Positive electrode for lithium secondary battery and lithium secondary battery comprising the same

Abstract

Disclosed is a positive electrode for a lithium secondary battery, which includes a positive electrode active material layer containing positive electrode active material secondary large particles and secondary fine particles having different average particle diameters to allow a sufficiently high roll pressure to be applied thereto at the time of manufacturing the electrode.

Description

Technical Field

[0001] The present invention relates to a cathode having a multilayer structure of positive electrode active material layer comprising a nickel-based lithium transition metal oxide, and a lithium secondary battery comprising the same.

[0002] This application claims priority to Korean Patent Application No. 10-2021-0082673, filed in Korea on June 24, 2021, the disclosure of which is incorporated herein by reference. Background Technology

[0003] Recently, with the rapid proliferation of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for small, lightweight, and relatively high-capacity rechargeable batteries has grown rapidly. In particular, lithium-ion batteries have attracted considerable attention as a power source for mobile devices due to their lightweight and high energy density. Consequently, much research and development has been undertaken 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), nickel-based lithium transition metal oxides, lithium manganese oxides (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 can be used as a high-voltage positive electrode active material. However, cobalt (Co) faces limitations in its large-scale use as a power source in electric vehicles due to its rising price and unstable supply. Therefore, there is a need to develop alternative positive electrode active materials, especially Ni-rich lithium composite transition metal oxide positive electrode active materials, which have attracted much attention due to their high capacity.

[0006] Currently available nickel-rich lithium composite transition metal oxide cathode active materials include secondary particles formed by the aggregation of primary microparticles with an average particle size D50 at the level of several hundred nm. In order to improve output and compaction density, bimodal cathode active materials are usually used, which include a mixture of two types of secondary particles with different average particle sizes D50, namely, a mixture of secondary large particles with a larger average particle size and secondary microparticles with a smaller average particle size.

[0007] Secondary particles formed from the aggregation of primary microparticles have a large specific surface area and low particle strength. Therefore, when rolling electrodes containing bimodal positive electrode active materials using a rolling mill, significant fragmentation occurs, particularly within the large secondary particles, leading to the generation of large amounts of gas during cell operation and reduced stability. Consequently, it becomes difficult to sufficiently increase the rolling mill pressure to prevent short circuits, or lifespan characteristics may be reduced. In particular, in the case of high-Ni lithium transition metal oxides with high nickel content to ensure high capacity, chemical stability deteriorates and thermal stability is difficult to ensure when particle fragmentation occurs due to structural issues. Summary of the Invention

[0008] Technical issues

[0009] One aspect of the present invention aims to provide a positive electrode for lithium secondary batteries, comprising a positive electrode active material layer containing secondary large particles and secondary micro particles of positive electrode active material with different average particle sizes, so as to allow sufficiently high rolling pressure during electrode manufacturing.

[0010] Another aspect of the present invention aims to provide a positive electrode for lithium secondary batteries, which comprises a positive electrode active material layer containing secondary large particles and secondary micro particles of positive electrode active material with different average particle sizes, so as to improve lifespan characteristics.

[0011] Another aspect of the present invention aims to provide a lithium secondary battery comprising a positive electrode for a lithium secondary battery having the above-described features.

[0012] Technical solution

[0013] One aspect of the present invention provides a positive electrode for a lithium secondary battery according to the following embodiments.

[0014] The first embodiment relates to a positive electrode for a lithium secondary battery, comprising:

[0015] current collector;

[0016] A first positive electrode active material layer is located on at least one surface of the current collector. The first positive electrode active material layer includes positive electrode active material particles and a conductive material. The positive electrode active material particles include at least one positive electrode active material particle selected from the group consisting of primary large particles with an average particle size D50 of 0.5 to 3 μm, secondary particles with an average particle size D50 of 3 to 7 μm formed by the aggregation of the primary large particles, and mixtures thereof.

[0017] A second positive electrode active material layer is located on top of the first positive electrode active material layer. The second positive electrode active material layer includes positive electrode active material particles and a conductive material. The positive electrode active material particles include:

[0018] Secondary microparticles of positive electrode active material with an average particle size D50 of 1 to 7 μm are formed by the aggregation of primary large particles with an average particle size D50 of 0.5 to 3 μm or by the aggregation of primary microparticles with an average particle size D50 smaller than the primary large particles.

[0019] The positive electrode active material consists of secondary large particles with an average particle size D50 of 7 to 20 μm, which are formed by the aggregation of primary microparticles with an average particle size D50 smaller than that of the primary large particles. The average particle size D50 of the secondary large particles is greater than that of the secondary microparticles.

[0020] The positive electrode active material particles are nickel-based lithium transition metal oxide positive electrode active materials, and

[0021] The conductive material contained in the second positive electrode active material layer includes single-walled carbon nanotubes.

[0022] The second embodiment relates to the positive electrode for a lithium secondary battery of the first embodiment, wherein the average particle size D50 of the primary microparticles is 100 to 900 nm, particularly 100 to 400 nm.

[0023] The third embodiment relates to a positive electrode for a lithium secondary battery according to the first or second embodiment, wherein the average grain size of the primary large particles contained in the first positive electrode active material layer is equal to or greater than 200 nm.

[0024] The fourth embodiment relates to a positive electrode for a lithium secondary battery in any one of the first to third embodiments, wherein the average particle size D50 of the primary large particles contained in each of the first and second positive electrode active material layers is 1 to 3 μm.

[0025] The fifth embodiment relates to a positive electrode for a lithium secondary battery in any one of the first to fourth embodiments, wherein the average particle size D50 of the secondary microparticles is 2 to 5 μm, and the average particle size D50 of the secondary large particles is 8 to 16 μm.

[0026] The sixth embodiment relates to a positive electrode for a lithium secondary battery in any one of the first to fifth embodiments, wherein the average particle size D50 of the secondary large particles and the average particle size D50 of the secondary micro particles are 5:1 to 2:1.

[0027] The seventh embodiment relates to a positive electrode for a lithium secondary battery in any one of the first to sixth embodiments, wherein the amount of the secondary microparticles is 10 to 100 parts by weight, based on 100 parts by weight of the secondary large particles.

[0028] The eighth embodiment relates to a positive electrode for a lithium secondary battery according to any one of the first to seventh embodiments, wherein the thickness 'a' of the second positive electrode active material layer relative to the thickness 'b' of the first positive electrode active material layer satisfies the following formula:

[0029] (Formula) 3b≤a.

[0030] The ninth embodiment relates to a positive electrode for a lithium secondary battery of any one of the first to eighth embodiments, wherein the secondary microparticles are an aggregate of only the primary microparticles.

[0031] The tenth embodiment relates to a positive electrode for a lithium secondary battery according to any one of the first to ninth embodiments, wherein the nickel-based lithium transition metal oxide is composed of Li a Ni 1-x-y Co x M 1 y M 2 w O2 represents the expression where 1.0 ≤ a ≤ 1.5, 0 ≤ x ≤ 0.2, 0 ≤ y ≤ 0.2, 0 ≤ w ≤ 0.1, 0 ≤ x + y ≤ 0.2, and M. 1 It is at least one metal selected from Mn or Al, and M 2 It is at least one metal selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo, and in particular, nickel-based lithium transition metal oxides are composed of Li a Ni 1-x- y Co x Mn y O2 represents the expression where 1.0≤a≤1.5, 0≤x≤0.2, 0≤y≤0.2, and 0≤x+y≤0.2.

[0032] The eleventh embodiment relates to a positive electrode for a lithium secondary battery in any one of the first to tenth embodiments, wherein the amount of the single-walled carbon nanotubes present is 0.001% by weight or more based on the total weight of the second positive electrode active material layer.

[0033] The twelfth embodiment relates to a positive electrode for a lithium secondary battery of any one of the first to eleventh embodiments, wherein the amount of conductive material present in the second positive electrode active material layer is 0.5 to 3 by weight, based on the total weight of the second positive electrode active material layer.

[0034] The thirteenth embodiment provides a lithium secondary battery including the positive electrode.

[0035] Beneficial effects

[0036] The second positive electrode active material layer of the positive electrode in the embodiments of the present invention simultaneously contains secondary large particles and secondary micro particles, thus having a high compaction density.

[0037] Furthermore, since the first positive electrode active material, positioned between the current collector and the second positive electrode active material layer, contains non-fractureable positive electrode active material particles, short circuits can be prevented even under sufficiently high rolling pressure applied during electrode manufacturing. Therefore, lithium-ion secondary batteries containing a positive electrode with non-fractureable positive electrode active material particles exhibit improved lifespan characteristics.

[0038] In addition, conductive materials containing single-walled carbon nanotubes (SW-CNTs) in the second positive electrode active material layer improve electrode resistance and cell resistance. Attached Figure Description

[0039] The accompanying drawings illustrate exemplary embodiments of the invention and, together with the foregoing description, are intended to aid in a further understanding of the technical aspects of the invention. Therefore, the invention should not be construed as being limited to the drawings. Furthermore, the shape, size, scale, or proportion of elements in the drawings may be exaggerated to emphasize a clearer description.

[0040] Figure 1 This is a schematic cross-sectional view of a positive electrode with a single-layer structure of positive active material layer, which is a prior art technology.

[0041] Figure 2 This is a schematic cross-sectional view of the positive electrode of the present invention, which has a multilayer structure of positive electrode active material layers.

[0042] Figure 3 This is a graph showing the capacity retention and resistance of the lithium secondary batteries of the embodiments and comparative examples. Detailed Implementation

[0043] Embodiments of the present invention 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 and dictionary meanings, but rather are interpreted based on the principle of allowing the inventors to appropriately define terms for best interpretation, and on the meanings and concepts corresponding to the technical aspects of the present invention. Therefore, the disclosure of the embodiments described herein is merely an exemplary embodiment of the present invention, and is not intended to fully describe the technical aspects of the present invention. Consequently, it should be understood that various other equivalents and modifications may be made thereto at the time of filing this application.

[0044] Unless the context clearly indicates otherwise, it should be understood that the terms “comprising” or “including” as used in this specification specify the presence of the stated element, but do not exclude the presence or addition of one or more other elements.

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

[0046] In the specification and appended claims, D50 can be defined as the particle size at 50% of the particle size distribution and can be measured using laser diffraction. 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 them into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT3000), irradiating them with ultrasound at an output power of 60W at approximately 28kHz, and calculating the average particle size D50 corresponding to 50% of the cumulative volume in the analyzer.

[0047] In this invention, "primary particles" refers to particles that do not appear to have grain boundaries when observed using a scanning electron microscope at a magnification of 5,000 to 20,000 times.

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

[0049] In this invention, "monolith" refers to a particle that exists independently of secondary particles and whose grain boundaries do not appear to exist; for example, it is a particle with a diameter of 0.5 μm or larger.

[0050] In this invention, "particles" may include any one or all of single blocks, secondary particles, and primary particles.

[0051] According to one aspect of the present invention, a positive electrode for a lithium secondary battery is provided, comprising:

[0052] current collector;

[0053] A first positive electrode active material layer is located on at least one surface of the current collector. The first positive electrode active material layer includes positive electrode active material particles and a conductive material. The positive electrode active material particles include at least one positive electrode active material particle selected from the group consisting of primary large particles with an average particle size D50 of 0.5 to 3 μm, secondary particles with an average particle size D50 of 3 to 7 μm formed by the aggregation of the primary large particles, and mixtures of these particles.

[0054] A second positive electrode active material layer is located on top of the first positive electrode active material layer. The second positive electrode active material layer includes positive electrode active material particles and a conductive material. The positive electrode active material particles include:

[0055] Secondary microparticles of positive electrode active material with an average particle size D50 of 1 to 7 μm are formed by the aggregation of primary large particles with an average particle size D50 of 0.5 to 3 μm, or by the aggregation of primary microparticles with an average particle size D50 smaller than the primary large particles.

[0056] The positive electrode active material consists of secondary large particles with an average particle size D50 of 7 to 20 μm, which are formed by the aggregation of primary microparticles with an average particle size D50 smaller than that of the primary large particles. The average particle size D50 of the secondary large particles is greater than that of the secondary microparticles.

[0057] The positive electrode active material particles are nickel-based lithium transition metal oxide positive electrode active materials, and

[0058] The conductive material contained in the second positive electrode active material layer includes single-walled carbon nanotubes (SW-CNTs).

[0059] Structure of the positive electrode active material layer

[0060] Figure 1 This is a schematic cross-sectional view of a positive electrode with a single-layer structure of positive active material layer, which is a prior art technology.

[0061] refer to Figure 1 The conventional positive electrode 10 has a single-layer positive electrode active material layer 3 by coating at least one surface of the current collector 1 with a bimodal positive electrode active material, the bimodal positive electrode active material comprising a mixture of secondary large particles formed by the aggregation of primary micro particles and secondary micro particles formed by the aggregation of primary micro particles.

[0062] On the contrary, such as Figure 2 As shown, the positive electrode 20 of the present invention has a multilayer positive electrode active material layer by the following process: forming a first positive electrode active material layer 15 containing positive electrode active material particles having predetermined characteristics on at least one surface of the current collector 11, and coating a bimodal positive electrode active material onto the first positive electrode active material layer 15 to form a second positive electrode active material layer 17.

[0063] Preferably, considering the output characteristics and the expected effects of the present invention, the thickness a of the second positive electrode active material layer relative to the thickness b of the first positive electrode active material layer satisfies the following formula.

[0064] (Formula) 3b≤a

[0065] current collector

[0066] The current collector, i.e., the positive electrode current collector, is not limited to a specific type and can include any type of material that is conductive and does not cause any chemical changes to the battery, such as stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, or silver. Furthermore, the thickness of the positive electrode current collector can typically be 3 to 500 μm, and it can have a fine texture on its surface to improve the adhesion strength of the positive electrode active material. For example, the positive electrode current collector can take many forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0067] First positive electrode active material layer

[0068] The positive electrode active material particles contained in the first positive electrode active material layer include at least one positive electrode active material particle selected from the group consisting of primary large particles with an average particle size D50 of 0.5 to 3 μm, secondary particles with an average particle size D50 of 3 to 7 μm formed by the aggregation of the primary large particles, and mixtures of these particles. That is, the positive electrode active material contained in the first positive electrode active material layer may contain primary large particles with an average particle size D50 of 0.5 to 3 μm and / or secondary particles with an average particle size D50 of 3 to 7 μm formed by the aggregation of the primary large particles. In particular, the positive electrode active material contained in the first positive electrode active material layer may contain only secondary particles with an average particle size D50 of 3 to 7 μm formed by the aggregation of primary large particles.

[0069] The primary large particles are nickel-based lithium transition metal oxide cathode active materials, specifically composed of Li a Ni 1-x- y Co x M 1 y M 2 w O2(1.0≤a≤1.5, 0≤x≤0.2,0≤y≤0.2, 0≤w≤0.1, 0≤x+y≤0.2, M 1 It is at least one metal selected from Mn or Al, and M 2 It is represented by at least one metal selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo, and in particular, by Li. a Ni 1-x-y Co x Mn y O2(1.0≤a≤1.5,0≤x≤0.2,0≤y≤0.2,0≤x+y≤0.2) represents this.

[0070] In the positive electrode active material particles contained in the first positive electrode active material layer, the average particle size D50 of the primary large particles can specifically be 1 to 3 μm. In addition, the average particle size D50 of the secondary particles formed by the aggregation of primary large particles can be 2 to 5 μm.

[0071] Compared to conventional primary microparticles as described below, primary macroparticles have a larger average primary particle size.

[0072] From a fracture perspective, it is advantageous to have a large average grain size and appear to be free of grain boundaries, like a monolith. When the average grain size D50 of the primary particles is increased only through over-sintering, rock salt forms on the surface of the primary particles, increasing the initial resistivity. Growing the primary particles along with their grain size reduces the resistivity. Therefore, in embodiments of the present invention, the primary large particles are preferably particles with a large average grain size and a large average grain size, and which appear to be free of grain boundaries.

[0073] Compared to monoliths (whose resistance increases significantly due to the formation of rock salt on the surface during high-temperature sintering), the simultaneous growth of primary particles with both average particle size and average grain size reduces resistance and is advantageous in terms of long lifespan.

[0074] Compared to monoliths, the microparticles used in one aspect of the invention, comprising "primary large particles," aggregates thereof, or mixtures thereof, are advantageous in terms of low electrical resistance due to the increased size of the primary particles themselves and the reduced formation of rock salt.

[0075] In this context, the average grain size of primary large particles can be quantitatively analyzed using Cu Kα X-ray-based X-ray diffraction (XRD). Specifically, the average grain size of primary large particles can be quantitatively analyzed by placing the prepared particles in a support and analyzing the diffraction grating of the X-rays irradiated onto the particles. The average grain size of primary large particles can be above 200 nm, specifically above 250 nm, and more specifically above 300 nm.

[0076] The first positive electrode active material layer containing the aforementioned positive electrode active material particles is less prone to breakage compared to the secondary large particles formed by the aggregation of primary microparticles, thereby preventing short circuits under sufficiently high rolling pressure applied during electrode manufacturing. Furthermore, it reduces the breakage of secondary large particles, thus improving lifespan characteristics.

[0077] Second positive electrode active material layer

[0078] The positive electrode active material particles contained in the second positive electrode active material layer include: positive electrode active material secondary micro particles with an average particle size of 1 to 7 μm formed by the aggregation of primary large particles with an average particle size D50 of 0.5 to 3 μm or by the aggregation of primary micro particles with an average particle size D50 smaller than the primary large particles; and positive electrode active material secondary large particles with an average particle size D50 of 7 to 20 μm formed by the aggregation of primary micro particles with an average particle size D50 smaller than the primary large particles, wherein the average particle size D50 of the secondary large particles is greater than the average particle size D50 of the secondary micro particles.

[0079] In the composition of the secondary microparticles, the secondary microparticles formed by the aggregation of primary large particles with an average particle size D50 of 0.5 to 3 μm are the same as those described in the first positive electrode active material layer. On the other hand, in the composition of the secondary microparticles, the secondary microparticles formed by the aggregation of primary microparticles are bimodal positive electrode active material secondary microparticles commonly used in this art. The average particle size D50 of the primary microparticles can specifically be 100 to 900 nm, particularly 100 to 400 nm. In particular, the secondary microparticles may consist only of aggregates of primary microparticles. Based on 100 parts by weight of the secondary large particles described below, the amount of secondary microparticles present can be 10 to 100 parts by weight.

[0080] On the other hand, the secondary large particles are positive electrode active material particles formed by the aggregation of primary microparticles with an average particle size D50 smaller than that of the primary large particles. These primary microparticles are nickel-based lithium transition metal oxide positive electrode active materials, specifically composed of Li... a Ni 1-x-y Co x M 1 y M 2 w O2(1.0≤a≤1.5, 0≤x≤0.2, 0≤y≤0.2, 0≤w≤0.1, 0≤x+y≤0.2, M 1 It is at least one metal selected from Mn or Al, and M 2 It is represented by at least one metal selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo, especially Li. a Ni 1-x-y Co x Mn y O2(1.0≤a≤1.5,0≤x≤0.2,0≤y≤0.2,0≤x+y≤0.2) represents this.

[0081] Secondary macroparticles can have a larger average particle size D50 than secondary microparticles. Specifically, the ratio of the average particle size D50 of secondary macroparticles to that of secondary microparticles can be 5:1 to 2:1. The average particle size D50 of secondary macroparticles is 7 to 20 μm, more specifically 8 to 16 μm.

[0082] Large particles with the above-mentioned size are commonly used as large particles for bimodal positive electrode active materials, and they are manufactured by conventional manufacturing methods as described below.

[0083] As mentioned above, large particles formed from the aggregation of primary microparticles have a large specific surface area and low particle strength. Therefore, during the rolling process of electrodes using positive electrode active material layers containing a mixture of large particles and microparticles with an average particle size smaller than that of the large particles, the pressure of the rolling mill exacerbates the breakage of large particles, making it difficult to sufficiently increase the pressure during the rolling process.

[0084] The inventors solved this problem by forming a first positive electrode active material layer and then forming a bimodal second positive electrode active material layer.

[0085] Composition of the first positive electrode active material layer and the second positive electrode active material layer

[0086] In addition to the positive electrode active material particles with the above-mentioned characteristics, the first and second positive electrode active material layers of the present invention may also contain positive electrode active material particles with different average particle sizes or different substances, without hindering the achievement of the purpose of the present invention.

[0087] The first and second positive electrode active material layers may contain conductive materials commonly used in this technical field.

[0088] Conductive materials are used to impart conductivity to the positive electrode and can include, but are not limited to, any type of conductive material capable of conducting electron flow without causing any chemical changes 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, thermally cracked carbon black, and carbon fibers; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives. Typically, based on the total weight of the first or second positive electrode active material layer, the content of conductive material in each of the first and second positive electrode active material layers can be from 0.5% to 30% by weight.

[0089] In particular, the second positive electrode active material layer incorporates single-walled carbon nanotubes as a conductive material. Single-walled carbon nanotubes have low resistance, thus reducing electrode resistance and cell resistance, thereby contributing to improved resistance characteristics. The single-walled carbon nanotubes are highly deentangled, and in particular, they effectively act as crack bridging agents between secondary large particles. For example, based on the total weight of the second positive electrode active material layer, the amount of single-walled carbon nanotubes can be 0.1% by weight or more, and in this case, based on the total weight of the second positive electrode active material layer, the amount of conductive material in the second positive electrode active material layer can be 0.5% to 3% by weight.

[0090] In addition, the first and second positive electrode active material layers may contain an adhesive.

[0091] Adhesives are used to improve the bonding strength between positive electrode active material particles and the adhesion strength between the positive electrode active material and the positive electrode current collector. Specific examples of adhesives may include, but are not limited to, at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or a variety of copolymers thereof. For example, based on the total weight of the first or second positive electrode active material layer, the content of adhesive in each of the first and second positive electrode active material layers may be from 1 to 30% by weight.

[0092] Method for manufacturing positive electrode

[0093] First, the manufacturing method of the positive electrode active material particles will be described in an explanatory manner.

[0094] The following is one aspect of the invention: a method for manufacturing secondary particles formed from the aggregation of primary large particles. However, the invention is not limited thereto.

[0095] A method for manufacturing a nickel-based lithium transition metal oxide cathode active material will be described by way of illustration, for example, from Li a Ni 1-x-y Co x Mn y M 2 w O2(1.0≤a≤1.5, 0≤x≤0.2, 0≤y≤0.2, 0≤w≤0.1, 0≤x+y≤0.2, M 1 It is at least one metal selected from Mn or Al, and M 2 It is a compound represented by at least one metal selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo.

[0096] It will contain nickel, cobalt, manganese, and M in a predetermined molar ratio. 2 The transition metal hydroxide precursor particles are mixed with a solution containing transition metals, an aqueous ammonia solution, and an alkaline solution to form transition metal hydroxide precursor particles, which are then separated and dried. The transition metal hydroxide precursor particles are then ground to a predetermined average particle size D50 (S1).

[0097] M 2 It is optional and described in detail based on the absence of Q.

[0098] First, prepare a positive electrode active material precursor containing nickel (Ni), cobalt (Co), and manganese (Mn).

[0099] 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 positive electrode active material precursor preparation method known in the relevant technical field.

[0100] For example, the precursor can be prepared by adding a chelating agent containing ammonium cations and a basic compound to a transition metal solution containing nickel-containing, cobalt-containing, and manganese-containing raw materials to induce a co-precipitation reaction.

[0101] Nickel-containing raw materials may include, for example, nickel-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides or hydroxyoxides. Specifically, they may include at least one of Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel salts of fatty acids or nickel halides, but are not limited thereto.

[0102] Cobalt-containing raw materials may include cobalt-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides or hydroxy oxides. Specifically, they may include at least one of Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4 or Co(SO4)2·7H2O, but are not limited thereto.

[0103] Manganese-containing raw materials may include at least one of manganese-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or hydroxyoxides. Specifically, they may include, for example, manganese oxides such as Mn2O3, MnO2, and Mn3O4; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylate, manganese citrate, and manganese fatty acid salts; and at least one of manganese hydroxyoxides or manganese chlorides, but are not limited thereto.

[0104] Transition metal solutions can be prepared by adding nickel-containing, cobalt-containing, and manganese-containing raw materials to a 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 an aqueous solution of nickel-containing raw materials, an aqueous solution of cobalt-containing raw materials, and a manganese-containing raw material.

[0105] Chelating agents containing ammonium cations may include, but are not limited to, at least one of, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, or (NH4)2CO3. Chelating agents containing ammonium cations may be used in the form of an aqueous solution, and in this case, the solvent may include water, or a mixture of water and an organic solvent (specifically, an alcohol, etc.) that is mixed with water to form a homogeneous mixture.

[0106] An alkaline solution can be an aqueous solution of an alkaline compound (e.g., at least one or a combination of hydroxides or hydrates of alkali metals or alkaline earth metals, such as NaOH, KOH, or Ca(OH)₂). In this case, the solvent may include water, or a mixture of water and an organic solvent (specifically, an alcohol, etc.) that is mixed with water to form a homogeneous mixture.

[0107] An alkaline solution can be added to adjust the pH of the reaction solution, and the amount added can make the pH of the metal solution between 9 and 12.

[0108] Transition metal hydroxide precursor particles can be produced by mixing a solution containing nickel, cobalt, and manganese, an aqueous ammonia solution, and an alkaline solution and performing a co-precipitation reaction.

[0109] In this case, the coprecipitation reaction can be carried out at a temperature of 25°C to 60°C in an inert atmosphere of nitrogen or argon.

[0110] The resulting transition metal hydroxide precursor particles are separated and dried in a reactor, and then ground to a predetermined average particle size D50 by a subsequent process to form secondary particles with the desired average particle size.

[0111] Subsequently, the ground transition metal hydroxide precursor particles are mixed with lithium raw materials and sintered in an oxygen atmosphere to produce secondary particles (S2) formed by the aggregation of primary large particles with an average particle size D50 of 0.5 to 3 μm.

[0112] Secondary particles formed by the aggregation of primary large particles with a predetermined average particle size can be manufactured according to steps (S1) and (S2) by manufacturing-grinding-sintering precursor particles.

[0113] In step (S2), the lithium raw material can be any type of material that is soluble in water, including but not limited to lithium sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or hydroxy oxides. Specifically, the lithium raw material can include at least one of Li₂CO₃, LiNO₃, LiNO₂, LiOH, LiOH·H₂O, LiH, LiF, LiCl, LiBr, LiI, CH₃COOLi, Li₂O, Li₂SO₄, CH₃COOLi, or Li₃C₆H₅O₇.

[0114] High-Ni NCM-based lithium composite transition metal oxides with a nickel (Ni) content of 80 mol% or higher can be sintered at 790°C to 950°C, and sintering can be carried out in an oxygen atmosphere for 5 to 35 hours. The oxygen atmosphere used herein includes ambient atmosphere and refers to an atmosphere containing sufficient oxygen for sintering. In particular, sintering is preferably carried out in an atmosphere with an oxygen partial pressure higher than that of the ambient atmosphere.

[0115] Secondary microparticles and secondary macroparticles formed from the aggregation of primary microparticles can include those commercially available and can be directly manufactured using known coprecipitation methods. More specifically, they can be manufactured by using a coprecipitation method known in the art to obtain secondary particles containing high-Ni complex transition metal hydroxide particles as a precursor, mixing them with a lithium source, and sintering them. Here, the method of controlling the precursor composition and the type of lithium source using the coprecipitation method can follow well-known technical knowledge.

[0116] The positive electrode active material prepared as described above can be mixed with a conductive material and a binder to form a positive electrode material mixture for forming the first and second positive electrode active material layers, and the positive electrode material mixture can be placed on a positive electrode current collector by conventional methods to form a positive electrode active material layer, thereby manufacturing a positive electrode.

[0117] Specifically, a mixture of positive electrode materials comprising a positive electrode active material, a conductive material, and a binder is added to a solvent to prepare a composition for forming a first positive electrode active material layer. This first positive electrode active material layer forming composition is then coated onto a positive electrode current collector and dried to form a first positive electrode active material layer. Subsequently, a mixture of positive electrode materials comprising a positive electrode active material, a conductive material containing single-walled carbon nanotubes, and a binder can be added to a solvent to prepare a composition for forming a second positive electrode active material layer. This second positive electrode active material layer forming composition can be coated onto the first positive electrode active material layer, then dried and rolled. The solvent may include solvents commonly used in the relevant technical field, such as at least one of dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water. Considering the slurry coating thickness and manufacturing yield, the amount of solvent used should be such that sufficient viscosity is achieved to obtain good thickness uniformity when dissolving or dispersing the positive electrode active material, conductive material, and binder and coating them to manufacture the positive electrode.

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

[0119] Lithium secondary batteries

[0120] According to another embodiment of the present invention, a lithium secondary battery including the positive electrode is provided.

[0121] A lithium secondary battery includes a positive electrode, a negative electrode opposite to the positive electrode, a separator between the positive and negative electrodes, and an electrolyte, wherein the positive electrode is the same as described above. Alternatively, the lithium secondary battery may also include a battery casing housing an electrode assembly containing the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery casing.

[0122] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material on the negative electrode current collector.

[0123] The negative electrode current collector can include any type of material with high conductivity that does not cause any chemical changes to the battery, such as copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel with a surface treated with carbon, nickel, nickel, or silver, and aluminum-cadmium alloys, but is not limited to these. Furthermore, the thickness of the negative electrode current collector is typically 3 to 500 μm, and like the positive electrode current collector, the negative electrode current collector can have fine textures on its surface to improve the bonding strength of the negative electrode active material. For example, the negative electrode current collector can take many forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0124] In addition to the negative electrode active material, the negative electrode active material layer may optionally include a binder and a conductive material. For example, the negative electrode active material layer may be formed by coating a negative electrode forming composition comprising the negative electrode active material and optionally a binder and a conductive material onto a negative electrode current collector and drying it, or by casting the negative electrode forming composition onto a support, peeling a film off the support, and laminating the film onto the negative electrode current collector.

[0125] Negative electrode active materials may include compounds capable of reversibly inserting and de-intercalating lithium. Specific examples of negative electrode active materials may include at least one of the following: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metallic substances capable of forming alloys with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and metal oxides capable of doping and de-doping lithium, such as SiO₂. β (0<β<2), SnO2, vanadium oxide, lithium vanadium oxide; or composites containing metallic substances 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, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and coke derived from petroleum or coal tar pitch.

[0126] In addition, the adhesive and conductive material can be the same as those in the positive electrode mentioned above.

[0127] On the other hand, in lithium-ion secondary batteries, the separator separates the negative electrode from the positive electrode and provides a channel for the movement of lithium ions. It can be any separator commonly used in lithium-ion secondary batteries, but those with low resistance to the movement of electrolyte ions and good wettability in the electrolyte solution are particularly preferred. Specifically, the separator can include, for example, a porous polymer membrane made of polyolefin polymers (e.g., ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), or a stack of two or more porous polymer membranes. Alternatively, the separator can include common porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers and polyethylene terephthalate fibers. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic or polymer materials can be used, and can be selectively used in single-layer or multi-layer structures.

[0128] In addition, the electrolyte used in this invention may include, but is 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.

[0129] Specifically, electrolytes can include organic solvents and lithium salts.

[0130] Organic solvents can include, but are not limited to, any type of organic solvent that acts as a medium for the movement of ions involved 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 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 to C20 straight-chain, branched, or cyclic hydrocarbon, and may contain double-bonded aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Carbonate solvents are ideal, and more preferably, cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, which contribute to improving the charge / discharge performance of the battery, can be mixed with low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate). In this case, cyclic carbonates and linear carbonates can be mixed in a volume ratio of about 1:1 to about 1:9 to improve the performance of the electrolyte solution.

[0131] Lithium salts can include, but are not limited to, any compound capable of providing lithium ions for use in lithium-ion secondary batteries. Specifically, lithium salts can include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt can range from 0.1 to 2.0 M. 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.

[0132] In addition to the constituent substances of the electrolyte described above, the electrolyte may also contain at least one of the following additives to improve battery life characteristics, prevent battery capacity decay, and increase battery discharge capacity: halogenated alkyl carbonate compounds (e.g., ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the content of the additives may be from 0.1% to 5% by weight, based on the total weight of the electrolyte.

[0133] Lithium secondary batteries with the degradation-reduced cathode material of the present invention can be used in mobile devices including mobile phones, laptops and digital cameras, as well as electric vehicles including hybrid electric vehicles (HEVs).

[0134] 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.

[0135] The battery module or battery pack can be used as a power source for at least one of the following medium to large-sized devices: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles and plug-in hybrid electric vehicles (PHEVs); or energy storage systems.

[0136] In the following description, embodiments of the invention will be fully and thoroughly described to enable those skilled in the art to readily implement the invention. However, the invention can be implemented in many different forms and is not limited to the disclosed embodiments.

[0137] <Example 1>

[0138] Manufacturing of positive electrode active material particles for forming the first positive electrode active material layer

[0139] Four liters of distilled water were placed in a coprecipitation reactor (capacity 20 L), where the temperature was maintained at 50 °C. 100 mL of a 28 wt% ammonia solution was added to the reactor. Then, a 3.2 mol / L transition metal solution (in which NiSO4, CoSO4, and MnSO4 were mixed in a nickel:cobalt:manganese molar ratio of 0.8:0.1:0.1) 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 with an impeller at 400 rpm, and the pH was maintained at 9 using a 40 wt% sodium hydroxide solution. Precursor particles were formed through a 10-hour coprecipitation reaction. These precursor particles were separated, washed, and dried in an oven at 130 °C to prepare the precursor.

[0140] Ni synthesized via coprecipitation reaction 0.8 Co 0.1 Mn 0.1 The (OH)₂ precursor was ground to approximately 1 μm in a mixer, and then mixed with LiOH at a molar ratio of 1.05. The mixture was then heat-treated at 800 °C in an oxygen atmosphere for 15 hours to produce LiNi. 0.8 Co 0.1 Mn 0.1 O2 lithium complex transition metal oxide.

[0141] The obtained particles are formed by the aggregation of large primary particles with an average grain size of 250 nm and an average particle size D50 of 2.5 μm, resulting in particles with an average particle size D50 of 4 μm.

[0142] Manufacturing of positive electrode active material particles for forming the second positive electrode active material layer

[0143] Manufacturing of secondary microparticles

[0144] Secondary particles containing high-nickel composite transition metal hydroxide particles were obtained using a known co-precipitation method as a precursor, and then mixed with a lithium source and sintered to prepare LiNi with an average particle size of 4 μm formed by the aggregation of primary microparticles with an average particle size D50 of 300 nm. 0.8 Co 0.1 Mn 0.1 O2 secondary microparticles.

[0145] Secondary large particle manufacturing

[0146] Secondary particles containing high-nickel composite transition metal hydroxide particles were obtained using a known co-precipitation method as a precursor, and then mixed with a lithium source and sintered to prepare LiNi with an average particle size of 15 μm formed by the aggregation of primary microparticles with an average particle size D50 of 500 nm. 0.8 Co 0.1 Mn 0.1 O2 secondary large particles.

[0147] Manufacturing of the positive electrode

[0148] 96.5 parts by weight of positive active material particles for forming a first positive active material layer obtained by the above method, 2 parts by weight of Ketjen black as a conductive material, and 1.5 parts by weight of KF9700 as a binder are dispersed in NMP solvent to prepare a composition for forming a first positive active material layer. The composition for forming a first positive active material layer is then coated onto an aluminum foil current collector and dried to form a first positive active material layer.

[0149] Subsequently, 97.5 parts by weight of a positive electrode active material comprising a mixture of large and micro particles (in a weight ratio of 8:2) obtained by the above method, 0.05 parts by weight of single-walled carbon nanotubes (OCSiAl, single-walled CNT) and 0.65 parts by weight of double-walled carbon nanotubes (LB-CNT) as conductive materials, and 1.5 parts by weight of KF9700 (DA288) as a binder are dispersed in NMP solvent to prepare a composition for forming a second positive electrode active material layer. The composition for forming a second positive electrode active material layer is then coated onto a first positive electrode active material layer and dried to form a second positive electrode active material layer, which is then rolled to manufacture a positive electrode.

[0150] After rolling, the thickness of the first positive electrode active material layer is 10.5 μm, and the thickness of the second positive electrode active material layer is 21 μm.

[0151] <Example 2>

[0152] The positive electrode was manufactured in the same manner as in Example 1, except that 0.008 parts by weight of single-walled carbon nanotubes and 0.69 parts by weight of double-walled carbon nanotubes were added as conductive materials when forming the second positive electrode active material layer.

[0153] <Comparative Example 1>

[0154] The positive electrode was manufactured in the same manner as in Example 1, except that only 0.7 parts by weight of double-walled carbon nanotubes were added as a conductive material when forming the second positive electrode active material layer.

[0155] [Experimental Example 1: Average Particle Size]

[0156] D50 can be defined as the particle size at 50% of the particle size distribution and is measured using laser diffraction.

[0157] [Experimental Example 2: Average Grain Size of Primary Particles]

[0158] The sample was measured using a Bruker Endeavor (Cu Kα, λ = 1.54 Å) equipped with a LynxEye XE-T position-sensitive detector, with a step size of 0.02° and a scan range of 90°FDS 0.5°, 2-θ15°, resulting in a total scan time of 20 minutes.

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

[0160] The following is a method for manufacturing lithium secondary batteries using the positive electrodes of the examples and comparative examples manufactured by the above method.

[0161] A negative electrode slurry was prepared by mixing a mixture of artificial graphite and natural graphite in a 5:5 ratio as the negative electrode active material, superC as the conductive material, and SBR / CMC as the binder in a 96:1:3 weight ratio. The negative electrode slurry was then coated onto the surface of a copper current collector, dried, and rolled to manufacture the negative electrode.

[0162] An electrode assembly comprising a positive and negative electrode and a porous polyethylene separator between the positive and negative electrodes, manufactured as described above, is placed in a housing, and an electrolyte solution is injected into the housing to manufacture a lithium secondary battery cell.

[0163] In this case, the electrolyte solution is prepared by dissolving 1.0M lithium hexafluorophosphate (LiPF6) in an organic solvent containing ethylene carbonate / ethyl methyl carbonate / diethyl carbonate / (EC / EMC / DEC in a mixed volume ratio of 3 / 4 / 3).

[0164] [Experiment Example 3. Measuring whether a short circuit occurs under the pressure of the roller press during the electrode rolling process]

[0165] When the positive electrodes of the examples and comparative examples were rolled using a roller press, the change in porosity with pressure and whether a short circuit occurred were measured. The results are shown in Table 1 below.

[0166] [Table 1]

[0167]

[0168] [Experiment Example 4. Measurement of Lifetime Characteristics and Rate of Resistance Increase]

[0169] For the lithium secondary battery cells manufactured according to the examples and comparative examples, the capacity retention rate and resistance increase rate after 400 cycles were measured by the following method.

[0170] The manufactured lithium-ion secondary battery cells were charged to 4.2V at 0.5C in CC-CV mode at 45°C, and then discharged to 2.5V at a constant current of 1C. After repeating this charge / discharge test 900 times, the capacity retention and resistivity increase rate were measured. The results are shown in... Figure 3 And in Table 2.

[0171] [Table 2]

[0172] Cyclic RPT unit Comparative Example 1 Example 1 Example 2 Capacity retention rate @ 900th time ％ 80.7 86.3 84.5 DCIR increase rate @ 900th time ％ 154.9 134.7 144.3

[0173] [Experimental Example 5. Multi-probe (MP) resistivity measurement]

[0174] The positive electrodes manufactured according to the embodiments and comparative examples were stamped into a 5*5 size, and the surface resistance was measured using a multi-probe resistivity measuring device. The results are shown in Table 3.

[0175] [Table 3]

[0176] Comparative Example 1 Example 1 Example 2 <![CDATA[MP Resistivity (mOhm*cm 2 )]]> 45.1(-) 18.8(▼58.3％) 57.1(▲26.6％) 0.1sR@SOC50(mOhm) 366.4(-) 319.9(▼12.7％) 351.4(▼4.1％) 1kHz R@SOC50 (mOhm) 162.8(-) 137.6(▼15.5％) 151.3(▼8.1％)

Claims

1. A positive electrode for a lithium secondary battery, comprising: current collector; A first positive electrode active material layer located on at least one surface of the current collector, the first positive electrode active material layer comprising positive electrode active material particles and a conductive material, wherein the positive electrode active material particles in the first positive electrode active material layer are composed of at least one positive electrode active material particle selected from the group consisting of primary large particles with an average particle size D50 of 0.5 to 3 μm, secondary particles with an average particle size D50 of 3 to 7 μm formed by the aggregation of the primary large particles, and mixtures thereof; and A second positive electrode active material layer is located on the first positive electrode active material layer. The second positive electrode active material layer includes positive electrode active material particles and a conductive material. The positive electrode active material particles in the second positive electrode active material layer include: Secondary microparticles of the positive electrode active material with an average particle size D50 of 1 to 7 μm are formed by the aggregation of primary microparticles with an average particle size D50 smaller than the primary large particles. The positive electrode active material consists of secondary large particles with an average particle size D50 of 7 to 20 μm, which are formed by the aggregation of primary micro particles with an average particle size D50 smaller than that of the primary large particles. The average particle size D50 of the secondary large particles is greater than that of the secondary micro particles. The average particle size D50 of the primary microparticles is 100 to 900 nm. Wherein, the positive electrode active material particles in the first and second positive electrode active material layers are nickel-based lithium transition metal oxide positive electrode active materials, and The conductive material contained in the second positive electrode active material layer includes single-walled carbon nanotubes.

2. The positive electrode for a lithium secondary battery as described in claim 1, wherein, Based on the total weight of the second positive electrode active material layer, the amount of the single-walled carbon nanotubes present is more than 0.1% by weight.

3. The positive electrode for a lithium secondary battery as described in claim 1, wherein, The average particle size D50 of the primary microparticles is 100 to 400 nm.

4. The positive electrode for a lithium secondary battery as described in claim 1, wherein, The average grain size of the primary large particles contained in the first positive electrode active material layer is equal to or greater than 200 nm.

5. The positive electrode for a lithium secondary battery as described in claim 1, wherein, The average particle size D50 of the primary large particles contained in the first positive electrode active material layer is 1 to 3 μm.

6. The positive electrode for a lithium secondary battery as described in claim 1, wherein, The average particle size D50 of the secondary microparticles is 2 to 5 μm, and the average particle size D50 of the secondary large particles is 8 to 16 μm.

7. The positive electrode for a lithium secondary battery as described in claim 1, wherein, The ratio of the average particle size D50 of the secondary large particles to the average particle size D50 of the secondary micro particles is 5:1 to 2:

1.

8. The positive electrode for a lithium secondary battery as described in claim 1, wherein, Based on 100 parts by weight of the secondary large particles, the amount of the secondary micro particles is 10 to 100 parts by weight.

9. The positive electrode for a lithium secondary battery as described in claim 1, wherein, The thickness 'a' of the second positive electrode active material layer relative to the thickness 'b' of the first positive electrode active material layer satisfies the following formula: (Formula) 3b≤a.

10. The positive electrode for a lithium secondary battery as described in claim 1, wherein, The secondary microparticles are simply aggregates of the primary microparticles.

11. The positive electrode for a lithium secondary battery as described in claim 1, wherein, The nickel-based lithium transition metal oxide is composed of Li a Ni 1-x-y Co x M 1 y M 2 w O2 represents the expression where 1.0 ≤ a ≤ 1.5, 0 ≤ x ≤ 0.2, 0 ≤ y ≤ 0.2, 0 ≤ w ≤ 0.1, 0 ≤ x + y ≤ 0.2, and M. 1 It is at least one metal selected from Mn or Al, and M 2 It is at least one metal selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo.

12. The positive electrode for a lithium secondary battery as described in claim 11, wherein, The nickel-based lithium transition metal oxide is composed of Li a Ni 1-x-y Co x Mn y O2 represents the expression where 1.0≤a≤1.5, 0≤x≤0.2, 0≤y≤0.2, and 0≤x+y≤0.

2.

13. The positive electrode for a lithium secondary battery as described in claim 1, wherein, Based on the total weight of the second positive electrode active material layer, the amount of the single-walled carbon nanotubes present is more than 0.001% by weight.

14. The positive electrode for a lithium secondary battery as described in claim 1, wherein, Based on the total weight of the second positive electrode active material layer, the amount of the conductive material present in the second positive electrode active material layer is 0.5 to 3 by weight.

15. A lithium secondary battery comprising a positive electrode according to any one of claims 1 to 14.

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