Cathode active material for lithium secondary battery, preparation method therefor, and lithium secondary battery comprising same

Abstract

The present embodiments relate to a cathode active material for a lithium secondary battery, a preparation method therefor, 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 metal oxide in a single particle form; and a coating layer formed on the surface of the metal oxide, wherein the coating layer includes a particle-form compound including a coating element, and the area of the coating layer including the particle-form compound can be 35% or higher on the basis of the entire surface area of the metal oxide.

Description

Positive electrode active material for lithium secondary batteries, method for producing the same, and lithium secondary batteries comprising the same

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

[0002] Driven by the recent explosive demand for electric vehicles and the need to increase driving range, the development of high-capacity, high-energy-density secondary batteries to meet these demands is actively underway worldwide.

[0003] To meet these requirements, a technology using a high-nickel NCM cathode material with a high Ni content and a secondary particle form has been proposed.

[0004] However, as the nickel content increases, particle strength decreases, causing microcracks to occur during charge and discharge, which increases the specific surface area of ​​the cathode material, leading to increased gas generation due to increased reaction with the electrolyte. Furthermore, the secondary particle strength is weak, which can cause secondary particles to break during the electrode rolling process, increasing the amount of fine particles generated, thereby deteriorating the battery's lifespan characteristics.

[0005] To solve this problem, a method was proposed to reduce the specific surface area and increase the strength of the particles by manufacturing the cathode material in the form of single particles by increasing the size of the primary particles as much as possible.

[0006]

[0007] 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 that of a secondary particle, and at this time, over-firing often occurs, causing crystal defects in the layered structure, which causes a problem of reduced output and life characteristics.

[0008] In this embodiment, it is intended to provide a positive electrode active material for a lithium secondary battery having excellent output and life characteristics, a method for manufacturing the same, and a lithium secondary battery including the same.

[0009] According to one embodiment, a cathode active material for a lithium secondary battery includes a metal oxide in the form of a single particle; and a coating layer positioned on the surface of the metal oxide; wherein the coating layer includes a compound in the form of particles including a coating element, and an area of ​​the coating layer including the compound in the form of particles may be 35% or more based on the entire surface area of ​​the metal oxide.

[0010] According to another embodiment, a method for manufacturing a cathode active material for a lithium secondary battery includes the steps of: preparing a metal hydroxide containing nickel, cobalt, and manganese; mixing the metal hydroxide, a lithium raw material, and a doping raw material to prepare a mixture; firing the mixture to obtain a fired product in the form of single particles; mixing the fired product and a coating raw material, and then heat-treating the mixed material, to obtain a metal oxide having a coating layer formed thereon; wherein the coating raw material may include a particle-shaped compound having an average particle diameter in the range of 150 nm to 300 nm.

[0011] According to another embodiment, a positive electrode for a lithium secondary battery may include a positive electrode active material according to one embodiment.

[0012] A lithium secondary battery according to another embodiment may include the positive electrode for a lithium secondary battery according to one embodiment.

[0013] According to this embodiment, by making a coating layer including a particle-shaped compound on the surface of a metal oxide in the form of a single particle occupy an area of ​​35% or more based on the entire surface area of ​​the metal oxide, it is possible to prevent crystal defects in a layered structure from occurring.

[0014] Accordingly, when the positive electrode active material of the present embodiment is applied, a lithium secondary battery with excellent output and high-temperature life characteristics can be implemented.

[0015] Figure 1 is an SEM-EDS image taken by enlarging the cross-section of the positive electrode active material manufactured in Example 1.

[0016] Figure 2 is an image (magnification 50,000 times) showing the cobalt compound present on the surface after mapping the Co element using EDS equipment for the positive electrode active material manufactured in Example 1.

[0017] Figure 3 shows the results of line scanning measured using EDS equipment for the positive electrode active material manufactured in Example 1.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0023] 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.

[0024] 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.

[0025]

[0026] Cathode active material for lithium secondary batteries

[0027] As described above, the positive electrode active material in the form of a single particle has a problem in that oversintering occurs, causing defects in the layered crystal structure, resulting in a decrease in output and high-temperature life characteristics.

[0028] However, in this embodiment, this problem was solved by positioning a coating layer containing a particle-shaped compound over a specific area on the surface of a metal oxide in the form of a single particle.

[0029] Specifically, a cathode active material for a lithium secondary battery according to one embodiment includes a metal oxide in the form of a single particle; and a coating layer positioned on the surface of the metal oxide; wherein the coating layer includes a compound in the form of particles including a coating element, and an area of ​​the coating layer including the compound in the form of particles may be 35% or more based on the entire surface area of ​​the metal oxide.

[0030] The area of ​​the coating layer including the compound in the form of particles may be in the range of 35% to 50%, or 36% to 45%, based on the total surface area of ​​the metal oxide.

[0031] 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.

[0032] 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.

[0033] The above coating layer may include a particle-shaped compound including a coating element, and the average particle diameter of the particle-shaped compound may be in the range of 50 nm to 300 nm, or 100 nm to 200 nm. When the average particle diameter of the particle-shaped compound including a coating element satisfies the above range, the coating layer may be uniformly formed.

[0034] In addition, the coating element included in the particle-shaped compound may be diffused to a thickness range of 75 nm or more, more specifically 75 nm to 180 nm or 80 nm to 170 nm, from the surface of the metal oxide on which the coating layer is formed in the center direction. When the coating element is diffused to the thickness range, it has an advantageous effect in that a positive electrode active material with excellent long-life characteristics can be realized.

[0035] In this embodiment, the particle-shaped compound containing the coating element is CoO, Co2O3, CO3O4, LiCoO2, Co(OH)2, CoCl2, CoF3, CoSO4·xH2O, CoSO4·7H2O, (CH3COO)2Co·4H2O, Co(NO3)2·6H2O, (CH3CO2)2Co, CoCO3· x It may contain at least one of H2O and Co3(PO4)2.

[0036] As described above, since the single particle type positive electrode active material is manufactured by firing at a high temperature compared to the conventional secondary particle type positive electrode active material, crystal defects in the layered structure may occur. In the present embodiment, by forming a coating layer including a particle type compound including the above-described coating element on the surface of a metal oxide, 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 the single particle and the average particle diameter of the single particle can be efficiently increased during the firing process.

[0037] The content of the coating element included in the particle-shaped compound in the coating layer 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 metal oxide on which the coating layer is formed. In the present embodiment, the coating element included in the particle-shaped compound may be cobalt. When the content of cobalt 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.

[0038] Next, the coating layer may further include an additional coating element, and the additional coating element may include, for example, aluminum.

[0039] Meanwhile, the metal oxide of the present embodiment may include nickel, cobalt, and manganese. At this time, the content of nickel 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 nickel, cobalt, and manganese. When the nickel content satisfies the above range, a high-capacity battery can be realized.

[0040] The content of the above cobalt may be 0.05 mol or less, more specifically, more than 0 and 0.05 mol or less, based on 1 mol of the total of nickel, cobalt, and manganese.

[0041] In addition, the content of the manganese may be 0.1 mol or less, more specifically, 0.05 mol to 0.1 mol, based on 1 mol of the total of nickel, cobalt, and manganese.

[0042] The above metal oxide may further contain a doping element.

[0043] Here, the doping element may include, for example, at least one of Y, Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, P, V, Sr, and B. In the present embodiment, the doping element may include, for example, Y, Al, and Zr.

[0044] At this time, the content of the doping element may be 0 or more and 0.2 mol or less, more specifically, 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 the nickel, cobalt, manganese, and doping elements. Specifically, based on the total of the nickel, cobalt, manganese, and doping elements, the content of Y may be in the range of 400 ppm to 2,000 ppm, the content of Al may be in the range of 200 ppm to 1,800 ppm, and the content of Zr may be in the range of 1,200 ppm to 2,800 ppm.

[0045] In this embodiment, the content of the doping element refers to the doping amount of the doping element included in the final obtained positive electrode active material.

[0046]

[0047] Method for manufacturing positive electrode active material for lithium secondary batteries

[0048] In another embodiment, a method for producing a cathode active material for a lithium secondary battery is provided, comprising: preparing a metal hydroxide containing nickel, cobalt, and manganese; mixing the metal hydroxide, a lithium raw material, and a doping raw material to produce a mixture; firing the mixture to obtain a fired product in the form of single particles; and mixing the fired product and a coating raw material and then performing a heat treatment to obtain a metal oxide having a coating layer formed thereon, wherein the coating raw material includes a particle-shaped compound having an average particle diameter in the range of 150 nm to 300 nm.

[0049] The step of preparing a metal hydroxide containing nickel, cobalt, and manganese may be performed, for example, by preparing a metal salt aqueous solution containing a nickel raw material, a cobalt raw material, a manganese raw material, and distilled water, and then supplying the metal salt aqueous solution to a co-precipitation reactor to prepare a metal hydroxide, and this may be performed according to a method for preparing a metal hydroxide generally known in the art.

[0050] At this time, the nickel raw material may be, for example, nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide or oxyhydroxide. More specifically, the nickel raw material may be NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, fatty acid nickel salt, nickel halide or a combination thereof.

[0051] The above cobalt raw material may be, for example, a cobalt-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide or oxyhydroxide. More specifically, the cobalt raw material may be CoSO 4, It can be CoSO4ㆍ7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2ㆍ4H2O, Co(NO3)2ㆍ6H2O or a combination thereof.

[0052] The manganese raw material may be, for example, a manganese-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, oxyhydroxide or a combination thereof.

[0053] More specifically, the manganese raw material may be a manganese salt such as MnSO4, MnSO4·H2O, MnCO3, Mn(NO3)2, manganese acetate, dicarboxylic acid manganese salt, manganese citrate and fatty acid manganese salt, manganese oxide such as Mn2O3, MnO2, and Mn3O4, oxyhydroxide, manganese chloride or a combination thereof.

[0054] Next, a step of preparing a mixture by mixing the above metal hydroxide, lithium raw material, and doping raw material is performed.

[0055] The lithium raw material may be, for example, lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it can be dissolved in water. More specifically, the lithium raw material may include at least one of LiOH, Li2CO3, LiNO3, LiNO2, LiOH H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a combination thereof.

[0056] At this time, the molar ratio (Li / Me) of lithium (Li) to the total metal (Me) excluding lithium in the mixture may be in the range of 1.0 to 1.1, or in the range of 1.01 to 1.08.

[0057] The above doping raw material may include, for example, at least one raw material selected from among Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, P, V, Sr, and B. More specifically, the above doping raw material may include an Al raw material, a Y raw material, and a Zr raw material.

[0058] The above Al raw material is, for example, Al(OH)3, It may include at least one of Al2(SO4)3, Al(NO)3, Al2O3, and AlCl3, but is not limited thereto.

[0059] The above Y raw material may include, for example, at least one of Y2O3, Y(SO4)2, Y2(SO4)3, and Y(NO3)3, but is not limited thereto.

[0060] The above Zr raw material may include, for example, at least one of ZrO2, Zr(SO4)2, ZrS2, and Zr(NO3)4, but is not limited thereto.

[0061] Afterwards, a step of calcining the mixture to obtain a calcined product in the form of single particles is performed.

[0062] In this embodiment, the step of obtaining the sintered product may be performed, for example, by subjecting the mixture to a three-step process of sintering in step 1, sintering in step 2, and sintering in step 3.

[0063] Specifically, the first-stage firing may be performed at a temperature ranging from 870°C to 930°C for a time ranging from 2 hours to 6 hours or at a temperature ranging from 880°C to 920°C for a time ranging from 3 hours to 5 hours. The second-stage firing may be performed at a temperature ranging from 890°C to 960°C for a time ranging from 0.5 hours to 2 hours or at a temperature ranging from 900°C to 940°C for a time ranging from 0.5 hours to 1.5 hours.

[0064] The above three-step firing can be performed at a temperature ranging from 750°C to 870°C for a time ranging from 5 hours to 14 hours or at a temperature ranging from 780°C to 840°C for a time ranging from 7 hours to 12 hours.

[0065] The step of obtaining the above-mentioned calcined product may be performed by the above-mentioned three-step process after preliminary calcination, if necessary.

[0066] Next, a step is performed to obtain a metal oxide on which a coating layer is formed by mixing the above-mentioned sintered material and the coating raw material and then heat-treating them.

[0067] At this time, heat treatment can be performed at a temperature ranging from 700°C to 800°C for 3 to 10 hours.

[0068] In this embodiment, the coating raw material may include a compound in the form of particles having an average particle diameter in the range of 150 nm to 300 nm, or 200 nm to 280 nm.

[0069] The coating raw material containing the compound in the form of the above particles is Co(OH)2, CoCl2, CoO, CoF3, CoSO4·xH2O, CoSO4·7H2O, (CH3COO)2Co·4H2O, Co(NO3)2·6H2O, (CH3CO2)2Co, CoCO3· x It may include at least one of H2O, Co3(PO4)2, and combinations thereof.

[0070] The coating raw material including the compound in the form of particles may be added in a content range of 1.5 mol% to 3 mol% or 2.0 mol% to 2.8 mol% based on 100 g of the sintered product.

[0071] The above coating raw material may further include an additional coating raw material in addition to the compound in particle form. The additional coating raw material may be, for example, Al(OH)3, It may be at least one of Al2(SO4)3, Al(NO)3, Al2O3, and AlCl3.

[0072] The above additional coating raw material can be added in a range of 500 ppm to 1,500 ppm based on the total weight of the sintered product.

[0073] In this embodiment, by using a coating raw material including a compound in the form of particles having an average particle diameter of 150 nm to 300 nm, the layered crystal structure of the positive electrode active material in the form of a single particle can be stabilized, and as a result, a positive electrode active material having excellent high-temperature life characteristics can be secured, which has a very advantageous effect.

[0074]

[0075] anode

[0076] 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 manufactured according to one embodiment described above.

[0077] 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.

[0078] 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.

[0079] Meanwhile, the positive electrode active material layer may include a binder and a conductive material.

[0080] 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.

[0081] And, the conductive material is used to provide conductivity to the electrode, and in the battery to be constructed, 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086]

[0087] lithium secondary battery

[0088] In another embodiment, a lithium secondary battery including the positive electrode is provided.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] As the 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 alloy, Sn alloy, or Al alloy; SiO β(0 < β < 2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and 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.

[0094] The above binder and conductive material may be the same as those described above for the positive electrode.

[0095] 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.

[0096] 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.

[0097] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0098] 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.

[0099] 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.

[0100]

[0101] 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).

[0102]

[0103] 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.

[0104]

[0105] Example 1

[0106] (1) Manufacturing of positive electrode active material

[0107] 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.

[0108] 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.

[0109] 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.

[0110] The above-mentioned sintered material was crushed to obtain a single particle metal oxide doped with Al, Y, and Zr.

[0111] Co(OH)2 and Al(OH)3 were dry mixed with the obtained single particle metal oxide as coating raw materials, and then heat-treated at 700°C for 5 hours in an oxygen atmosphere to manufacture a cathode active material having a coating layer formed thereon. At this time, Co(OH)2 was used as a raw material having an average particle diameter of 247 nm. In addition, Co(OH)2 and Al(OH)3 were mixed in a content corresponding to 2.5 mol% of Co and a content corresponding to 1000 ppm of Al based on the single particle metal oxide.

[0112]

[0113] Examples 2 to 3 and Comparative Examples 1 to 2

[0114] A positive electrode active material was manufactured in the same manner as in Example 1, except that the average particle size of the coating raw material and the heat treatment temperature for forming the coating layer were adjusted as shown in Table 1 below.

[0115] Classification Co Raw material particle size (nm) Heat treatment temperature (℃) Example 1 2 4 7 700 Example 2 2 3 5 750 Example 3 2 4 2 800 Comparative example 1 5 5 1 700 Comparative example 2 5 2 2 750

[0116] Experimental Example 1 - EDS (Energy dispersive x-ray spectroscopy) analysis Figure 1 is an SEM-EDS image taken by enlarging the cross-section of the positive electrode active material manufactured in Example 1.

[0117] Figure 2 is an image (magnification 50,000 times) showing the cobalt compound present on the surface after mapping the Co element on the surface of the positive electrode active material manufactured in Example 1 using EDS equipment.

[0118] Figure 3 shows the results of line scanning measured using EDS equipment for the positive electrode active material manufactured in Example 1.

[0119] Referring to Fig. 1, it can be confirmed that cobalt elements exist on the surface, i.e., inside the surface, of the positive electrode active material manufactured in Example 1.

[0120] Referring to Fig. 2, it can be confirmed that a cobalt compound in particle form is formed on the surface of the positive electrode active material manufactured in Example 1 and is distributed at a rate of 43% or more on the surface.

[0121] Referring to Figure 3, it can be confirmed that a particle-shaped compound containing cobalt exists at a position 120 nm thick from the metal oxide surface toward the particle center.

[0122]

[0123] Next, for the positive electrode active materials manufactured in Examples 1 to 3 and Comparative Examples 1 to 2, the particle-shaped compounds containing the coating elements were identified through EDS mapping, their sizes were measured, and the distribution ratio, i.e., the coating layer area, was calculated. In addition, the diffusion thickness of the coating elements from the metal oxide surface was confirmed using EDS line scanning. The respective results are shown in Table 2 below.

[0124] Particle size of compound containing Co (nm) Co diffusion thickness (nm) Distribution ratio of compound in particle form containing Co (%) Example 1 1 2 0 9 0 4 3.2 Example 2 1 3 0 1 2 0 4 0.1 Example 3 1 5 0 1 5 0 3 8.5 Comparative Example 1 3 5 0 6 5 18.4 Comparative Example 2 3 7 0 7 2 2 0.6

[0125] In addition, referring to Table 2, it can be seen that the particle size including the coating element located on the surface of the positive electrode active material manufactured in Examples 1 to 3 is in the range of 50 nm to 300 nm, and the distribution ratio of the compound in the form of particles including the coating element is 35% or more. In addition, the range of the diffusion thickness of the coating element from the surface of the metal oxide is also 75 nm or more in the case of Examples 1 to 3.

[0126] Therefore, it can be seen that if the particle size of the coating source is appropriately controlled, the coating element is diffused from the surface of the metal oxide to a deeper range toward the particle center, and the coating layer formation area is also widened.

[0127]

[0128] Experimental Example 2: Coin Cell Manufacturing and High-Temperature Lifespan Evaluation

[0129] (1) Manufacturing of coin cells

[0130] A CR2032 coin cell was manufactured using the positive electrode active material manufactured in the examples and comparative examples using the following method.

[0131] Specifically, a positive electrode active material, a conductive agent (acetylene black FX35, Denka), and a polyvinylidene fluoride binder (trade name: KF9709) were mixed in a weight ratio of 96.5:1.5:2 95:2.2:2.8, and the mixture was added to an N-methyl-2-pyrrolidone solvent so that the solid content was about 65 to 69 wt% to prepare a positive electrode active material slurry.

[0132] The above slurry was coated on an aluminum foil (Al foil, thickness: 20 μm), 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.

[0133] A 2032 coin-type half-cell was manufactured using the above positive electrode, lithium metal negative electrode (400 μm thick, NEBA), electrolyte, and polypropylene polyethylene separator in a conventional manner. The electrolyte was manufactured by dissolving 1 M LiPF6 in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate (mixing ratio EC:DMC:DEC=1:2:1 vol%) to prepare a mixed solution, to which 2 wt% of vinylene carbonate (VC) was added.

[0134] (2) Capacity maintenance rate measurement

[0135] After aging the coin-shaped half-cell manufactured in the above (1) at room temperature (25°C) for 10 hours, a charge / discharge test was conducted.

[0136] 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 based on the capacity measured at the 50th cycle compared to the capacity of the first cycle. The results are shown in Table 3 below.

[0137] Classification 50 cycle capacity retention rate (%) Example 194.2 Example 293.7 Example 393.8 Comparative example 191.5 Comparative example 291.9

[0138] Referring to Table 3, it can be confirmed that the high-temperature capacity retention rate of Examples 1 to 3 is significantly higher than that of Comparative Examples 1 to 2. As described above, by appropriately controlling the particle size of the coating source, the coating element is diffused from the surface of the metal oxide to a deeper range toward the particle center, and the coating layer formation area is also formed wider, thereby significantly improving the high-temperature life characteristics of the positive electrode active material. (3) Measurement of the change in residual lithium

[0139] For the positive electrode active materials manufactured according to Examples 1 to 3 and Comparative Examples 1 to 2, the residual lithium was measured using a T50 model from METTLER TOLEDO. The results are shown in Table 4 below.

[0140] Classification LiOHLi2CO3totalExample 10.1250.1760.301Example 20.1140.1860.300Example 30.1170.1950.312Comparative Example 10.1250.2620.387Comparative Example 20.1150.2350.350

[0141] Referring to Table 4, it can be confirmed that the residual lithium in Examples 1 to 3 is significantly lower than in Comparative Examples 1 to 2. As described above, it can be confirmed that by appropriately controlling the particle size of the coating source, the coating layer area can be formed to be wide, thereby significantly reducing the residual lithium in the positive electrode active material.

[0142] 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. Metal oxide in the form of single particles; and A coating layer positioned on the surface of the metal oxide; The above coating layer comprises a compound in the form of particles containing a coating element, A positive electrode active material for a lithium secondary battery, wherein the area of ​​the coating layer containing the compound in the form of particles is 35% or more based on the total surface area of ​​the metal oxide.

2. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the area of ​​the coating layer containing the compound in the form of particles is in the range of 35% to 50% of the total surface area of ​​the metal oxide.

3. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the average particle diameter of the compound in the form of particles is in the range of 50 nm to 300 nm.

4. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the coating element included in the above particle-shaped compound is diffused from the surface of the metal oxide on which the coating layer is formed to a thickness range of 75 nm or more in the center direction.

5. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the coating element included in the above particle-shaped compound is diffused from the surface of the metal oxide on which the coating layer is formed to a thickness range of 75 nm to 180 nm in the center direction.

6. In paragraph 1, Compounds in particle form containing the above coating elements are CoO, Co2O3, CO3O4, LiCoO2, Co(OH)2, CoCl2, CoF3, CoSO4·xH2O, CoSO4·7H2O, (CH3COO)2Co·4H2O, Co(NO3)2·6H2O, (CH3CO2)2Co, CoCO3· x A cathode active material for a lithium secondary battery, comprising at least one of H2O and Co3(PO4)2.

7. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein the content of the coating element included in the particle-shaped compound in the above coating layer is in the range of 0.035 mol to 0.08 mol based on the total metal excluding lithium in the metal oxide in the single particle shape.

8. In paragraph 6, A positive electrode active material for a lithium secondary battery, wherein the coating layer may further include an additional coating element, and the additional coating element includes aluminum.

9. In paragraph 1, The above metal oxides include nickel, cobalt and manganese, A positive electrode active material for a lithium secondary battery, wherein the content of nickel is 0.8 mol or more based on 1 mol of the total of nickel, cobalt, and manganese.

10. In paragraph 9, The above metal oxide further contains a doping element, A cathode active material for a lithium secondary battery, wherein the doping element comprises at least one of Y, Al, Zr, Nb, Mo, W, Ti, Ce, Mg, B, P, V, Sr, and B.

11. A step of preparing a metal hydroxide containing nickel, cobalt and manganese; A step of preparing a mixture by mixing the above metal hydroxide, lithium raw material, and doping raw material; A step of calcining the above mixture to obtain a calcined product in the form of single particles; and A step of mixing the above-mentioned sintered material and the coating raw material and then heat-treating them to obtain a metal oxide on which a coating layer is formed; A method for producing a positive electrode active material for a lithium secondary battery, wherein the above coating raw material comprises a particle-shaped compound having an average particle diameter in the range of 150 nm to 300 nm.

12. In paragraph 11, A method for producing a positive electrode active material for a lithium secondary battery, wherein in the step of obtaining a metal oxide on which the coating layer is formed, heat treatment is performed at a temperature in the range of 700°C to 800°C for 3 to 10 hours.

13. In paragraph 11, The coating raw material containing the compound in the form of the above particles is Co(OH)2, CoCl2, CoO, CoF3, CoSO4·xH2O, CoSO4·7H2O, (CH3COO)2Co·4H2O, Co(NO3)2·6H2O, (CH3CO2)2Co, CoCO3· x A method for producing a positive electrode active material for a lithium secondary battery, comprising at least one of H2O, Co3(PO4)2, and a combination thereof.

14. In paragraph 11, The above coating raw material further includes an additional coating raw material, The above additional coating raw material is Al(OH)3, A method for producing a positive electrode active material for a lithium secondary battery, comprising at least one of Al2(SO4)3, Al(NO)3, Al2O3, and AlCl3.

15. In paragraph 11, The step of obtaining the above-mentioned product is: A method for producing a positive electrode active material for a lithium secondary battery, wherein the step of obtaining the above-mentioned sintered material is performed by subjecting the mixture to a three-step process of sintering in step 1, sintering in step 2, and sintering in step 3.

16. In paragraph 11, A method for producing a positive electrode active material for a lithium secondary battery, wherein, in the step of obtaining a metal oxide having a coating layer formed thereon, the coating raw material including the compound in the form of particles is added in a content range of 1.5 mol% to 3 mol% based on 100 g of the sintered product.

17. A positive electrode for a lithium secondary battery, comprising the positive electrode active material of any one of claims 1 to 10.

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

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