 liters of distilled water were placed in a coprecipitation reactor (capacity 20 L), and a 3.2 mol / L transition metal solution (NiSO4, CoSO4, and MnSO4 were mixed in a molar ratio of nickel:cobalt:manganese of 0.8:0.1:0.1) and a 28 wt% ammonia solution were continuously added to the reactor at a rate of 300 ml / hour and 42 ml / hour, respectively, while the temperature was maintained at 50°C. Stirring was performed at a propeller speed of 400 rpm, and the pH was maintained at 9 using a 40 wt% sodium hydroxide solution. Precursor particles were formed by a 10-hour coprecipitation reaction. The precursor particles were separated, washed, and dried in an oven at 130°C to prepare a precursor.

[0159] Ni synthesized by coprecipitation reaction 0.8 Co 0.1 Mn 0.1The (OH)2 precursor was mixed with LiOH so that the molar ratio of Li / Me(Ni, Co, Mn) was 1.05 and heat treated at 850°C for 10 hours in an oxygen atmosphere to prepare a LiNi 0.8 Co 0.1 Mn 0.1 O2 nickel-based lithium transition metal oxide secondary particles as positive electrode active materials.

[0160] In Comparative Example 1, the secondary particles included primary large particles.

[0161] Example 1

[0162] The secondary particles prepared in Comparative Example 1 and Ketjen black were mixed in a weight ratio of 99:1, introduced into a Nobilta mixer, and milled at a rotation speed of 3000 rpm for 10 minutes, thereby preparing a positive electrode active material having Ketjen black carbon material coated on the surface of the secondary particles.

[0163] Example 2

[0164] A positive electrode active material having Ketjen black carbon material coated on the surface of the secondary particles was prepared by the same method as in Example 1, except that the secondary particles prepared in Comparative Example 1 were mixed with Ketjen black at a weight ratio of 99.5:0.5.

[0165] Comparative Example 2

[0166] 4 liters of distilled water were placed in a coprecipitation reactor (capacity 20 L), and 100 mL of 28 wt% ammonia solution was added while maintaining the temperature at 50° C., and a 3.2 mol / L transition metal solution (wherein NiSO 4 , CoSO 4 and MnSO 4 were mixed in a molar ratio of 0.8:0.1:0.1 for nickel:cobalt:manganese) and a 28 wt% ammonia solution were continuously added to the reactor at a rate of 300 ml / hour and 42 ml / hour, respectively. The mixture was stirred at a propeller speed of 400 rpm, and the pH was maintained at 11.0 using a 40 wt% sodium hydroxide solution. Precursor particles were formed by a 24-hour coprecipitation reaction. The precursor particles were separated, cleaned, and dried in an oven at 130° C. to prepare a precursor.

[0167] Ni synthesized by coprecipitation reaction 0.8 Co 0.1 Mn 0.1 The (OH)2 precursor was mixed with Li2CO3 at a Li / Me(Ni, Co, Mn) molar ratio of 1.05 and heat treated at 800 °C for 10 h in an oxygen atmosphere to prepare a LiNi 0.8 Co 0.1 Mn 0.1 O2 lithium composite transition metal oxide secondary particles are positive electrode active materials.

[0168] In Comparative Example 2, the secondary particles included primary fine particles.

[0169] Comparative Example 3

[0170] The secondary particles prepared in Comparative Example 2 and Ketjen black were mixed in a weight ratio of 99:1, introduced into a Nobilta mixer, and milled at a rotation speed of 3000 rpm for 10 minutes, thereby preparing a positive electrode active material in which the secondary particles were coated with Ketjen black carbon material.

[0171] [Experimental Example 1: Conductivity Test]

[0172] The electrical conductivities of the positive electrode active materials of Comparative Examples 1 to 3 and Example 1 were measured after being subjected to roll pressing under 1 ton conditions. The results are shown in Table 1.

[0173] The electrical conductivity was measured using a powder resistance measuring device. Specifically, after introducing 5 g of each of the positive electrode active material of Example 1 and Comparative Examples 1 to 3 into a cylindrical 4-pin probe mold, the mold containing the positive electrode active material was pressed under a pressure of 1 ton, and after measuring the powder resistance, the electrical conductivity was calculated.

[0174]

Table 1

[0175] Conductivity (S / cm) Comparative Example 1 Example 1 Example 2 Comparative Example 2 Comparative Example 3 Apply 1 ton of pressure <![CDATA[2.71×10 -4 ]]> <![CDATA[1.43×10 -2 ]]> <![CDATA[9.51×10 -3 ]]> <![CDATA[3.94×10 -4 ]]> <![CDATA[3.55×10 -3 ]]>

[0176] As can be seen from Table 1, in the case of Examples 1 and 2, the electrical conductivity is 53 times and 35 times higher than that of Comparative Example 1, respectively. In contrast, in the case of Comparative Examples 2 and 3 using secondary particles comprising conventional primary microparticles instead of the secondary particles comprising primary large particles of the present invention, the electrical conductivity after carbon material coating (Comparative Example 3) is 9 times higher than the electrical conductivity before carbon material coating (Comparative Example 2). Therefore, it can be seen that according to one aspect of the present invention, this effect is clearly found in the carbon material coating of secondary particles comprising primary large particles. In addition, objective numerical results also show that Example 1 has a higher electrical conductivity than Comparative Example 3, and Example 2 having half a carbon material coating also has a higher electrical conductivity than Comparative Example 3.

[0177] [Experimental Example 2: Measurement of compacted density]

[0178] After the positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were pressed under 1 ton conditions, the compaction density was measured and the results are shown in Table 2 below.

[0179] The compaction density was measured using an HPRM-1000. Specifically, 5 g of the positive electrode active material from Example 1 and Comparative Examples 1 to 3 were placed in a cylindrical mold. A pressure of 1 ton was applied to the mold containing the positive electrode active material. The height of the pressing mold was then measured using a vernier caliper, and the compaction density was calculated.

[0180]

Table 2

[0181] Compacted density (g / cc) Comparative Example 1 Example 1 Example 2 Comparative Example 2 Comparative Example 3 Apply 1 ton of pressure 2.81 3.09 2.95 2.6 2.84

[0182] As can be seen from Table 2, it was found that the compacted density increased by about 5% to 10% in the case of the carbon material coating. In this case, the carbon material coating on the secondary particles comprising primary large particles according to one aspect of the present invention showed a higher compacted density value than the carbon material coating on the secondary particles comprising conventional primary microparticles.

[0183] [Experimental Example 3: Existence ratio of fine particles smaller than 1 μm under 9-ton roller pressure]

[0184] 5 g of the positive electrode active material prepared in Examples 1 and 2 and Comparative Examples 1 to 3 was placed in a cylindrical metal mold with a diameter of 2 cm, and roller pressed under a pressure of 9 tons using a metal cylinder of the same diameter, and collected to measure the particle size distribution of each positive electrode active material using particle size distribution (PSD). The results are shown in Table 3 below.

[0185]

Table 3

[0186] The presence ratio of fine particles smaller than 1 μm Comparative Example 1 Example 1 Example 2 Comparative Example 2 Comparative Example 3 Before rolling 0 0 0 0 0 After rolling 1.91 0.18 0.51 9.14 13.63

[0187] As can be seen from Table 3, Examples 1 and 2 showed improvements of approximately 90.6% and 73.3%, respectively, in terms of fine particle formation. In contrast, Comparative Example 3 having a carbon material coating on secondary particles comprising primary microparticles did not show any improvement in fine particle formation, but rather a decrease of 49.1%, compared to Comparative Example 2 before carbon material coating.

[0188] [Experimental Example 4: Comparison of Remaining Capacity of Batteries after 100 Charge / Discharge Cycles]

[0189] Lithium secondary battery half cells were fabricated using the positive electrode active materials prepared in Examples 1 and 2 and Comparative Examples 1 to 3, and the capacity retention rate and the resistance increase rate were measured by the following methods.

[0190] The positive electrode active material, carbon black conductive material and PVdF binder prepared in each of the examples and comparative examples were mixed in an N-methylpyrrolidone solvent at a weight ratio of 96:2:2 to prepare a positive electrode material mixture, and the positive electrode material mixture was coated on one surface of an aluminum current collector, dried at 100° C. and roll-pressed to manufacture a positive electrode.

[0191] Lithium metal was used as the negative electrode.

[0192] An electrode assembly (the electrode assembly includes the positive and negative electrodes manufactured as described above, and a porous polyethylene separator between the positive and negative electrodes) is manufactured and placed in a box, and an electrolyte solution is injected into the box to manufacture a lithium secondary battery. In this case, the electrolyte solution is prepared by dissolving 1.0M lithium hexafluorophosphate (LiPF6) in an organic solvent comprising ethylene carbonate / ethyl methyl carbonate / diethyl carbonate / (EC / EMC / DEC=3 / 4 / 3 in a mixed volume ratio).

[0193] The fabricated lithium secondary battery half-cell was charged to 4.2 V in CC-CV mode at 0.7 C and 45°C, and discharged to 3.0 V at a constant current of 0.5 C. The capacity retention rate over 100 charge / discharge cycles was measured to evaluate the lifespan characteristics. The results are shown in Table 4 below.

[0194]

Table 4

[0195] After 100 cycles Comparative Example 1 Example 1 Example 2 Comparative Example 2 Comparative Example 3 Capacity retention rate (%) 94.0 97.2 96.5 92.9 93.0 Resistance increase rate (%) 158.5 112.4 120.3 114.4 118.6

[0196] As can be seen from Table 4, Examples 1 and 2 were found to be superior to Comparative Example 1 in terms of capacity retention and resistance increase rate. In contrast, in the case of Comparative Examples 2 and 3 involving secondary particles containing primary microparticles, it can be seen that Comparative Example 3 having a carbon material coating layer has a capacity retention rate at the same level as Comparative Example 2 having no carbon material coating layer, and shows an increase in resistance.

Claims

1. A positive electrode active material for a lithium secondary battery, comprising: at least one secondary particle comprising agglomerates of primary large particles; and a coating disposed on the surface of the secondary particle, the coating comprising a carbon material; in, The average particle size D50 of the primary large particles is greater than 1.5 μm, The average particle size D50 of the secondary particles is 3 μm or more and less than 10 μm. The positive electrode active material comprises a nickel-based lithium transition metal oxide, The ratio of the average particle size D50 of the primary large particles to the average crystal size of the primary large particles is 2 or more, and When the positive electrode active material is subjected to roll pressing under 9 tons, the presence ratio of fine particles smaller than 1 μm is 1% or less.

2. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The carbon material contained in the coating layer may be present in an amount of 0.3 parts by weight to 5 parts by weight based on 100 parts by weight of the secondary particles.

3. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The thickness of the coating layer is 10 nm to 50 nm.

4. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The carbon material comprises at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, carbon nanorods, carbon nanobelts, carbon nanorods, graphene, graphene oxide, reduced graphene oxide, carbon black, activated carbon, and mesoporous carbon.

5. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The nickel-based lithium transition metal oxide is Li a [Ni x Co y Mn 1-x-y ]O 2+b , where 0.9≤a≤1.5, -0.1≤b≤1.0, 0.5≤x≤0.95, 0<y≤0.

5.

6. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The ratio of the average particle diameter D50 of the primary large particles / the average crystal size of the primary large particles is 2 or more and 50 or less.

7. The positive electrode active material for lithium secondary batteries according to claim 1, wherein The average crystal size of the primary large particles is 130 nm or more.

8. The positive electrode active material for lithium secondary batteries according to claim 1, wherein 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 5 times.

9. The positive electrode active material for lithium secondary batteries according to claim 1, wherein In the roll-pressing process of the positive electrode active material, the primary large particles are separated from the secondary particles and are not cracked themselves.

10. The positive electrode active material for lithium secondary batteries according to claim 9, wherein The rolling process was performed under a 1-ton condition. 11 . A positive electrode for a lithium secondary battery, comprising the positive electrode active material according to claim 1 . 12 . A lithium secondary battery comprising the positive electrode active material according to claim 1 .

13. A method for preparing a positive electrode active material for a lithium secondary battery, comprising: (S1): mixing a precursor comprising nickel, cobalt, and manganese with a hydroxide to prepare a porous nickel-based lithium transition metal hydroxide precursor; (S2): mixing the porous nickel-based lithium transition metal hydroxide precursor with a lithium raw material and heat-treating the mixture to prepare secondary particles; and (S3): mixing the secondary particles with a carbon material to form a coating layer comprising the carbon material on the surface of the secondary particles, wherein the positive electrode active material comprises at least one secondary particle comprising an agglomerate of primary large particles, and a coating provided on the surface of the secondary particle, the coating comprising the carbon material, The average particle size D50 of the primary large particles is greater than 1.5 μm, The average particle size D50 of the secondary particles is 3 μm or more and less than 10 μm. The positive electrode active material comprises a nickel-based lithium transition metal oxide, The ratio of the average particle size D50 of the primary large particles to the average crystal size of the primary large particles is 2 or more, and When the positive electrode active material is subjected to roll pressing under 9 tons, the presence ratio of fine particles smaller than 1 μm is 1% or less.

14. The method for preparing a positive electrode active material according to claim 13, wherein: The step (S1) is performed at 35°C to 80°C, and the step (S2) is performed at 700°C to 1000°C.

15. The method for preparing a positive electrode active material according to claim 13, wherein: The step (S3) is performed at room temperature.

16. The method for preparing a positive electrode active material according to claim 13, wherein: The step (S1) is carried out at a pH value of 8 to 12.

17. The method for preparing a positive electrode active material according to claim 13, wherein: The method does not include a cleaning process between step (S2) and step (S3).

18. The method for preparing a positive electrode active material according to claim 13, wherein: The tap density of the porous nickel-based lithium transition metal hydroxide precursor in the step (S2) is less than 2.0 g / cc.

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