Positive electrode active material for lithium secondary battery, method for producing the same, and lithium secondary battery including the same

Abstract

The present embodiment relates to a cathode active material, a manufacturing method thereof, and a lithium secondary battery including the same. The cathode active material according to the embodiment may have a single particle structure with a D50 of 2 to 7 μm, and the number of grains measured within one particle in ASTAR analysis may be 20 or less.

Description

[Technical Field]

[0001] The present example relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the same. [Background technology]

[0002] Recently, as environmental problems have become more serious, electric vehicles have been attracting attention as one of the solutions to overcome these problems. Driven by the explosive demand for electric vehicles and the demand for increased driving range, the development of secondary batteries with high capacity and high energy density to meet these needs has been actively pursued worldwide.

[0003] To meet these demands, active research is being conducted on NCM cathode materials that can ensure high capacity, especially NCMs with a high Ni content.

[0004] However, as the Ni content in NCM cathode materials increases, problems such as increased resistance, reduced output, and reduced lifespan occur.

[0005] Therefore, there is a need to develop technology for NCM cathode materials that have high Ni content but excellent electrochemical performance. Summary of the Invention [Problem to be solved by the invention]

[0006] In the present embodiment, a positive electrode active material having excellent life characteristics and reduced resistance increase rate and gas generation, a method for producing the same, and a lithium secondary battery including the same are provided. [Means for solving the problem]

[0007] The positive electrode active material according to one embodiment has a single particle structure with a D50 of 2 to 7 μm, and the number of grains measured within one particle in ASTAR analysis is 20 or less.

[0008] Specifically, in this example, the number of grains measured within one particle during ASTAR analysis may be in the range of 5 to 20.

[0009] The grain size of the positive electrode active material may be in the range of 500 nm to 5 μm.

[0010] The positive electrode active material may also include metal oxide particles containing nickel, cobalt, and manganese; and two or more doping elements doped into the metal oxide particles.

[0011] The doping elements may include at least two of Zr, Al, Nb, B, Ti, Ta, V, W, and Mo.

[0012] The doping amount of Zr may be in the range of 0.0005 mol to 0.005 mol per 1 mol of the total of nickel, cobalt, manganese and the doping element.

[0013] The doping amount of Al may be in the range of 0.001 mol to 0.008 mol per 1 mol of the total of nickel, cobalt, manganese and the doping element.

[0014] Another embodiment of a method for manufacturing a positive electrode active material includes: preparing a metal salt aqueous solution containing a nickel source material, a cobalt source material, a manganese source material, and water; supplying the metal salt aqueous solution to a coprecipitation reactor to obtain a metal hydroxide; and mixing the metal hydroxide particles, the lithium source material, and the doping source material, followed by firing to obtain a lithium metal oxide, wherein the firing may include performing a first firing process and successively performing a second firing process at a temperature 50°C to 150°C lower than that of the first firing process.

[0015] The first firing step may be carried out at a temperature in the range of 800° C. to 890° C. for 3 to 5 hours.

[0016] The second firing step may be carried out at a temperature in the range of 750° C. to 800° C. for 9 to 20 hours.

[0017] The first and second firing steps may be carried out in succession while maintaining a temperature difference of 50°C to 80°C.

[0018] In addition, the method may further include a coating step of forming a coating layer on the surface of the positive electrode active material after the second baking step.

[0019] The coating step may be carried out so that the coating element is contained in an amount of 1 mol to 2 mol based on the entire positive electrode active material.

[0020] The coating elements contained in the coating layer may include Co and Al.

[0021] A lithium secondary battery according to yet another embodiment may include a positive electrode including the positive electrode active material according to an embodiment. [Effects of the Invention]

[0022] According to one embodiment, the degree of monoparticulation can be measured using an ASTAR image and then the monoparticulation can be defined.

[0023] Furthermore, when the degree of monoparticulation is high according to the criteria defined in this example, a positive electrode active material can be realized that has excellent life characteristics and reduced resistance increase rate and gas generation rate. [Brief explanation of the drawings]

[0024] [Figure 1] 1 shows a TEM image and an ASTAR image of a positive electrode active material prepared in Example 1. [Figure 2] 1 shows a TEM image and an ASTAR image of a positive electrode active material prepared in Example 2. [Figure 3] 1 shows a TEM image and an ASTAR image of a positive electrode active material prepared in Example 3. [Figure 4] 1 shows a TEM image and an ASTAR image of a positive electrode active material prepared according to Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0025] Terms such as "first," "second," and "third" are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, 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.

[0026] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used in the specification, the term "comprising" embodies certain features, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0027] When a part is referred to as being "on" another part, it may be directly on top of the other part, or there may be other parts between them. In contrast, when a part is referred to as being "directly on top" of another part, there are no other parts between them.

[0028] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless otherwise defined.

[0029] According to an embodiment, the positive electrode active material for a lithium secondary battery may have a single particle structure with a D50 of 2 to 7 μm, and the number of grains measured in one particle by ASTAR analysis may be 20 or less. More specifically, the number of grains measured in one particle by ASTAR analysis may be in the range of 6 to 20, or 5 to 15.

[0030] A positive electrode active material with a single particle structure, in which the number of grains measured within one particle during ASTAR analysis satisfies the above range, has a longer lifespan than a positive electrode active material with a polycrystalline structure, and can also significantly reduce the gas generation rate.

[0031] In particular, when the number of grains measured within one particle in the ASTAR analysis exceeds the above range, the D50 size, which is the average diameter of the particle, increases, and the electron diffusion distance increases, resulting in a decrease in the capacity of the positive electrode active material.

[0032] Therefore, in this embodiment, by providing a cathode active material that maintains a large grain size while maintaining the D50 size, a lithium secondary battery with excellent electrochemical performance and improved lifespan can be realized.

[0033] In other words, in this example, when the number of grains measured within one particle during ASTAR analysis satisfies the above range, the degree of single particle is defined as excellent. NCM cathode materials with excellent degree of single particle have relatively less cracking and excellent life characteristics.

[0034] When a lithium secondary battery is manufactured using a positive electrode active material with such an excellent degree of single particle size, the resistance increase rate can be reduced while maintaining life characteristics at the same level or higher, even compared to when a polycrystalline positive electrode active material is used.

[0035] Meanwhile, the grain size of the positive electrode active material may be in the range of 500 nm to 5 μm, more specifically, 1 μm to 3 μm, as determined by ASTAR analysis. When the grain size satisfies this range, a positive electrode active material with a single particle structure can be realized that has a lifespan similar to that of a polycrystalline positive electrode active material while maintaining an appropriate D50.

[0036] If the grain size is less than 500nm, the surface area of ​​the metal oxide particles becomes large, which increases the rate of gas generation, while if the grain size exceeds 5μm, the diffusion distance of lithium ions increases, which reduces capacity.

[0037] In this specification, the ASTAR analysis was performed using a JEOL JEM-2100F instrument equipped with an ASTAR instrument manufactured by NanoMEGAS.

[0038] In this embodiment, the positive electrode active material may include metal oxide particles containing nickel, cobalt, and manganese; and two or more doping elements doped into the metal oxide particles. The doping elements may include at least two of Zr, Al, Nb, B, Ti, Ta, V, W, and Mo.

[0039] In order to dope lithium metal oxides and ensure their longevity and various electrochemical performances, it is important to select the doping element. Known doping elements to date include Ag. + , Na + Monovalent ions such as Co 2+ , Cu 2+ , Mg 2+ , Zn 2+ , Ba 2+ , Al 3+ , Fe 3+ , Cr 3+ , Ga 3+ , Zr 4+ , Ti 4+These elements have different effects on the battery life and output characteristics.

[0040] In this embodiment, by including at least two of the doping elements Zr, Al, Nb, B, Ti, Ta, V, W, and Mo, it is possible to improve the room temperature and high temperature life characteristics and thermal stability while maintaining a high capacity, and to significantly reduce the initial resistance characteristics and the rate of increase in resistance.

[0041] Specifically, Zr 4+ In the case of lithium-ion batteries, Zr ions occupy the Li site, acting as a kind of pillar, mitigating the contraction of the lithium ion path during the charge-discharge process and stabilizing the layered structure. This phenomenon reduces cation mixing, increases the lithium diffusion coefficient, and can extend the cycle life. Also, Al 3+ This prevents Al ions from migrating to the tetragonal lattice sites, causing the layered structure to deteriorate into a spinel structure. The layered structure allows for easy insertion and removal of Li ions, but the spinel structure does not allow for smooth migration of Li ions.

[0042] In this embodiment, the doping amount of Zr may be in the range of 0.0005 mol to 0.005 mol, more specifically, 0.001 mol to 0.005 mol, per 1 mol of the total of nickel, cobalt, manganese, and the doping element. When the doping amount of Zr satisfies the above range, the life and room temperature life characteristics of the lithium secondary battery can be significantly improved.

[0043] The doping amount of Al may be in the range of 0.001 mol to 0.008 mol, more specifically, 0.002 mol to 0.006 mol, per 1 mol of the total of nickel, cobalt, manganese, and the doping element. When the Al content satisfies the above range, a lithium secondary battery with excellent life characteristics and a reduced rate of increase in resistance can be realized.

[0044] According to another embodiment, a method for manufacturing a positive electrode active material includes: preparing a metal salt aqueous solution containing a nickel source material, a cobalt source material, a manganese source material, and water; supplying the metal salt aqueous solution to a coprecipitation reactor to obtain a metal hydroxide; and mixing the metal hydroxide particles, the lithium source material, and the doping source material, followed by firing to obtain a lithium metal oxide, wherein the firing may include performing a first firing process and successively performing a second firing process at a temperature 20°C to 100°C lower than that of the first firing process.

[0045] In this embodiment, the first firing step and the second firing step are performed continuously, so that the production time of the positive electrode active material can be shortened, and thus more positive electrode active material can be produced in the same time, improving economic efficiency.

[0046] Furthermore, since the temperatures of the first and second firing steps are controlled in this continuous process, the temperature setting is extremely important.

[0047] Specifically, the first firing step is a step for growing the grain size of the single-particle structure positive electrode active material. The temperature range for the first firing step is controlled to allow sufficient grain growth by heat treatment at a temperature 50°C to 150°C higher than the temperature at which the layered structure stabilizes. However, if this temperature is maintained for a long period of time, the layered structure may be destroyed, reducing the electrochemical performance of the positive electrode active material. Therefore, the first firing step is maintained for as short a time as possible.

[0048] Next, the second firing step is performed to restore the layer structure damaged during the first firing step. Therefore, the second firing step may be performed at a temperature range that is approximately 50°C to 150°C lower than that of the first firing step. More specifically, the first firing step and the second firing step may be performed in succession while maintaining a temperature difference of 50°C to 80°C.

[0049] The method for manufacturing a cathode active material according to this embodiment may further include a coating process for forming a coating layer on the surface of the cathode active material after the second baking process. By performing this coating process, the amount of residual lithium present on the surface of the cathode active material can be controlled, thereby further improving the electrochemical performance of the cathode active material according to this embodiment.

[0050] Specifically, the coating step may be carried out so that 1 mole to 2 moles of the coating element is contained based on the entire positive electrode active material, and the coating element contained in the coating layer may include Co and Al.

[0051] In yet another embodiment of the present invention, there is provided a lithium secondary battery including a positive electrode including the positive electrode active material according to the embodiment of the present invention, a negative electrode including the negative electrode active material, and an electrolyte disposed between the positive electrode and the negative electrode.

[0052] The description of the positive electrode active material is the same as that of the above-described embodiment of the present invention, and therefore will be omitted.

[0053] The positive electrode active material layer may include a binder and a conductive material.

[0054] The binder serves to firmly adhere the positive electrode active material particles to each other and to the current collector.

[0055] The conductive material is used to impart electrical conductivity to the electrode, and any material can be used as long as it is electron-conductive without causing chemical changes in the battery that is constructed.

[0056] The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector, and the negative electrode active material layer contains a negative electrode active material.

[0057] Examples of the negative electrode active material include substances capable of reversibly intercalating / deintercalating lithium ions, lithium metal, alloys of lithium metal, substances capable of doping and undoping lithium, or transition metal oxides.

[0058] The substance capable of reversibly intercalating / deintercalating lithium ions is a carbonaceous substance, and any of the carbon-based negative electrode active materials generally used in lithium-ion secondary batteries can be used. Representative examples thereof include crystalline carbon, amorphous carbon, or both of these can be used.

[0059] Examples of the alloy of lithium metal include alloys of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0060] Examples of the substance capable of doping and undoping lithium include Si, SiO x (0 < x < 2), Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO2, Sn-Y (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), and the like.

[0061] Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, and the like. The negative electrode active material layer may also contain a binder and may further selectively contain a conductive material. The binder serves to firmly adhere the negative electrode active material particles to each other and to the current collector.

[0062] The conductive material is used to impart electrical conductivity to the electrode, and any material can be used as long as it is electron-conductive without causing chemical changes in the battery that is constructed.

[0063] The current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0064] The negative and positive electrodes are fabricated by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and then coating the composition on a current collector. Since this electrode fabrication method is well known in the art, a detailed description thereof will be omitted. Examples of the solvent include, but are not limited to, N-methylpyrrolidone.

[0065] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries.

[0066] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0067] The organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0068] The lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions in the battery, enabling basic operation of a lithium secondary battery, and facilitating the movement of lithium ions between the positive electrode and the negative electrode.

[0069] Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. Such a separator can be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more of these layers. Of course, 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 can also be used.

[0070] Lithium secondary batteries are classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used, and may be classified into cylindrical, prismatic, coin, pouch, etc. depending on the shape, and into bulk and thin film types depending on the size. The structure and manufacturing method of these batteries are widely known in the field, so detailed description will be omitted. [Example]

[0071] The following detailed description of the present invention is provided by way of example only and does not limit the scope of the present invention, which is defined solely by the scope of the claims that follow.

[0072] Example 1 - Single particle positive electrode active material (1) Preparation of precursor The precursor was prepared by a conventional coprecipitation method.

[0073] Specifically, NiSO4·6H2O was used as the nickel source material, CoSO4·7H2O was used as the cobalt source material, and MnSO4·H2O was used as the manganese source material. These raw materials were dissolved in distilled water to produce metal salt aqueous solutions.

[0074] After preparing the coprecipitation reactor, N2 was purged to prevent oxidation of metal ions during the coprecipitation reaction, and the reactor temperature was maintained at 50°C.

[0075] NH4(OH) was added as a chelating agent to the co-precipitation reactor, and NaOH was used to adjust the pH. The precipitate obtained by the co-precipitation process was filtered, washed with distilled water, and dried in an oven at 100°C for 24 hours to prepare a cathode active material precursor.

[0076] The composition of the produced precursor was (Ni 0.955 Co 0.02 Mn 0.02 Al 0.5 )(OH)2, and the average particle size (D50) was approximately 4 μm.

[0077] (2) Manufacturing of positive electrode active material The precursor prepared in (1) above was uniformly mixed with LiOH·H2O (Samchun Chemicals, battery grade), ZrO2 (Aldrich, 4N), and Al(OH)3 (Aldrich, 4N), and the mixture was then fired in a box-type firing furnace with an oxygen inflow of 1,000 mL / min.

[0078] The first firing step was carried out at 850°C for 3.75 hours, and then the second firing step was carried out at 790°C for 9.75 hours.

[0079] At this time, the molar ratio (Li / Me) of lithium (Li) to all metals (Me) excluding lithium was designed to be 1.01, and the doping amount was LiNi 0.955 Co 0.02 Mn 0.02 Al 0.5 M=Ni based on O2 0.955 Co 0.02 Mn 0.02 Al 0.5 The amount of doping material added was adjusted so that the sum of M and the doped amount was 1 mol. In other words, Li(M) 1-x (D) x It has the structure O2 (M=NCMA, D=doping material).

[0080] Next, the fired material was pulverized into powder using a rotor mill or a jet mill, and then mixed with Al and Co raw materials. The mixture was heat-treated at 680 to 700°C for 5 hours to prepare a cathode active material having a coating layer formed thereon.

[0081] The positive electrode active material of Example 1 thus prepared has a single particle structure as defined in the present invention, and the total composition is Li(M). 0.995 Zr 0.001 Al 0.004 It was O2.

[0082] Example 2 A positive electrode active material was produced in the same manner as in Example 1, except that the first firing step was carried out at 890°C and the second firing step was carried out at 790°C.

[0083] Example 3 A positive electrode active material was produced in the same manner as in Example 1, except that the first firing step was carried out at 850°C and the second firing step was carried out at 820°C.

[0084] Comparative Example 1 The precursor, lithium source, and doping source prepared in Example 1 were uniformly mixed and fired in a Roller Hearth Kiln (hereinafter referred to as RHK) type firing furnace with an oxygen inflow rate of 1,000 mL / min. The firing conditions were maintained at 765°C for 12 hours with a temperature increase rate of 3°C / min.

[0085] The lithium source used was LiOH·H2O (Samchun Chemicals, battery grade), and the doping sources were ZrO2 (Aldrich, 3N) and Al(OH)3 (Aldrich, 3N).

[0086] At this time, the molar ratio (Li / Me) of lithium (Li) to all metals (Me) excluding lithium was designed to be 1.03, and the doping amount was LiNi 0.92 Co 0.04 Mn 0.04 M=Ni based on O2 0.92 Co0.04 Mn 0.04 The amount of doping material added was adjusted so that the sum of M and the doped amount was 1 mol. In other words, Li(M) 1-x (D) x O2 (M=NCMA, D=doping material) structure. The total composition of the positive electrode active material of Comparative Example 1 prepared in this manner was Li(M) 0.993 Zr 0.002 Al 0.005 O2 and is a small grain with a polycrystalline structure.

[0087] Comparative Example 2 A precursor was produced in the same manner as in Example 1, except that the precursor was produced by controlling the average particle size (D50) to be about 15 μm in the precursor production step. Next, using the precursor, a large-particle positive electrode active material having a polycrystalline structure was produced in the same manner as in Comparative Example 1.

[0088] Experimental example 1 - Measurement of life characteristics (1) Manufacturing of coin-type half cells A CR2032 coin cell was fabricated using the positive electrode active material prepared as described above, and then electrochemical evaluation was carried out.

[0089] Specifically, the positive electrode active material, conductive material (Denka Black), and polyvinylidene fluoride binder (product name: KF1120) were mixed in a weight ratio of 96.25:1.65:2.1, and this mixture was added to N-methyl-2-pyrrolidone solvent so that the solid content was approximately 30 wt % to prepare a positive electrode active material slurry.

[0090] The slurry was coated on an aluminum foil (thickness: 10 μm) as a positive electrode current collector using a doctor blade, dried, and then rolled to prepare a positive electrode. The loading amount of the positive electrode was about 15 mg / cm. 2 The rolling density is about 3.5 g / cm 3 It was.

[0091] A 2032 coin-type half-cell was fabricated using the cathode, lithium metal anode (300 μm thick, MTI), electrolyte, and polypropylene separator in a conventional manner. The electrolyte was prepared by dissolving 1M LiPF6 in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (EMC) (mixing ratio EC:DMC:EMC = 3:4:3 vol%) to prepare a mixed solution, to which 3 wt% vinylene carbonate (VC) was added.

[0092] (2) Charge / discharge characteristics evaluation The coin-type half cell prepared in (1) above was aged at room temperature (25° C.) for 10 hours, and then a charge / discharge test was carried out.

[0093] The capacity evaluation was performed with 200 mAh / g as the reference capacity, and the charge / discharge conditions were constant current (CC) / constant voltage (CV) 2.5 V to 4.25 V with a 1 / 20 C cutoff. The initial capacity was measured by 0.1 C charge / 0.1 C discharge.

[0094] (3) Lifetime characteristic evaluation The life characteristics of the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were measured at a high temperature (45° C.) under 0.5 C charge / 1 C discharge conditions after 30 and 50 cycles, respectively.

[0095] (4) Measurement of resistance characteristics The room temperature initial resistance (DC-IR (Direct current internal resistance)) was calculated by charging the battery at 25°C with a constant current and constant voltage of 2.5V to 4.25V, with a 1 / 20C cutoff, once at 0.1C and discharging at 0.1C, and then measuring the voltage 60 seconds after applying the discharge current at 4.25V, 100% charge.

[0096] The resistance increase rate was measured by comparing the resistance measured initially at high temperature (45°C) (initial resistance at room temperature) with the resistance after 30 and 50 cycles in the same manner as the initial resistance measurement, and the increase rate was converted into a percentage (%).

[0097] [Table 1]

[0098] Referring to Table 1, it can be seen that the positive electrode active materials prepared according to Examples 1 to 3, despite having a single particle structure, have superior life characteristics compared to the positive electrode active materials of Comparative Examples 1 and 2, which have a polycrystalline structure. In addition, it can be seen that the positive electrode active materials prepared according to Examples 1 to 3 have significantly reduced resistance increase rates compared to the positive electrode active materials of Comparative Examples 1 and 2.

[0099] Experimental Example 2 - Grain size measurement The grain size of the positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 and 2 was measured using a JEOL JEM-2100F device equipped with an ASTAR device manufactured by NanoMEGAS, Inc. The results are shown in Table 2 below.

[0100] [Table 2]

[0101] Experimental Example 3 - Analysis of the structure of the positive electrode active material The TEM images and ASTAR images of the positive electrode active materials prepared in Examples 1 to 3 and Comparative Example 1 are shown in FIGS. 1 to 4, respectively.

[0102] Specifically, Fig. 1 shows a TEM image and an ASTAR image of the cathode active material prepared according to Example 1, Fig. 2 shows a TEM image and an ASTAR image of the cathode active material prepared according to Example 2, Fig. 3 shows a TEM image and an ASTAR image of the cathode active material prepared according to Example 3, and Fig. 4 shows a TEM image and an ASTAR image of the cathode active material prepared according to Comparative Example 1.

[0103] In TEM images, it is difficult to determine the grain size and number because the distinction between grains within a particle is unclear. However, using the ASTAR method, this distinction becomes clear, making it much easier to compare grain size and number. Looking at the ASTAR images in Figures 1 to 3, it can be seen that the number of grains measured within a particle is very small. In contrast, looking at the ASTAR image in Figure 4, it can be seen that there are a larger number of grains than in the Example.

[0104] [Table 3]

[0105] The present invention is not limited to the above-described embodiments, and can be manufactured in various different forms, and those skilled in the art will understand that the present invention can be embodied in other specific forms without changing the technical spirit or essential characteristics of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and not limiting.

Claims

1. It has a single particle structure with a D50 of 2 to 7 μm, A positive electrode active material for a lithium secondary battery, in which the number of grains measured within one particle during ASTAR analysis is 20 or less.

2. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the number of grains measured within one particle during ASTAR analysis is in the range of 5 to 20.

3. 10. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the grain size of the positive electrode active material is 500 nm to 5 μm.

4. The positive electrode active material is Metal oxide particles containing nickel, cobalt, and manganese; and Two or more doping elements doped into the metal oxide particles The positive electrode active material for a lithium secondary battery according to claim 1 , comprising:

5. 5. The positive electrode active material for a lithium secondary battery according to claim 4, wherein the doping element comprises at least two of Zr, Al, Nb, B, Ti, Ta, V, W, and Mo.

6. 6. The positive electrode active material for a lithium secondary battery according to claim 5, wherein the doping amount of Zr is 0.0005 mol to 0.005 mol per 1 mol of the total of nickel, cobalt, manganese and the doping element.

7. 6. The positive electrode active material for a lithium secondary battery according to claim 5, wherein the doping amount of Al is 0.001 mol to 0.008 mol per 1 mol of the total of nickel, cobalt, manganese and the doping element.

8. preparing an aqueous metal salt solution comprising a nickel source material, a cobalt source material, a manganese source material, and water; supplying the metal salt aqueous solution to a coprecipitation reactor to obtain a metal hydroxide; mixing the metal hydroxide particles, a lithium source material, and a doping source material, and then calcining the mixture to obtain a lithium metal oxide; Including, The firing step comprises: performing a first firing step; and subsequently carrying out a second baking process at a temperature 50° C. to 150° C. lower than that of the first baking process.

9. The method for producing a positive electrode active material according to claim 8, wherein the first baking step is performed at a temperature in the range of 800°C to 890°C for 3 to 5 hours.

10. The method for producing a positive electrode active material according to claim 8, wherein the second baking step is performed at a temperature in the range of 750°C to 800°C for 9 to 20 hours.

11. 9. The method for producing a positive electrode active material according to claim 8, wherein the first baking step and the second baking step are performed in succession while maintaining a temperature difference of 50°C to 80°C.

12. The method for producing a positive electrode active material according to claim 8 , further comprising a coating step of forming a coating layer on a surface of the positive electrode active material after the second baking step.

13. The method for producing a positive electrode active material according to claim 12, wherein the coating step is performed so that the coating element is contained in an amount of 1 mol to 2 mol based on the entire positive electrode active material.

14. The method for producing a positive electrode active material according to claim 12 , wherein coating elements contained in the coating layer include Co and Al.

15. A lithium secondary battery comprising a positive electrode containing the positive electrode active material according to any one of claims 1 to 7.

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