Method for preparing positive electrode active material for lithium secondary battery, and lithium secondary battery comprising positive electrode active material prepared using same

Abstract

The present embodiments relate to a method for preparing a positive electrode active material for a lithium secondary battery, and a lithium secondary battery comprising same. The method for preparing a positive electrode active material for a lithium secondary battery, according to one embodiment, comprises the steps of: preparing metal hydroxides containing nickel, cobalt and manganese; mixing the metal hydroxides, a lithium raw material and a doping raw material, thereby preparing a mixture; pre-firing the mixture, thereby obtaining a pre-fired product; firing the pre-fired product through the three steps of first firing, second firing and third firing, thereby obtaining a fired product in the form of a discrete particle; and mixing the fired product and a coating raw material, and then heat treating same, thereby obtaining a metal oxide having a coating layer, wherein, in the step of obtaining a fired product, the second firing can be performed at a temperature higher than that of the first firing, and the third firing can be performed at a temperature lower than that of the first firing.

Description

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

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

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

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

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

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

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

[0007] In this embodiment, a method for manufacturing a positive electrode active material for a lithium secondary battery having excellent electrochemical properties and improved lifespan and resistance characteristics, and a lithium secondary battery including the same are provided.

[0008] According to one 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; pre-firing the mixture to obtain a pre-firing product; performing a first-stage firing, a second-stage firing, and a third-stage firing of the pre-firing product in a three-step process 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 step of obtaining the fired product may be such that the second-stage firing is performed at a higher temperature than the first-stage firing, and the third-stage firing is performed at a lower temperature than the first-stage firing.

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

[0010] According to the present embodiment, the first, second, and third sinterings are performed in a three-step (STEP) process, and the second sintering is performed at a higher temperature than the first sintering, and the third sintering is performed at a lower temperature than the first sintering, thereby stabilizing the crystal structure and improving particle strength.

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

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

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

[0017] 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.

[0018] 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.

[0019]

[0020] Method for manufacturing positive electrode active material for lithium secondary batteries

[0021] As described above, the positive electrode active material in the form of a single particle may have a problem in that oversintering may occur, causing defects in the layered crystal structure or reducing particle strength, which may result in a decrease in high-temperature life and resistance characteristics.

[0022] However, in this embodiment, this problem was solved by manufacturing a single-particle type positive electrode active material by performing the first, second, and third step firings in a three-step (STEP) process, performing the second step firing at a higher temperature than the first step firing, and performing the third step firing at a lower temperature than the first step firing.

[0023] Specifically, a method for manufacturing a cathode active material for a lithium secondary battery according to one embodiment may include: preparing a metal hydroxide including nickel, cobalt, and manganese; mixing the metal hydroxide, a lithium raw material, and a doping raw material to prepare a mixture; pre-firing the mixture to obtain a pre-firing product; performing a first-step firing, a second-step firing, and a third-step firing of the pre-firing product in a three-step process 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.

[0024] At this time, the step of obtaining the sintered material may include performing a second-stage sintering at a higher temperature than the first-stage sintering, and performing a third-stage sintering at a lower temperature than the first-stage sintering. By performing the second-stage sintering process at a high temperature for a short time as in this example, and then performing the third-stage sintering process, a positive electrode active material in the form of a single particle with improved particle strength and a stabilized crystal structure can be realized.

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

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

[0027] First, a step is performed to prepare a metal hydroxide containing nickel, cobalt and manganese.

[0028] At this time, the nickel-containing metal hydroxide may be manufactured by, for example, adding a complexing agent-containing solution and a pH adjusting agent-containing solution to a transition metal-containing solution including a nickel raw material, optionally a cobalt raw material and / or a manganese raw material, and performing a co-precipitation reaction.

[0029] The above nickel raw material is not particularly limited as long as it is used in the art for manufacturing a positive electrode active material precursor. For example, the nickel raw material may be a nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, 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, but is not limited thereto.

[0030] The above cobalt raw material is not particularly limited as long as it is used in the art for manufacturing a positive electrode active material precursor. For example, the cobalt raw material may be a cobalt-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, CoSO 4,It may be, but is not limited to, CoSO4ㆍ7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2ㆍ4H2O, Co(NO3)2ㆍ6H2O or a combination thereof.

[0031] The manganese raw material is not particularly limited as long as it is used in the art for manufacturing a precursor of a cathode active material. For example, the manganese raw material may be a manganese-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof, and specifically, may be a manganese salt such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylic acid salt, manganese citrate, and manganese fatty acid salt, manganese oxide such as Mn2O3, MnO2, and Mn3O4, oxyhydroxide, manganese chloride, or a combination thereof, but is not limited thereto.

[0032] The above transition metal-containing solution may be prepared by adding a nickel raw material and optionally 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, etc.) that can be uniformly mixed with water.

[0033] The above complexing agent-containing solution performs the function of forming a complex, and may include, but is not limited to, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3 or a combination thereof as the complexing agent. Meanwhile, the complexing agent-containing solution may be used in the form of an aqueous solution, and at this time, water or a mixture of water and an organic solvent (e.g., alcohol, etc.) that can be uniformly mixed with water may be used as the solvent.

[0034] Next, a step of preparing a mixture by mixing the above metal hydroxide, lithium raw material, and doping raw material is performed.

[0035] The above lithium raw material is not particularly limited as long as it is commonly used in the art, but may be, for example, Li2CO3, LiOH, or LiOH·H2O. In this embodiment, LiOH·H2O may be used as the lithium raw material.

[0036] At this time, the mixture can be prepared so that the molar ratio (Li / Me) of lithium (Li) to the total metal (Me) excluding lithium is in the range of 1.0 to 1.1, or in the range of 1.01 to 1.08.

[0037] The above doping raw material may include an Al raw material, a Y raw material, and a Zr raw material.

[0038]

[0039] 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.

[0040] 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.

[0041] 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.

[0042] The above Al raw material can be mixed by adding it in a content range of 200 to 1,800 ppm or 500 to 1,500 ppm based on 100 g of the metal hydroxide, for example.

[0043] The above Y raw material can be mixed by adding it in a content range of 400 to 2,000 ppm or 700 to 1,700 ppm based on 100 g of the metal hydroxide, for example.

[0044] The above Zr raw material can be mixed by adding it in a content range of, for example, 1,200 to 2,800 ppm or 1,500 to 2,500 ppm based on 100 g of the metal hydroxide.

[0045] When the input contents of Al raw material, Y raw material, and Zr raw material satisfy the above range, a cathode active material with improved capacity retention and resistance characteristics can be manufactured.

[0046] Next, a step of pre-firing the above mixture to obtain a pre-firing product is performed.

[0047] The above preliminary calcination can be performed at a temperature ranging from 650°C to 770°C for 2 to 12 hours or at a temperature ranging from 680°C to 740°C for 3 to 10 hours. When the preliminary calcination process is performed in this manner, the production amount of the positive electrode active material can be increased while maintaining the electrochemical characteristics, thereby improving economic efficiency.

[0048] Afterwards, the preliminary fired product is subjected to a 3-STEP process of 1-step firing, 2-step firing, and 3-step firing to obtain a fired product in the form of a single particle.

[0049] The above first-stage firing can 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.

[0050] The above two-step firing can be performed at a temperature ranging from 890°C to 960°C for a time ranging from 0.5 to 2 hours or at a temperature ranging from 900°C to 940°C for a time ranging from 0.5 to 1.5 hours.

[0051] 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.

[0052] Specifically, in the present embodiment, the second-stage firing may be performed at a higher temperature than the first-stage firing, and the third-stage firing may be performed at a lower temperature than the first-stage firing. By performing the two-stage firing process at a high temperature for a short period of time, i.e., the firing process in three stages including the shooting section, it is possible to realize a single-particle type cathode active material with improved particle strength and a stabilized crystal structure.

[0053] 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.

[0054] The above coating raw material may include a Co coating raw material and an Al coating raw material.

[0055] The above 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.

[0056] The above Al coating raw material is Al(OH)3, It may include at least one of Al2(SO4)3, Al(NO)3, Al2O3, and AlCl3, but is not limited thereto.

[0057] Here, the Co coating raw material can be mixed by adding it in a content range of 1.5 mol% to 3 mol% or 2.0 mol% to 2.8 mol% based on the total weight of the sintered product.

[0058] The above Al coating raw material can be mixed by adding it in a content range of 500 ppm to 1,500 ppm or 800 ppm to 1,200 ppm based on the total weight of the sintered product.

[0059] When the content of the Co coating raw material and the Al coating raw material satisfies the above range, the interfacial side reaction with the positive electrode active material and the electrolyte can be suppressed, and a lithium secondary battery with improved capacity and resistance characteristics can be manufactured.

[0060] In the step of obtaining the metal oxide on which the coating layer is formed, the heat treatment may be performed, 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.

[0061] In the present embodiment, a step of crushing the sintered material may be further included after the step of obtaining the sintered material, if necessary. That is, the crushing process may be included after obtaining the sintered material and before the coating process.

[0062] The above-mentioned crushing step may be performed after cooling the sintered material to 50 to 200°C. Cooling to the above-mentioned cooling temperature can suppress the reaction between external moisture and the sintered material and inhibit the increase of residual lithium.

[0063] The above disintegration can be performed by a method commonly performed in the art.

[0064]

[0065] The above-mentioned crushing can be performed using, for example, a rotor mill, a ball mill, a pin mill, a jet mill, a bead mill, or a roll mill, but is not limited thereto.

[0066] The metal oxide having a single particle-shaped coating layer formed by the above method can be represented by the following chemical formula 1.

[0067] [Chemical Formula 1]

[0068] Li a [Ni x Co y Mn z M1 w1 M2w2 ]O2

[0069] In the above chemical formula 1, 0.8≤a≤1.2, 0.8≤x≤0.99, 0 <y≤0.06, 0<z≤0.14, 0<w1≤0.1, 0≤w2≤0.05이고, x+y+z+w1+w2=1이고, M1은 Al, Y 및 Zr이고, M2는 B, Al, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La 및 Sr 중 1종 이상을 포함한다.

[0070] In Chemical Formula 1, 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 transition metals included in the nickel-containing metal oxide on which the coating layer is formed. When the nickel content satisfies the above range, a high-capacity battery can be realized.

[0071] In addition, the total content of the doping elements M1 and M2 in the chemical formula 1 may be greater than 0 and less than or equal to 0.2 mol, more specifically, in the range of 0.0005 mol to 0.1 mol, 0.0005 mol to 0.08 mol, 0.0005 mol to 0.04 mol, or 0.001 mol to 0.03 mol, based on 1 mol of the total of nickel, cobalt, manganese, and the doping elements. The content of the doping element in the chemical formula refers to the doping amount of the doping element included in the positive electrode active material finally obtained.

[0072] Meanwhile, the average particle diameter (D50) of the cathode active material according to the present embodiment may be 3 μm or more, and more specifically, 3 μm to 6 μm. When the average particle diameter of the single-particle cathode active material satisfies the above range, a lithium secondary battery with excellent electrochemical properties, such as lifespan characteristics and resistance increase rate, can be realized. In addition, it has a very advantageous effect because it can also increase the energy density per volume.

[0073] The cathode active material of the present embodiment has a very low fine particle generation rate. Specifically, when the cathode active material 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 may be 2% or less. When the fine particle generation rate satisfies the above range, high-temperature life and resistance characteristics can be improved.

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

[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 thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, and Al alloy; metallic oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fiber-like forms, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[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 total weight of the precursor.

[0109] The above mixture was placed in a kiln with 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 with an oxygen atmosphere and heated to 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 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] Comparative Example 1

[0114] After preliminary firing at 680℃ for 6.5 hours to obtain a preliminary fired product, the obtained preliminary fired product was put into a kiln in an oxygen atmosphere and then heated up to be fired at 890℃ for 4 hours (1 st After step), it was fired at 780℃ for 11 hours (2 nd A single-particle type positive electrode active material was manufactured in the same manner as in Example 1, except that the sintering process was performed in the step (step).

[0115]

[0116] Experimental Example 1 - Measurement of particle breakage

[0117] The degree of particle breakage was measured using the positive electrodes manufactured according to Example 1 and Comparative Example 1, and the results are shown in Table 1 below.

[0118] Specifically, 10 g of the positive electrode active material was mixed with 3.5 g of NMP, cast on a 20 μm thick aluminum foil (Al foil) (70 mm x 210 mm), and dried in a 120°C convection oven for 30 minutes. Then, a sample was prepared by covering the aluminum foil coated with the positive electrode active material with an aluminum foil of the same size.

[0119] The above sample was pressed 5 times using a roll press with a press gauge of 0.01 mm to obtain 2 g of active material particles. The amount of fine particles generated was analyzed by particle size analysis using a Malvern (MS3000) analyzer using the obtained active material particles. The degree of particle breakage was indicated by the sum of the Vol% of fine particles less than 1 μm in the particle size analysis results.

[0120] Breakage of particle size Example 11.85 vol% Comparative example 12.28 vol%

[0121] Referring to Table 1, it can be confirmed that the rate of fine particle generation in Example 1, which is a positive electrode active material manufactured by a 3-STEP process, is very low compared to Comparative Example 1, which is a positive electrode active material manufactured by a 2-STEP process.

[0122] Experimental Example 2 - Measurement of Residual Lithium

[0123] For the positive electrode active materials manufactured according to Example 1 and Comparative Example 1, residual lithium was measured using a T50 model from METTLER TOLEDO. The results are shown in Table 2 below.

[0124] Classification Total-LiExample 10.7194Comparative Example 10.8781

[0125] Referring to Table 2, it can be seen that the residual lithium content of the positive electrode active material manufactured according to Example 1 is lower than that of the positive electrode active material manufactured according to Comparative Example 1.

[0126] Experimental Example 3 - Grain Size Measurement

[0127] For the positive electrode active materials manufactured according to Example 1 and Comparative Example 1, the crystal grain size, c-axis, and a-axis values ​​were measured as follows. The results are shown in Table 3 below.

[0128]

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

[0130] 2) Smart lab equipment configuration

[0131] Goniometer radius: 300.0 mm

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

[0133] Theta_s arm: BB Slit

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

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

[0136] Theta_d arm: 8.0mm Receiving slit

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

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

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

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

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

[0142]

[0143] 5) Crystal grain size was calculated using Rigaku's SmartLab Studio II x64 v4.2.82.0 S / W.

[0144] 6) Calculation is done using WPPF (Whole powder pattern fitting) in S / W.

[0145]

[0146] Crystal size Example 1195 nm Comparative example 1181 nm

[0147] Referring to Table 3, it can be confirmed that the crystal grain size of the positive electrode active material manufactured according to Example 1 is 190 nm or more, but the crystal grain size of the positive electrode active material manufactured according to Comparative Example 1 is less than 190 nm.

[0148] Experimental Example 4 - Particle Size Distribution Measurement

[0149] For the positive electrode active materials manufactured according to Example 1 and Comparative Example 1, the Span value and Dn10 value were measured. Specifically, particle size analysis was performed using the S3500 equipment from Microtrac.

[0150] -. Sample amount: 0.02 g

[0151] -. Dispersant: 10 wt.% (NaPO3)6: 0.5 g

[0152] -. Pure: 5 g

[0153] - External ultrasound: 1 min

[0154] -. Measurement conditions

[0155] A. SDC

[0156] -. SDC Control Parameters

[0157]

[0158] · Number of Rinses: 3

[0159] · Deaeration Cycles: 1

[0160] · Flow rate: 40

[0161] B. Analysis

[0162] -. Particle Information

[0163] · Particle Characteristics: Refractive Index (1.55)

[0164] -. Fluid Information

[0165] · Fluid Characteristics: Refractive Index (1.333)

[0166] All. Timing

[0167] -. Setzero Time: 10

[0168] -. Measurement Run

[0169] · Run Time: 10

[0170] · Number of Runs: 3

[0171] The results are shown in Table 4 below.

[0172]

[0173] Particle size distribution SpanDn10 Example 10.86 1.60 Comparative example 10.98 1.44

[0174] Referring to Table 4, Example 1, which was manufactured using the same method as the present example, has a Span value of 0.9 or less and a Dn10 value of 1.5 or more. In contrast, the Span value of Comparative Example 1 exceeds 0.9 and the Dn10 is less than 1.5. Therefore, it can be confirmed that the positive electrode active material of Example 1 has superior particle size uniformity and less fine particle generation, resulting in superior single crystallinity compared to Comparative Example 1.

[0175]

[0176] 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. 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 pre-firing the above mixture to obtain a pre-firing product; A step of obtaining a single-particle sintered product by performing a three-step process of 1st-step sintering, 2nd-step sintering, and 3rd-step sintering of the above-mentioned preliminary sintered product; 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 step of obtaining the above-mentioned sintered product comprises performing a second-stage sintering at a higher temperature than the first-stage sintering, and performing a third-stage sintering at a lower temperature than the first-stage sintering.

2. In paragraph 1, A method for producing a positive electrode active material for a lithium secondary battery, wherein the above first step sintering is performed at a temperature ranging from 870°C to 930°C for a time of 2 to 6 hours.

3. In paragraph 1, A method for producing a positive electrode active material for a lithium secondary battery, wherein the above two-step calcination is performed at a temperature ranging from 890°C to 960°C for a time of 0.5 to 2 hours.

4. In paragraph 1, A method for producing a positive electrode active material for a lithium secondary battery, wherein the above three-step firing is performed at a temperature ranging from 750°C to 870°C for a time of 5 to 14 hours.

5. In paragraph 1, A method for producing a positive electrode active material for a lithium secondary battery, wherein the above preliminary firing is performed at a temperature ranging from 650°C to 770°C for 3 to 10 hours.

6. In paragraph 1, In the step of preparing the above mixture, A method for producing a cathode active material for a lithium secondary battery, wherein the above doping raw material comprises an Al raw material, a Y raw material, and a Zr raw material.

7. In paragraph 6, The above Al raw material is, A method for producing a positive electrode active material for a lithium secondary battery, wherein the positive electrode active material is mixed by adding the metal hydroxide in a content range of 500 ppm to 1,500 ppm based on the above metal hydroxide.

8. In paragraph 6, The above Y raw material is, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the positive electrode active material is mixed by adding a content ranging from 400 ppm to 2,000 ppm based on the above metal hydroxide.

9. In paragraph 6, The above Zr raw material is, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the positive electrode active material is mixed by adding a content ranging from 1,200 ppm to 2,800 ppm based on the above metal hydroxide.

10. In paragraph 1, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the above coating raw material comprises a Co coating raw material and an Al coating raw material.

11. In paragraph 10, The above Co coating raw material is, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the positive electrode active material is mixed by adding a content ranging from 1.5 mol% to 3 mol% based on 100 g of the above-mentioned sintered material.

12. In paragraph 10, The above Al coating raw material is, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the positive electrode active material is mixed by adding a content ranging from 500 ppm to 1,500 ppm based on 100 g of the above-mentioned sintered material.

13. In paragraph 10, A method for producing a positive electrode active material for a lithium secondary battery, wherein the Co coating raw material comprises at least one of Co(OH)2, CoO, Co3O4, CoCO3, cobalt acetate, and cobalt oxalate.

14. In paragraph 10, The above Al 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 1, In the step of obtaining the metal oxide on which the above coating layer is formed, the heat treatment is A method for producing a positive electrode active material for a lithium secondary battery, the method being performed at 660°C to 760°C for 3 to 8 hours.

16. In paragraph 1, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the metal oxide on which the coating layer is formed is represented by the following chemical formula 1: [Chemical Formula 1] Li a [Ni x Co y Mr z M1 w1 M2 w2 ]O2 In the above chemical formula 1, 0.8≤a≤1.2, 0.8≤x≤0.99, 0 <y≤0.06, 0<z≤0.14, 0<w1≤0.05, 0≤w2≤0.05이고, x+y+z+w1+w2=1이고, M1은 Al, Y 및 Zr이고, M2는 B, Al, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La 및 Sr 중 1종 이상을 포함한다.

17. In paragraph 1, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the positive electrode active material has a total value of fine particles less than 1㎛ of 2 vol% or less when pressed 5 times with a press gauge of 0.01 mm using a roll press.

18. A positive electrode for a lithium secondary battery comprising a positive electrode active material manufactured according to any one of claims 1 to 17.

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