Cathode active material for lithium secondary battery and lithium secondary battery comprising the same

Abstract

The present embodiments relate to a positive electrode active material for a lithium secondary battery and a lithium secondary battery including the same. A positive electrode active material for a lithium secondary battery according to one embodiment comprises a nickel-containing metal oxide in the form of a single particle; and a doping element doped into the nickel-containing metal oxide; wherein the doping element may include Al, Y, and Zr.

Description

Technology Field

[0001] The present embodiments relate to a positive electrode active material for a lithium secondary battery and a lithium secondary battery containing the same. Background Technology

[0002] Driven by the recent explosive demand for electric vehicles and the need for increased driving range, the development of high-capacity, high-energy-density secondary batteries to meet these demands is actively underway worldwide. In particular, high-nickel NCM cathode materials with high nickel content are being used to satisfy these requirements.

[0003] However, as nickel content increases, particle strength decreases, leading to the occurrence of microcracks during charging and discharging. Furthermore, this results in an increased specific surface area of ​​the cathode material, which in turn increases reactivity with the electrolyte and leads to increased gas generation. Additionally, due to structural instability, unstable Ni 3+ stable Ni 2+ The phenomenon of cation mixing, in which it is reduced and converted into stable NiO, increases. Therefore, it is difficult to actually apply this as a positive electrode active material for lithium-ion batteries for electric vehicles or energy storage.

[0004] To solve this, a method was proposed to manufacture a cathode material in the form of a single particle with the size of the primary particle maximized, rather than in the form of a multi-particle secondary particle formed by the aggregation of primary particles, and then apply it.

[0005] However, in general, to manufacture a cathode material in the form of a single particle, firing must be carried out at a higher temperature compared to multi-particle materials, and at this time, under-firing often occurs, resulting in layered structure crystal defects, which causes electrochemical properties such as capacity and output to deteriorate and resistance to increase. The problem to be solved

[0006] In this embodiment, we aim to provide a positive electrode active material for a lithium secondary battery that has excellent electrochemical properties, improved lifespan and resistance characteristics, and excellent particle strength, as well as a lithium secondary battery containing the same. means of solving the problem

[0007] A positive electrode active material for a lithium secondary battery according to one embodiment comprises a nickel-containing metal oxide in the form of a single particle; and a doping element doped into the nickel-containing metal oxide; wherein the doping element may include Al, Y, and Zr.

[0008] A positive electrode for a lithium secondary battery according to another embodiment may include a positive electrode according to one embodiment.

[0009] A lithium secondary battery according to another embodiment may include a positive electrode for the lithium secondary battery according to one embodiment. Effects of the invention

[0010] According to the present embodiment, by doping a nickel-containing metal oxide in the form of a single particle with at least three types of doping elements, specifically, doping elements including Al, Y, and Zr, the crystal structure can be stabilized and the particle strength can be improved at the same time.

[0011] Accordingly, in this embodiment, a positive electrode active material can be realized that is in the form of a single particle, has excellent electrochemical properties, and has improved lifespan and resistance characteristics. Specific details for implementing the invention

[0012] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0013] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0014] When it is stated that one part is "on" or "on" another part, it may be directly on or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly on" another part, no other part is interposed in between.

[0015] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0016] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0017] In this specification, the term “combination(s) of these” described in the Markush-type expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush-type expression, and means including any one or more selected from the group consisting of said components.

[0018] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0020] Cathode active material for lithium secondary batteries

[0021] As mentioned above, the single-particle cathode active material may undergo under-sintering, which can cause defects in the layered crystal structure and lead to problems such as reduced high-temperature lifespan and resistance characteristics.

[0022] However, in this embodiment, this problem was solved by doping the metal oxide using at least three types of doping elements.

[0023] Specifically, a positive electrode active material for a lithium secondary battery according to one embodiment comprises a nickel-containing metal oxide in the form of a single particle; and a doping element doped into the nickel-containing metal oxide; wherein the doping element may include Al, Y, and Zr.

[0024] In this specification, a single particle may include at least one of a single crystal structure consisting of a single particle and a structure in which 2 to 20 or 2 to 10 particles are clustered together and are distinguished as a single mass when the cross-section of the powder is observed through a scanning electron microscope (SEM). Here, a single particle refers to a single grain or crystallite.

[0025] As shown in this embodiment, the single-particle active material has a smaller specific surface area compared to the conventional secondary-particle active material formed by the aggregation of tens to hundreds of primary particles, which reduces the amount of gas generated due to side reactions with the electrolyte. Additionally, the particle strength is higher, which can suppress particle breakage during rolling and reduce the occurrence of cracks due to repeated charging and discharging. Accordingly, it has the advantage of superior lifespan and safety compared to secondary particles, and enables the realization of high energy density of the electrode.

[0026] However, as mentioned above, the single-particle cathode active material is manufactured by sintering at a high temperature compared to the conventional secondary-particle cathode active material. At this time, over-sintering often occurs, which can result in layered structure crystal defects.

[0027] In this embodiment, by doping the nickel-containing metal oxide with at least three types of doping elements including Al, Y, and Zr, crystal defects such as an increase in the cation mixing ratio due to high-temperature sintering can be prevented, and the crystal grain size within the single particle and the average particle size of the single particle can be efficiently increased during the sintering process.

[0028] In this specification, “grain” refers to a distinct region in which atoms within a primary particle form a lattice structure in a certain direction.

[0029] Here, the content of Al may be in the range of 200 ppm to 1,800 ppm based on the total nickel-containing metal oxide, and more specifically, in the range of 500 ppm to 1,500 ppm. When the content of Al satisfies the above range, the deterioration of the layered structure into a spinel structure can be effectively suppressed. Since the layered structure facilitates the extraction and insertion of lithium ions, while the spinel structure does not allow for smooth movement of lithium ions, suppressing the deterioration of the layered structure into a spinel structure allows for smooth movement of lithium ions, and consequently, the electrochemical characteristics of the battery can be improved.

[0030] The content of Y above may be in the range of 400 ppm to 2,000 ppm based on the total nickel-containing metal oxide, and more specifically, in the range of 700 ppm to 1,700 ppm. When the content of Y satisfies the above range, grain growth can be promoted to efficiently increase the crystal grain size within the single grain and the average grain diameter of the single grain. In addition, since the degree of single grain formation can be increased, the grain strength can be improved.

[0031] The Zr content may be in the range of 1,200 ppm to 2,800 ppm based on the total doped nickel-containing metal oxide, and more specifically, in the range of 1,500 ppm to 2,500 ppm. When the Zr content satisfies the above range, it can alleviate the contraction of lithium ion pathways during the charging and discharging process of the battery, thereby stabilizing the layered structure. Accordingly, the cation mixing ratio can be lowered, and consequently, resistance characteristics and lifespan characteristics can be improved.

[0032] In this embodiment, the cation mixing ratio of nickel cations in the lithium layer within the crystal structure of the doped nickel-containing metal oxide may be 1.5% or less, more specifically in the range of 0.8% to 1.2% or 0.69% to 1.1%. When the cation mixing ratio satisfies the above range, a lithium secondary battery with excellent resistance characteristics and lifespan characteristics can be realized.

[0033] Meanwhile, in the nickel-containing metal oxide of the present embodiment, the nickel content may be 0.8 moles or more, more specifically in the range of 0.8 to 0.99 moles, 0.82 to 0.95 moles, or 0.82 to 0.93 moles, based on 1 mole of the total transition metal contained in the doped nickel-containing metal oxide. When the nickel content satisfies the above range, a high-capacity battery can be realized.

[0034] The nickel-containing metal oxide further comprises cobalt, and the content of the cobalt may be 0.06 moles or less, more specifically, greater than 0 and 0.06 moles or less, based on 1 mole of the total amount of transition metals contained in the doped nickel-containing metal oxide.

[0035] In addition, the nickel-containing metal oxide further comprises manganese, and the content of the manganese may be 0.15 moles or less, more specifically in the range of 0.05 moles to 0.1 moles, based on 1 mole of the total transition metal contained in the doped nickel-containing metal oxide.

[0036] More specifically, the nickel-containing metal oxide can be represented by the following chemical formula 1.

[0037] [Chemical Formula 1]

[0038] Li a [Ni x Co y Mn z M1 w1 M2 w2 ]O2

[0039] In the above Chemical Formula 1, 0.8≤a≤1.2, 0.8≤x≤0.99, 0 <y≤0.06, 0<z≤0.14, 0<w1≤0.1, 0≤w2≤0.05이고, x+y+z+w1+w2=1이고, M1은 Al, Y 및 Zr이고, M2는 B, Al, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La 및 Sr 중 1종 이상을 포함한다.

[0040] The total content of doping elements M1 and M2 in Chemical Formula 1 may be greater than 0 and less than or equal to 0.2 moles, based on 1 mole of the total sum of the nickel, cobalt, manganese, and doping elements, more specifically, in the range of 0.0005 moles to 0.1 moles, 0.0005 moles to 0.08 moles, 0.0005 moles to 0.04 moles, or 0.001 moles to 0.03 moles. In the above chemical formula, the content of the doping element refers to the doping amount of the doping element included in the final obtained cathode active material.

[0041] Meanwhile, the average particle size (D50) of the positive electrode active material according to the present embodiment may be 3 μm or more, more specifically in the range of 3 μm to 6 μm. When the average particle size of the positive electrode active material in the form of a single particle satisfies the above range, a lithium secondary battery with excellent electrochemical properties such as lifespan characteristics and resistance increase rate can be realized. In addition, since the energy density per unit volume can also be increased, it has a very advantageous effect.

[0042] The positive electrode active material of this embodiment has a very low fine particle generation rate. Specifically, when the positive electrode active material is pressed five times with a press gauge of 0.01 mm using a roll press, the sum of fine particles smaller than 1 μm may be 2% or less. When the fine particle generation rate satisfies the above range, high-temperature life and resistance characteristics can be improved.

[0043] In addition, the positive electrode active material of the present embodiment may have a peak temperature obtained by Differential Scanning Calorimetry (DSC) analysis of 230°C or higher, more specifically, in the range of 230°C to 280°C.

[0045] anode

[0046] In another embodiment, a positive electrode is provided comprising a current collector and a positive electrode active material layer located on one side of the current collector and comprising a positive electrode active material manufactured according to the above-described embodiment.

[0047] The characteristics of the positive active material constituting the above positive active material layer are the same as those previously described. Therefore, a detailed description of the positive active material will be omitted.

[0048] The above current collector may be, for example, made of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc.

[0049] Meanwhile, the above positive active material layer may include a binder and a conductive material.

[0050] At this time, the binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the positive current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof. One of these alone or a mixture of two or more may be used, but is not limited thereto. The binder may be included in an amount of 1 to 30 weight% based on the total weight of the positive active material layer.

[0051] In addition, the conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. 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 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, and one of these alone or a mixture of two or more may be used, but is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 weight% relative to the total weight of the positive electrode active material layer.

[0052] The above-mentioned anode can be manufactured according to a conventional anode manufacturing method, except for using the above-mentioned anode active material.

[0053] Specifically, the anode can be manufactured by applying a composition for forming an anode active material layer, comprising the aforementioned anode active material and optionally a binder, conductive material, or solvent as needed, onto an anode current collector, followed by drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above.

[0054] The above solvent may be a solvent commonly used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that allows for the dissolution or dispersion of the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0055] Alternatively, the anode may be manufactured by casting the composition for forming the anode active material layer onto a separate support, and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0057] lithium secondary battery

[0058] In another embodiment, a lithium secondary battery including the anode is provided.

[0059] Specifically, the lithium secondary battery may include a positive electrode, a negative electrode positioned opposite to the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is as described above. Additionally, the lithium secondary battery may optionally further include a battery container housing an electrode assembly comprising the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

[0060] In the above 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.

[0061] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0062] The above-mentioned cathode active material layer may optionally include a binder and a conductive material together with the cathode active material. The above-mentioned cathode active material layer may be manufactured, as an example, by applying a composition for forming a cathode active material layer, comprising a cathode active material and optionally a binder and a conductive material, onto a cathode current collector and drying it, or by casting the composition for forming a cathode onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0063] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. 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, or Al alloys; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the above-mentioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. Furthermore, the carbon material may include both low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0064] The binder and conductive material mentioned above may be the same as those previously described in the anode.

[0065] Next, depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and a mixed multilayer film 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.

[0066] In addition, regarding the above lithium secondary battery, the electrolyte may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing a lithium secondary battery, but is not limited to these.

[0067] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0068] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having C2 to C20 structures and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0069] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may 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 concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0071] As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0073] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0075] Example 1

[0076] (1) Preparation of positive electrode active material

[0077] Ni 0.90 Co 0.03 Mn 0.07After preparing a precursor of (OH)2 composition, a mixture was prepared by uniformly mixing LiOH·H2O (Samjeon Chemical, battery grade) as a lithium raw material and Y2O3, ZrO2, and Al(OH)3 as doping raw materials with the said precursor.

[0078] At this time, the molar ratio of lithium (Li) to the total metal (Me) excluding lithium (Li / Me) was designed to be 1.05, and doping raw materials were added so that Zr was 2000 ppm, Y was 1200 ppm, and Al was 1000 ppm based on the above precursor.

[0079] The above mixture was introduced into a kiln under an oxygen atmosphere and pre-fired at 680°C for 6.5 hours to obtain a pre-fired product. Subsequently, the obtained pre-fired product was introduced into a kiln under an oxygen atmosphere and heated to 890°C for 3 hours (1 st step) followed by firing at 940℃ for 1 hour (2 nd step) then calcined at 780℃ for 11 hours (3 rd A sintered product was obtained by firing using a 3-step method.

[0080] The above calcined product was crushed to produce a single-particle cathode active material doped with Al, Y, and Zr.

[0081] (2) Manufacture of monocell

[0082] A monocell was manufactured using the positive active material prepared in (1) in the following way.

[0083] Specifically, a positive electrode active material, a conductive material (acetylene black), and a polyvinylidene fluoride binder (product name: KF1120) were mixed in a weight ratio of 96.5:1.5:2, and this mixture was added to an N-methyl-2-pyrrolidone solvent so that the solid content was about 30 wt% to prepare a positive electrode active material slurry.

[0084] The above slurry was coated onto an aluminum foil (thickness: 15 μm), which serves as an anode current collector, using a doctor blade, and an anode was manufactured by drying and rolling. The loading amount of the anode was approximately 15-16 mg / cm², and the rolling density was approximately 3.5 g / cm³. 3 It was.

[0085] A monocell was manufactured using the above anode, graphite cathode, electrolyte, and polypropylene separator in a conventional manner. Here, the electrolyte was prepared by dissolving 0.7M LiPF6 and 0.3M LiFSI in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (mixing ratio EC:EMC = 3:7 volume%) to prepare a mixed solution, which was then used.

[0087] Comparative Example 1

[0088] In Example 1 (1), when manufacturing the positive active material, Zr2O and Al(OH)3 were uniformly mixed as doping raw materials to prepare a mixture, and the positive active material was manufactured in the same manner as in Example 1, except that the doping raw materials were added such that Zr was 2000 ppm and Al was 1000 ppm based on the precursor.

[0090] Experimental Example 1 - Measurement of particle breakage degree

[0091] The degree of particle breakage was measured using the anodes prepared according to Example 1 and Comparative Example 1 and is shown in Table 1 below.

[0092] Specifically, 10g of positive active material was mixed with 3.5g of NMP and cast onto a 20㎛ thick aluminum foil (Al foil) (70mm*210mm), then dried in a 120℃ Convection Oven for 30 minutes. Afterward, a sample was prepared by covering the aluminum foil coated with the positive active material with an aluminum foil of the same size.

[0093] The above sample was pressed five times using a roll press with a press gauge of 0.01 mm, and 2 g of active material particles were obtained. The amount of fine particles generated was analyzed by performing particle size analysis using a Malvern (MS3000) analyzer with the obtained active material particles. The degree of particle breakage was indicated by the sum of the Vol% values ​​of fine particles smaller than 1 µm in the particle size analysis results.

[0094] division particle breakage Example 1 1.85 vol% Comparative Example 1 2.28 vol%

[0095] Referring to Table 1, it can be seen that the fine particle generation rate of Example 1, a positive electrode active material prepared by doping with three types of doping elements, is very low compared to Comparative Example 1, a positive electrode active material prepared by doping with only two types of doping elements.

[0097] Experimental Example 2 - DSC Measurement

[0098] (1) Manufacturing of coin-type half-batteries

[0099] According to the examples and comparative examples, a CR2032 coin cell was manufactured using a positive electrode active material in the following manner.

[0100] Specifically, a positive electrode active material, a conductive material (acetylene black FX35, Denka), and a polyvinylidene fluoride binder (product name: KF9709) were mixed in weight ratios of 96.5:1.5:2 and 95:2.2:2.8, and the mixture was added to an N-methyl-2-pyrrolidone solvent to produce a positive electrode active material slurry such that the solid content was approximately 65-69% by weight.

[0101] The above slurry was coated onto an aluminum foil (Al foil, thickness: 20 μm), which serves as an anode current collector, using a doctor blade, and an anode was manufactured by drying and rolling. The loading amount of the anode was approximately 15-16 mg / cm², and the rolling density was approximately 3.5 g / cm³. 3 It was.

[0102] A 2032 coin-type half-cell was manufactured using the above-mentioned positive electrode, lithium metal negative electrode (thickness 400 μm, NEBA), electrolyte, and polypropylene polyethylene separator by a conventional method. The electrolyte was prepared by dissolving 1M LiPF6 in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate (mixing ratio EC:DMC:DEC = 1:2:1 volume%) to prepare a mixed solution.

[0103] (2) DSC measurement

[0104] Differential Scanning Calorimetry (DSC) analysis was performed using the coin cell prepared in (1). Specifically, the coin cell was charged to 4.25V under an initial charging condition of 0.1C, then the half-cell was disassembled to obtain only the positive electrode separately, and this positive electrode was prepared by washing it five times with dimethyl carbonate. After impregnating the washed positive electrode with electrolyte in a DSC crucible, the temperature was raised to 350℃, and the change in calorimetry was measured using a Mettler Toledo DSC1 star system as a DSC instrument. The obtained DSC peak temperatures are shown in Table 2 below.

[0105] division DSC peak temperature (°C) Example 1 232 Comparative Example 1 223

[0106] Referring to Table 2, it can be seen that the thermal stability of the positive electrode active material according to Example 1 is superior to that of the positive electrode active material of Comparative Example 1.

[0108] Experimental Example 3 - Measurement of Dose Retention Rate

[0109] After a formation cycle of 0.1C / 0.1C constant current charge / discharge at 45℃ and a voltage of 2.5 to 4.25 V, a constant current charge / discharge test was performed at 0.5C / 1C, and the capacity retention rate was calculated using the capacity measured every 50 cycles from the 50th cycle to the 700th cycle relative to the capacity of the first cycle. The results are shown in Table 3 below.

[0111] Experimental Example 4 - Measurement of Resistance Increase Rate

[0112] The resistance increase rate was converted into a percentage (%) of the increase in resistance measured every 50 cycles from the 50th cycle to the 700th cycle, relative to the resistance measured at the first 0.5C charge / 1.0C discharge at high temperature (45℃). Resistance (DC internal resistance: DC-IR (Direct current internal resistance)) was calculated by measuring the voltage value 60 seconds after applying the discharge current in a 4.25V charge state and using the formula '(Voltage before current application - Voltage after 60 seconds of current application) / Applied current'. The results are shown in Table 3 below.

[0113] Cycle Cap. retention [%] ΔDCIR [%] Example 1 Comparative Example 1 Example 1 Comparative Example 1 50 97.8 97.5 5.7 7.0 100 96.6 96.2 10.9 12.8 150 95.3 94.9 15.7 18.9 200 94.2 93.8 20.0 23.9 250 93.2 92.5 24.9 30.2 300 92.1 91.4 29.5 35.1 350 91.4 90.3 35.2 41.0 400 90.3 89.2 40.7 46.9 450 88.9 87.8 47.8 53.8 500 87.6 86.7 53.7 59.9 550 85.9 85.1 63.2 69.1 600 84.6 84.1 69.8 75.7 650 83.9 83.4 73.9 79.4 700 82.5 82.2 82.3 87.7

[0114] Referring to Table 3, it can be seen that the positive active material according to Example 1 has excellent capacity retention rate and resistance characteristics even as the number of cycles increases compared to the positive active material according to Comparative Example 1.

[0116] Example 5 - Measurement of Cation Mixing Ratio

[0117] For the cathode active materials prepared according to Example 1 and Comparative Example 1, the cation mixing ratio was measured by the following method. The results are shown in Table 4 below.

[0118] 1) Analysis of sample structure using Rigaku's smart lab equipment

[0119] 2) Smart Lab Equipment Configuration

[0120] Goniometer radius: 300.0 mm

[0121] Rotating anode x-ray tube (DPTA-II)

[0122] Theta_s arm : BB Slit

[0123] CBO(cross beam optics for Cu target)

[0124] Soller slit 5.0 deg, 10 mm Incident slit

[0125] Theta_d arm: 8.0mm Receiving slit

[0126] Diffracted beam monochromator (DBM) unit for D / teX Ultra, D / teX Ultra

[0127] Sample stage: ASC-6 (auto sample changer), Reflection knife edge

[0128] 2) Apply 45kV, 200mA (9kW) to the Cu anode to generate X-rays

[0129] 3) Set the equipment optic to Incident slit 1 / 2 degree and Receiving slit 8.0 mm.

[0130] 4) XRD measurement was performed at a scan of 10–80°, a step of 0.02°, and a speed of 10° / min.

[0131] 5) The cation mixing value was calculated using Li / Ni% with Rigaku's SmartLab Studio II x64 v4.2.82.0 software.

[0132] 6) Use WPPF (Whole Powder Pattern Fitting) in the software for calculations

[0134] division cation mixing [%] Example 1 1.1 Comparative Example 1 1.7

[0135] Referring to Table 3, it can be seen that the cation mixing ratio of the positive electrode active material prepared according to Example 1 is significantly lower than that of Comparative Example 1.

[0137] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

Claim 1 A positive electrode active material for a lithium secondary battery comprising: a nickel-containing metal oxide in the form of a single particle; and a doping element doped into the nickel-containing metal oxide; wherein the doping element comprises Al, Y, and Zr, and the nickel-containing metal oxide further comprises cobalt, and the content of the cobalt is 0.06 mole or less based on 1 mole of the total amount of transition metals contained in the doped nickel-containing metal oxide, wherein the average particle size (D50) of the positive electrode active material is 3 μm to 6 μm, and the positive electrode active material has a sum of fine particles less than 1 μm of 2 vol% or less when pressed 5 times with a press gauge of 0.01 mm using a roll press. Claim 2 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the cation mixing ratio of nickel cations in the lithium layer within the crystal structure of the doped nickel-containing metal oxide is 1.5% or less. Claim 3 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the content of Al is in the range of 200 ppm to 1,800 ppm based on the nickel-containing metal oxide. Claim 4 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the content of Y is in the range of 400 ppm to 2,000 ppm based on the nickel-containing metal oxide. Claim 5 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the content of Zr is in the range of 1,200 ppm to 2,800 ppm based on the nickel-containing metal oxide. Claim 6 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the nickel content is 0.8 moles or more based on 1 mole of the total amount of transition metals contained in the nickel-containing metal oxide. Claim 7 delete Claim 8 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the nickel-containing metal oxide further comprises manganese, and the content of the manganese is 0.15 moles or less based on 1 mole of the total amount of transition metals contained in the nickel-containing metal oxide. Claim 9 In claim 1, the nickel-containing metal oxide is a positive electrode active material for a lithium secondary battery represented by the following chemical formula 1: [Chemical Formula 1]Li a [Ni x Co y Mn z M1 w1 M2 w2 ]O2 In the above chemical formula 1, 0.8≤a≤1.2, 0.8≤x≤0.99, 0 <y≤0.06, 0<z≤0.14, 0<w1≤0.05, 0≤w2≤0.05이고, x+y+z+w1+w2=1이고, M1은 Al, Y 및 Zr이고, M2는 B, Al, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La 및 Sr 중 1종 이상을 포함한다. Claim 10 delete Claim 11 delete Claim 12 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the peak temperature obtained by Differential Scanning Calorimetry (DSC) analysis is 230°C or higher Claim 13 A positive electrode for a lithium secondary battery comprising a positive electrode active material according to any one of claims 1 to 6, 8, 9 and 12. Claim 14 A lithium secondary battery comprising a positive electrode for a lithium secondary battery according to claim 13.