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 positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery including the same. The positive electrode active material for a lithium secondary battery according to one embodiment includes a core portion and a shell portion located on the surface of the core portion, The shell portion includes needle-shaped particles whose major axes are oriented in the direction from the core portion to the shell portion, and is represented by the following chemical formula 1: [Chemical formula 1] Li 1+q (Ni x Co y Mn z ) 1-w (Zr a Nb b ) w O2 In the above chemical formula 1, q, x, y, z, a, b, and w are -0.1≦q≦0.2, 0.0032, respectively.

Description

[Technical Field]

[0001] The present disclosure 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] In recent years, driven by the need for electric vehicles that can travel more than 600 km on a single charge, the development of high-capacity, high-energy-density secondary batteries to power these vehicles has been actively pursued worldwide.

[0003] Cathode materials are crucial for producing superior secondary batteries, and in the case of NCM-based layered systems where the nickel content is increased to achieve high capacity, performance improvements are required in terms of initial efficiency, lifespan, output, resistance, and stability. One method for improving this performance is a concentration-gradient cathode material, which increases the nickel concentration in the core and decreases the nickel concentration in the shell, significantly improving the stability of the shell, which is in direct contact with the electrolyte.

[0004] However, this method has the drawback of requiring a series of solution feeding tanks to be connected in series during precursor production to change the co-precipitation composition in real time, resulting in a long co-precipitation time, low productivity, and increased costs.

[0005] Therefore, there is a need to develop a positive electrode active material for a lithium secondary battery that has improved performance and a method for manufacturing the same through a simple process. Summary of the Invention [Problem to be solved by the invention]

[0006] One embodiment of the present invention provides a cathode active material for a lithium secondary battery having a structure that allows lithium ions to easily intercalate on the surface of the cathode material without using a conventional concentration gradient structure, a method for producing the same, and a lithium secondary battery including the same. [Means for solving the problem]

[0007] The positive electrode active material for a lithium secondary battery according to one embodiment of the present invention comprises a core portion; and a shell portion located on the surface of the core portion; and the shell portion includes needle-shaped particles whose major axes are located in the direction from the core portion to the shell portion, and may be represented by the following chemical formula 1. [Chemical formula 1] Li 1+q (Ni x Co y Mn z ) 1-w (Zr a Nb b ) w O2 In the above chemical formula 1, q, x, y, z, a, b, and w are each 0≦q≦0.5, 0.0032, <w<0.013、0.7≦x<1.0、0<y<0.3、0<z<0.3、x+y+z=1、0.2≦a≦0.7、0.3≦b≦0.8、a+b=1である。

[0008] The acicular particles may have an aspect ratio in the range of 4 to 15, and the shell portion may have a thickness in the range of 0.5 μm to 3 μm.

[0009] When a lithium secondary battery including a positive electrode using the positive electrode active material is fully charged, the core portion remains unchanged, and the shell portion may be transformed into a comb shape in which void channels are formed in a direction from the core portion to the shell portion.

[0010] Meanwhile, a boron (B) coating layer may be further included on the outside of the shell part.

[0011] In addition, rod-shaped primary particles may be further located on the surface of the positive electrode active material for a lithium secondary battery, and the rod-shaped primary particles may have an average diameter of 300 nm to 800 nm and an average width of 50 nm to 200 nm.

[0012] The positive electrode active material for a lithium secondary battery may have an average particle size (D50) in the range of 10 μm to 16 μm.

[0013] A method for manufacturing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention may include the steps of preparing a metal hydroxide containing nickel, manganese, and cobalt; mixing the metal hydroxide, lithium hydroxide, niobium (Nb) oxide, and zirconium (Zr) oxide to obtain a mixture; and heat-treating the mixture to form a shell portion. In this case, the niobium (Nb) oxide raw material may have two or more different crystal structures, and may be Nb2O5 having a monoclinic crystal structure and Nb2O5 having an orthorhombic crystal structure. 16.8 O 42 and wherein the Nb 16.8 O 42 The molar ratio of Nb2O5 to NbO can range from 2:1 to 4:1.

[0014] The molar ratio of niobium (Nb) in the niobium (Nb) oxide to zirconium (Zr) in the zirconium (Zr) oxide may range from 0.5:1 to 4.5:1.

[0015] The step of heat-treating the mixture to form the shell portion may include a step of performing a first heat treatment at a temperature range of 400°C to 600°C for 1 hour to 5 hours; and a step of performing a second heat treatment at a temperature range of 700°C to 800°C for 12 hours to 24 hours.

[0016] In the step of preparing the metal hydroxide containing nickel, manganese, and cobalt, the metal hydroxide may have an average particle size (D50) ranging from 14 μm to 16 μm.

[0017] In another embodiment of the present invention, a positive electrode for a lithium secondary battery may be provided, the positive electrode for a lithium secondary battery including: a current collector; and a positive electrode active material layer for a lithium secondary battery located on at least one surface of the current collector, the positive electrode active material being included in the positive electrode active material. A lithium secondary battery including the positive electrode for a lithium secondary battery may be provided. [Effects of the Invention]

[0018] According to one embodiment of the present invention, it is possible to provide a cathode active material for a lithium secondary battery with improved performance, which has a structure that allows lithium ions to easily intercalate on the surface of the cathode active material in a simple manner without using a concentration gradient structure. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram showing a method for producing a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention. [Figure 2] FIG. 2 shows a surface SEM image of the positive electrode active material for a lithium secondary battery according to Example 1. As shown in FIG. [Figure 3] FIG. 3 shows a surface SEM image of the positive electrode active material for a lithium secondary battery according to Comparative Example 1. As shown in FIG. [Figure 4] FIG. 4 shows a cross-sectional FIB image of the positive electrode active material for a lithium secondary battery according to Example 1. [Figure 5] FIG. 5 shows a cross-sectional FIB image of the positive electrode active material for a lithium secondary battery according to Comparative Example 1. As shown in FIG. [Figure 6] FIG. 6 shows a cross-sectional SEM image of the positive electrode active material in a discharged state after 300 charge / discharge cycles of a coin half-cell using the positive electrode active material for a lithium secondary battery according to Example 1. [Figure 7]FIG. 7 shows a cross-sectional SEM image of the positive electrode active material in a discharged state after 300 charge / discharge cycles of a coin half-cell using the positive electrode active material for a lithium secondary battery according to Comparative Example 1. [Figure 8] FIG. 8 shows cross-sectional SEM images of the electrode and the positive electrode active material in a charged state after 300 charge / discharge cycles of a coin half-cell using the positive electrode active material for a lithium secondary battery according to Example 1. [Figure 9] FIG. 9 shows cross-sectional SEM images of the electrode and the positive electrode active material in a charged state after 300 charge / discharge cycles of a coin half-cell using the positive electrode active material for a lithium secondary battery according to Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0020] In describing the present invention, terms such as 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 only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Thus, a first part, component, region, layer, or section described below may also be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0021] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. The singular forms used herein include the plural forms unless the context clearly dictates otherwise. The term "comprising" as used herein 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.

[0022] 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.

[0023] DETAILED DESCRIPTION OF THE INVENTION The following detailed description of the present invention is provided by way of example only and is not intended to limit the scope of the present invention, which is defined by the claims that follow.

[0024] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention includes a core portion containing nickel, manganese, and cobalt, and a shell portion located on a surface of the core portion, the shell portion including acicular particles located in a direction from the core portion to the shell portion, and the acicular particles may have a radial shape with their major axes located in a direction from the core portion to the shell portion.

[0025] The positive electrode active material for a lithium secondary battery according to one embodiment of the present invention may be represented by the following Chemical Formula 1. [Chemical formula 1] Li 1+q (Ni x Co y Mn z ) 1-w (Zr a Nb b ) w O2 In the above chemical formula 1, q, x, y, z, a, b, and w are -0.1≦q≦0.2, 0.0032, respectively. <w<0.013、0.7≦x<1.0、0<y<0.3、0<z<0.3、x+y+z=1、0.2≦a≦0.7、0.3≦b≦0.8、a+b=1である。

[0026] By mixing two types of first transition metal oxides with different crystal structures in the above ratio, the shell portion forms a comb shape when fully charged, forming void channels that act as migration paths for easy lithium intercalation and deintercalation. This is advantageous for improving the capacity and initial efficiency of the battery and reducing the initial resistance, and for suppressing the occurrence of microcracks in the positive electrode active material due to charge and discharge, thereby extending the life of the secondary battery.

[0027] Meanwhile, the acicular particles may be uniformly positioned radially from the center of the core toward the surface, and the aspect ratio of the acicular particles may be in the range of 2 to 30, specifically, 4 to 15. When the aspect ratio of the primary particles of the acicular particles is in this range, the shell easily forms a comb shape upon full charge, which is advantageous for efficient lithium ion intercalation and deintercalation. In the present invention, the aspect ratio can be calculated as the ratio of the major axis length to the minor axis length (length / width ratio) of the primary particles of the acicular particles. When the major axis indicates the direction of the relatively long region of the primary particle, the minor axis indicates the length of the relatively short region of the primary particle. In this case, the minor axis may be perpendicular to the major axis. The "aspect ratio" of the primary particles can be calculated as the ratio of the major axis to the minor axis of the primary particles measured from the cross section of the primary particles. Specifically, for the acicular primary particles, the major axis length refers to the longest length of the acicular primary particle observed in an SEM image, and the minor axis length refers to the longest length perpendicular to the major axis length.

[0028] The thickness of the shell portion may be in the range of 0.5 μm to 3 μm, and more specifically, in the range of 0.5 μm to 2 μm.

[0029] Meanwhile, the nickel content of the core portion may be 70 mol % or more, more specifically, 80 mol % or more, based on the total molar content of the nickel, manganese, and cobalt.

[0030] In one embodiment of the present invention, when a half-cell using the positive electrode active material as a positive electrode and lithium metal as a negative electrode is charged to 4.2 V at a constant current of 0.5 C, the core portion of the positive electrode active material remains unchanged, and the shell portion may transform into a comb shape with void channels formed therein. Specifically, the void channels may be formed radially from the center of the core portion toward the surface. This is advantageous for efficient intercalation and deintercalation of lithium ions, reducing battery resistance and improving battery performance.

[0031] In addition, the shell may further include a boron (B) coating layer on the outside thereof. The boron content is not particularly limited as long as it satisfies the target battery capacity, initial efficiency, resistance, and lifespan of the present invention.

[0032] Meanwhile, rod-shaped primary particles may be located on the outer surface of a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention. The rod-shaped primary particles may have an average diameter of 100 nm to 1000 nm, specifically 300 nm to 800 nm. The rod-shaped primary particles may also have an average width of 10 nm to 300 nm, specifically 50 nm to 200 nm. In the present invention, the rod-shaped primary particles may be particles observed on the surface of the positive electrode active material in an SEM image. The average diameter and average width of the rod-shaped primary particles may be the average values ​​of the diameters and widths of 20 to 50 primary particles observed in the SEM image. The diameter of a rod-shaped primary particle refers to the longest length of the cross section of the primary particle observed in the SEM image, and the width refers to the longest length perpendicular to the diameter.

[0033] Meanwhile, the cathode active material for a lithium secondary battery may have an average particle diameter (D50) in the range of 5 μm to 20 μm, specifically, in the range of 10 μm to 16 μm. In the present invention, the average particle diameter of the cathode active material for a lithium secondary battery may be the average value of particle diameters of 10 to 30 cathode active material particles observed in an SEM image. Meanwhile, the particle diameter of the cathode active material particle means the longest length of the cross section observed in the SEM image.

[0034] FIG. 1 is a schematic diagram showing a method for producing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention.

[0035] Referring to FIG. 1, a method for manufacturing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention may include the steps of: preparing a metal hydroxide containing nickel, manganese, and cobalt; mixing the metal hydroxide, lithium hydroxide, niobium (Nb) oxide, and zirconium (Zr) oxide to obtain a mixture; and heat-treating the mixture to form a shell portion.

[0036] First, a metal hydroxide containing nickel, manganese, and cobalt is prepared.

[0037] In this example, a metal salt aqueous solution containing nickel source material, manganese source material, cobalt source material, and water is prepared, and then the metal salt aqueous solution is fed into a coprecipitation reactor to obtain a metal hydroxide by a method commonly known in the art for preparing a cathode active material precursor. The cathode active material precursor may have an average particle size (D50) of 10 μm or more, specifically, in the range of 14 μm to 16 μm. When the precursor particles have a size within this range, a shell made of rod-shaped primary particles can be sufficiently and effectively formed on the surface of the precursor. This allows blending with smaller particle sizes to minimize voids during electrode plate fabrication, thereby advantageously producing a cathode active material with improved performance.

[0038] Thereafter, a step of mixing the metal hydroxide, lithium hydroxide, niobium (Nb) oxide, and zirconium (Zr) oxide to obtain a mixture can be performed.

[0039] The niobium (Nb) oxide may have a monoclinic crystal structure or an orthorhombic crystal structure. Specifically, the niobium (Nb) oxide may have a monoclinic crystal structure, Nb2O5, or an orthorhombic crystal structure. 16.8 O 42 and wherein the Nb 16.8 O 42 to Nb2O5 can be mixed in a molar ratio ranging from 2:1 to 4:1.

[0040] In addition, the zirconium (Zr) in the zirconium (Zr) oxide and the niobium (Nb) in the niobium (Nb) oxide may be mixed in a molar ratio ranging from 0.5:1 to 4.5:1.

[0041] A step of heat treating the mixture to form a shell portion may then be performed.

[0042] The heat treatment step may specifically include a step of performing a first heat treatment at a temperature range of 400°C to 600°C for 1 hour to 5 hours, and a step of performing a second heat treatment at a temperature range of 700°C to 800°C for 10 hours to 20 hours. At this time, the temperature may be increased to the heat treatment temperature at a rate of 1°C / min to 10°C / min, specifically, 3°C / min to 7°C / min. This is advantageous for uniformly mixing transition metal oxides with different crystal structures to form a uniform shell portion.

[0043] Meanwhile, the step of heat-treating the mixture to form the shell portion may be performed in an atmosphere where oxygen is continuously supplied at a flow rate of 100 mL / min to 500 mL / min, specifically, 100 mL / min to 300 mL / min.

[0044] The cathode active material obtained through the heat treatment may be subjected to post-processing processes such as cooling, pulverization, and classification. After washing and drying, the material may be further subjected to dry mixing and heat treatment with H3BO3 (Aldrich) to form a boron (B) coating layer.

[0045] In another embodiment, a positive electrode may be provided, including a current collector and a positive electrode active material layer positioned on one surface of the current collector, the positive electrode active material layer including the positive electrode active material prepared according to the above embodiment.

[0046] The characteristics of the positive electrode active material constituting the positive electrode active material layer are the same as those described above, and therefore, a detailed description of the positive electrode active material will be omitted.

[0047] The positive electrode active material layer may include a binder and a conductive material.

[0048] The binder can improve the adhesion between positive electrode active material particles and the adhesive strength between the positive electrode active material and the positive electrode current collector. The type of binder is not particularly limited, and one or more binders can be used as long as they are used in manufacturing positive electrodes for lithium secondary batteries. 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.

[0049] The conductive material is used to impart conductivity to the electrode, and the type is not particularly limited as long as it has electronic conductivity without causing chemical changes in the battery that is constructed. The conductive material may be contained in an amount of 1 to 30 wt % based on the total weight of the positive electrode active material layer.

[0050] The positive electrode may be manufactured by a conventional method for manufacturing a positive electrode, except that the positive electrode active material is used.

[0051] In another embodiment, a lithium secondary battery is provided that includes the positive electrode.

[0052] The lithium secondary battery may include a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, as described above. The lithium secondary battery may further include a battery container that houses the electrode assembly including the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0053] The lithium secondary battery may be manufactured by a conventional method for manufacturing a lithium secondary battery, except for using the positive electrode active material, and is not particularly limited. [Example]

[0054] The following detailed description of the present invention is provided by way of example only and is not intended to limit the scope of the present invention, which is defined solely by the claims that follow.

[0055] (Preparation of metal hydroxides containing nickel, manganese, and cobalt) Metal hydroxides containing nickel, manganese, and cobalt were prepared using a standard coprecipitation method. Specifically, NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O were dissolved in DI water to prepare a 2.5M metal salt aqueous solution. N2 gas was purged to prevent oxidation of the metal ions during the coprecipitation reaction, and the internal temperature of the reactor was maintained at 50°C. The metal salt aqueous solution and NH4(OH), used as a coprecipitation chelating agent, were charged into a coprecipitation reactor (100 L), and NaOH was added to adjust the pH of the mixed solution inside the reactor. After the final metal hydroxide precursor was grown to an average particle size (D50) of 14 μm, the final metal hydroxide precursor was filtered, washed with DI water, and dried in a 100°C oven for 24 hours. Finally, a solution with a composition of (Ni 0.88 Co 0.10 Mn 0.02 )(OH)2, a metal hydroxide precursor, was obtained.

[0056] (Example 1: Production of positive electrode active material) Based on 1 mole of the prepared metal hydroxide precursor, 1.05 moles of LiOH·H2O (SAMCHUN CHEMICALS, battery grade) was mixed, and ZrO2 (Aldrich, 4N) was mixed so that Zr was 0.0022 moles. 16.8 O 42The mixture was mixed with niobium oxide in a 76:24 ratio by mass to achieve a final Nb content of 0.005 mol, and then loaded into a tube furnace (inner diameter 50 mm, length 1,000 mm) and fired while injecting oxygen at a rate of 200 mL / min. Specifically, the mixture was heated to 480°C at a heating rate of 5°C / min, maintained at that temperature for 5 hours, and then heated again to 740-780°C at a heating rate of 5°C / min and maintained at that temperature for 16 hours. The mixture was then cooled to room temperature and crushed and classified to produce a Zr-Nb-doped NCM cathode active material.

[0057] 100g of the previously prepared positive electrode active material was added to 100g of DI water, stirred for 10 minutes, and then filtered to recover the positive electrode active material. The recovered positive electrode active material was dried in a chamber above 100°C, dry mixed with H3BO3 (Aldrich), and then heat-treated in an air atmosphere at 300-350°C for 5 hours to produce the final positive electrode active material.

[0058] (Examples 2 to 4 and Comparative Examples 1 and 2: Preparation of Positive Electrode Active Materials) Monoclinic structure Nb2O5 and orthorhombic structure Nb 16.8 O 42 A positive electrode active material was prepared in the same manner as in Example 1, except that niobium oxide and niobium stearate were mixed in a ratio of 76:24 by mass to finally adjust the NbO content as shown in Table 1 below.

[0059] [Table 1]

[0060] (Characteristic analysis 1-SEM analysis) The surfaces of the positive electrode active materials prepared in Example 1 and Comparative Example 1 were subjected to SEM analysis, and the results are shown in FIGS.

[0061] Referring to FIG. 2, it can be seen that long rod-shaped primary particles were formed on the surface of the cathode active material prepared in Example 1, and the primary particles were found to have widths ranging from about 50 to 200 nm and lengths ranging from 300 to 800 nm.

[0062] 3, it can be seen that angular particles, specifically square or rectangular primary particles, were formed on the surface of the cathode active material prepared in Comparative Example 1. The primary particles were confirmed to have a width of about 200 nm to 600 nm and a length of about 200 nm to 600 nm.

[0063] (Characteristic analysis 2-FIB analysis) Cross-sectional FIB analysis was performed on the positive electrode active materials prepared in Example 1 and Comparative Example 1, and the results are shown in FIGS.

[0064] 4, the cathode active material prepared in Example 1 has acicular particles uniformly distributed over a region of approximately 1 μm thickness extending from the surface toward the core. The acicular particles have their major axes radiating from the center of the core toward the surface. The acicular particles have lengths ranging from approximately 0.8 μm to approximately 1.0 μm and widths ranging from approximately 80 nm to 200 nm.

[0065] 5, it can be seen that quadrangular particles having a square or rectangular cross section were formed in the cathode active material prepared in Comparative Example 1. The quadrangular particles were also confirmed to have a width of about 200 nm to 600 nm and a length of about 200 nm to 600 nm.

[0066] (Manufacturing coin-type half-cells) CR2032 coin cells were manufactured using the positive electrode active materials prepared in the Examples and Comparative Examples, and electrochemical evaluation was performed. The results are summarized in Table 2 below.

[0067] Specifically, the cathode active material, conductive material (Denka Black), and binder (PVDF, KF1100) were mixed in a ratio of 92.5:3.5:4 by weight, and NMP (N-Methyl-2-pyrrolidone) was added to adjust the slurry viscosity so that the solid content was approximately 30% to prepare a slurry for electrode plate production. The prepared slurry was coated onto a 15 μm thick aluminum foil using a doctor blade, dried, and then rolled. The electrode loading was approximately 14 mg / cm. 2 The rolling density is about 3.4 g / cm 3 The electrolyte was a mixture of 1M LiPF6 and EC:DMC:EMC = 3:4:3 (vol%), to which 1.5 wt% vinylene carbonate (VC) was added. A coin-shaped half cell was fabricated using a PP separator and a lithium anode (200 μm, Honzo metal), and then aged at room temperature for 10 hours.

[0068] A charge-discharge test was carried out using the coin-type half cell manufactured above.

[0069] FIG. 6 shows a cross-sectional SEM image of the positive electrode active material in a discharged state after 300 charge-discharge cycles of a coin half-cell using the positive electrode active material for a lithium secondary battery according to Example 1, and FIG. 7 shows a cross-sectional SEM image of the positive electrode active material in a discharged state after 300 charge-discharge cycles of a coin half-cell using the positive electrode active material for a lithium secondary battery according to Comparative Example 1.

[0070] Referring to FIG. 6, in the case of the coin half cell using the cathode active material for a lithium secondary battery according to Example 1, a cross section of the cathode active material in a discharged state after 300 charge / discharge cycles showed that almost no microcracks were observed in the cathode active material itself, except for cracks that were likely generated during the initial electrode preparation.

[0071] In contrast, referring to FIG. 7, in the case of the coin half cell using the positive electrode active material for a lithium secondary battery according to Comparative Example 1, it can be seen that severe cracks occurred in the positive electrode active material particles in a discharged state after 300 charge / discharge cycles.

[0072] FIG. 8 shows cross-sectional SEM images of the positive electrode and the positive electrode active material in a charged state after 300 charge-discharge cycles of a coin half-cell using the positive electrode active material for a lithium secondary battery according to Example 1.

[0073] Specifically, FIG. 8(a) shows an SEM image of a cross section of the positive electrode of a coin half-cell using the positive electrode active material for a lithium secondary battery according to Example 1 in a charged state after 300 charge-discharge cycles, and FIG. 8(b) shows an SEM image of a cross section of the positive electrode active material.

[0074] Referring to Figure 8, it can be seen that the positive electrode active material for a lithium secondary battery according to Example 1 does not significantly experience cracking even in a fully charged state where significant volume expansion occurs after charge and discharge. It can also be seen that the core of the positive electrode active material maintains its shape in a fully charged state, while the shell portion forms a comb-like shape when lithium ions are released. It is believed that the core portion, which maintains its shape, strongly supports the shell portion, which changes to a comb shape, thereby suppressing the occurrence of microcracks. Therefore, it is believed that the shortening of battery life due to the occurrence of microcracks can be prevented.

[0075] FIG. 9 shows cross-sectional SEM images of the electrode and the positive electrode active material in a charged state after 300 charge / discharge cycles of a coin half-cell using the positive electrode active material for a lithium secondary battery according to Comparative Example 1.

[0076] Referring to FIG. 9, it can be seen that the positive electrode active material for a lithium secondary battery according to Comparative Example 1 exhibits severe cracks in the electrode in a fully charged state, where significant volume expansion occurs after charging and discharging, and the gaps between the primary particles of the positive electrode active material are significantly widened, resulting in a weak strength.

[0077] The results of the charge / discharge test of the coin-hole cells using the positive electrode active materials according to Examples 1 to 4 and Comparative Examples 1 to 3 are summarized in Table 2 below.

[0078] [Table 2]

[0079] Referring to Table 2 above, it can be seen that the coin-type half cells using the positive electrode active materials according to Examples 1 to 4 have high initial charge / discharge capacity and initial efficiency, and are excellent in lifespan characteristics.

[0080] Based on this, it is believed that the cathode active material prepared according to the examples of the present invention reduces the occurrence of microcracks during charge and discharge, thereby improving the battery life and cycle characteristics.

[0081] The present invention is not limited to the above-described embodiments, but can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains should understand that the present invention can be embodied in other specific forms without changing the technical concept or essential features of the present invention.

[0082] Therefore, the above-described embodiments should be considered in all respects as illustrative and not restrictive.

Claims

1. a core; and a shell portion located on the surface of the core portion; the shell portion includes needle-shaped particles whose major axes are positioned in a direction from the core portion to the shell portion, A positive electrode active material for a lithium secondary battery, represented by the following chemical formula 1. [Chemical formula 1] Li １＋ｑ (N ｘ Co ｙ Mn ｚ ) １－ｗ (Zr ａ Nb ｂ ) ｗ O ２ In the above Chemical Formula 1, q, x, y, z, a, b, and w are 0≦q≦0.5, 0.0032<w<0.013, 0.7≦x<1.0, 0<y<0.3, 0<z<0.3, x+y+z=1, 0.2≦a≦0.7, 0.3≦b≦0.8, and a+b=1, respectively.

2. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the acicular particles have an aspect ratio of 4 to 15.

3. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the shell portion has a thickness in the range of 0.5 μm to 3 μm.

4. In a fully charged state, a lithium secondary battery using the positive electrode active material is The core portion does not undergo any change, 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the shell portion is transformed into a comb shape in which void channels are formed in a direction from the core portion to the shell portion.

5. The positive electrode active material for a lithium secondary battery according to claim 1 , further comprising a boron (B) coating layer on the outside of the shell portion.

6. The positive electrode active material for a lithium secondary battery according to claim 5, wherein the positive electrode active material for a lithium secondary battery further comprises rod-shaped primary particles located on a surface thereof.

7. 7. The positive electrode active material for a lithium secondary battery according to claim 6, wherein the rod-shaped primary particles have an average diameter of 300 nm to 800 nm and an average width of 50 nm to 200 nm.

8. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the average particle size (D50) of the positive electrode active material for a lithium secondary battery is in the range of 10 μm to 16 μm.

9. providing a metal hydroxide containing nickel, manganese, and cobalt; mixing the metal hydroxide, lithium hydroxide, niobium (Nb) oxide, and zirconium (Zr) oxide to obtain a mixture; and heat treating the mixture to form a shell portion; The method for producing a positive electrode active material for a lithium secondary battery, wherein the niobium (Nb) oxide raw material contains two or more different crystal structures.

10. The niobium (Nb) oxide is a monoclinic crystal structure of Nb ２ O ５ and Nb with an orthorhombic crystal structure １６．８ O ４２ The method for producing a positive electrode active material for a lithium secondary battery according to claim 9, comprising:

11. The Nb １６．８ O ４２ Nb ２ O ５ The method for producing a positive electrode active material for a lithium secondary battery according to claim 10, wherein the molar ratio of is in the range of 2:1 to 4:

1.

12. 10. The method of claim 9, wherein a molar ratio of zirconium (Zr) in the zirconium (Zr) oxide to niobium (Nb) in the niobium (Nb) oxide is in the range of 0.5:1 to 4.5:

1.

13. The step of heat treating the mixture to form a shell portion comprises: performing a first heat treatment at a temperature range of 400°C to 600°C for 1 hour to 5 hours; and 10. The method of claim 9, further comprising: performing a second heat treatment at a temperature in the range of 700 to 800°C for 12 to 24 hours.

14. In the step of preparing a metal hydroxide containing nickel, manganese, and cobalt, 10. The method for preparing a positive electrode active material for a lithium secondary battery according to claim 9, wherein the metal hydroxide has an average particle size (D50) ranging from 14 μm to 16 μm.

15. a current collector; and A positive electrode for a lithium secondary battery, comprising: a positive electrode active material layer for a lithium secondary battery, the positive electrode active material layer being located on at least one surface of the current collector and comprising the positive electrode active material according to claim 1 .

16. A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 15.

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