Method for manufacturing a positive electrode active material for lithium secondary batteries and a lithium secondary battery containing a positive electrode active material manufactured using the same.

Abstract

This embodiment relates to a method for producing a positive electrode active material for a lithium secondary battery and a lithium secondary battery containing the same. A method for producing a positive electrode active material for a lithium secondary battery according to one embodiment includes the steps of: preparing a metal hydroxide containing nickel, cobalt, and manganese; mixing the metal hydroxide, lithium raw material, and doping raw material to produce a mixture; pre-calcining the mixture to obtain a pre-calcined product; calcining the pre-calcined product in a two-step process to obtain a calcined product in the form of single particles; and mixing the calcined product and coating raw material and then heat-treating it to obtain a metal oxide on which a coating layer has been formed. In the step of obtaining the calcined product, the first calcination can be carried out in the range of 870°C to 915°C for 2 to 6 hours.

Description

[Technical Field]

[0001] This embodiment relates to a method for producing a positive electrode active material for lithium secondary batteries and a lithium secondary battery containing a positive electrode active material produced using this method. [Background technology]

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

[0003] However, as the nickel content increases, the particle strength decreases, leading to the formation of microcracks during charging and discharging. Furthermore, this increases the specific surface area of ​​the cathode material, resulting in increased gas generation as the reaction with the electrolyte increases. Additionally, structural instability leads to unstable Ni... 3+ Stable Ni 2+ The cation mixing phenomenon, in which cations are reduced to stable NiO, increases. Therefore, it is impractical to actually apply this as a positive electrode active material for lithium-ion batteries used in electric vehicles and energy storage.

[0004] To address this, a proposed method involves manufacturing the cathode material in a form of secondary particles where primary particles are aggregated, i.e., a single-particle form where the size of the primary particles is maximized, rather than a multi-particle form, and then applying this material.

[0005] However, generally, manufacturing single-particle cathode materials requires firing at higher temperatures compared to multi-particle materials. This often leads to over-firing, causing layered structure crystal defects and degrading electrochemical properties such as capacitance and power output.

[0006] Furthermore, lowering the firing temperature to solve this problem resulted in insufficient growth of crystal grain size within a single particle, leading to a deterioration in particle strength and lifetime characteristics.

[0007] Furthermore, in order to apply this technology to cathode material manufacturing sites, it is also necessary to improve productivity for single-particle cathode materials. [Overview of the project] [Problems that the invention aims to solve]

[0008] In this embodiment, we aim to provide a method for producing a positive electrode active material for lithium secondary batteries that offers excellent electrochemical properties while also improving productivity, and a lithium secondary battery containing the same. [Means for solving the problem]

[0009] A method for producing a positive electrode active material for a lithium secondary battery according to one embodiment includes the steps of: preparing a metal hydroxide containing nickel, cobalt, and manganese; mixing the metal hydroxide, lithium raw material, and doping raw material to produce a mixture; pre-calcining the mixture to obtain a pre-calcined product; first-stage calcination and second-stage calcination of the pre-calcined product in a two-step process to obtain a calcined product in the form of single particles; and finally, mixing the calcined product and coating raw material and then heat-treating it to obtain a metal oxide on which a coating layer has been formed, wherein the first calcination in the step of obtaining the calcined product can be carried out at a temperature in the range of 870°C to 915°C for 2 to 6 hours.

[0010] The positive electrode active material for a lithium secondary battery according to another embodiment comprises a nickel-containing metal oxide in single-particle form; and a coating layer located on the surface of the nickel-containing metal oxide, wherein the nickel-containing metal oxide contains at least three doping elements, and the number of ungrown particles measured in a 2.5 cm × 1.0 cm SEM image after 5000x magnification on the metal oxide on which the coating layer is formed may be two or less.

[0011] Lithium secondary batteries according to other embodiments may include a positive electrode containing the positive electrode active material for lithium secondary batteries according to one embodiment described above. [Effects of the Invention]

[0012] According to this embodiment, by performing pre-firing before the main firing and simultaneously performing the main firing as a 1SEPT process with two stages of firing (primary and secondary), it is possible to provide a method for manufacturing positive electrode active materials for lithium secondary batteries that offers excellent electrochemical properties while improving productivity. [Brief explanation of the drawing]

[0013] [Figure 1] This is an SEM image of the positive electrode active material produced by Example 1, measured at 5,000x magnification. [Figure 2] This is an SEM image of the positive electrode active material produced by Comparative Example 1, measured at 5,000x magnification. [Modes for carrying out the invention]

[0014] The terms first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used solely to distinguish one part, component, region, layer, or section from other parts, components, regions, layers, or sections. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0015] The technical terms used herein are for the sole purpose of referring to specific embodiments and are not intended to limit the invention. The singular form used herein also includes the plural form unless the phrase explicitly indicates otherwise. The meaning of “including” as used in this specification embodies a particular characteristic, area, integer, stage, operation, element, and / or component, and does not exclude the presence or addition of other characteristics, areas, integers, stages, operations, elements, and / or components.

[0016] When referring to a part as being "on" or "above" another part, this means directly on or above the other part, or there may be other parts in between. In contrast, when referring to a part as being "directly above" another part, there are no other parts intervening therebetween.

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

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

[0019] As used herein, the term "these combinations" recited in Markush format expressions means one or more mixtures or combinations selected from the group consisting of the components described in the Markush format expressions, and means including any one or more selected from the group consisting of the said components.

[0020] Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention belongs can easily implement them. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0021] Method for manufacturing a positive electrode active material for a lithium secondary battery

[0022] The method for manufacturing a positive electrode active material for a lithium secondary battery according to an embodiment includes the steps of preparing a metal hydroxide containing nickel, cobalt, and manganese; mixing the metal hydroxide, a lithium raw material substance, and a doping raw material substance to produce a mixture; pre-firing the mixture to obtain a pre-fired product; subjecting the pre-fired product to primary firing and secondary firing in a 1SEPT process to obtain a fired product in a single-particle form; and heat-treating after mixing the fired product and a coating raw material substance to obtain a metal oxide having a coating layer formed thereon. In the step of obtaining the fired product, the primary firing can be performed at 870°C to 930°C for 2 to 6 hours.

[0023] In this embodiment, by performing pre-firing and at the same time performing the main firing process in two steps, it is possible to provide a method for manufacturing a positive electrode active material in a single-particle form that has excellent electrochemical characteristics and improved productivity.

[0024] In this specification, a single particle can include at least one of the structures that are distinguished as one lump when observing the cross-section of the powder through a scanning electron microscope (SEM) in the form of a single crystal structure composed of one particle or a form in which about 2 to 20 or 2 to 10 particles are aggregated. Here, one particle means one grain or crystallite.

[0025] The active material in the single-particle form as in this embodiment has a smaller specific surface area compared to the positive electrode active material in the form of secondary particles formed by aggregation of dozens to hundreds of primary particles in the prior art, a reduced amount of gas generation due to side reactions with the electrolyte, a large particle strength, and can suppress cracking of the particles during rolling, and can reduce crack generation due to repeated charging and discharging. As a result, it has advantages in terms of lifespan and safety compared to secondary particles and can achieve a high energy density of the electrode.

[0026] First, the step of preparing a metal hydroxide containing nickel, cobalt, and manganese is performed.

[0027] In this case, the nickel-containing metal hydroxide may be produced, for example, by adding a complexing agent-containing solution and a pH adjusting agent-containing solution to a transition metal-containing solution containing a nickel raw material, selectively a cobalt raw material, and / or a manganese raw material, and causing a coprecipitation reaction.

[0028] The nickel raw material is not particularly limited as long as it is used in the industry during the production of cathode active material precursors. For example, the nickel raw material may be nickel-containing sulfates, acetates, nitrates, halides, sulfides, hydroxides, oxides, or oxyhydroxides, and may specifically be, but not limited to, NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, fatty acid nickel salts, nickel halides, or combinations thereof.

[0029] The aforementioned cobalt raw material is not particularly limited as long as it is used in the industry during the production of cathode active material precursors. For example, the cobalt raw material may be a cobalt-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and may specifically be, but not limited to, CoSO4, CoSO4·7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, or a combination thereof.

[0030] The manganese raw material is not particularly limited as long as it is used in the industry during the production of cathode active material precursors. For example, the manganese raw material may be manganese-containing sulfates, acetates, nitrates, halides, sulfides, hydroxides, oxides, oxyhydroxides, or combinations thereof, and may, but is not limited to, manganese salts such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylate salts, manganese citrate, and manganese fatty acid salts, manganese oxides such as Mn2O3, MnO2, and Mn3O4, oxyhydroxides, manganese chloride, or combinations thereof.

[0031] The transition metal-containing solution may be prepared by adding a nickel raw material and, selectively, a cobalt raw material or a manganese raw material to a solvent, specifically water, or a mixture of water and an organic solvent (e.g., alcohol) that can be homogeneously mixed with water.

[0032] The complexing agent-containing solution plays a role in complex formation, and the complexing agent may include, but is not limited to, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or combinations thereof. On the other hand, the complexing agent-containing solution can be used in the form of an aqueous solution, in which case water or a mixture of water and an organic solvent that can be homogeneously mixed with water (e.g., alcohol) can be used as the solvent.

[0033] Next, the metal hydroxide, lithium raw material, and doping raw material are mixed to produce a mixture.

[0034] The lithium raw material is not particularly limited as long as it is commonly used in the industry, but may be, for example, LiCO3, LiOH, or LiOH·H2O. In this embodiment, production costs can be lowered and economic efficiency improved by using LiCO3 as the lithium raw material.

[0035] At this time, the mixture can be manufactured such that the molar ratio of lithium (Li) to the total metal (Me) excluding lithium (Li / Me) is in the range of 1.0 to 1.1 or 1.01 to 1.08.

[0036] The doping material may include an Al material, a Y material, and a Zr material.

[0037] The Al raw material may, but is not limited to, include at least one of Al(OH)3, Al2(SO4)3, Al(NO)3, Al2O3, and AlCl3.

[0038] The aforementioned Y raw material may include, but is not limited to, at least one of Y2O3, Y(SO4)2, Y2(SO4)3, and Y(NO3)3.

[0039] The Zr raw material may include, but is not limited to, at least one of ZrO2, Zr(SO4)2, ZrS2, and Zr(NO3)4.

[0040] The Al raw material can be added and mixed in, for example, in a content range of 500 ppm to 1000 ppm or 800 ppm to 1000 ppm based on the total weight of the metal hydroxide.

[0041] The aforementioned Y raw material can be added and mixed in, for example, at a content range of 500 to 1,200 ppm or 800 to 1,200 ppm based on the total weight of the metal hydroxide.

[0042] The Zr raw material can be added and mixed in, for example, at a content range of 500 to 2,000 ppm or 800 to 2,000 ppm based on the total weight of the metal hydroxide.

[0043] When the input content of Al raw material, Y raw material, and Zr raw material satisfies the above range, a positive electrode active material with improved capacity retention and resistance characteristics can be produced.

[0044] Next, the mixture is pre-fired to obtain a pre-fired product.

[0045] The aforementioned pre-sintering can be carried out at a temperature range of 650°C to 770°C for 2 to 12 hours or at a temperature range of 680°C to 740°C for 3 to 10 hours. By performing the pre-sintering process in this manner, the production volume of the positive electrode active material can be increased while maintaining the electrochemical properties, thereby improving economic efficiency.

[0046] Subsequently, the pre-fired product is subjected to primary and secondary firing in a 1SEPT process to obtain a single-particle shaped product.

[0047] The aforementioned primary firing can be carried out at a temperature of 870°C to 930°C for 2 to 6 hours or at a temperature of 880°C to 920°C for 3 to 5 hours.

[0048] The aforementioned secondary firing can be carried out at a temperature range of 750°C to 870°C for 5 to 14 hours or at a temperature range of 780°C to 840°C for 7 to 12 hours.

[0049] Specifically, in this embodiment, by performing primary and secondary firing together with pre-firing in a single step, a positive electrode active material in single-particle form with excellent electrochemical properties can be manufactured. Furthermore, productivity is improved, resulting in superior cost-effectiveness.

[0050] Next, the process involves mixing the calcined product and the coating raw material, followed by heat treatment to obtain a metal oxide with a coating layer formed on top.

[0051] The coating raw material may include a Co coating raw material and an Al coating raw material.

[0052] The aforementioned Co coating raw material may include, but is not limited to, at least one of Co(OH)2, CoO, Co3O4, CoCO3, cobalt acetate, and cobalt oxalate.

[0053] The Al coating raw material may include, but is not limited to, at least one of Al(OH)3, Al2(SO4)3, Al(NO)3, Al2O3, and AlCl3.

[0054] Here, the Co coating raw material can be added and mixed in a content range of 1.5 mol% to 3 mol%, more specifically, 2.0 mol% to 2.8 mol%, based on the calcined product.

[0055] The Al coating raw material can be added and mixed in a content range of 500 to 1,000 ppm or 800 to 1,000 ppm based on the calcined product.

[0056] When the content of the Co coating raw material and the Al coating raw material satisfies the above range, interfacial side reactions with the positive electrode active material and electrolyte can be suppressed, and a lithium secondary battery with improved capacity and resistance characteristics can be manufactured.

[0057] The heat treatment in the step of obtaining the metal oxide on which the coating layer is formed can be carried out, for example, at 660°C to 760°C for 3 to 8 hours or at 690°C to 750°C for 4 to 6 hours. When the heat treatment process satisfies the above conditions, the amount of lithium remaining on the surface can be reduced while simultaneously stabilizing the surface structure. Furthermore, the initial resistance of the positive electrode active material in this embodiment can be reduced.

[0058] In this embodiment, the process may further include a step of crushing the calcined material after obtaining the calcined material, if necessary. That is, the crushing step may be included after obtaining the calcined material and before the coating step.

[0059] The crushing step can be performed after the calcined material has been cooled to 50-200°C. Cooling to this temperature can suppress the reaction between external moisture and the calcined material, thereby suppressing the increase in residual lithium.

[0060] The aforementioned crushing can be carried out using methods commonly used in this industry.

[0061] The aforementioned crushing can be carried out using, for example, a rotary mill, ball mill, pin mill, jet mill, bead mill, or roll mill.

[0062] A metal oxide with a single-particle coating layer produced by the method described above can be represented by the following chemical formula 1.

[0063] [Chemical Formula 1] Li a [Ni x Co y Mn z M1 w1 M2 w2 O2

[0064] In Chemical Formula 1 above, 0.8 ≦ a ≦ 1.2, 0.8 ≦ x ≦ 0.99, 0 < y ≦ 0.06, 0 < z ≦ 0.14, 0 < w1 ≦ 0.1, 0 ≦ w2 ≦ 0.1, x + y + z + w1 + w2 = 1, M1 is Al, Y, and Zr, and M2 contains one or more of B, Al, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, and Sr.

[0065] In Chemical Formula 1, the nickel content is 0.8 mol or more, more specifically in the range of 0.8 mol to 0.99 mol, 0.82 to 0.95 mol, or 0.82 to 0.93 mol, based on 1 mol of the total transition metals contained in the doped nickel-containing metal oxide. When the nickel content satisfies the above range, a high-capacity battery can be realized.

[0066] Also, the total content of doping elements M1 and M2 in Chemical Formula 1 is more than 0 and 0.2 mol or less, 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 the nickel, cobalt, manganese, and doping elements. The content of the doping element in the above chemical formula means the doping amount of the doping element contained in the finally obtained positive electrode active material.

[0067] On the other hand, the average particle size (D50) of the positive electrode active material in this embodiment may be 3 μm or more, more specifically in the range of 3 μm to 6 μm. When the average particle size of the single-particle positive electrode active material satisfies the above range, a lithium secondary battery with excellent electrochemical properties such as lifetime characteristics and resistance increase rate can be realized. At the same time, the energy density per unit volume can also be increased, which has a very advantageous effect.

[0068] In other embodiments, a current collector and a positive electrode are provided, which includes a positive electrode active material layer located on one surface of the current collector and containing the positive electrode active material manufactured according to the above-described embodiment.

[0069] The positive electrode active material comprises a nickel-containing metal oxide in single-particle form; and a coating layer located on the surface of the nickel-containing metal oxide, wherein the nickel-containing metal oxide contains at least three doping elements, and there may be two or fewer ungrown particles measured in a 2.5 cm × 1.0 cm SEM image after 5000x magnification of the metal oxide on which the coating layer is formed.

[0070] In this specification, undeveloped particles refer to secondary particles formed by the aggregation of more than 20 primary particles, while simultaneously having an average particle size (D50) of 5 μm or less.

[0071] In the positive electrode active material of this embodiment, the ratio of lithium hydroxide to lithium carbonate in the surface residual lithium (lithium hydroxide / lithium carbonate) may be in the range of 1.0 to 2.0 or 1.5 to 2.0.

[0072] Furthermore, the positive electrode active material may have a total value of fine particles less than 1 μm when subjected to five pressurizations using a roll press with a press gauge of 0.01 mm, which may be 2.5 vol% or less.

[0073] The characteristics of the positive electrode active material constituting the positive electrode active material layer are the same as those described above. Therefore, a detailed explanation of the positive electrode active material will be omitted.

[0074] The current collector can be made of, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc.

[0075] On the other hand, the positive electrode active material layer may include a binder and a conductive material.

[0076] At this time, the binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion 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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these can be used, but are not limited to these. The binder may be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0077] The conductive material is used to impart conductivity to the electrodes and can be used in the battery without any special restrictions as long as it does not cause chemical changes and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more can be used, but are not limited to these. The conductive material may usually be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0078] The positive electrode can be manufactured by a conventional positive electrode manufacturing method, except that the positive electrode active material is used.

[0079] Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, which includes the aforementioned positive electrode active material and optionally a binder, conductive material, or solvent, onto 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 material are as described above.

[0080] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these can be used alone or in mixtures of two or more. The amount of solvent used should be sufficient to dissolve or disperse the cathode active material, conductive material, and binder, taking into consideration the coating thickness and production yield of the slurry, and to have a viscosity that allows for excellent thickness uniformity during subsequent coating for cathode manufacturing.

[0081] Alternatively, the positive electrode can also be manufactured by casting the positive electrode active material layer forming composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0082] Lithium-ion battery Another embodiment provides a lithium secondary battery including the positive electrode.

[0083] The lithium secondary battery may specifically include a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive and negative electrodes, and an electrolyte, wherein the positive electrode is as described above. The lithium secondary battery may also selectively further include a battery container housing the electrode assembly including the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0084] In the lithium secondary battery, the negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0085] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. The negative electrode current collector can also typically have a thickness of 3 to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in a variety of forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0086] The negative electrode active material layer may selectively include a binder and a conductive material along with the negative electrode active material. For example, the negative electrode active material layer can be manufactured by applying a negative electrode active material layer forming composition, which includes the negative electrode active material and selectively a binder and a conductive material, onto a negative electrode current collector and drying it, or by casting the negative electrode forming composition onto a separate support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0087] As the anode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metallic oxides that can be doped and dedoped with lithium, such as SiOβ (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites. One or more of these can be used. A metallic lithium thin film can also be used as the anode active material. Furthermore, all types of carbon materials, including low-crystallinity carbon and high-crystallinity carbon, can be used. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0088] The binder and conductive material may be the same as those described earlier for the positive electrode.

[0089] Next, depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators can be polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof. Mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, or polypropylene / polyethylene / polypropylene three-layer separators can also be used.

[0090] Furthermore, in the lithium secondary battery, the electrolyte can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte, and is not limited to these, and is not limited to those usable during the manufacture of lithium secondary batteries.

[0091] Specifically, the organic liquid electrolyte may contain an organic solvent and a lithium salt.

[0092] The aforementioned organic solvent can be used without special limitations as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the aforementioned organic solvents 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; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group of C2-C20, and may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the performance of the electrolyte may be superior when the cyclic carbonate and linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9.

[0093] The lithium salt can 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 can 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, etc. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. If 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.

[0094] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention can stably exhibit excellent discharge capacity, output characteristics, and capacity retention rate, and thus is useful in portable devices such as mobile phones, notebook computers, digital cameras, etc., and in the field of electric vehicles such as hybrid electric vehicles (HEV).

[0095] Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, and the present invention is not limited thereby. The present invention is only defined by the scope of the claims described later.

Examples

[0096] Example 1 - Al, Y, Zr doping (1) Production of positive electrode active material Ni 0.90 Co 0.03 Mn 0.07 After preparing a precursor of the composition of (OH)2, LiOH·H2O (Samchun Chemical, battery grade) as a lithium raw material substance, Y2O3, ZrO2, and Al(OH)3 as doping raw material substances were uniformly mixed with the precursor to produce a mixture.

[0097] 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 materials were added to the aforementioned precursor so that the concentrations were Zr 2000 ppm, Y 1200 ppm, and Al 1000 ppm.

[0098] The mixture was placed in a furnace under an oxygen atmosphere and pre-fired at 680°C for 6.5 hours to obtain a pre-fired product. Subsequently, the obtained pre-fired product was placed in a furnace under an oxygen atmosphere, heated to 890°C for 4 hours in a single-stage firing, and then fired at 780°C for 11 hours in a second-stage firing, i.e., fired in a two-step process to obtain a fired product.

[0099] The calcined material was crushed to obtain single-particle metal oxides doped with Al, Y, and Zr.

[0100] The obtained single-particle metal oxide was dry-mixed with Co(OH)2 and Al(OH)3 as coating raw materials, and then heat-treated in an oxygen atmosphere at 700°C for 5 hours to produce a positive electrode active material with a coating layer. At this time, the Co(OH)2 and Al(OH)3 were mixed so that the Co content was 2.5 mol% and the Al content was 1000 ppm, based on the single-particle metal oxide.

[0101] Comparative Example 1 A single-particle cathode active material was produced in the same manner as in Example 1, except that the pre-calcination process was omitted.

[0102] Experimental Example 1 - Measurement of the number of undeveloped particles Figures 1 and 2 show the results of measurements taken using a 2.5 cm × 1.0 cm SEM image after magnification of 5000 times, for the positive electrode active materials produced by Example 1 and Comparative Example 1, respectively.

[0103] Referring to Figures 1 and 2, the positive electrode active material produced by Example 1 after pre-calcination did not contain ungrown particles, but ungrown particles were observed in the positive electrode active material produced by Comparative Example 1 without the pre-calcination process.

[0104] Experimental Example 2 - Measurement of Particle Cracking Degree The degree of particle cracking was measured using the positive electrodes produced in Example 1 and Comparative Example 1, and the results are shown in Table 1 below.

[0105] Specifically, 10 g of positive electrode active material was mixed with 3.5 g of NMP and cast onto 20 μm thick aluminum foil (70 mm x 210 mm), then dried in a 120°C convection oven for 30 minutes. After that, a sample was prepared by covering the aluminum foil coated with positive electrode active material with another aluminum foil of the same size.

[0106] The aforementioned sample was subjected to five presses using a roll press with a press gauge of 0.01 mm, yielding 2 g of active material particles. The amount of fine powder generated from the obtained active material particles was analyzed by performing particle size analysis using a Malvern (MS3000) analyzer. The degree of particle fracture was indicated by the total vol% value of fine powder particles smaller than 1 μm in the particle size analysis results.

[0107] [Table 1]

[0108] Referring to Table 1, it can be confirmed that in Example 1, which was manufactured by performing a 2-STEP process after a pre-sintering process, the fine particle generation rate is significantly lower compared to Comparative Example 1, which was a positive electrode active material manufactured without pre-sintering.

[0109] Example 3 - Production volume measurement The amount of saggar added to the positive electrode active material produced by Example 1 and Comparative Example 1 was measured as follows. The results are shown in Table 2 below.

[0110] [Table 2]

[0111] Referring to Table 2, it can be seen that the amount of sagger charged in Example 1 is more than 2.5 times that of Comparative Example 1. In other words, it can be confirmed that this example is effective in increasing the production volume when manufacturing positive electrode active material.

[0112] Experimental Example 4 - Measurement of Residual Lithium Residual lithium was measured for the cathode active materials produced in Example 1 and Comparative Example 1 using a METTLER TOLEDO T50 model. The results are shown in Table 3 below.

[0113] [Table 3]

[0114] Referring to Table 3, it can be confirmed that the ratio of lithium hydroxide to lithium carbonate (lithium hydroxide / lithium carbonate) in the surface residual lithium of Example 1, which was manufactured by performing a 2-STEP process after a pre-calcination process, is significantly lower than that of Comparative Example 1, which is a positive electrode active material manufactured without a pre-calcination process.

[0115] The present invention is not limited to the embodiments described above and can be manufactured in a variety of different forms. Those with ordinary skill in the art to which the present invention belongs should understand that it can be implemented in other specific forms without altering the technical idea or essential features of the present invention. Therefore, the embodiments described above should be understood to be illustrative and not limiting in all respects.

Claims

1. The step of preparing metal hydroxides containing nickel, cobalt, and manganese; A step of mixing the metal hydroxide, lithium raw material, and doping raw material to produce a mixture; The step of pre-calcining the mixture to obtain a pre-calcined product; The pre-fired product is subjected to a two-step process of firing in one stage and two stages to obtain a single-particle shaped product; and The step of obtaining a metal oxide in which a coating layer is formed by heat treatment after mixing the aforementioned fired product and coating raw material material; A method for producing a positive electrode active material for a lithium secondary battery, wherein, in the step of obtaining the aforementioned fired product, the one-stage firing is performed at a temperature in the range of 870°C to 915°C for 2 to 6 hours.

2. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein the pre-firing is performed at a temperature in the range of 650°C to 770°C for 3 to 10 hours.

3. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein the two-stage firing is performed at a temperature in the range of 750°C to 870°C for 5 to 14 hours.

4. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein in the step of producing the mixture, the doping raw material includes an Al raw material, a Y raw material, and a Zr raw material.

5. The method for producing a positive electrode active material for a lithium secondary battery according to claim 4, wherein the Al raw material is added and mixed in a content range of 500 ppm to 1000 ppm based on the metal hydroxide.

6. The method for producing a positive electrode active material for a lithium secondary battery according to claim 4, wherein the aforementioned Y raw material is added and mixed in a content range of 500 to 1,200 ppm based on the metal hydroxide.

7. The method for producing a positive electrode active material for a lithium secondary battery according to claim 4, wherein the Zr raw material is added and mixed in a content range of 500 to 2,000 ppm based on the metal hydroxide.

8. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein the coating raw material includes a Co coating raw material and an Al coating raw material.

9. The method for producing a positive electrode active material for a lithium secondary battery according to claim 8, wherein the Co coating raw material is added and mixed in an amount ranging from 1.5 mol% to 3 mol% based on the calcined product.

10. The method for producing a positive electrode active material for a lithium secondary battery according to claim 8, wherein the Al coating raw material is added and mixed in a content range of 500 to 1,500 ppm based on the calcined product.

11. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein in the step of obtaining the metal oxide on which the coating layer is formed, the heat treatment is performed at 660°C to 760°C for 3 to 8 hours.

12. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1, wherein the amount of sagger added to the pre-fired product at the stage of obtaining the aforementioned firing product is 4 kg or more.

13. Nickel-containing metal oxides in single-particle form; and The coating layer located on the surface of the nickel-containing metal oxide is included, The nickel-containing metal oxide contains at least three doping elements. A positive electrode active material for lithium secondary batteries, wherein the metal oxide on which the coating layer is formed has two or fewer ungrown particles as measured by a 2.5 cm × 1.0 cm SEM image after being magnified 5000 times.

14. The positive electrode active material for a lithium secondary battery according to claim 13, wherein the ratio of lithium hydroxide to lithium carbonate (lithium hydroxide / lithium carbonate) of the surface residual lithium of the positive electrode active material is in the range of 1.0 to 2.

0.

15. The positive electrode active material is such that when it is pressed five times using a roll press with a press gauge of 0.01 mm, the total value of fine particles smaller than 1 μm is 2.5 vol% or less, as described in claim 13.

16. A positive electrode for a lithium secondary battery comprising a positive electrode active material manufactured according to any one of claims 1 to 12.

17. A lithium secondary battery comprising a positive electrode for a lithium secondary battery according to claim 16.

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