Method for manufacturing a cathode active material for a lithium secondary battery, a cathode manufactured using the same, and a lithium secondary battery including the same

Abstract

The present embodiment relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery including the same. The positive electrode active material for a lithium secondary battery according to one embodiment may include a metal oxide composed of single particles, a first coating layer in the form of fibers located on the surface of the metal oxide, and a second coating layer in the form of dots located on the surface of the metal oxide.

Description

[Technical Field]

[0001] The present embodiment relates to a method for manufacturing a positive electrode active material for a lithium secondary battery, a positive electrode manufactured using the same, and a lithium secondary battery including the same. [Background technology]

[0002] Due to the rapid expansion of the lithium-ion battery market and the demand for high energy density, research into ternary cathode materials with high energy density and large capacity per area is steadily progressing.

[0003] Ternary cathode materials can develop microcracks inside the particles due to volume expansion caused by continuous lithium intercalation and deintercalation, and these microcracks can induce side reactions with the electrolyte at the new interface, leading to a rapid decrease in battery capacity.

[0004] In addition, to achieve high energy density, electrode density must be increased, but this process can cause secondary particles to break down, which can induce side reactions with the electrolyte, resulting in a significant reduction in the initial lifespan of the battery.

[0005] Therefore, it is necessary to develop a positive electrode material that can achieve high energy density without causing microcracks inside even after long-term charge / discharge. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present embodiment is to provide a positive electrode active material for a lithium secondary battery having excellent electrical conductivity and electrochemical performance, a method for producing the same, and a lithium secondary battery including the same. [Means for solving the problem]

[0007] A positive electrode active material for a lithium secondary battery according to one embodiment may include: a metal oxide composed of single particles; a first coating layer located on a surface of the metal oxide and having a fiber shape; and a second coating layer located on a surface of the metal oxide and having a dot shape.

[0008] According to one embodiment, a method for manufacturing a positive electrode active material for a lithium secondary battery may include the steps of: preparing a metal hydroxide containing nickel, cobalt, and manganese; calcining a mixture of the metal hydroxide and a lithium raw material to obtain a metal oxide composed of single particles; forming a first coating layer on a surface of the metal oxide using a first coating layer raw material; and loading the metal oxide with the first coating layer formed thereon into a mixer and mixing them using a dry method to form a second coating layer on the surface of the metal oxide.

[0009] The positive electrode according to an embodiment may include a current collector; and a positive electrode active material layer located on at least one surface of the current collector and including the positive electrode active material according to the embodiment.

[0010] A lithium secondary battery according to an embodiment may include the positive electrode. [Effects of the Invention]

[0011] According to this embodiment, a positive electrode active material with dramatically improved electrical conductivity can be realized by performing surface treatment so that first and second coating layers with different shapes are positioned on the surface of a metal oxide composed of single particles.

[0012] The positive electrode active material of this embodiment also has high output, long life, and excellent resistance characteristics. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram shown as an example to explain a positive electrode active material for a lithium secondary battery according to an embodiment. [Figure 2] 1 shows the results of SEM analysis of the positive electrode active material of Example 1, measured at 50,000 times magnification. [Figure 3] 1 shows the results of SEM analysis of the positive electrode active material of Comparative Example 1, measured at 50 times magnification. [Figure 4] 1 shows the results of SEM analysis of the positive electrode active material of Example 1, measured at 3,000 magnifications. [Figure 5] 1 shows the results of SEM analysis of the positive electrode active material of Example 1, measured at 30,000 times magnification. [Figure 6] 1 shows the results of SEM analysis of the positive electrode active material of Comparative Example 1, measured at 3,000 times magnification. [Figure 7] 1 shows the results of SEM analysis of the positive electrode active material of Comparative Example 1, measured at 20,000 times magnification. [Figure 8] 1 shows the results of SEM analysis of the positive electrode active material of Comparative Example 2, measured at 3,000 times magnification. [Figure 9] 1 shows the results of SEM analysis of the positive electrode active material of Comparative Example 2, measured at 20,000 times magnification. [Figure 10] 1 shows the results of SEM analysis of the positive electrode active material of Example 1, measured at 30,000 times magnification. [Figure 11] This is an enlarged image of the box portion shown in 1 in Figure 10. [Figure 12] This is an enlarged image of the box part shown in 2 in Figure 10. [Figure 13] 1 shows the results of Raman analysis of the positive electrode active materials prepared in Example 1 and Comparative Example 1. FIG. [Figure 14] FIG. 10 is a diagram showing the results of measuring the high efficiency characteristics of the examples. [Figure 15] 1 is a graph showing the results of measuring the charge-discharge characteristics of the positive electrode active materials prepared in Example 1 and Comparative Example 1. FIG. [Figure 16] 1 is a graph showing the results of measuring the room-temperature life maintenance rate of the positive electrode active materials produced in Example 1 and Comparative Example 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, a first part, component, region, layer, or section described below can be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0015] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used in the specification, the term "comprising" refers to the inclusion of particular features, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0016] When a part is referred to as being "on" or "above" another part, it means that it is exactly on or above the other part, or there may be other parts between them. In contrast, when a part is referred to as being "directly on" another part, there are no other parts between them.

[0017] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless otherwise defined.

[0018] Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0019] Although the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein, the present invention will be described in detail below so that those skilled in the art can easily understand and practice the present invention.

[0020] Each embodiment will be described in detail below.

[0021] FIG. 1 is shown as an example to explain a positive electrode active material for a lithium secondary battery according to one embodiment.

[0022] Referring to FIG. 1, a positive electrode active material for a lithium secondary battery according to one embodiment includes a metal oxide 100 composed of single particles, a first coating layer 200 located on the surface of the metal oxide and having a fiber shape, and a second coating layer 300 located on the surface of the metal oxide and having a dot shape.

[0023] Conventional ternary cathode active materials are in the form of secondary particles, which are aggregates of primary particles. As the nickel content of secondary-particle cathode active materials increases, the particle strength decreases, leading to the generation of microcracks during charge / discharge. As mentioned above, these microcracks increase the reaction with the electrolyte, which can lead to increased gas generation.

[0024] Therefore, it has been difficult to actually apply this to positive electrode active materials for lithium-ion batteries used in electric vehicles and energy storage. To address this issue, a method has been proposed in which the positive electrode active material is prepared in a single-crystalline form by maximizing the size of the primary particles, rather than in a polycrystalline form, where primary particles are aggregated into secondary particles. However, single-crystalline positive electrode active materials have low conductivity due to the increased size of the primary particles, which limits the rate of lithium intercalation and deintercalation, thereby reducing battery performance. However, in this embodiment, this issue is resolved by surface-modifying the metal oxide so that first and second coating layers with different shapes are positioned on the surface, thereby achieving a lithium secondary battery with significantly improved electrical conductivity even when using a single-crystalline positive electrode active material.

[0025] The first coating layer and the second coating layer may contain carbon. Since the first and second carbon layers contain carbon with high conductivity, the positive electrode active material according to this embodiment may have excellent electrical conductivity.

[0026] Here, the diameter of the fiber shape may be 100 nm or less, more specifically, in the range of 10 nm to 100 nm. The length of the fiber shape may be 10 nm to 30 μm, more specifically, in the range of 50 nm to 5 μm. When the fiber shape of the first coating layer satisfies the above size range, it is easily connected to the second coating layer, resulting in a positive electrode active material with excellent electrical conductivity.

[0027] In this embodiment, the surface of the positive electrode active material is 2 The second coating layer may contain 1 to 20 dot shapes per layer. The dot shapes of the second coating layer are located in an island type. When the second coating layer is located in this numerical range, it can be connected to the first coating layer to provide a positive electrode active material with better electrical conductivity.

[0028] The number of the fiber shapes and the dot shapes connected on the surface of the metal oxide is 1 μm 2 The number of particles per coating layer may be in the range of 1 to 10. When the first and second coating layers are connected in this range, a positive electrode active material having excellent electrical conductivity and improved tap density can be provided.

[0029] In the positive electrode active material of this embodiment, the weight ratio of the first coating layer to the second coating layer may be in the range of 1:99 to 99:1, more specifically, 0.1:99.9 to 5.0:95. When the ratio of the first and second coating layers satisfies this range, a positive electrode active material having excellent electrical conductivity, high output, long life, and resistance characteristics can be realized, as described above.

[0030] The positive electrode active material may have an average particle size (D50) of 2 μm to 7 μm, more specifically, 3 μm to 6 μm. When the average particle size (D50) satisfies this range, it is possible to reduce the amount of gas generation and realize a lithium secondary battery that is excellent in electrochemical properties such as life span and resistance increase rate.

[0031] The electrical conductivity of the positive electrode active material is 2.0×10 -5 S / cm or more, more specifically, 2.0×10 -5 S / cm~9.0×10 -5 S / cm or 3.0 x 10 -5 S / cm~5.0×10 -5 As described above, the positive electrode active material of this embodiment includes the first and second coating layers, which modifies the surface structure and significantly improves the electrical conductivity.

[0032] The tap density of the positive electrode active material may be 2.20 g / cc or more, more specifically, in the range of 2.20 g / cc to 2.6 g / cc. When the tap density satisfies this range, the electrochemical performance such as the life and the rate of increase in resistance of the positive electrode active material can be further improved.

[0033] In this embodiment, the single particle may include at least one of a single crystal structure consisting of one particle and a monolith structure consisting of 2 to 8 particles.

[0034] The metal oxide may also include nickel, cobalt, and manganese.

[0035] In this case, the nickel content may be 0.5 mol or more based on 1 mol of the nickel, cobalt, and manganese combined. More specifically, it may be in the range of 0.6 mol to 0.99 mol, 0.8 mol to 0.99 mol, or 0.87 mol to 0.99 mol based on 1 mol of the nickel, cobalt, and manganese combined. When the nickel content of the metal oxide is 0.5 mol or more, as in this embodiment, a positive electrode active material with high output characteristics can be realized. Furthermore, when the nickel content is 0.8 mol or more, the positive electrode active material prepared using this material has a high energy density per volume, thereby improving the capacity of the battery to which it is applied, making it highly suitable for use in electric vehicles.

[0036] Manganese may be contained in an amount of 0.01 mol to 0.1 mol, more specifically, 0.01 mol to 0.06 mol, based on 1 mol of the total amount of nickel, cobalt, and manganese.

[0037] The cobalt may be included in an amount of 0.01 mol to 0.1 mol, more specifically, 0.01 mol to 0.06 mol, based on 1 mol of the total of the nickel, cobalt, and manganese.

[0038] According to one embodiment, a method for manufacturing a positive electrode active material for a lithium secondary battery may include the steps of: preparing a metal hydroxide containing nickel, cobalt, and manganese; calcining a mixture of the metal hydroxide and a lithium raw material to obtain a metal oxide composed of single particles; forming a first coating layer on a surface of the metal oxide using a first coating layer raw material; and loading the metal oxide with the first coating layer formed thereon into a mixer and mixing them using a dry method to form a second coating layer on the surface of the metal oxide.

[0039] First, a metal hydroxide containing nickel, cobalt, and manganese is prepared.

[0040] In this embodiment, a metal salt aqueous solution containing a nickel source material, a cobalt source material, a manganese source material, and water is prepared, and then the metal salt aqueous solution is supplied to a coprecipitation reactor to obtain a metal hydroxide.

[0041] Next, the mixture of the metal hydroxide and the lithium source material is calcined to obtain a metal oxide composed of single particles. At this time, the mixture can be prepared so that the molar ratio of lithium (Li) to the total metal (Me) excluding lithium (Li / Me) is in the range of 1.0 to 1.1, or 1.01 to 1.08.

[0042] The calcination can be carried out for 20 to 30 hours at a temperature ranging from 800 to 900° C. When the calcination temperature and time conditions satisfy the above ranges, a positive electrode material in the form of a single particle or monolith can be produced.

[0043] Thereafter, a step of forming a first coating layer on the surface of the metal oxide using a first coating layer source material is performed.

[0044] The step of forming the first coating layer may be performed by an incipient wetness impregnation method.

[0045] The raw material for the first coating layer may include a carbon raw material and a solvent, and the solvent may include at least one of ethanol, distilled water, and N-methyl-2-pyrrolidone (NMP).

[0046] The carbon raw material may include, for example, at least one of carbon, carbon nanotubes (CNT), single-walled carbon nanotubes (SWCNT), and multi-walled carbon nanotubes (MWCNT).

[0047] The step of forming the first coating layer may be performed so that the weight ratio of the metal oxide to the carbon raw material is in the range of 50:1 to 150:1, where the weight ratio refers to the weight ratio after the solvent is removed after the first coating layer is formed.

[0048] Next, the metal oxide on which the first coating layer is formed is introduced into a mixer and mixed by a dry method, thereby forming a second coating layer on the surface of the metal oxide.

[0049] The step of forming the second coating layer may be performed using a mechano-fusion method.

[0050] In the step of forming the second coating layer, the metal oxide on which the first coating layer is formed is mixed again using a mechanofusion method without adding another carbon raw material, thereby forming the second coating layer.

[0051] In this manner, a positive electrode active material having a fiber-shaped first coating layer and a dot-shaped second coating layer formed on the surface of a metal oxide composed of single particles as in one embodiment can be manufactured.

[0052] In one embodiment, a positive electrode is provided, including a current collector and a positive electrode active material layer positioned on one surface of the current collector and including the positive electrode active material prepared according to the above-described embodiment.

[0053] The characteristics of the positive electrode active material constituting the positive electrode active material layer are as described above, and therefore, a detailed description of the positive electrode active material will be omitted.

[0054] The current collector may be made of, for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like.

[0055] Meanwhile, the positive electrode active material layer may include a binder and a conductive material.

[0056] The binder serves to improve adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be present in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer.

[0057] The conductive material is used to impart conductivity to the electrode and can be any material that does not cause chemical changes in the resulting battery and has electronic conductivity. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials can be used alone or in combination. The conductive material is typically present in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer.

[0058] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material.

[0059] Specifically, the positive electrode can be manufactured by coating a positive electrode active material layer-forming composition containing the above-described positive electrode active material and, optionally, a binder, a conductive material, or a solvent on a positive electrode current collector, followed by drying and rolling. In this case, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0060] The solvent may be a solvent commonly used in the art, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into consideration the coating thickness of the slurry and the production yield, and to provide a viscosity that allows excellent thickness uniformity when the slurry is subsequently applied to produce a positive electrode.

[0061] Alternatively, the positive electrode can be produced by casting the positive electrode active material layer-forming composition on a separate support, peeling the composition from the support, and laminating the resulting film on a positive electrode current collector.

[0062] In one embodiment, a lithium secondary battery is provided that includes the positive electrode.

[0063] The lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, as described above. The lithium secondary battery may further include a battery container that houses the electrode assembly including the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0064] In the lithium secondary battery, the negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0065] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys can be used. The negative electrode current collector typically has a thickness of 3 to 500 μm. As with the positive electrode current collector, the current collector surface can be provided with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector can be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0066] The negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material. For example, the negative electrode active material layer may be formed by coating a negative electrode active material layer-forming composition containing the negative electrode active material and, optionally, the binder and the conductive material on a negative electrode current collector and drying the coating, or by casting the negative electrode-forming composition on a separate support, peeling it off from the support, and laminating the resulting film on the negative electrode current collector.

[0067] The negative electrode active material may be a compound capable of reversible lithium intercalation and deintercalation. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; metal oxides capable of doping and dedoping lithium, such as SiOβ(0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; and composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. A mixture of one or more of these may also be used. Alternatively, a thin film of metallic lithium may also be used as the negative electrode active material. Carbon materials, such as low-crystalline carbon and high-crystalline carbon, may both be used. Typical low-crystalline carbons are soft carbon and hard carbon, while typical high-crystalline carbons are amorphous, plate-like, scaly, spherical, or fibrous natural or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0068] The binder and conductive material may be the same as those described above for the positive electrode.

[0069] Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such a separator may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more of these materials. Mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0070] In addition, in the lithium secondary battery, examples of the electrolyte include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used when manufacturing a lithium secondary battery, but are not limited to these.

[0071] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0072] The organic solvent can be any organic solvent that can act as a medium for the movement of ions involved in the electrochemical reaction of the battery. Specific examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; dibutyl ether; ether-based solvents such as ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; carbonate-based solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylenecarbonate (EC), and propylenecarbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; tolyls such as R-CN (where R is a C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of a battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, which can result in excellent electrolyte performance.

[0073] The lithium salt can be any compound capable of providing lithium ions used in lithium secondary batteries without any particular limitations. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The lithium salt concentration is preferably within a range of 0.1 to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0074] As described above, the lithium secondary battery including the cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in the fields of portable devices such as mobile phones, laptops, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs). [Example]

[0075] Hereinafter, the present invention will be described in detail with reference to examples, but these examples are presented by way of example only and do not limit the present invention, which is defined only by the scope of the claims set forth below.

[0076] Example 1 - Positive Electrode Active Material (1) Preparation of precursor The precursor was prepared by a common co-precipitation method.

[0077] Specifically, NiSO4·6H2O was used as the nickel source material, CoSO4·7H2O as the cobalt source material, and MnSO4·H2O as the manganese source material. These raw materials were dissolved in distilled water to produce metal salt aqueous solutions.

[0078] After preparing the coprecipitation reactor, N2 was purged to prevent oxidation of metal ions during the coprecipitation reaction, and the reactor temperature was maintained at 50°C.

[0079] NH4(OH) was added to the co-precipitation reactor as a chelating agent, and NaOH was used to adjust the pH. The precipitate obtained by the co-precipitation process was filtered, washed with distilled water, and dried in an oven at 100°C for 24 hours to prepare a cathode active material precursor.

[0080] The composition of the produced precursor was (Ni 0.88 Co 0.07 Mn 0.05 )(OH)2, and the average particle size (D50) was in the range of 3 μm to 14 μm.

[0081] (2) Manufacture of positive electrode active material The precursor prepared in (1) and LiOH·H2O were uniformly mixed and then calcined at 800~900℃ for 24 hours in a box-shaped calciner with an oxygen inlet of 1,000mL / min to produce a metal oxide (Li(NCM)O2) with a single crystal structure.

[0082] A first coating layer was formed on the surface of the metal oxide by an incipient wetness impregnation method using an ethanol mixture containing 0.5 wt % of CNTs.

[0083] Specifically, the metal oxide and CNT were treated so that the weight ratio was 100:1, and then the solvent was completely evaporated at 120°C.

[0084] Next, the metal oxide on which the first coating layer was formed was introduced into equipment using a mechano-fusion method and then dry-mixed to prepare a cathode active material in which the first coating layer and the second coating layer were formed on the surface of the metal oxide.

[0085] Example 2 A positive electrode active material having a first coating layer and a second coating layer formed thereon was prepared in the same manner as in Example 1, except that an ethanol mixture containing 1 wt % of CNTs was used when forming the first coating layer.

[0086] Example 3 A positive electrode active material having a first coating layer and a second coating layer formed thereon was prepared in the same manner as in Example 1, except that an ethanol mixture containing 1.5 wt % of CNTs was used to form the first coating layer.

[0087] Comparative Example 1 (1) Preparation of precursor The precursor was prepared in the same manner as in Example 1.

[0088] (2) Manufacture of positive electrode active material The precursor prepared in step 1 and LiOH·H2O were uniformly mixed and then calcined at 800~900℃ for 24 hours in a box-shaped calcination furnace with an oxygen inlet of 1,000mL / min to produce a cathode active material containing a metal oxide (Li(NCM)O2) with a single crystal structure.

[0089] Comparative Example 2 (1) Preparation of precursor The precursor was prepared in the same manner as in Example 1.

[0090] (2) Manufacture of positive electrode active material The precursor prepared in step 1 and LiOH·H2O were uniformly mixed and then calcined at 800~900℃ for 24 hours in a box-shaped calciner with an oxygen inlet of 1,000mL / min to produce a metal oxide (Li(NCM)O2) with a single crystal structure.

[0091] 0.5 wt % of CNTs was added to the surface of the metal oxide, and only a dry mixing process was carried out to prepare a positive electrode active material.

[0092] Experimental Example 1 - SEM analysis FIG. 2 shows the results of SEM analysis of the positive electrode active material of Example 1 at a magnification of 50,000 times, and FIG. 3 shows the results of SEM analysis of the positive electrode active material of Comparative Example 1 at a magnification of 50,000 times.

[0093] Referring to FIG. 2, it can be seen that the positive electrode active material of Example 1 has a solid-shaped first coating layer and a dot-shaped second coating layer well formed on the metal oxide surface.

[0094] On the other hand, referring to FIG. 3, the positive electrode active material of Comparative Example 1 does not have a coating layer formed on the metal oxide surface.

[0095] For more detailed observation, SEM analysis was additionally performed on the positive electrode active materials of Example 1 and Comparative Example 1.

[0096] FIG. 4 shows the results of SEM analysis of the positive electrode active material of Example 1 at 3,000x magnification, and FIG. 5 shows the results of SEM analysis of the positive electrode active material of Example 1 at 30,000x magnification.

[0097] FIG. 6 shows the results of SEM analysis of the positive electrode active material of Comparative Example 1 at 3,000 magnifications, and FIG. 7 shows the results of SEM analysis of the positive electrode active material of Comparative Example 1 at 20,000 magnifications.

[0098] FIG. 8 shows the results of SEM analysis of the positive electrode active material of Comparative Example 2 at 3,000 magnifications, and FIG. 9 shows the results of SEM analysis of the positive electrode active material of Comparative Example 2 at 20,000 magnifications.

[0099] 4, 6, and 8, which are low-magnification SEM images, show that the CNTs were uniformly dispersed on the surface of the cathode active material prepared in Example 1. However, the cathode active material prepared in Comparative Example 2 showed that the CNTs were not uniformly distributed on the surface and clumped together.

[0100] Referring to high-magnification SEM images of FIGS. 5, 7, and 9, it can be seen that a fiber-shaped first coating layer and a dot-shaped second coating layer coexist on the surface of the cathode active material prepared according to Example 1, and that a coating layer was well formed.

[0101] On the other hand, no coating layer was observed in the positive electrode active material of Comparative Example 1, and it was found that the coating layer was not formed uniformly in the positive electrode active material of Comparative Example 2 due to the aggregation of CNTs.

[0102] FIG. 10 shows the results of SEM analysis of the positive electrode active material of Example 1 at a magnification of 30,000 times. FIG. 11 is an enlarged image of the box portion indicated by 1 in FIG. 10. FIG. 12 is an enlarged image of the box portion indicated by 2 in FIG. 10.

[0103] 10 to 12, it can be seen again that the cathode active material prepared according to Example 1 has both a fiber-shaped first coating layer and a dot-shaped second coating layer on the surface.

[0104] Experimental Example 2 - Raman Analysis The positive electrode active materials prepared in Example 1 and Comparative Example 1 were subjected to Raman analysis, and the results are shown in FIG.

[0105] Raman analysis was performed using a Bruker Confocal Raman Microscope: SENTERRA II (excitation wavelength: 532.06 nm, ND filter: 40.97%, spectrograph center wave number: 2450.00 cm). -1 )did.

[0106] Referring to FIG. 13, no carbon-based peaks were observed in the positive electrode active material of Comparative Example 1, but the positive electrode active material of Example 1 had a peak in the range of 1200 to 1700 cm -1 and 2300-2700 cm-1 Therefore, it can be confirmed that a carbon-based peak is present.

[0107] Experimental Example 3 - Electrical Conductivity Measurement The electric conductivity was measured using the positive electrode active material powders prepared in Example 1 and Comparative Examples 1 and 2.

[0108] Specifically, 0.5 g of powder was sieved evenly and then pressed at 10 bar for 20 minutes using a 12 mm diameter pellet mold and press equipment to produce pellets. The resistance of the pellets was then measured using a 4-point probe method with ChangminTech's CMT Series equipment. Electrical conductivity, which is the reciprocal of the measured resistance, was calculated. The results are shown in Table 1 below.

[0109] [Table 1]

[0110] Referring to Table 1, it can be seen that the positive electrode active material prepared in Example 1 has significantly improved electrical conductivity compared to Comparative Examples 1 and 2.

[0111] Experimental Example 4: Electrochemical property measurement (1) Coin cell half cell manufacturing CR2032 coin cells were fabricated using the positive electrode active materials prepared in the Examples and Comparative Examples, and electrochemical evaluation was performed.

[0112] Specifically, the positive electrode active material, conductive material (Super-P), and polyvinylidene fluoride (PVdF) binder were mixed in a weight ratio of 96:2:2, and this mixture was added to N-methyl-2-pyrrolidone solvent so that the solid content was approximately 30 wt% to prepare a positive electrode active material slurry.

[0113] The slurry was coated on an aluminum foil (thickness: 15 μm) as a positive electrode current collector using a doctor blade, dried in vacuum at 120° C. for 5 hours, and then rolled to prepare a positive electrode.

[0114] A 2032 coin-type half cell was fabricated using the cathode, lithium metal anode (300 μm thick, MTI), electrolyte, and polypropylene separator in a conventional manner. The electrolyte was a mixed solution of 1M LiPF6 dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (EMC) (mixing ratio EC:DMC:EMC = 3:4:3 vol%). The fabricated coin cell was aged at room temperature for 12 hours, and then its electrochemical properties were measured.

[0115] (2) High-rate characteristic measurement The high rate characteristics of the coin cell manufactured in (1) above were measured, and the results are shown in Figure 14.

[0116] The high rate characteristics were measured at 3.0 to 4.3 V in a 25°C constant temperature chamber.

[0117] Specifically, the battery was charged / discharged four times each under the conditions of 0.2C, 0.33C, 0.5C, 1C, 2C, 3C, and 0.2C.

[0118] (3) Charge / discharge characteristics evaluation The capacity evaluation was performed with 200 mAh / g as the reference capacity, and the charge / discharge conditions were constant current (CC) / constant voltage (CV) 2.8 V to 4.3 V with a 1 / 20 C cutoff. The initial capacity was measured by 0.1 C charge / 0.1 C discharge. The results are shown in Figure 15 and Table 2 below.

[0119] (4) Room temperature life maintenance rate measurement After a formation cycle of 0.1C constant current charge / discharge at 2.8V to 4.3V at 25°C, a constant current charge / discharge test was performed at 1C. The capacity retention was measured based on the first cycle capacity versus the 50th cycle capacity. The results are shown in Figure 16 and Table 2 below.

[0120] (5) High temperature resistance increase rate After applying a discharge current of 4.3V at 100% charge at 45°C, the voltage was measured after 60 seconds to confirm the high temperature initial resistance (DC-IR, Direct current internal resistance).

[0121] Next, the resistance was measured in the same manner as the initial resistance measurement method after 50 cycles compared to the resistance measured initially at a high temperature of 45°C (high temperature initial resistance), and the resistance increase rate was recorded by converting the increase rate into a percentage (%).

[0122] (6) Tap density (T / D) measurement 10 g of the positive electrode active material powders of Example 1 and Comparative Example 1 were weighed and placed in a dedicated container, and then tapped 3,000 times to measure the volume. The weight was then divided by the volume to calculate the tap density. A JEL STAV II Jolting Volumeter was used as the measuring device.

[0123] [Table 2]

[0124] 14, it can be seen that the CNT content increases in the order of Examples 1, 2, and 3, but the high-rate characteristics show that the positive electrode active material of Example 1 exhibits the highest capacity and rate retention. Specifically, it can be seen that the capacity retention rate at a low rate compared to a high rate of 3C / 0.2C was excellent at 87.6%.

[0125] 15 and Table 2, it was confirmed that the positive electrode active material of Example 1 achieved a higher capacity than the positive electrode active material of Comparative Example 1 in terms of the initial charge-discharge capacity comparison result.

[0126] 16 and Table 2, the positive electrode active material of Example 1 exhibited a relatively small life cycle degradation compared to the positive electrode active material of Comparative Example 1. In addition, it was confirmed that the 50th discharge capacity retention rate of Example 1 was 95.0% of the 1st discharge capacity, which was significantly superior to 91.3% of Comparative Example 1.

[0127] At the same time, referring to Table 2, it can be seen that the positive electrode active material of Example 1 has a significantly reduced high temperature resistance increase rate compared to the positive electrode active material of Comparative Example 1.

[0128] It can be seen that the tap density of the positive electrode active material of Example 1 is significantly superior to that of the positive electrode active material of Comparative Example 1.

[0129] The present invention is not limited to the above-described embodiments, and can be manufactured in various different forms, and those skilled in the art will understand that the present invention can be embodied in other specific forms without changing the technical concept or essential characteristics of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and are not limiting. [Explanation of symbols]

[0130] 100: Metal oxides 200: First coating layer 300: Second coating layer

Claims

1. Metal oxides composed of single particles; a first coating layer located on the metal oxide surface and having a fiber shape; and a second coating layer located on the metal oxide surface and having a dot shape; A positive electrode active material for a lithium secondary battery comprising:

2. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the first coating layer and the second coating layer contain carbon.

3. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the fiber shape has a diameter of 100 nm or less.

4. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the length of the fiber shape is in the range of 10 nm to 30 μm.

5. The positive electrode active material is Surface 1 μm of the positive electrode active material ２ 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material contains 1 to 20 dot shapes per one dot.

6. The number of the fiber shapes and the dot shapes connected on the surface of the metal oxide is ２ 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the number of particles is in the range of 1 to 10 per particle.

7. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the weight ratio of the first coating layer to the second coating layer is in the range of 1:99 to 99:

1.

8. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the average particle size (D50) of the positive electrode active material is in the range of 2 μm to 7 μm.

9. The electrical conductivity of the positive electrode active material is 2.0×10 －５ 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material has a specific resistance of 100 S / cm or more.

10. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the tap density of the positive electrode active material is 2.20 g / cc or more.

11. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the single particle has at least one of a single crystal structure consisting of one particle and a monolith structure consisting of 2 to 8 particles.

12. The metal oxide is 2. The positive electrode active material for a lithium secondary battery according to claim 1, comprising nickel, cobalt, and manganese.

13. The content of nickel in the metal oxide is: The positive electrode active material for a lithium secondary battery according to claim 12 , wherein the amount of nickel, cobalt, and manganese is 0.5 moles or more based on 1 mole in total.

14. providing a metal hydroxide containing nickel, cobalt, and manganese; calcining the mixture of the metal hydroxide and the lithium source material to obtain a metal oxide composed of single particles; forming a first coating layer on the metal oxide surface using a first coating layer source material; and adding the metal oxide having the first coating layer thereon to a mixer and then mixing the metal oxide by a dry method to form a second coating layer on the surface of the metal oxide; The method for producing a positive electrode active material for a lithium secondary battery includes the steps of:

15. 15. The method of claim 14, wherein the forming of the first coating layer is performed by an incipient wetness impregnation method.

16. The method of claim 14, wherein the raw material for the first coating layer comprises a carbon raw material and a solvent.

17. 17. The method of claim 16, wherein the solvent comprises at least one of ethanol, distilled water, and N-methyl-2-pyrrolidone (NMP).

18. The step of forming the first coating layer comprises: The method for producing a positive electrode active material for a lithium secondary battery according to claim 16, wherein the weight ratio of the metal oxide to the carbon raw material is 50:1 to 150:

1.

19. The step of forming the second coating layer includes: The method for producing a positive electrode active material for a lithium secondary battery according to claim 14, which is carried out using a mechano-fusion method.

20. 17. The method of claim 16, wherein the carbon raw material comprises at least one of carbon, a carbon nanotube (CNT), a single-walled carbon nanotube (SWCNT), and a multi-walled carbon nanotube (MWCNT).

21. In the step of obtaining the metal oxide, The method for producing a positive electrode active material for a lithium secondary battery according to claim 14, wherein the firing is carried out at a temperature in the range of 800°C to 900°C for 20 to 30 hours.

22. a current collector; and a positive electrode active material layer located on at least one surface of the current collector, the positive electrode active material layer comprising the positive electrode active material according to any one of claims 1 to 13; A positive electrode for a lithium secondary battery comprising:

23. A lithium secondary battery comprising the positive electrode of claim 22.

Images