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

Abstract

The present embodiments relate to a cathode active material for a lithium secondary battery, and a lithium secondary battery comprising same. The cathode active material for a lithium secondary battery, according to one embodiment of the present invention, comprises: a nickel-containing metal oxide in a discrete form; a doping element doped into the nickel-containing metal oxide; and a coating layer positioned on the surface of the nickel-containing metal oxide, wherein the doping element includes three or more types, and the coating layer can include two or more types of coating elements.

Description

Cathode active material for lithium secondary batteries and lithium secondary batteries containing the same

[0001] These examples relate to a positive electrode active material for a lithium secondary battery and a lithium secondary battery including the same.

[0002] Driven by the recent explosive demand for electric vehicles and the growing demand for longer driving ranges, 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 meet these demands.

[0003] However, as the nickel content increases, the particle strength decreases, causing microcracks to occur during charge and discharge. In addition, this increases the specific surface area of ​​the cathode material, which increases the reaction with the electrolyte, leading to the problem of increased gas generation. In addition, the structural instability of unstable Ni 3+ Ni is stable 2+ The phenomenon of cation mixing, which is converted into stable NiO by reduction, increases. Therefore, it is difficult to apply this as a cathode active material for lithium-ion batteries for electric vehicles or energy storage.

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

[0005] However, in general, in order to manufacture a cathode material in the form of a single particle, firing must be performed at a higher temperature than for a multi-particle one, and at this time, over-firing often occurs, causing layered structure crystal defects, which has the problem of deteriorating electrochemical characteristics such as capacity and output.

[0006] In addition, when the sintering temperature was lowered to solve this problem, there was a problem that the grain size within the single particle did not grow sufficiently, resulting in deterioration of particle strength and life characteristics.

[0007] In this embodiment, it is intended to provide a cathode active material for a lithium secondary battery having excellent electrochemical properties and improved lifespan and resistance characteristics, and a lithium secondary battery including the same.

[0008] According to one embodiment, a cathode active material for a lithium secondary battery includes a nickel-containing metal oxide in the form of a single particle; a doping element doped into the nickel-containing metal oxide; and a coating layer positioned on a surface of the nickel-containing metal oxide, wherein the doping element includes three or more types, and the coating layer may include two or more types of coating elements.

[0009] A lithium secondary battery according to another embodiment may include a positive electrode including the positive electrode active material for a lithium secondary battery according to the above-described embodiment.

[0010] According to the present embodiment, by including at least three types of doping elements in a nickel-containing metal oxide in the form of a single particle and including a coating layer located on the surface of the nickel-containing metal oxide and including at least two types of coating elements, the crystal structure can be stabilized and particle strength can be improved.

[0011] Accordingly, in this embodiment, a cathode active material having excellent electrochemical properties and improved lifespan and resistance characteristics can be realized in the form of a single particle.

[0012] In addition, when applying the positive electrode active material according to the present embodiment, an electrode of excellent quality can be manufactured.

[0013] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0014] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0015] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0016] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0017] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0018] In this specification, the term "combination(s) thereof" described in the expression in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expression in the Makushi format, and means including any one or more selected from the group consisting of said components.

[0019] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0020]

[0021] Cathode active material for lithium secondary batteries

[0022] As described above, the positive electrode active material in the form of a single particle may have a problem in that oversintering may occur, causing defects in the layered crystal structure or reducing particle strength, which may result in a deterioration in high-temperature life and resistance characteristics.

[0023] However, in this embodiment, this problem was solved by doping a metal oxide using at least three types of doping elements and forming a coating layer containing two or more types of coating elements.

[0024] Specifically, a cathode active material for a lithium secondary battery according to one embodiment includes a nickel-containing metal oxide in the form of a single particle; a doping element doped into the nickel-containing metal oxide; and a coating layer positioned on a surface of the nickel-containing metal oxide, wherein the doping element includes three or more types, and the coating layer may include two or more types of coating elements.

[0025] In this specification, a single particle may include at least one of a single crystal structure composed of a single particle and a structure in which 2 to 20 or 2 to 10 particles are clumped together and can be distinguished as a single lump when observing a cross-section of the powder through a scanning electron microscope (SEM). Here, one particle means one grain or crystallite.

[0026] As in this example, the single particle-type active material has a smaller specific surface area than the conventional secondary particle-type positive electrode active material formed by the agglomeration of tens to hundreds of primary particles, thereby reducing the amount of gas generated by side reactions with the electrolyte. In addition, the particle strength is large, which can suppress particle breakage during rolling and reduce the occurrence of cracks due to repeated charging and discharging. Accordingly, it has superior lifespan and safety compared to secondary particles, and has the advantage of being able to realize high energy density of the electrode.

[0027] However, as previously mentioned, single-particle cathode active materials are manufactured through sintering at higher temperatures than conventional secondary particle cathode active materials. In this process, oversintering often occurs, which can lead to layered crystal defects.

[0028] In this embodiment, by doping the nickel-containing metal oxide using at least three doping elements including Al, Y, and Zr, and forming a coating layer using at least two coating elements including Co and Al, crystal defects such as an increase in the cation mixing ratio due to high-temperature firing can be prevented, and the crystal grain size within a single particle and the average particle diameter of a single particle can be efficiently increased during the firing process.

[0029] In this specification, “crystal grain” means a distinct region in which atoms within a primary particle form a lattice structure with a certain direction.

[0030] Here, the content of Co in the positive electrode active material on which the coating layer is formed may be in the range of 0.035 mol to 0.08 mol, more specifically, in the range of 0.05 mol to 0.07 mol, based on 1 mol of the total of transition metals included in the nickel-containing metal oxide on which the coating layer is formed. When the content of Co satisfies the above range, crystal grains can be grown to an appropriate size, and the production cost can be appropriately controlled, resulting in excellent economic efficiency.

[0031] The content of Al in the positive electrode active material on which the coating layer is formed may be in the range of 0.001 mol to 0.015 mol, and more specifically, in the range of 0.003 mol to 0.012 mol or 0.005 mol to 0.009 mol, based on 1 mol of the total of transition metals included in the nickel-containing metal oxide on which the coating layer is formed. When the content of Al satisfies the above range, the deterioration of the layered structure into a spinel structure can be effectively suppressed. The layered structure facilitates the desorption and insertion of lithium ions, but the spinel structure does not allow for smooth movement of lithium ions. Therefore, by suppressing the deterioration of the layered structure into a spinel structure, the movement of lithium ions can be facilitated, and as a result, the electrochemical characteristics of the battery can be improved.

[0032] The content of Y may be in the range of 400 ppm to 2,000 ppm, and more specifically, in the range of 700 ppm to 1,700 ppm, based on the total weight of the nickel-containing metal oxide on which the coating layer is formed. When the content of Y satisfies the above range, grain growth can be promoted, thereby efficiently increasing the crystal grain size within a single particle and the average particle diameter of the single particle.

[0033] The content of Zr may be in the range of 1,200 ppm to 2,800 ppm, and more specifically, in the range of 1,500 ppm to 2,500 ppm, based on the total weight of the nickel-containing metal oxide on which the coating layer is formed. When the content of Zr satisfies the above range, the shrinkage of the path of lithium ions during the charging and discharging process of the battery can be alleviated, thereby stabilizing the layered structure. Accordingly, the cation mixing ratio can be reduced, and as a result, the resistance characteristics and life characteristics can be improved.

[0034] Meanwhile, the content of nickel in the nickel-containing metal oxide of the present embodiment may be 0.8 mol or more, more specifically, 0.8 mol to 0.99 mol, 0.82 mol to 0.95 mol, or 0.82 mol to 0.93 mol, based on 1 mol of the total of transition metals included in the doped nickel-containing metal oxide. When the nickel content satisfies the above range, a high-capacity battery can be realized.

[0035] The nickel-containing metal oxide further includes manganese, and the content of the manganese may be 0.15 mol or less, more specifically, 0.05 mol to 0.1 mol, based on 1 mol of the total of transition metals included in the nickel-containing metal oxide on which the coating layer is formed. When the content of manganese satisfies the above range, the stability of the positive electrode active material can be improved, and consequently, the stability of the battery can be improved.

[0036] The nickel-containing metal oxide on which the above coating layer is formed 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≤0.1이고, 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] In the chemical formula 1, the total content of the doping elements M1 and M2 may be greater than 0 and less than or equal to 0.2 mol, more specifically, in the range of 0.0005 mol to 0.1 mol, 0.0005 mol to 0.08 mol, 0.0005 mol to 0.04 mol, or 0.001 mol to 0.03 mol, based on 1 mol of the total of nickel, cobalt, manganese, and the doping elements. In the chemical formula, the content of the doping element refers to the doping amount of the doping element included in the positive electrode active material finally obtained.

[0041] Meanwhile, the average particle diameter (D50) of the cathode active material according to the present embodiment may be 3 μm or more, and more specifically, 3 μm to 6 μm. When the average particle diameter of the single-particle cathode active material 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, it has a very advantageous effect because it can also increase the energy density per volume.

[0042] The above-described positive electrode active material may have a moisture increase rate of 80% or less at a temperature of 25±3°C and a relative humidity of 50±15%. In addition, the above-described positive electrode active material may have a residual lithium increase rate of 20% or less at a temperature of 25±3°C and a relative humidity of 50±15%. Since the positive electrode active material of the present embodiment has a coating layer containing two elements positioned on the surface of a nickel-containing metal oxide, the moisture increase rate and the residual lithium increase rate can be significantly reduced. Accordingly, a positive electrode active material with excellent high-temperature lifespan and resistance characteristics can be realized.

[0043] In addition, the crystal size of the nickel-containing metal oxide on which the coating layer is formed may be 200 nm or more, more specifically, in the range of 200 nm to 250 nm. When the crystal size satisfies the above range, both the lifespan and electrochemical characteristics of the positive electrode active material of the present embodiment can be improved.

[0044]

[0045] anode

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

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

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

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

[0050] At this time, the binder plays a role of improving the adhesion between the positive electrode active material particles and the adhesive strength 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, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one kind alone or a mixture of two or more kinds thereof may be used, but is not limited thereto. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0051] And, the conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. 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, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One type alone or a mixture of two or more types among these may be used, but the present invention is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0052] The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the above positive electrode active material is used.

[0053] Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, including the positive electrode active material described above and optionally a binder, a conductive agent, or a solvent, on a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive agent are as described above.

[0054] The solvent may be a solvent generally used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0055] Alternatively, the positive electrode may be manufactured by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating the resulting film on a positive electrode current collector by peeling it off from the support.

[0056]

[0057] lithium secondary battery

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

[0059] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite 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. In addition, the lithium secondary battery may optionally further include a battery container that houses an electrode assembly including the positive electrode, the negative electrode, and the separator, and a sealing member that seals 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 positioned on the negative electrode current collector.

[0061] The negative electrode 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., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0062] The negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material. As an example, the negative electrode active material layer may be manufactured by applying a composition for forming a negative electrode active material layer comprising the negative electrode active material and optionally a binder and a conductive material onto a negative electrode current collector and drying the composition, or by casting the negative electrode forming composition onto a separate support and then laminating the resulting film onto a negative electrode current collector by peeling the film off from the support.

[0063] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof 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 alloy, Sn alloy, and Al alloy; metallic oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fiber-like forms, 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 above binder and conductive material may be the same as those described above for the positive electrode.

[0065] Next, depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators may include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof, and 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.

[0066] In addition, in the lithium secondary battery, examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

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

[0068] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, 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 linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0069] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0070]

[0071] As described above, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0072]

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

[0074]

[0075] Example 1

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

[0077] Ni0.90 Co 0.03 Mn 0.07 After preparing a precursor of (OH)2 composition, a mixture was prepared by uniformly mixing LiOH·H2O (Samsung Chemical, battery grade) as a lithium raw material and Y2O3, ZrO2 and Al(OH)3 as doping raw materials into the 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 placed in a kiln in an oxygen atmosphere and pre-fired at 680°C for 6.5 hours to obtain a pre-fired product. Afterwards, the obtained pre-fired product was placed in a kiln in an oxygen atmosphere and pre-fired at 890°C for 3 hours (1 st After step), it was fired at 940℃ for 1 hour (2 nd step) and then fired at 780℃ for 11 hours (3 rd The sintered product was obtained by sintering using a 3-step method.

[0080] The above-mentioned sintered material was crushed to obtain a single particle metal oxide doped with Al, Y, and Zr.

[0081] A positive electrode active material having a coating layer was manufactured by dry mixing Co(OH)2 and Al(OH)3 as coating raw materials to the obtained single particle metal oxide, and then heat treating at 700°C for 5 hours in an oxygen atmosphere. At this time, Co(OH)2 and Al(OH)3 were mixed by adding Co in an amount corresponding to 2.5 mol% and Al in an amount corresponding to 1000 ppm based on the single particle metal oxide.

[0082] (2) Manufacturing of monocells

[0083] (1) A monocell was manufactured using the positive electrode active material manufactured in the following manner.

[0084] Specifically, a positive electrode active material, a conductive agent (acetylene black), and a polyvinylidene fluoride binder (trade name: KF1120) were mixed in a weight ratio of 96.5:1.5:2, and the 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.

[0085] The above slurry was coated on an aluminum foil (Al foil, thickness: 15 ㎛), which is a positive electrode collector, using a doctor blade, dried, and rolled to manufacture a positive electrode. The loading amount of the positive electrode was about 15-16 mg / cm2, and the rolling density was about 3.5 g / cm 3 It was.

[0086] A monocell was manufactured using the above positive electrode, graphite negative electrode, electrolyte, and polypropylene separator in a conventional manner. Here, the electrolyte was prepared by dissolving 0.7 M LiPF6 and 0.3 M 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, and then used.

[0087] Comparative Example 1

[0088] A single-particle positive electrode active material was manufactured in the same manner as in Example 1, except that a coating layer was not formed.

[0089]

[0090] Experimental Example 1 - Capacity Retention Rate Measurement

[0091] After a formation cycle of 0.1C / 0.1C constant current charge / discharge within a voltage range of 2.5 to 4.25 V at 45°C, a constant current charge / discharge test was performed at 0.5C / 1C, and the capacity retention was calculated through the capacity measured every 50 cycles from the 50th to the 700th cycle compared to the first cycle capacity. The results are shown in Table 1 below.

[0092]

[0093] Experimental Example 2 - Measurement of Resistance Increase Rate

[0094] The resistance increase rate was calculated as a percentage (%) of the resistance increase rate measured every 50 cycles from the 50th to the 700th cycle compared to the resistance measured at the first 0.5C charge / 1.0C discharge at high temperature (45℃). The 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 4.25 V charging state and calculating it as '(voltage before current application - voltage 60 seconds after current application) / applied current'. The results are shown in Table 1 below.

[0095] CycleCap. retention [%]ΔDCIR [%]Example 1Comparative Example 1Example 1Comparative Example 15097.797.83.95.710096.396.67.610.915094.995.311.215.720093.794.213.620.025093.193.215.524.930092.092.119.229.535091.191.4 22.235.240089.990.326.040.745088.888.930.947.850087.787.634.753.755086.885.939.263.260085.984.643.869.865084.883.949.273.970083.882.554.282.3

[0096] Referring to Table 1, it can be confirmed that the positive electrode active material according to Example 1 has superior capacity retention and resistance characteristics even when the cycle increases compared to the positive electrode active material according to Comparative Example 1.

[0097] Experimental Example 3 - Measurement of Residual Lithium Changes

[0098] The amount of residual lithium was measured for the positive electrode active materials manufactured according to Example 1 and Comparative Example 1. Specifically, 5 g of the positive electrode active material was added to 100 ml of pure water, stirred, and filtered under reduced pressure to obtain a solution. The solution was analyzed using an Autotitrator T5 (METTLER). The residual lithium value was calculated using the following formula.

[0099] LiOH = ((VEQ1+VEQ2)-2*VEQ2)*C*Mw*1000 / M

[0100] Li2CO3= VEQ2*C*Mw*1000 / M

[0101] - VEQ1: Consumption ml when VEQ1 of 0.1N_HCL

[0102] - VEQ2: Consumption of 0.1N_HCl ml from VEQ1 to VEQ2

[0103] - C: Concentration of HCL (N) - 0.1N

[0104] - M: (Sample Weight * Soultion Weight) / DIW Weight

[0105] - M w: Molecular weight Li 2 CO 3 73.89 (g / mol), LiOH 23.94 (g / mol)

[0106] TTL is a numerical value that represents only the amount of lithium (Li) remaining on the surface of the positive electrode active material, and was calculated using the following formula.

[0107] TTL = LiOH result value * (Li molar mass / LiOH molar mass) + Li2CO3 result value * (2 * Li molar mass / Li2CO3 molar mass)

[0108] The results are shown in Table 2 below.

[0109] Residual LithiumLiOH (wt%)Li2CO3 (wt%)Total (wt%)TTL (ppm)Example 10.10900.17810.2871650.2Comparative Example 10.40010.31930.71941758.9

[0110] Referring to Table 2, it can be confirmed that the residual lithium of Example 1, which is a positive electrode active material with a coating layer formed, is reduced by more than 55% compared to Comparative Example 1, which is a positive electrode active material without a coating layer formed. This shows that the residual lithium remaining on the surface of the positive electrode active material reacts with the coating element, resulting in a reduction in the residual lithium.

[0111] Experimental Example 4 - Measurement of changes in residual lithium over time

[0112] The amount of residual lithium change over time was measured for the positive electrode active materials manufactured according to Example 1 and Comparative Example 1. Specifically, the positive electrode active material of Experimental Example 3 was stored at a temperature of 25±3°C and a relative humidity of 50±15%, and the residual lithium was analyzed according to the storage time.

[0113] The results are shown in Table 3 below.

[0114] Residual lithium change over timeR-Li0 min30 min60 min120 minExample 1LiOH (wt%)0.09000.06240.04480.0389Li2CO3(wt%)0.21510.26350.29520.3189Total (wt%)0.30510.32590.34000.3578Comparative Example 1LiOH (wt%)0.23870.18810.17990.1283Li2CO3(wt%)0.44990.52380.58930.7385Total (wt%)0.68860.71190.76920.8668

[0115] Referring to Table 3, it can be seen that the positive electrode active material of Example 1 has a lower rate of increase in residual lithium over time than the positive electrode active material of Comparative Example 1. Accordingly, it can be confirmed that the surface stability of the positive electrode active material has increased through coating.

[0116] Experimental Example 5 - Measurement of moisture content change over time

[0117] The change in moisture content over time was measured for the positive electrode active materials manufactured according to Example 1 and Comparative Example 1. Specifically, the positive electrode active materials were stored at a temperature of 25±3°C and a relative humidity of 50±15%, and then the moisture content was analyzed according to the storage time. The moisture content was analyzed using 851KF (Metrohm) equipment under the following conditions.

[0118] - Measurement temperature: 200 ℃

[0119] - Stirrer rate: 8

[0120] - Flow rate: 60 mL / min

[0121] - Blank conditions: Blank sample size 1 g

[0122] The results are shown in Table 4 below.

[0123]

[0124] Change in moisture content over time 0 min 5 min 10 min 30 min Example 1465.5 ppm 676.4 ppm 732.8 ppm 775.2 ppm Comparative Example 1592.3 ppm 884.7 ppm 1023.6 ppm 1280.4 ppm

[0125] Referring to Table 4, it can be seen that the rate of increase in moisture content over time of the positive electrode active material of Example 1 is significantly lower than that of the positive electrode active material of Comparative Example 1. Accordingly, it can be confirmed that the surface stability of the positive electrode active material has increased through coating.

[0126] Experimental Example 6 - Grain Size Measurement

[0127] For the positive electrode active materials manufactured according to Example 1 and Comparative Example 1, the crystal grain size, c-axis, and a-axis values ​​were measured as follows. The results are shown in Table 5 below.

[0128]

[0129] 1) Sample structure analysis using Rigaku's smart lab equipment

[0130] 2) Smart lab equipment configuration

[0131] Goniometer radius: 300.0 mm

[0132] Rotating anode x-ray tube (DPTA-II)

[0133] Theta_s arm: BB Slit

[0134] CBO(cross beam optics for Cu target)

[0135] Soller slit 5.0 deg, 10 mm Incident slit

[0136] Theta_d arm: 8.0mm Receiving slit

[0137] Diffracted beam monochromator (DBM) unit for D / teX Ultra, D / teX Ultra

[0138] Sample stage: ASC-6 (auto sample changer), Reflection knife edge

[0139] 2) Apply 45kV, 200mA (9kW) to the Cu anode to generate X-rays.

[0140] 3) The equipment optics are set to Incident slit 1 / 2 deg, Receiving slit 8.0 mm.

[0141] 4) XRD measurement was performed at Scan 10~80°, Step 0.02°, 10° / min.

[0142] 5) Crystal grain size was calculated using Rigaku's SmartLab Studio II x64 v4.2.82.0 S / W.

[0143] 6) Calculation is done using WPPF (Whole powder pattern fitting) in S / W.

[0144]

[0145] Crystal size Example 1228 nm Comparative example 1195 nm

[0146] Referring to Table 5, it can be confirmed that the crystal grain size of the positive electrode active material manufactured according to Example 1 is 200 nm or more, but the crystal grain size of the positive electrode active material manufactured according to Comparative Example 1 is less than 200 nm.

[0147] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. Nickel-containing metal oxide in the form of single particles; A doping element doped into the above nickel-containing metal oxide; and Comprising a coating layer located on the surface of the nickel-containing metal oxide, The above doping elements include three or more types, A positive electrode active material for a lithium secondary battery, wherein the coating layer comprises two or more types of coating elements.

2. In paragraph 1, The above coating layer is a positive electrode active material for a lithium secondary battery, comprising Co and Al.

3. In paragraph 2, A positive electrode active material for a lithium secondary battery, wherein the content of Co in the positive electrode active material on which the coating layer is formed is in the range of 0.035 mol to 0.08 mol based on 1 mol of the total amount of transition metals included in the nickel-containing metal oxide on which the coating layer is formed.

4. In paragraph 2, A cathode active material for a lithium secondary battery, wherein the above doping elements include Al, Y and Zr.

5. In paragraph 4, A positive electrode active material for a lithium secondary battery, wherein the content of Al in the positive electrode active material on which the coating layer is formed is in the range of 0.001 mol to 0.015 mol based on 1 mol of the total of transition metals included in the nickel-containing metal oxide on which the coating layer is formed.

6. In paragraph 4, A positive electrode active material for a lithium secondary battery, wherein the content of Y is in the range of 400 ppm to 2,000 ppm based on the total weight of the nickel-containing metal oxide on which the coating layer is formed.

7. In paragraph 4, A positive electrode active material for a lithium secondary battery, wherein the content of Zr is in the range of 1,200 ppm to 2,800 ppm based on the total weight of the nickel-containing metal oxide on which the coating layer is formed.

8. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the content of the nickel is 0.8 mol or more based on 1 mol of the total of transition metals contained in the nickel-containing metal oxide on which the coating layer is formed.

9. In paragraph 8, The above nickel-containing metal oxide further contains manganese, A positive electrode active material for a lithium secondary battery, wherein the manganese content is 0.15 mol or less based on 1 mol of the total of transition metals included in the nickel-containing metal oxide on which the coating layer is formed.

10. In paragraph 1, The nickel-containing metal oxide on which the above coating layer is formed 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 Mr 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≤0.1, 0≤w2≤0.1이고, 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.

11. In paragraph 1, The above positive electrode active material is a positive electrode active material for a lithium secondary battery, having a moisture content increase rate of 80% or less at a temperature of 25±3°C and a relative humidity of 50±15%.

12. In paragraph 1, The above positive electrode active material is a positive electrode active material for a lithium secondary battery, having a residual lithium increase rate of 20% or less at a temperature of 25±3℃ and a relative humidity of 50±15%.

13. In paragraph 1, A positive electrode active material having the above coating layer formed thereon is a positive electrode active material for a lithium secondary battery, wherein the residual lithium reduction rate is 55% or more compared to the doped nickel-containing metal oxide.

14. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the average particle diameter (D50) of the cathode active material is 3 μm or more.

15. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the crystal size of the nickel-containing metal oxide on which the coating layer is formed is 200 nm or more.

16. A positive electrode for a lithium secondary battery comprising the positive electrode active material of any one of claims 1 to 15.

17. A lithium secondary battery comprising the positive electrode for a lithium secondary battery of Article 16.