Cathode active material for sodium secondary battery, manufacturing method therefor, and sodium secondary battery comprising same

Abstract

The present invention relates to a cathode active material for a sodium secondary battery, the cathode active material comprising secondary particles composed of a group of a plurality of primary particles, wherein the primary particles comprise a nanocomposite in which a rocksalt (Fm3m) structure and a layered (R-3m) structure are mixed at the nanoscale.

Description

Cathode active material for sodium secondary batteries, method for producing the same, and sodium secondary batteries containing the same

[0001] The present invention relates to a positive electrode active material for a sodium secondary battery manufactured by a novel method with improved electrochemical properties and lifespan characteristics, a method for manufacturing the same, and a sodium secondary battery including the same.

[0002] The development of portable electronic devices such as smartphones, MP3 players, and tablet PCs has led to an explosive increase in demand for secondary batteries capable of storing electrical energy. In particular, the emergence of electric vehicles, medium- to large-scale energy storage systems, and portable devices requiring high energy density is driving demand for lithium secondary batteries.

[0003] Lithium secondary batteries have safety issues due to the high reactivity of lithium, and lithium is an expensive element, so various studies are being conducted to solve this problem.

[0004] Among these solutions, sodium secondary batteries are being studied, and sodium secondary batteries are being actively studied for use in medium and large-sized batteries for power storage and electric vehicles, as they are environmentally friendly, have excellent price competitiveness, and have high energy storage characteristics compared to lithium secondary batteries.

[0005] On the other hand, sodium secondary batteries have a disadvantage in that their lifespan characteristics are poor compared to lithium secondary batteries due to the transition of the crystal structure according to the change in the oxidation number of the central metal during charging and discharging, and their discharge capacity is low due to the high content of inactive sodium in the crystal structure.

[0006] Therefore, there is still a need for a cathode active material that can provide a sodium secondary battery with improved discharge capacity and life characteristics.

[0007] Korean Patent No. 10-2061731 (December 26, 2019)

[0008] The present invention is intended to solve the above problems, and its specific purposes are as follows.

[0009] The purpose of the present invention is to improve the electrochemical characteristics and life characteristics of a sodium secondary battery by improving the crystal structure and orientation of particles constituting the sodium secondary battery using a novel manufacturing method.

[0010] In addition, the present invention aims to provide a positive electrode active material for a sodium secondary battery having improved electrochemical properties by improving the mobility of sodium ions and preventing side reactions with an electrolyte, a method for producing the same, and a sodium secondary battery including the same.

[0011] In order to achieve the above-mentioned purpose, the present invention is implemented by an embodiment having the following configuration.

[0012] In one embodiment, a cathode active material for a sodium secondary battery according to an embodiment of the present invention includes a secondary particle formed of a group of a plurality of primary particles, and the primary particle includes a nanocomposite in which a rock salt (Fm3m) structure and a layered (R-3m) structure are mixed at a nanoscale.

[0013] In one embodiment, a cathode active material for a sodium secondary battery according to an embodiment of the present invention includes a secondary particle formed of a group of a plurality of primary particles, wherein the primary particle includes a first primary particle provided at a center of the secondary particle, and a second primary particle provided at a surface portion of the secondary particle, wherein the first primary particle is formed of an average length a1 of a major axis of the first primary particle and an average length a2 of a minor axis perpendicular to a1, wherein a1 is provided to be equal to or greater than a2, and the second primary particle is formed of an average length b1 of a major axis of the second primary particle and an average length b2 of a minor axis perpendicular to b1, wherein b1 may be provided to be greater than b2.

[0014] In one embodiment, in the diffraction peak intensities of the (0-14) plane, (0-11) plane, (006) plane, and (003) plane obtained from the SAED electron diffraction image during TEM analysis, I(0-14) > I(0-11) and I(006) > I(003).

[0015] In one embodiment, the surface portion of the secondary particle may be within 20% of the average diameter of the secondary particle in a direction from the outermost surface of the secondary particle toward the center of the secondary particle.

[0016] In one embodiment, at least some of the primary particles provided on the surface of the secondary particles are provided in a rod shape, and the rod-shaped primary particles are provided with a short axis length that is a short length passing through the center of the rod shape, and a long axis length that is longer than the short axis length and is perpendicular to the short axis length, and the long axis length is provided to be 1.5 to 25 times the short axis length, and the long axis length may be provided in a direction toward the center of the secondary particles.

[0017] In one embodiment, the primary particle includes an orientation particle formed in the form of a columnar structure having a short axis and a long axis, the orientation particle includes an orientation particle having an a-axis and a c-axis, and the length in the a-axis direction is provided to be longer than the length in the c-axis direction, and the length in the a-axis direction of the primary particle provided on the surface portion of the secondary particle among the orientation particles is provided to be longer than the length in the a-axis direction of the primary particle provided at the center of the secondary particle, and the c-axis corresponds to the

[0001] direction in an SAED pattern obtained by observing the orientation particle with a transmission electron microscope, and the a-axis may be provided to be perpendicular to the c-axis and parallel to the long axis of the orientation particle.

[0018] In one embodiment, the cathode active material is prepared by mixing a complex metal hydroxide as a precursor with a sodium compound and calcining the mixed metal hydroxide, and the oriented particles may be prepared before calcining the complex metal hydroxide.

[0019] In one embodiment, the cathode active material is prepared by mixing and calcining a complex metal hydroxide as a precursor with a sodium compound, and the complex metal hydroxide can be prepared by a co-precipitation reaction using one or more transition metal compounds.

[0020] In one embodiment, the average diameter of the secondary particles may be from 2 μm to 20 μm.

[0021] In one embodiment, it has an O3 crystal structure and can be represented by the following chemical formula 1.

[0022] [Chemical Formula 1]

[0023] [Na 1-x A1 x ][Ni y TM z A2 1-y-z ]O2

[0024] In the above chemical formula 1, TM is at least one of Mn and Fe, A1 is selected from the group consisting of Li, Ca, and combinations thereof, A2 is selected from the group consisting of Mg, Ti, Li, V, Sb, Mo, W, Zr, Sn, Y, B, Al, Co, and combinations thereof, and 0≤x≤0.1, 0.2≤y≤0.7, 0≤z≤0.8.

[0025] In one embodiment, the A1 is provided by dry doping, and the A2 is provided by dry doping or wet doping, wherein the dry doping includes dry mixing the complex metal hydroxide and a sodium compound together and then calcining, and the wet doping includes introducing a compound including the A2 together with a nickel compound including Ni and a transition metal compound including TM in the process of preparing the complex metal hydroxide by a co-precipitation reaction, and the A1 may be substituted at a Na site, and the A2 may be substituted at a Ni site or a TM site.

[0026] In one embodiment, the method for producing a cathode active material for a sodium secondary battery as described above may include a coprecipitation reaction step of putting a nickel compound including nickel (Ni) and a transition metal compound including a transition metal (TM) into a coprecipitation reactor and producing a complex metal hydroxide as a precursor through a coprecipitation reaction for 30 to 60 hours; a sintering step of mixing the complex metal hydroxide with a sodium compound and heat-treating it; and a quenching step of rapidly cooling it after the heat treatment is completed.

[0027] In one embodiment, in the co-precipitation reaction step, the process of performing the co-precipitation reaction may include removing the solution remaining inside the co-precipitation reactor to the outside of the co-precipitation reactor.

[0028] In one embodiment, the composite metal hydroxide comprises secondary particles in which a plurality of primary particles are aggregated, wherein the primary particles comprise oriented particles having a rod-shaped shape with a short axis and a long axis, and the oriented particles comprise oriented particles having an a-axis and a c-axis, and the length in the a-axis direction is provided to be longer than the length in the c-axis direction, and the oriented particles of the composite metal hydroxide can be maintained in the cathode active material manufactured after the sintering step.

[0029] In one embodiment, the c-axis corresponds to the

[0001] direction in the SAED pattern obtained by observing the oriented particle with a transmission electron microscope, and the a-axis may be provided perpendicular to the c-axis and parallel to the long axis of the oriented particle.

[0030] In one embodiment, the concentration of the complex metal hydroxide, which is a precursor prepared in the co-precipitation reaction step, is 0.3 kg. 전구체 / L 용액 It could be strange.

[0031] In one embodiment, the temperature in the firing step may be 730°C to 850°C, and the time may be 15 hours to 30 hours.

[0032] In one embodiment, in the quenching step, rapid cooling can be performed from 35°C to 20°C at a rate of 5°C / min to 16°C / min while maintaining a vacuum state in the chamber.

[0033] The present invention can obtain the following effects through the above-described examples.

[0034] The present invention can provide a positive electrode active material for a sodium secondary battery having improved orientation of primary particles and improved reversibility of insertion and de-insertion of sodium ions, a method for producing the same, and a sodium secondary battery including the same.

[0035] In addition, the present invention can provide a cathode active material for a sodium secondary battery having improved structural stability, a method for producing the same, and a sodium secondary battery including the same, which is provided in the form of a secondary particle composed of a group of primary particles produced by a novel production method.

[0036] FIG. 1 is a drawing showing a cathode active material for a sodium secondary battery according to one embodiment of the present invention.

[0037] Figure 2 is a drawing showing a cross-section of the positive electrode active material for the sodium secondary battery of Figure 1.

[0038] FIG. 3 is a schematic drawing showing primary particles provided in the center and surface portions of the secondary particles in the positive electrode active material for a sodium secondary battery of FIG. 2.

[0039] FIG. 4 is a drawing showing the orientation of primary particles provided on the surface of secondary particles in a positive electrode active material for a sodium secondary battery according to an embodiment of the present invention.

[0040] Figure 5 is an SEM image of the composite metal hydroxide and positive electrode active material of Comparative Example 1.

[0041] Figure 6 is an SEM image of the composite metal hydroxide and positive electrode active material of Example 1.

[0042] Figure 7 shows a TEM image of the cathode active material of Comparative Example 1 and the results showing the intensity ratio of crystal planes using SAED.

[0043] Figure 8 shows a TEM image of the cathode active material of Example 1 and the results showing the intensity ratio of crystal planes using SAED.

[0044] Figure 9 is a TEM image of the cathode active material of Example 1, showing the results of confirming the inner side of the primary particle existing on the surface of the secondary particle.

[0045] Figure 10 shows the XRD analysis results of the positive electrode active materials of Comparative Example 1 (left) and Example 1 (right).

[0046] Figure 11 is an SEM image of the composite metal hydroxide and positive electrode active material of Example 2.

[0047] Figure 12 shows a TEM image of the cathode active material of Example 2 and the results showing the intensity ratio of crystal planes using SAED.

[0048] Figure 13 is a TEM image of the positive electrode active material of Example 2, which is the result of confirming the inside of the primary particle existing on the surface of the secondary particle.

[0049] Figure 14 shows the XRD analysis results of the positive electrode active materials of Comparative Example 1 (left) and Example 2 (right).

[0050] Figure 15 is an SEM image of the composite metal hydroxide and positive electrode active material of Example 3.

[0051] Figure 16 shows a TEM image of the cathode active material of Example 3 and the results showing the intensity ratio of crystal planes using SAED.

[0052] Figure 17 is a TEM image of the positive electrode active material of Example 3, which is the result of confirming the inside of the primary particle existing on the surface of the secondary particle.

[0053] Figure 18 is an SEM image of the composite metal hydroxide and positive electrode active material of Example 4.

[0054] Figure 19 shows a TEM image of the cathode active material of Example 4 and the results showing the intensity ratio of crystal planes using SAED.

[0055] Figure 20 is a TEM image of the positive electrode active material of Example 4, which is the result of confirming the inside of the primary particle existing on the surface of the secondary particle.

[0056] Figure 21 is an SEM image of the composite metal hydroxide and positive electrode active material of Comparative Example 2.

[0057] Figure 22 is an SEM image of the composite metal hydroxide and positive electrode active material of Example 5.

[0058] Figure 23 shows a TEM image of the cathode active material of Comparative Example 2 and the results showing the intensity ratio of the crystal plane using SAED.

[0059] Figure 24 shows a TEM image of the cathode active material of Example 5 and the results showing the intensity ratio of crystal planes using SAED.

[0060] Figure 25 is a TEM image of the positive electrode active material of Example 5, which is the result of confirming the inside of the primary particle existing on the surface of the secondary particle.

[0061] Figure 26 shows the XRD analysis results of the positive electrode active materials of Comparative Example 2 and Example 5.

[0062] Figure 27 is an SEM image of the composite metal hydroxide and positive electrode active material of Example 6.

[0063] Figure 29 is a TEM image of the positive electrode active material of Example 6, showing the results of confirming the inner side of the primary particle present in the center of the secondary particle.

[0064] Figure 30 is an SEM image of the composite metal hydroxide and positive electrode active material of Example 7.

[0065] Figure 31 shows a TEM image of the cathode active material of Example 7 and the results showing the intensity ratio of crystal planes using SAED.

[0066] Figure 32 is a TEM image of the positive electrode active material of Example 7, showing the results of confirming the inner side of the primary particle present in the center of the secondary particle.

[0067] Figure 33 is an SEM image of the composite metal hydroxide and positive electrode active material of Example 8.

[0068] Figure 34 shows a TEM image of the cathode active material of Example 8 and the results showing the intensity ratio of crystal planes using SAED.

[0069] Figure 35 is a TEM image of the positive electrode active material of Example 8, showing the results of confirming the inner side of the primary particle present in the center of the secondary particle.

[0070] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. However, the technical concept of the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosure is thorough and complete and to sufficiently convey the spirit of the present invention to those skilled in the art.

[0071] In this specification, when a component is referred to as being on another component, it means that it can be formed directly on the other component, or a third component may be interposed between them. In addition, in the drawings, the thicknesses of films and regions are exaggerated for the purpose of effectively explaining the technical contents.

[0072] Also, although terms such as first, second, and third have been used to describe various components in various embodiments of this specification, these components should not be limited by these terms. These terms are only used to distinguish one component from another. Thus, what is referred to as a first component in one embodiment may be referred to as a second component in another embodiment. Each embodiment described and illustrated herein also includes its complementary embodiments. Also, the term "and / or" has been used herein to mean including at least one of the components listed before and after.

[0073] In the specification, singular expressions include plural expressions unless the context clearly dictates otherwise. Furthermore, terms such as "comprises" or "has" are intended to specify the presence of a feature, number, step, component, or combination thereof described in the specification, but should not be construed as excluding the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0074] In addition, when describing the present invention below, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

[0075]

[0076] FIG. 1 is a drawing showing a cathode active material for a sodium secondary battery according to an embodiment of the present invention. FIG. 2 is a drawing showing a cross-section of the cathode active material for a sodium secondary battery of FIG. 1. FIG. 3 is a drawing schematically showing primary particles provided in the center and surface portions of secondary particles in the cathode active material for a sodium secondary battery of FIG. 2. FIG. 4 is a drawing showing the orientation of primary particles provided in the surface portions of secondary particles in the cathode active material for a sodium secondary battery according to an embodiment of the present invention.

[0077] Referring to FIG. 1, the present invention relates to a cathode active material for a sodium secondary battery including a secondary particle (200) formed of a group of a plurality of primary particles (100), wherein the primary particle (100) may include a nanocomposite in which a rock salt (Fm3m) structure and a layered (R-3m) structure are mixed at a nanoscale.

[0078] The above-mentioned cathode active material for a sodium secondary battery may have an O3 crystal structure, including the above-mentioned nanocomposite, and in the diffraction peak intensities of the (0-14) plane, (0-11) plane, (006) plane, and (003) plane obtained from the SAED electron diffraction image during TEM analysis, I(0-14) > I(0-11) and I(006) > I(003).

[0079] In the cathode active material according to one embodiment of the present invention, the primary particle (100) may include a rock salt region whose crystal structure includes a rock salt structure and a layered region whose crystal structure includes a layered structure. The cross-sectional area of ​​the rock salt region is 1 nm. 2 Within 10,000 nm 2 It can be. Specifically, the cross-sectional area of ​​the above rock salt region is 1 nm 2 Within 2,500 nm 2 It could be.

[0080] The above nanocomposite may be provided on the inside or outside surface of the primary particle (100) and the inside or outside surface of the secondary particle (200). Specifically, the cathode active material for a sodium secondary battery according to the present embodiment includes a nanocomposite in which a rock salt structure and a layered structure are mixed, and the nanocomposite does not distinguish between the inside or outside surface of the secondary particle and the primary particle, and may be found both on the inside or outside surface of the secondary particle and the inside or outside surface of the primary particle. The nanocomposite may be irregularly provided on the inside or outside surface of the primary particle (100) in a form having a nanoscale size.

[0081] Through the coprecipitation reaction and calcination reaction, the as-prepared cathode active material develops into an overall layered structure. Typically, when a secondary battery is manufactured using a cathode active material for a sodium secondary battery and multiple charge / discharge cycles are performed, a rock salt crystal structure is formed on the surface due to a degradation phenomenon occurring on the surface of the secondary particles or primary particles. This is caused by oxygen loss of the secondary particles or primary particles. On the other hand, in the present invention, a rock-salt nanocomposite structure in which a layered structure and a rock salt structure are mixed can be provided in the as-prepared cathode active material using a novel coprecipitation reaction and calcination reaction, and the layered structure and the rock salt structure can be controlled in a nanoscale size to improve the physical properties of the cathode active material of the present invention.

[0082] In addition, the cathode active material for a sodium secondary battery according to the present embodiment can exhibit a rock salt structure mixed not only on the surface but also inside the primary particle (100) and the secondary particle (200) by controlling the manufacturing method. By controlling the rock salt structure at the nanoscale, the physical strength of the primary particle (100) and the secondary particle (200) can be improved while preventing a decrease in electrochemical efficiency due to the rock salt structure. Accordingly, by preventing structural collapse that may occur during the insertion and deintercalation process of sodium ions larger than conventional lithium ions, the long-term cycle characteristics of the cathode active material for a sodium secondary battery can be improved.

[0083] Referring to FIGS. 2 to 4, a cathode active material for a sodium secondary battery according to one embodiment of the present invention includes a secondary particle (200) formed of a group of a plurality of primary particles (100), and the secondary particle (200) may be provided as a central portion (A) and a surface portion (B) of the secondary particle. The primary particle (100) may include a first primary particle (110) provided in the central portion (A) of the secondary particle (200), and a second primary particle (120) provided in the surface portion (B) of the secondary particle (200). The first primary particle (110) is arranged and provided at the center (A) of the secondary particle (200), and the second primary particle (120) is arranged to surround the first primary particle (110) and can be provided at the surface (B) of the secondary particle (200).

[0084] The first primary particle (110) is composed of a1, which is an average length of the major axis of the first primary particle (110), and a2, which is an average length of the minor axis perpendicular to a1, wherein a1 is provided to be equal to or greater than a2 (a1 ≥ a2), and the second primary particle (120) is composed of b1, which is an average length of the major axis of the second primary particle (120), and b2, which is an average length of the minor axis perpendicular to b1, wherein b1 may be provided to be greater than b2 (b1 > b2).

[0085] The above second primary particles (120) may be formed in a rod shape whose cross-section is formed by an average length of the major axis b1 and an average length of the minor axis b2 perpendicular to the b1. At least a portion of the second primary particles (120) may be aligned in a radial direction. The radial direction means that the second primary particles (120) are aligned in a direction (R) from the center (c) of the secondary particles (200) toward the outermost surface of the secondary particles (200), as shown in FIG. 4.

[0086] For example, the second primary particle (120) may be aligned so that the long axis of the second primary particle (120) is aligned parallel to the radial direction, thereby facilitating diffusion of sodium ions from the surface to the inside of the secondary particle (200). In addition, the second primary particle (120) may be aligned parallel to the direction of movement of the sodium ions. Accordingly, by providing the orientation direction of the second primary particle (120) and the direction of movement of the sodium ions to be parallel, the volume change of the secondary particle (200) due to the expansion and contraction of the secondary particle (200) caused by reversible charge and discharge during the cycle of the sodium secondary battery is mitigated, and cracks between the primary particles (100) that may occur due to the volume change of the primary particle (100) are reduced, thereby improving the life characteristics of the secondary battery. For example, the direction (R) from the center (c) of the secondary particle (200) toward the surface of the secondary particle (200) may be parallel to the a-axis direction of the primary particle (100), and the c-axis direction of the primary particle (100) may be a direction perpendicular to the a-axis direction.

[0087] The surface portion (B) of the secondary particle (200) may be within 20% of the average diameter of the secondary particle (200) in a direction from the outermost surface of the secondary particle (200) toward the center (c) of the secondary particle (200). For example, the thickness of the surface portion (B) may be 20% of the average diameter of the primary particle (200), and the second primary particle (120) may be arranged on the surface portion (B) in a direction toward the center (c) of the secondary particle (200).

[0088] At least a portion of the second primary particle (120), which is a primary particle (100) provided on the surface portion (B) of the secondary particle (200), is provided in a rod shape, and the rod-shaped primary particle may be provided with a short axis length (b2) that is a short length passing through the center of the rod shape, and a long axis length (b1) that is longer than the short axis length (b2) and is perpendicular to the short axis length (b2). The long axis length (b1) is provided to be 1.5 to 25 times the short axis length (b2), and the long axis length (b1) may extend in a direction toward the center of the secondary particle (200).

[0089] If the major axis length (b1) is less than 1.5 times the minor axis length (b2), a space is formed between the second primary particles (200), and cracks extending from the surface of the secondary particles (200) to the center (c) are likely to form after a long-term cycle, and if the major axis length (b1) is more than 25 times the minor axis length (b2), problems such as the second primary particles (120) being easily destroyed by external force may occur. Specifically, the major axis length (b1) may be 1.5 to 20 times, or 1.5 to 15 times, or 1.5 to 10 times, or 2 to 10 times, relative to the minor axis length (b2).

[0090] In the second primary particle (120), the average length of b1 may be 0.1 µm to 2.0 µm. By controlling the lengths of b1 and b2 of the second primary particle (120) within the aforementioned range, the orientation of the second primary particle (120) constituting the secondary particle (200) may be further improved. Specifically, the range of the average length of b1 may be 0.015 µm to 0.8 µm, or 0.02 µm to 0.6 µm, or 0.03 µm to 0.5 µm, or 0.03 µm to 0.25 µm.

[0091] In the second primary particle (120), the average length of b2 may be 2.0 μm or less. If the length of b2 of the second primary particle (120) exceeds 2.0 μm, the life characteristics of the secondary battery may deteriorate, which may be problematic. Specifically, the b2 may be 0.005 μm to 2.0 μm, or 0.01 μm to 2.0 μm, 0.05 μm to 2.0 μm, 0.1 μm to 2.0 μm, 0.05 μm to 1.5 μm, 0.05 μm to 1.2 μm, or 0.1 μm to 1.2 μm.

[0092] The second primary particle (120) is provided with the lengths b1 and b2 within the aforementioned range, so that the orientation of the second primary particle (120) on the surface portion (B) of the secondary particle (200) is improved, and the second primary particles (120) are aligned more densely, thereby improving structural stability and preventing the electrolyte from sinking into the center portion (A) of the secondary particle (200).

[0093] The primary particle (100) may be formed in the form of a columnar structure having a short axis and a long axis, and may include an orientation particle aligned such that the direction of the long axis is toward the center (c) of the secondary particle (200). The orientation particle may include an orientation particle having an a-axis and a c-axis, and the length in the a-axis direction may be longer than the length in the c-axis direction, and the length in the a-axis direction of the primary particle provided at the center of the secondary particle among the orientation particles may be longer than the length in the a-axis direction of the primary particle provided at the surface portion of the secondary particle. The c-axis corresponds to the

[0001] direction in an SAED pattern obtained by observing the orientation particle with a transmission electron microscope, and the a-axis may be provided perpendicular to the c-axis and parallel to the long axis of the orientation particle.

[0094] In the cathode active material according to the present embodiment, the second primary particle (120) may include an oriented particle having an a-axis and a c-axis aligned with a high degree of orientation, and the a-axis of the second primary particle (120) may be provided to face a direction toward the center (c) of the secondary particle (200).

[0095] The above cathode active material is prepared by mixing and calcining a complex metal hydroxide as a precursor with a sodium compound, and the oriented particles may be prepared before calcining the complex metal hydroxide. The above cathode active material is prepared by mixing and calcining a complex metal hydroxide as a precursor with a sodium compound, and the complex metal hydroxide may be prepared by a coprecipitation reaction using one or more transition metal compounds.

[0096] In the positive electrode active material for a sodium secondary battery according to the present embodiment, the oriented particles, which are primary particles aligned to have the high orientation, can be already formed at the stage of the composite metal hydroxide, which is a precursor, before sintering, and the oriented particles can be maintained as is even after the subsequent heat treatment at high temperature, and can be maintained in the sintered body, the positive electrode active material for a sodium secondary battery.

[0097] The average diameter of the secondary particles (200) may be 2 ㎛ to 20 ㎛. If the average diameter of the secondary particles is less than 2 ㎛, the surface area of ​​the positive electrode active material in contact with the electrolyte increases, which may rapidly cause deterioration of the secondary battery during the cycle. If the average diameter exceeds 20 ㎛, the specific capacity of the positive electrode using the positive electrode active material may decrease. Specifically, the average diameter of the secondary particles (200) may be 2 ㎛ to 18 ㎛, or 2 ㎛ to 15 ㎛, or 3 ㎛ to 15 ㎛, or 3 ㎛ to 12 ㎛.

[0098] A cathode active material for a sodium secondary battery according to an embodiment of the present invention has an O3 crystal structure and can be represented by the following chemical formula 1.

[0099] [Chemical Formula 1]

[0100] [Na 1-x A1 x ][Ni y TM z A2 1-y-z ]O2

[0101] In the above chemical formula 1, TM is at least one of Mn and Fe, A1 is selected from the group consisting of Li, Ca, and combinations thereof, A2 is selected from the group consisting of Mg, Ti, Fe, Li V, Sb, Mo, W, Zr, Sn, Y, B, Al, Co, and combinations thereof, and 0≤x≤0.1, 0.2≤y≤0.7, 0≤z≤0.8.

[0102] The above chemical formula 1 can be prepared by mixing and calcining a complex metal hydroxide, which is a precursor containing nickel (Ni) and a transition metal (TM), with a sodium compound. In the above chemical formula 1, A1 can be substituted at the Na site, and A2 can be substituted at the Ni site or the TM site.

[0103] In the above chemical formula 1, A1 is provided by dry doping, and A2 can be provided by dry doping or wet doping. The dry doping may include dry mixing the complex metal hydroxide and a sodium compound and then calcining, and the wet doping may include introducing a compound including A2 together with a nickel compound including Ni and a transition metal compound including TM during the process of preparing the complex metal hydroxide by a co-precipitation reaction.

[0104] In the above chemical formula 1, A1 can substitute for a sodium ion site in the sodium layer. A1 is prepared by preparing the complex metal hydroxide by a co-precipitation reaction, and then adding the complex metal hydroxide in powder form together with a sodium compound, and the content of the complex metal hydroxide can be reduced by the mole number of A1 added.

[0105] The above A2 can control the morphology of the complex metal hydroxide by chelating Ni or TM. The complex metal hydroxide can be formed of spherical secondary particles formed by agglomeration of multiple primary particles, and the above A2 can control the shape and orientation of the primary particles of the complex metal hydroxide during the co-precipitation reaction process, thereby improving the structural stability of the secondary particles.

[0106]

[0107] According to another aspect of the present invention, an embodiment of the present invention includes a method for producing a cathode active material for a sodium secondary battery as described above. The method for producing a cathode active material for a sodium secondary battery may include a coprecipitation reaction step of putting a nickel compound including nickel (Ni) and a transition metal compound including a transition metal (TM) into a coprecipitation reactor and producing a complex metal hydroxide as a precursor through a coprecipitation reaction for 30 to 60 hours; a sintering step of mixing the complex metal hydroxide with a sodium compound and heat-treating it; and a quenching step of rapidly cooling it after the heat treatment is completed.

[0108] In the above coprecipitation reaction step, the process of performing the coprecipitation reaction may include removing the solution remaining inside the coprecipitation reactor to the outside of the coprecipitation reactor. The composite metal hydroxide may be provided in the form of secondary particles in which a plurality of primary particles are aggregated through the coprecipitation reaction. The coprecipitation reaction step may perform a solid-liquid coprecipitation reaction. The solid-liquid coprecipitation reaction may be performed by removing the solution accumulated inside the coprecipitation reactor during the process of performing the coprecipitation reaction. When removing the solution from the coprecipitation reactor, the precursor particles in a solid state generated during the coprecipitation reaction process may be maintained in the coprecipitation reactor, while only the solvent may be removed. Therefore, the weight ratio of the precursor to the solution continuously increases within the coprecipitation reactor, thereby inducing the precursor particles to grow at a low rate. In the above-described high-liquidity co-precipitation reaction process, the growth rate of the precursor particles is performed at a lower rate than in a general notebook reaction, so that the primary particles can be arranged in a column shape and grown while being aligned in one direction, and at the same time, the primary particles can be aggregated to have a high orientation during the agglomeration process, thereby improving the alignment and orientation of the primary particles within the secondary particles.

[0109] In the above coprecipitation reaction step, the solidification coprecipitation reaction can be performed for 30 to 60 hours. In addition, after the solidification coprecipitation reaction is completed, the complex metal hydroxide precursor is added to the coprecipitation reactor at a concentration of 0.3 kg in the solution. 전구체 / L 용액 It can be prepared in high concentrations. Specifically, the concentration of the precursor is 0.3 kg. 전구체 / L 용액 Inland 0.9 kg 전구체 / L 용액It can be. After the above-mentioned high-liquidity coprecipitation reaction is completed, by maintaining the concentration within the coprecipitation reactor at the aforementioned concentration, the morphology of the primary particles constituting the composite metal oxide can be controlled to produce a columnar shape extending in one direction, and the primary particles can have a high orientation so that they face the center of the secondary particles.

[0110] Typically, a coprecipitation reaction involves circulating a solution containing a transition metal and ammonia, which is introduced into a coprecipitation reactor, to the outside of the reactor to increase the concentration of the solution. Therefore, a difference in solution concentration occurs between the inside and outside of the coprecipitation reactor, which hinders the uniform growth of primary particles during the production of the precursor, the complex metal hydroxide. Consequently, the orientation of the produced primary particles is also impaired. Furthermore, the process of circulating the solution to the outside of the coprecipitation reactor causes non-uniformity in the transition metal-ammonia complex ion formation reaction, leading to discontinuous and non-uniform coprecipitation. This process inhibits the growth of oriented particles.

[0111] On the other hand, the coprecipitation reaction according to the embodiment of the present invention is performed as a solid-liquid coprecipitation reaction, and the solid-liquid coprecipitation reaction can remove only the solvent from the internal solution in real time and continuously without circulating the solution inside the coprecipitation reactor to the outside. Accordingly, the overall concentration of the solution that reacts inside the coprecipitation reactor to produce a complex metal hydroxide as a precursor is maintained uniformly, and the transition metal-ammonia chelating reaction and the hydroxide group substitution reaction can occur continuously. Therefore, the solid-liquid coprecipitation reaction can promote the continuous growth of oriented particles and improve the orientation of the primary particles constituting the complex metal hydroxide.

[0112] The above composite metal hydroxide may include secondary particles in which a plurality of primary particles are aggregated, wherein the primary particles may include oriented particles having a rod-shaped shape with a short axis and a long axis. The oriented particles may include oriented particles having an a-axis and a c-axis, and the length in the a-axis direction may be longer than the length in the c-axis direction. In addition, the oriented particles of the composite metal hydroxide may be maintained in a similar morphology in the positive electrode active material manufactured after the sintering step of heat-treating at a high temperature. The c-axis corresponds to the

[0001] direction in an SAED pattern obtained by observing the oriented particles with a transmission electron microscope, and the a-axis may be provided perpendicular to the c-axis and parallel to the long axis of the oriented particles.

[0113] The above composite metal hydroxide may be provided with primary particles in the form of rods or columns with a small length relative to the c-axis direction, and the primary particles may be provided with a high degree of orientation such that the a-axis points toward the center of the secondary particles. Since the composite metal hydroxide is provided with a high degree of structural stability, even after the sintering step, the primary particles only slightly expand and do not change significantly, and the morphology and arrangement of the primary particles may be directly reflected in the positive electrode active material.

[0114] In the above-mentioned sintering step, the temperature may be 730 ℃ to 850 ℃, and the time may be 15 hours to 30 hours. If the temperature is lower than 730 ℃ in the above-mentioned sintering step, the sodium compound and the composite metal hydroxide may not be sufficiently uniformly mixed, which may be problematic, and if it exceeds 850 ℃, the volume expansion of the primary particles of the positive electrode active material may occur excessively, which may deteriorate the orientation of the primary particles. In the above-mentioned sintering step, by performing the above-mentioned temperature range for the above-mentioned time, a positive electrode active material for a sodium secondary battery having high performance can be manufactured, and specifically, the best performance is exhibited at 800 ℃. In the above-mentioned sintering step, the temperature may be increased at a rate of 1 ℃ / min to 5 ℃ / min under temperature conditions of 20 ℃ to 35 ℃. If the heating rate in the above-mentioned sintering step is less than 1 ℃ / min, the process efficiency during sintering is low, which is problematic, and if it exceeds 5 ℃ / min, heat is rapidly applied to the positive electrode active material, which may impair the structural stability of the positive electrode active material.

[0115] In the above quenching step, rapid cooling can be performed from 35 ℃ to 20 ℃ at a rate of 5 ℃ / min to 16 ℃ / min while maintaining a vacuum state in the chamber. If the heating rate in the quenching step is less than 5 ℃ / min, sodium ions may escape from the positive electrode active material and the layered structure may collapse, and if it exceeds 16 ℃ / min, problems such as impurities being formed on the surface of the primary particles may occur. Specifically, the heating rate in the quenching step may be 10 ℃ / min to 16 ℃ / min, or 10 ℃ / min to 15 ℃ / min, or 12 ℃ / min to 15 ℃ / min, or 12 ℃ / min to 14 ℃ / min.

[0116] Alternatively, wet doping may be further included in the co-precipitation reaction step. The wet doping may be performed by introducing a heterogeneous element compound containing a heterogeneous element other than Ni, Mn, or Fe into the co-precipitation reactor. The heterogeneous element compound may be at least one of a metal hydroxide, a metal oxide, and a metal sulfide. The heterogeneous element may be at least one of Sb, Mo, W, Zr, Ti, Sn, Y, Mg, B, Al, Fe, and Co.

[0117] The above wet doping can be performed by a similar process as general co-precipitation synthesis by preparing a synthesis process, but there is a difference in that the heterogeneous element compound is dissolved in a transition metal aqueous solution or a caustic soda aqueous solution by adding it to the co-precipitation reactor. A solution containing the heterogeneous element compound is continuously introduced into the co-precipitation reactor, but the introduction ratio or pH or ammonia concentration needs to be adjusted differently depending on the type of the heterogeneous element. Through the wet doping, the heterogeneous element can perform a chelating reaction with Ni, Mn or Fe elements, and the precursor composite metal hydroxide produced thereby can form fine primary particles while further extending the length of the primary particles and allowing the primary particles to have a high orientation toward the center of the secondary particles. In addition, when a heterogeneous element is included in the composite metal hydroxide through the wet doping, it acts as a particle coarsening inhibitor in the subsequent sintering step, so that the oriented particles shown in the composite metal hydroxide can be well maintained in the cathode active material manufactured through sintering.

[0118]

[0119] According to another aspect of the present invention, the method for manufacturing a cathode active material for a sodium secondary battery according to the present invention may further include dry doping in the sintering step. The dry doping may be performed in the sintering step by mixing the composite metal hydroxide and the sodium compound with a doping element compound containing a doping element.

[0120] In the above dry doping, the doping element can be doped into a nickel layer, a transition metal layer, and a sodium ion layer in a positive electrode active material for a sodium secondary battery having a layered structure.

[0121] When the above doping element is doped into the transition metal layer, the ratio of the complex metal hydroxide may be reduced by the molar fraction of the doping element added in the sintering step and mixed with the sodium compound. For example, when the doping element M1 is doped into the transition metal layer in the ratio of m1, the ratio of the complex metal hydroxide, the doping element, and the sodium compound may be mixed in a ratio of 1-m1: m1: 1.01. The doping element doped into the transition metal layer may be at least one of Li, Fe, Ca, Mg, Ti, Co, and Sn. When the doping element is doped into the transition metal layer, the stability and rate characteristics can be improved by increasing the interlayer distance while improving the bonding strength.

[0122] When the above doping element is doped into the sodium ion layer, the ratio of the sodium compound can be reduced by the molar fraction by considering the oxidation number of the doping element added in the firing step. For example, M2, where the oxidation number of the doping element is +1 When doping the sodium ion layer with a ratio of m2, the composite metal hydroxide, doping element, and sodium compound may be mixed in a ratio of 1: m2: 1.01-m2. For example, when doping M3, whose oxidation number of the doping element is +2, into the sodium ion layer with a ratio of m3, the composite metal hydroxide, doping element, and sodium compound may be mixed in a ratio of 1: m3: 1.01-2m3. The doping element doped into the sodium ion layer may be at least one of Li and Ca. When the sodium ion layer is doped with a doping element, when the sodium ion escapes during the charge / discharge process, the doping element fills the space, thereby preventing the layer from collapsing and improving stability.

[0123] According to another embodiment of the present invention, the method for producing a cathode active material for a sodium secondary battery of the present invention may further include using a seed precursor in the coprecipitation reaction step. The coprecipitation reaction step may be sequentially performed as a first coprecipitation reaction and a second coprecipitation reaction, and after producing the seed precursor through the first coprecipitation reaction, the second coprecipitation reaction may be performed using the seed precursor, thereby producing a composite metal hydroxide.

[0124] The seed precursor has an average diameter of 1.5 to 3.5 μm, and can be manufactured by performing the first coprecipitation reaction in the same manner as the method for manufacturing the composite metal hydroxide, but shortening the time to about 5 to 10 hours. The second coprecipitation reaction can be performed by stirring a coprecipitation reactor equipped with the seed precursor and distilled water, and after stirring for a certain period of time, continuously adding a transition metal aqueous solution, an ammonia aqueous solution, and a caustic soda aqueous solution to the coprecipitation reactor. In the second coprecipitation reaction, primary particles can be formed in an aligned manner on the surface of the seed precursor, and the seed precursor can induce the primary particles to have improved orientation.

[0125]

[0126] Hereinafter, examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the scope of the present invention is not limited by the following examples.

[0127]

[0128] 1. Manufacturing of sodium cathode active material

[0129]

[0130] Comparative Example 1 (Na-NM5050 (layered))

[0131] A nickel sulfate aqueous solution (NiSO4·6H2O, Daejung Gold) and a manganese sulfate aqueous solution (MnSO4·H2O, Daejung Gold) were mixed so that the molar ratio of nickel (Ni) and manganese (Mn) was 50:50 to prepare a metal solution with a concentration of 2.5 M. N2 gas was introduced at a rate of 150 L min into a co-precipitation reactor (capacity 2000 L, output of a rotary motor of 30 kW or more) equipped with 500 L of distilled water. -1 The metal solution was prepared by supplying at a rate of , stirring at 250 rpm while maintaining the temperature of the co-precipitation reactor at 50 ℃. The prepared metal solution was 40 L hr -1 , 20M concentrated ammonia solution (NH4OH, Daejung Chemical) is 4.5L hr -1 , 25 L hr of 6M sodium hydroxide solution (NaOH, Daejung Chemical) -1 Each was continuously fed into the co-precipitation reactor for 20 hours. The pH in the co-precipitation reactor was maintained at 10 to 12, and the co-precipitation reaction was performed to produce the precursor, a complex metal hydroxide. The concentration of the precursor in the solution synthesized through the co-precipitation reaction was 0.1 kg. 전구체 / L 용액 It corresponds to .

[0132] The sintering process was performed by mixing the complex metal hydroxide precursor synthesized by the aforementioned coprecipitation reaction with a sodium compound (NaOH, Daejung gold) and performing high-temperature heat treatment in an oxygen atmosphere. The precursor complex metal hydroxide and the sodium compound were mixed in a molar ratio of 1:1.01 to prepare a mixture, and the prepared mixture was placed in a sintering furnace, heated to 800 ℃ at a rate of 2 ℃ / min, and maintained at 800 ℃ for 24 hours. During the sintering, oxygen gas was passed through the sintering furnace at a flow rate of 1 ml / min. After the sintering process was completed, the prepared sintered body was rapidly cooled from 800 ℃ to 30 ℃ at a rate of 4 ℃ / min to 5 ℃ / min in a vacuum condition in a chamber to prepare a positive electrode active material, which is a sodium metal oxide.

[0133]

[0134] Example 1 (Na-NM5050 (rock-salt nanocomposite))

[0135] A nickel sulfate aqueous solution (NiSO4·6H2O, Daejung Gold) and a manganese sulfate aqueous solution (MnSO4·H2O, Daejung Gold) were mixed so that the molar ratio of nickel (Ni) and manganese (Mn) was 50:50 to prepare a metal solution with a concentration of 2.5 M. N2 gas was introduced at a rate of 150 L min into a co-precipitation reactor (capacity 2000 L, output of a rotary motor of 30 kW or more) equipped with 500 L of distilled water. -1 The metal solution was prepared by supplying at a rate of , stirring at 250 rpm while maintaining the temperature of the co-precipitation reactor at 50 ℃. The prepared metal solution was 40 L hr -1 , 20M concentrated ammonia solution (NH4OH, Daejung Chemical) is 4.5L hr -1 , 25 L hr of 6M sodium hydroxide solution (NaOH, Daejung Chemical) -1Each of them was continuously fed into the co-precipitation reactor for 50 hours, while simultaneously removing the accumulated solution inside the co-precipitation reactor. At this time, only the solution in the co-precipitation reactor was removed, and the solid precursor particles were not removed. The pH inside the co-precipitation reactor was maintained at 10 to 12, and the co-precipitation reaction was performed to manufacture the precursor, a complex metal hydroxide. The concentration of the precursor content in the solution synthesized through the co-precipitation reaction was 0.5 kg. 전구체 / L 용액 It corresponds to .

[0136] The sintering process was performed by mixing the complex metal hydroxide precursor synthesized by the aforementioned solid-liquid coprecipitation reaction with a sodium compound (NaOH, Daejung gold) and performing high-temperature heat treatment in an oxygen atmosphere. The precursor complex metal hydroxide and the sodium compound were mixed in a molar ratio of 1:1.01 to prepare a mixture, and the prepared mixture was placed in a sintering furnace, heated to 800 ℃ at a rate of 2 ℃ / min, and maintained at 800 ℃ for 24 hours. During the sintering, oxygen gas was passed through the sintering furnace at a flow rate of 1 ml / min. After the sintering process was completed, the prepared sintered body was placed in a chamber under vacuum conditions and rapidly cooled from 800 ℃ to 30 ℃ for 1 hour at a rate of 12 ℃ / min to 14 ℃ / min while maintaining the vacuum, thereby preparing a cathode active material, which is a sodium metal oxide.

[0137]

[0138] Table 1 below shows the positive electrode active materials of Comparative Example 1 and Example 1.

[0139] Classification Chemical formula NiMn Comparative example 1 Na[Ni 0.50 Mn 0.50 ]O2Ni 50mol%Mn 50mol%Example 1Na[Ni 0.50 Mn 0.50 ]O2Ni 50mol%Mn 50mol%

[0140]

[0141] Example 2 (Mg 7% wet-doped Na-NM5050)

[0142] A nickel sulfate aqueous solution (NiSO4·6H2O, Daejung Gold), a manganese sulfate aqueous solution (MnSO4·H2O, Daejung Gold), and a magnesium sulfate aqueous solution (MgSO4·6H2O, Daejung Gold) were mixed so that the molar ratio of nickel (Ni), manganese (Mn), and magnesium (Mg) was 43:50:7, thereby preparing a metal solution having a concentration of 2.5 M. A cathode active material was prepared in the same manner as in Comparative Example 1, except that the prepared metal solution was placed in a coprecipitation reactor to perform a coprecipitation reaction, and the rapid cooling conditions were performed after the following calcination process was completed.

[0143] In Example 2, after the firing process was completed, the manufactured sintered body was placed in a chamber under vacuum conditions and rapidly cooled from 800°C to 30°C for 1 hour at a rate of 12°C / min to 14°C / min while maintaining the vacuum state, thereby manufacturing a cathode active material, which is sodium metal oxide.

[0144]

[0145] Example 3 (Ti 1% wet-doped Na-NM5050)

[0146] A nickel sulfate aqueous solution (NiSO4·6H2O, Daejung Chemical), a manganese sulfate aqueous solution (MnSO4·H2O, Daejung Chemical), and a titanium sulfate aqueous solution (TiSO4·6H2O, Junsei Chemical) were mixed so that the molar ratio of nickel (Ni), manganese (Mn), and titanium (Ti) was 49:50:1 to prepare a metal solution with a concentration of 2.5 M. A cathode active material was prepared in the same manner as in Comparative Example 1, except that the prepared metal solution was placed in a co-precipitation reactor to perform a co-precipitation reaction, and the rapid cooling conditions performed after the following calcination process were completed. A cathode active material was prepared in the same manner as in Comparative Example 1.

[0147] In Example 3, after the firing process was completed, the manufactured sintered body was placed in a chamber under vacuum conditions and rapidly cooled from 800°C to 30°C for 1 hour at a rate of 12°C / min to 14°C / min while maintaining the vacuum state, thereby manufacturing a cathode active material, which is sodium metal oxide.

[0148]

[0149] Example 4 (Ca 1% dry-doped Na-NM5050)

[0150] The composite metal hydroxide precursor synthesized by the solid-liquid coprecipitation reaction manufactured in Comparative Example 1 was used in the same manner, and a mixture was prepared by mixing the precursor composite metal hydroxide, calcium, and sodium compounds in a molar ratio of 1:0.01:0.99 during the following calcination process. The prepared mixture was calcined in the same manner as in Comparative Example 1, but only the rapid cooling conditions performed after the following calcination process were different to manufacture a cathode active material.

[0151] In Example 4, after the firing process was completed, the manufactured sintered body was placed in a chamber under vacuum conditions and rapidly cooled from 800°C to 30°C for 1 hour at a rate of 12°C / min to 14°C / min while maintaining the vacuum state, thereby manufacturing a cathode active material, which is sodium metal oxide.

[0152]

[0153] Table 2 below shows the positive electrode active materials of Comparative Example 1 and Examples 2 to 4.

[0154] Classification Chemical formula NiMn Doping element Doping method Comparative example 1 Na[Ni 0.50 Mn 0.50 ]O2Ni 50mol%Mn 50mol%--Example 2Na[Ni 0.43 Mg 0.07 Mn 0.50 ]O2Ni 43mol%Mn 50mol%Mg 7mol%wet-dopingExample 3Na[Ni 0.49 Mg 0.50 Ti 0.01]O2Ni 49mol%Mn 50mol%Ti 1mol%wet-dopingExample 4Na 0.98 Ca 0.01 [Ni 0.50 Mn 0.50 ]O2Ni 50mol%Mn 50mol%Ca 1mol%dry-doping

[0155]

[0156] Comparative Example 2 (Na-NFM402040 (layered))

[0157] A nickel sulfate aqueous solution (NiSO4·6H2O, Daejung Gold), iron (II) sulfate aqueous solution (FeSO4·7H2O, Daejung Gold), and manganese sulfate aqueous solution (MnSO4·H2O, Daejung Gold) were mixed so that the molar ratio of nickel (Ni), iron (Fe), and manganese (Mn) was 40:20:40, thereby preparing a metal solution with a concentration of 2.5 M. N2 gas was introduced at a rate of 150 L min into a co-precipitation reactor (capacity 2000 L, output of a rotation motor of 30 kW or more) equipped with 500 L of distilled water. -1 The mixture was supplied at a rate of 1000 rpm and stirred at 250 rpm while maintaining the temperature of the co-precipitation reactor at 50°C. The prepared metal solution was 40 L hr -1 , 20 M concentration ammonia solution (NH4OH, Daejung Chemical) is 4.5 L hr -1 , 25 L hr of 6 M sodium hydroxide solution (NaOH, Daejung Chemical) -1 Each was continuously fed into the co-precipitation reactor for 20 hours. The pH in the co-precipitation reactor was maintained at 9.5 to 12, and the co-precipitation reaction was performed to produce the precursor, a complex metal hydroxide. The concentration of the precursor in the solution synthesized through the co-precipitation reaction was 0.1 kg. 전구체 / L 용액 It corresponds to .

[0158] The sintering process was performed by mixing the complex metal hydroxide precursor synthesized by the aforementioned coprecipitation reaction with a sodium compound (NaOH, Daejung gold) and performing a high-temperature heat treatment in an oxygen atmosphere. The precursor complex metal hydroxide and the sodium compound were mixed in a molar ratio of 1:1.01 to prepare a mixture, and the prepared mixture was placed in a sintering furnace, heated to 800 ℃ at a rate of 2 ℃ / min, and maintained at 800 ℃ for 24 hours. During the sintering, oxygen gas was passed through the sintering furnace at a flow rate of 1 ml / min. After the sintering process was completed, the prepared sintered body was rapidly cooled from 800 ℃ to 30 ℃ at a rate of 4 ℃ / min to 5 ℃ / min in a vacuum chamber while maintaining the vacuum state, thereby preparing a cathode active material, which is a sodium metal oxide.

[0159]

[0160] Example 5 (Na-NFM402040)

[0161] A nickel sulfate aqueous solution (NiSO4·6H2O, Daejung Gold), iron (II) sulfate aqueous solution (FeSO4·7H2O, Daejung Gold), and manganese sulfate aqueous solution (MnSO4·H2O, Daejung Gold) were mixed so that the molar ratio of nickel (Ni), iron (Fe), and manganese (Mn) was 40:20:40, thereby preparing a metal solution with a concentration of 2.5 M. N2 gas was introduced at a rate of 150 L min into a co-precipitation reactor (capacity 2000 L, output of a rotation motor of 30 kW or more) equipped with 500 L of distilled water. -1 The mixture was supplied at a rate of 1000 rpm and stirred at 250 rpm while maintaining the temperature of the co-precipitation reactor at 50°C. The prepared metal solution was 40 L hr -1 , 20 M concentration ammonia solution (NH4OH, Daejung Chemical) is 4.5 L hr -1 , 25 L hr of 6 M sodium hydroxide solution (NaOH, Daejung Chemical) -1Each of them was continuously fed into the co-precipitation reactor for 12 hours. The pH in the co-precipitation reactor was maintained at 9.5 to 12, and the first co-precipitation reaction was performed for 12 hours to produce seed particles with an average particle size of 3.5 μm. Subsequently, the solution was removed from the co-precipitation reactor, leaving only the seed particles. Then, a 2.5 M metal solution was added to the co-precipitation reactor in the same manner as the first co-precipitation reaction, and the second co-precipitation reaction was performed for 10 hours in the same manner as the first co-precipitation reaction to produce a complex metal hydroxide as a precursor with an average particle size of 10 μm. The concentration of the precursor in the solution synthesized through the co-precipitation reaction was 0.1 kg. 전구체 / L 용액 It corresponds to .

[0162] The sintering process was performed by mixing the complex metal hydroxide precursor synthesized by the aforementioned coprecipitation reaction with a sodium compound (NaOH, Daejung gold) and performing a high-temperature heat treatment in an oxygen atmosphere. The precursor complex metal hydroxide and the sodium compound were mixed in a molar ratio of 1:1.01 to prepare a mixture, and the prepared mixture was placed in a sintering furnace, heated to 800 ℃ at a rate of 2 ℃ / min, and maintained at 800 ℃ for 24 hours. During the sintering, oxygen gas was passed through the sintering furnace at a flow rate of 1 ml / min. After the sintering process was completed, the prepared sintered body was rapidly cooled from 800 ℃ to 30 ℃ for 1 hour at a rate of 12 ℃ / min to 14 ℃ / min in a vacuum chamber while maintaining the vacuum condition, thereby preparing a cathode active material, which is a sodium metal oxide.

[0163]

[0164] Table 3 below shows the positive electrode active materials of Comparative Example 2 and Example 5.

[0165] Classification Chemical formula NiMnFe Comparative example 2Na[Ni 0.40 Fe 0.20 Mn 0.40 ]O2Ni 40mol%Mn 40mol%Fe 20mol%Example 5Na[Ni 0.40 Fe 0.20 Mn0.4 0]O2Ni 40mol%Mn 40mol%Fe 20mol%

[0166]

[0167] Example 6 (Mg 3% wet-doped Na-NFM402040)

[0168] A nickel sulfate aqueous solution (NiSO4·6H2O, Daejunggum), an iron (II) sulfate aqueous solution (FeSO4·7H2O, Daejunggum), a manganese sulfate aqueous solution (MnSO4·H2O, Daejunggum), and a magnesium sulfate aqueous solution (MgSO4·6H2O, Daejunggum) were mixed so that the molar ratio of nickel (Ni), iron (Fe), manganese (Mn), and magnesium (Mg) was 38.8:38.8:19.4:3, thereby preparing a metal solution having a concentration of 2.5 M. A cathode active material was prepared in the same manner as in Comparative Example 2, except that the prepared metal solution was placed in a coprecipitation reactor to perform a coprecipitation reaction, and the rapid cooling conditions were performed after the following calcination process was completed.

[0169] In Example 6, after the firing process was completed, the manufactured sintered body was placed in a chamber under vacuum conditions and rapidly cooled from 800°C to 30°C for 1 hour at a rate of 12°C / min to 14°C / min while maintaining the vacuum state, thereby manufacturing a cathode active material, which is sodium metal oxide.

[0170]

[0171] Example 7 (Ti 3% wet-doped Na-NFM402040)

[0172] A nickel sulfate aqueous solution (NiSO4·6H2O, Daejung Chemical), iron (II) sulfate aqueous solution (FeSO4·7H2O, Daejung Chemical), manganese sulfate aqueous solution (MnSO4·H2O, Daejung Chemical), and titanium sulfate aqueous solution (TiSO4·6H2O, Junsei Chemical) were mixed so that the molar ratio of nickel (Ni), iron (Fe), manganese (Mn), and titanium (Ti) was 37:40:20:3 to prepare a metal solution having a concentration of 2.5 M. A cathode active material was prepared in the same manner as in Comparative Example 2, except that the prepared metal solution was placed in a coprecipitation reactor to perform a coprecipitation reaction, and the rapid cooling conditions were performed after the following calcination process was completed.

[0173] In Example 7, after the firing process was completed, the manufactured sintered body was placed in a chamber under vacuum conditions and rapidly cooled from 800°C to 30°C for 1 hour at a rate of 12°C / min to 14°C / min while maintaining the vacuum state, thereby manufacturing a cathode active material, which is sodium metal oxide.

[0174]

[0175] Example 8 (Ca 1% dry-doped Na-NFM402040)

[0176] The composite metal hydroxide precursor synthesized by the solid-liquid coprecipitation reaction manufactured in Comparative Example 2 was used in the same manner, and a mixture was prepared by mixing the precursor composite metal hydroxide, calcium, and sodium compounds in a molar ratio of 1:0.01:0.99 during the following calcination process. The prepared mixture was calcined in the same manner as in Comparative Example 2, but only the rapid cooling conditions performed after the following calcination process were different to manufacture a cathode active material.

[0177] In Example 8, after the firing process was completed, the manufactured sintered body was placed in a chamber under vacuum conditions and rapidly cooled from 800°C to 30°C for 1 hour at a rate of 12°C / min to 14°C / min while maintaining the vacuum state, thereby manufacturing a cathode active material, which is sodium metal oxide.

[0178]

[0179] Table 4 below shows the positive electrode active materials of Comparative Example 2 and Examples 6 to 8.

[0180] Classification Chemical formula NiMnFe Doping element Doping method Comparative example 2Na[Ni 0.4 0Fe 0.20 Mn 0.40 ]O2Ni 40mol%Mn 40mol%Fe 20mol%--Example 6Na[(Ni 0.40 Fe 0.20 Mn 0.40 ) 0.97 Mg 0.03 ]O2Ni 38.8mol%Mn 38.8mol%Fe 19.4mol%Mg 3mol%wet-doping Example 7Na[Ni 0.37 Fe 0.20 Mn 0.40 Ti 0.03 ]O2Ni 37mol%Mn 40mol%Fe 20mol%Ti 3mol%wet-dopingExample 8Na 0.98 Ca 0.01 [Ni 0.40 Fe 0.20 Mn 0.40 ]O2Ni 40mol%Mn 40mol%Fe 20mol%Ca 1mol%dry-doping

[0181]

[0182] 2. Evaluation of sodium cathode active material

[0183]

[0184] The crystal structure was analyzed by XRD (Empyrean, Malvern Panalytical) using Cu Kα radiation in the 2θ range of 10–110°. The obtained XRD data were used to verify that the profiles matched with the FullProf Suite.

[0185] The particle morphology of the cathode active material was characterized using SEM (scanning electron microscopy, Verios G4UC, Thermo Fisher Scientific) and TEM (transmission electron microscopy; JEM 2100F, JEOL). For TEM analysis, the sample was polished into a 100 nm thin foil using FIB (focused ion beam; SCIOS, FEI and Crossbeam 540, ZEISS) and loaded onto a Mo grid.

[0186] Each of the cathode active materials (85 wt %) manufactured in the Examples and Comparative Examples, carbon black (10 wt %), and polyvinylidene fluoride (5 wt %) were mixed in N-methyl-2-pyrrolidone (N-Methyl-2-pyrrolidone, Daejung, Korea) to prepare a slurry. The prepared slurry was coated on aluminum foil to a loading level of 3 to 4 mg / cm2, followed by roll pressing and vacuum drying at 110°C to prepare a cathode. Propylene carbonate (PC; Tokyo Chemical Industry, Japan) containing 1.0 mol / L NaPF6 (Tokyo Chemical Industry, Japan) and 2 vol % fluoroethylene carbonate (FEC; Tokyo Chemical Industry, Japan) was used as the electrolyte. The experiment was performed with a 2032 coin-type half-cell (Sigma Aldrich, USA) using Na metal as the counter electrode. The positive electrode and the Na metal negative electrode manufactured using the examples and comparative examples were separated using glass fiber (Advantec, USA) to manufacture half cells. At this time, all half cells were assembled in an argon-filled glove box (MBRAUN, Germany).

[0187] Cycle tests were performed at a constant current density of 75 mA / g (0.5C) over a voltage range of 2.0 to 4.0 V at 30°C.

[0188] Electrochemical impedance was measured at a charge state of 4.0 V over a frequency range of 1.0 MHz to 1.0 mHz using a multichannel potentiostat (VMP3, Bio-Logics).

[0189] The rock salt (Fm3m) structure and layered (R-3m) structure in the primary particles were confirmed using the following method. The rock salt (Fm3m) structure and layered (R-3m) structure of the cathode active materials according to comparative examples and examples were confirmed using transmission electron microscopy (TEM). As measurement samples, the primary particles protruding from the outermost surface of the secondary particles of the cathode active material and the primary particles located inside the secondary particles were selected for the cathode active materials according to each manufacturing example, and the rock salt structure and the layered structure were confirmed for the surface and inside of each selected primary particle using selected area electron diffraction (SAED) pattern and high-resolution transmission electron microscopy (HR-TEM), respectively. SAED patterns are used to compare the intensity of each crystal structure plane, and HR-TEM provides images that can confirm atomic-level whether the rock salt structure and the layered structure are mixed.

[0190] The SAED pattern, which is the result of analyzing the crystal structure of the secondary and primary particles of the positive electrode material, was analyzed using the GATAN program. The intensity intensities for the (0-11), (0-14), (006), and (003) planes of the SAED pattern were confirmed graphically using the profile (draw a line profile) function. In each graph, the maximum height of the peak for each plane was compared, and the intensity intensities for each (0-11), (0-14), (006), and (003) plane were numerically compared.

[0191]

[0192] 3. Evaluation of Examples and Comparative Examples

[0193]

[0194] Fig. 5 is an SEM image of the composite metal hydroxide and the cathode active material of Comparative Example 1. Fig. 6 is an SEM image of the composite metal hydroxide and the cathode active material of Example 1. Fig. 7 is a TEM image of the cathode active material of Comparative Example 1 and the results showing the intensity ratio of the crystal planes using SAED. Fig. 8 is a TEM image of the cathode active material of Example 1 and the results showing the intensity ratio of the crystal planes using SAED. Fig. 9 is a TEM image of the cathode active material of Example 1, and is the result of confirming the inside of the primary particle existing on the surface of the secondary particle. Fig. 10 is an XRD analysis result of the cathode active materials of Comparative Example 1 (left) and Example 1 (right).

[0195] Table 5 shows the results of evaluating the initial charge / discharge efficiency and 100 cycles of the half-cell according to the 4.0 V charge of Comparative Example 1 and Example 1. Table 6 shows the results of evaluating the initial charge / discharge efficiency and 100 cycles of the half-cell according to the 4.3 V charge of Comparative Example 1 and Example 1.

[0196] Classification Cathode 0.1 C Disch. Capacity (mAh / g) Efficiency 0.2 C Pacity (mAh / g) 0.2 C / 0.1 C 0.5 C Pacity (mAh / g) 0.5 C / 0.1 C Cycle 0.5 C Cycle Retention Comparative Example 1 Na-NM5050 (layered) 147.5 94.9% 146.4 99.3% 144.5 98.7% 10075.6% Example 1 Na-NM5050 (rock-salt nanocomposite) 146.4 96.1% 145.2 9.1% 142.9 97.6% 10085.2%

[0197] Classification Cathode 0.1 C Disch. Capacity (mAh / g) Efficiency 0.2 C Pacity (mAh / g) 0.2 C / 0.1 C 0.5 C Pacity (mAh / g) 0.5 C / 0.1 C Cycle 0.5 C Cycle Retention Comparative Example 1 Na-NM5050 (layered) 207.8 8 6.6% 198.3 9 5.4% 182.4 8 7.8% 100 28.6% Example 1 Na-NM5050 (rock-salt nanocomposite) 212.0 9 1.5% 203.5 9 6.0% 192.8 9 1.0% 100 47.4%

[0198] Referring to FIGS. 5 and 6, in the case of Comparative Example 1 and Example 1, the chemical formula in the precursor and positive electrode active material is Na[Ni 0.50 Mn 0.50 ]O2, but the manufacturing method is different. In Example 1, unlike Comparative Example 1, the complex metal hydroxide precursor (Ni) for Na-NM5050 cathode material was prepared through a solid-liquid synthesis process while removing the solution in the co-precipitation reactor during the co-precipitation reaction process. 0.5 Mn 0.5)(OH)2 was synthesized. In Example 1, the solidification process was applied, so that the orientation of the primary particles from the precursor was excellent, and the primary particles were formed in a columnar structure. In addition, in Example 1, it was confirmed that the shape of the primary particles hardly changed after mixing the manufactured precursor with a sodium compound and then calcining it, and that it was formed in a columnar structure with high orientation. The composite metal hydroxide of Example 1 was oriented so that the primary particles of the columnar structure were oriented toward the center of the secondary particles, and this orientation was maintained in the positive electrode active material.

[0199] On the other hand, in the case of Comparative Example 1, it was confirmed that the primary particles of the composite metal hydroxide were randomly oriented regardless of the center of the secondary particles, and in particular, the primary particles located at the center of the secondary particles were randomly arranged without any directionality. In addition, in the case of Comparative Example 1, it was confirmed that the positive electrode active material manufactured after calcining the composite metal hydroxide had a more expanded volume of the primary particles, and the orientation was also poor, similar to the orientation of the primary particles of the composite metal hydroxide.

[0200] In Example 1, a composite metal hydroxide was prepared by a solid-liquid coprecipitation reaction, and then calcined with a sodium compound to prepare a cathode active material. During the solid-liquid coprecipitation reaction, the accumulated solution inside the coprecipitation reactor was removed, and the particles of the precursor composite metal hydroxide were not removed and maintained, so that the weight ratio of the precursor in the solution inside the coprecipitation reactor continuously increased, and the precursor particles were induced to grow slowly. Accordingly, it was confirmed that the growth of fine-sized primary particles and secondary particles composed of bundles thereof was promoted. In addition, in the solid-liquid coprecipitation reaction as in Example 1, since only the solvent was continuously removed in real time from the internal solution without circulating the solution outside the coprecipitation reactor, the overall concentration of the solution inside the coprecipitation reactor was maintained uniform. As a result, the transition metal-ammonia chelating reaction and the hydroxide group substitution reaction occurred continuously within the co-precipitation reactor, promoting the multiplication of fine-sized primary particles and the continuous growth of oriented particles, and easily inducing the synthesis of the proposed oriented composite metal hydroxide precursor. That is, it was confirmed that the primary particles with high orientation that appeared in the precursor stage in Example 1 were maintained as is in the sintered cathode active material. On the other hand, in the case of Comparative Example 1, the orientation of the primary particles was not good even in the precursor, and the width (thickness) of the primary particles was also larger than in Example 1.

[0201] Referring to FIGS. 7 and 8, it was confirmed that Comparative Example 1 had a layered (R-3m) structure with crystal structures of (0-17), (0-14), (0-11), (006), and (003). In Comparative Example 1, I(006) / I(003) was 0.37, indicating that I(003) was higher, and I(0-14) / I(0-11) was 0.67, indicating that I(0-11) was higher. Example 1 showed a mixed state of a layered structure with crystal structures of (0-17), (0-14), (0-11), (006), and a rocksalt (Fm3m) structure. In Example 1, I(006) / I(003) was 1.52, indicating that I(006) was higher, and I(0-14) / I(0-11) was 2.31, indicating that I(0-14) was higher. In other words, while Comparative Example 1 and Example 1 had the same chemical formula, they were different in crystal structure.

[0202] Referring to Fig. 9, it was confirmed that in Example 1, at the end of the primary particle, the primary particle formed a nanocomposite in which a rock salt structure (indicated by the dotted line area) and a layered structure (indicated by the solid line area) were mixed at the nanoscale. In the primary particle of the positive electrode material of Example 1, nanocomposites were formed in both regions 1 and 2. In the lower right drawing of Fig. 9, it was confirmed that a rock salt structure appeared, and the diffraction points representing the rock salt structure were indicated by solid circles.

[0203] Referring to Fig. 10, in Comparative Example 1 consisting of only a layered structure and Example 1 having a mixed layered structure and rock salt structure, both (003) and (104) peaks appeared, and it was confirmed through XRD analysis that it was an O3-type layered structure. Example 1 had an O3-type layered structure overall, but it was confirmed that the layered structure and rock salt structure were mixed at the nanoscale at the ends of the primary particles.

[0204] Referring to Table 5, Comparative Example 1 and Example 1 (Na-NM5050, Na[Ni)) having an O3 structure and different crystal structures and fine particle structures 0.5 Mn 0.5 ]O2) was used as a cathode active material, and a 2032 coin type half-cell was manufactured and evaluated. After performing charge and discharge at 0.1 C and 0.2 C once each under the conditions of 2.0 V - 4.0 V, 30 ℃, 0.5 C and 100 cycle evaluations were performed. It was confirmed that Example 1 was superior to Comparative Example 1 in both initial charge and discharge efficiency and cycle characteristics. That is, in the case of Example 1, the structural stability was improved by having a nanocomposite structure in which a layered structure and a rock salt structure were mixed in the nanoscale while having an O3 structure, and thus the charge and discharge efficiency and cycle characteristics were improved.

[0205] Referring to Table 6, in a 2032 coin type half-cell using the cathode active materials of Comparative Example 1 and Example 1, 0.1 C and 0.2 C charge / discharge were performed once each under the conditions of 2.0 V - 4.3 V, 30 ℃, and then 0.5 C and 100 cycle evaluations were performed. Even in the high voltage evaluation of 4.3 V, it was confirmed that Example 1 had superior charge / discharge efficiency and cycle characteristics compared to Comparative Example 1.

[0206]

[0207] Table 7 shows the results of evaluating the charge characteristics of half-cells according to the C-rate of Comparative Example 1 and Example 1. Table 8 shows the results of evaluating the discharge characteristics of half-cells according to the C-rate of Comparative Example 1 and Example 1.

[0208] Classification Cathode 0.1 CPacity (mAh / g) 0.2 CPacity (mAh / g) (0.2 C / 0.1 C) 0.5 CPacity (mAh / g) (0.5 C / 0.1 C) 1 CPacity (mAh / g) (1 C / 0.1 C) 2 CPacity (mAh / g) (2 C / 0.1 C) 5 CPacity (mAh / g) (5 C / 0.1 C) 10 CPacity (mAh / g) (10 C / 0.1 C) Comparative Example 1 Na-NM5050 (layered) 147.3 144.3 (98.0%) 143.0 (97.1%) 142.1 (96.5%) 140.7 (95.5%) 138.2 (93.8%) 130.7 (88.7%) Example 1 Na-NM5050 (rock-salt) nanocomposite)146.3143.8(98.3%)142.7(97.5%)141.6(96.8%)140.5(96.0%)138.3(94.5%)132.7(90.7%)

[0209] Classification Cathode 0.1 CPacity (mAh / g) 0.2 CPacity (mAh / g) (0.2 C / 0.1 C) 0.5 CPacity (mAh / g) (0.5 C / 0.1 C) 1 CPacity (mAh / g) (1 C / 0.1 C) 2 CPacity (mAh / g) (2 C / 0.1 C) 5 CPacity (mAh / g) (5 C / 0.1 C) 10 CPacity (mAh / g) (10 C / 0.1 C) Comparative Example 1 Na-NM5050 (layered) 146.8 143.6 (97.8%) 139.2 (94.8%) 133.7 (91.1%) 125.1 (85.2%) 110.5 (75.3%) 79.6 (54.2%) Example 1 Na-NM5050 (rock-salt) nanocomposite)145.6143.2(98.3%)139.4(95.7%)134.9(92.6%)127.9(87.8%)113.9(78.2%)97.0(66.6%)

[0210] Tables 7 and 8 show that half-cells were manufactured using the positive electrode materials of Example 1 and Comparative Example 1, and the rate characteristics were confirmed by increasing the C-rate from 0.1 C to 10 C under the conditions of 2.0 V - 4.0 V and 30 ℃. Referring to Table 7, Example 1 was Na + It was confirmed that the charging rate characteristics corresponding to the desorption process gradually increased, but in Comparative Example 1, it gradually decreased. In addition, in Table 8, Example 1 showed Na + The discharge rate characteristics gradually increased during the insertion process, and the rate characteristics of Comparative Example 1 decreased and decreased significantly at 10 C. Example 1 has a stable structure compared to Comparative Example 1, so Na + (sodium ions) gradually increased during the insertion process, and Na + During the discharge process, it exhibited stable discharge characteristics even at a high current of 10 C.

[0211] This means that Example 1 has higher structural stability than Comparative Example 1, and at the same time, Na + It was confirmed that irreversibility hardly occurs even for reversible movement.

[0212]

[0213] Table 9 shows the results of evaluating the initial charge / discharge efficiency and 100 cycles of the half-cells according to the 4.0 V charge of Comparative Example 1 and Examples 2 to 4. Table 10 shows the results of evaluating the initial charge / discharge efficiency and 100 cycles of the half-cells according to the 4.3 V charge of Comparative Example 1 and Examples 2 to 4.

[0214] Classification Cathode 0.1 C Disch. Capacity (mAh / g) Efficiency 0.2 C Pacity (mAh / g) 0.2 C / 0.1 C 0.5 C Pacity (mAh / g) 0.5 C / 0.1 C Cycle 0.5 C Cycle Retention Comparative Example 1 Na-NM5050 (layered) 147.5 94.9% 146.4 99.3% 144.5 98.7% 1007 5.6% Example 2 Mg 7% wet-doped Na-NM5050 141.6 95.1% 139.8 98.7% 139.1 98.2% 1009 0.7% Example 3 Ti 1% wet-doped Na-NM5050 147.19 7.1% 145.29 8.7% 142.59 6.9% 10088.3% Example 4 Ca 1% dry-doped Na-NM5050 148.89 4.3% 147.39 9.0% 142.69 5.8% 10098.5%

[0215] Classification Cathode 0.1 C Disch. Capacity (mAh / g) Efficiency 0.2 C Pacity (mAh / g) 0.2 C / 0.1 C 0.5 C Pacity (mAh / g) 0.5 C / 0.1 C Cycle 0.5 C Cycle Retention Comparative Example 1 Na-NM5050 (layered) 147.5 94.9% 146.4 99.3% 144.5 98.7% 1007 5.6% Example 2 Mg 7% wet-doped Na-NM5050 141.6 95.1% 139.8 98.7% 139.1 98.2% 1009 0.7% Example 3 Ti 1% wet-doped Na-NM5050 147.19 7.1% 145.29 8.7% 142.59 6.9% 10088.3% Example 4 Ca 1% dry-doped Na-NM5050 148.89 4.3% 147.39 9.0% 142.69 5.8% 10098.5%

[0216] Fig. 11 is an SEM image of the composite metal hydroxide and the cathode active material of Example 2. Fig. 12 is a TEM image of the cathode active material of Example 2 and the results showing the intensity ratio of crystal planes using SAED. Fig. 13 is a TEM image of the cathode active material of Example 2, showing the results of confirming the inside of the primary particles existing on the surface of the secondary particles. Fig. 14 is an XRD analysis result of the cathode active materials of Comparative Example 1 (left) and Example 2 (right).

[0217] Referring to Fig. 11, Example 2 was manufactured by doping 7 mol% of Mg in a wet manner in Comparative Example 1, and it was confirmed that both the precursor, the composite metal hydroxide, and the sintered body, the cathode active material, had primary particles that were oriented and aligned toward the center of the secondary particles. In addition, it was confirmed that the columnar primary particles that appeared in the precursor also appeared in the sintered body. In Example 2, the morphology of the precursor changed due to wet doping, and it was confirmed that due to this change in the precursor, the morphology of the sintered body, the cathode active material, also had a columnar structure in the primary particles.

[0218] Example 2 was manufactured using the same method as Comparative Example 1, but it is believed that the structural stability of the cathode active material was improved by adding more Mg through wet doping. In Example 2, when a Mg compound is added to a co-precipitation reactor through wet doping, a chelating reaction is performed with the Ni and Mn elements added together, which further extends the length of the primary particles having a columnar structure in the manufactured composite metal hydroxide and promotes the growth of oriented particles in which the primary particles are arranged to face the center of the secondary particles. As a result, it was confirmed that the oriented particles, which are primary particles having a high degree of orientation, were well maintained in the sintered body of the cathode active material manufactured in the composite metal hydroxide in which the oriented particles formed by wet doping were strongly developed during the process of mixing with a sodium compound and sintering.

[0219] Referring to Figure 12, Example 2 showed that I(006) / I(003) was 1.31, indicating that I(006) was higher, and I(0-14) / I(0-11) was 4.72, indicating that I(0-14) was higher. That is, when compared to Comparative Example 1, Example 2 showed a difference in crystal structure due to the Mg added by wet doping.

[0220] Referring to Fig. 13, it was confirmed that in Example 2, at the end of the primary particle, the primary particle formed a nanocomposite in which a rock salt structure (indicated by the dotted line area) and a layered structure (indicated by the solid line area) were mixed at the nanoscale. In the lower right drawing of Fig. 13, a diffraction point representing the rock salt structure is indicated by a solid circle.

[0221] In Fig. 14, Example 2 showed the same (003) and (104) peaks as Comparative Example 1, and it was confirmed through XRD analysis that it was an O3-type layered structure. In Example 2, even when wet-doped with Mg, it was confirmed that the overall structure was an O3-type layered structure, but at the ends of the primary particles, the layered structure and the rock salt structure were mixed on a nanoscale.

[0222] Tables 9 and 10 show that Example 2 (Mg 7% wet-doped Na-NM5050, Na[Ni)) has an O3 structure and a different crystal structure and fine particle structure from Comparative Example 1 (Na-NM5050 (layered)). 0.43 Mg0 .07 Mn 0.5]O2) was evaluated for the cathode active material. After performing charge and discharge at 0.1 C and 0.2 C once each under the conditions of 2.0 V - 4.0 V, 30 ℃, 100 cycles were evaluated at 0.5 C. It was confirmed that Example 2 exhibited relatively lower initial capacity than Comparative Example 1 due to Mg wet doping, but exhibited excellent cycle characteristics. In addition, even when evaluated at a high voltage of 2.0 V - 4.3 V, the initial capacity was slightly lower than that of Comparative Example 1, but the cycle characteristics were very excellent.

[0223]

[0224] Figure 15 is a SEM image of the composite metal hydroxide and the cathode active material of Example 3. Figure 16 is a TEM image of the cathode active material of Example 3 and the results showing the intensity ratio of crystal planes using SAED. Figure 17 is a TEM image of the cathode active material of Example 3, showing the results of confirming the inner side of the primary particle existing on the surface of the secondary particle.

[0225] Figures 15 to 17 are drawings of the positive electrode active material of Example 3, in which wet doping was performed using Ti, an element other than Mg, as in Example 2, to confirm the characteristics of the positive electrode active material.

[0226] Referring to Fig. 15, it was confirmed that the morphology of the precursor composite metal hydroxide changed in Example 2 due to the wet doping of Ti compared to Comparative Example 1. In the composite metal hydroxide of Example 2, the primary particles constituting the secondary particles were formed in a columnar shape and had a high orientation toward the center of the secondary particles, and it was confirmed that the morphology of the composite metal hydroxide was also reflected in the cathode active material, which was a sintered body. That is, the Ti compound added by wet doping during the process of manufacturing the composite metal hydroxide affected the columnar shape and orientation of the primary particles through a chelating reaction with the Ni and Mn elements, and it was confirmed that the morphology of the composite metal hydroxide was maintained in the cathode active material even after sintering at high temperatures.

[0227] In Fig. 16, Example 3 showed that I(006) / I(003) was 1.61, indicating that I(006) was higher, and I(0-14) / I(0-11) was 1.10, indicating that I(0-14) was higher. In other words, it was similar to Example 3, and there was a difference in the crystal structure from Comparative Example 1.

[0228] Referring to Fig. 17, in the cathode active material of Example 3, it was confirmed that a nanocomposite with a rock salt structure (indicated by the dotted line area) and a layered structure (indicated by the solid line area) mixed at the nanoscale appeared at the ends of the primary particles provided on the surface of the secondary particles. As shown in the lower right drawing of Fig. 17, a diffraction point indicating the rock salt structure (indicated by the solid line circle) was confirmed. That is, it was confirmed that Example 3 had improved structural stability by including a crystal structure having a nanocomposite through wet doping.

[0229] Tables 9 and 10 show that the crystal structure and fine particle structure of the O3 structure are different from that of Comparative Example 1 (Na-NM5050 (layered)) and Example 3 (Ti 1% wet-doped Na-NM5050, Na[Ni 0.49 Ti 0.01 Mn0.50 ]O2) material was fabricated into a 2032 coin type half cell and the electrochemical and cycle characteristics were evaluated. After performing charge and discharge at 0.1 C and 0.2 C once each under 30 ℃ conditions, 100 cycles at 0.5 C were evaluated at 2.0 V - 4.0 V and 2.0 V - 4.3 V, respectively. In both 2.0 V - 4.0 V and 2.0 V - 4.3 V, Example 3 showed superior performance compared to Comparative Example 1, and it was confirmed that the cycle characteristics were improved due to wet doping of Ti.

[0230]

[0231] Figure 18 is an SEM image of the composite metal hydroxide and the cathode active material of Example 4. Figure 19 is a TEM image of the cathode active material of Example 4 and the results showing the intensity ratio of crystal planes using SAED. Figure 20 is an SEM image and TEM image of the cathode active material of Example 4, showing the results of confirming the inside of the primary particles existing on the surface of the secondary particles.

[0232] Figures 18 to 20 show the morphology, crystal structure, and electrochemical properties of the cathode active material of Example 4, which is a cathode active material to which Ca is added by dry doping, in comparison with Comparative Example 1.

[0233] Referring to FIG. 5 and FIG. 18, Example 4 has a chemical composition of Na 0.98 Ca 0.01 [Ni 0.50 Mn 0.50] By adding CaO2 during the sintering process and dry doping, potassium was substituted for the sodium site. In Example 4, the SEM image of the composite transition metal oxide appeared similar to the SEM image of the composite transition metal oxide of Comparative Example 1. On the other hand, the SEM image of the cathode active material of Example 4, which was manufactured by mixing the composite transition metal oxide with a sodium compound and a potassium compound and then sintering it, showed a morphology in which the column-shaped primary particles had a high degree of orientation toward the center of the secondary particles, unlike the SEM image of the cathode active material of Comparative Example 1.

[0234] The positive electrode active material of Example 4 has poor alignment in the composite metal hydroxide, but potassium ions are doped into the sodium ion layer during the sintering process. In addition, in the process of mixing the composite metal hydroxide, potassium compound, and sodium compound and sintering, the ratio of the composite metal hydroxide is reduced by the mole fraction of the added potassium compound, thereby forming a sintered body. The potassium ions added by dry doping increase the cohesion of the sodium ion layer and widen the interlayer distance, thereby improving the structural stability of the positive electrode active material. When the heterogeneous element potassium ions are doped by dry doping, the potassium ions fill the vacant positions of the sodium ions when charging and discharging the positive electrode material, thereby preventing the layers from collapsing, thereby improving the cycle characteristics.

[0235] Referring to Figure 19, Example 4 showed that I(006) / I(003) was 1.48, indicating that I(006) was higher, and I(0-14) / I(0-11) was 1.22, indicating that I(0-14) was higher. That is, when compared to Comparative Example 1, Example 4 had a similar morphology of the composite metal hydroxide, but due to the Ca added by dry doping, the primary particles in the sintered positive electrode active material were arranged as secondary particles with a high degree of orientation, and it was confirmed that there was a difference in the crystal structure from Comparative Example 1.

[0236] Referring to Fig. 20, it was confirmed that in Example 4, a nanocomposite was formed in which a rock salt structure (indicated by the dotted line area) and a layered structure (indicated by the solid line area) were mixed at the nanoscale in the primary particles. In the lower right drawing of Fig. 20, a diffraction point indicating a rock salt structure (indicated by the solid line circle) was confirmed. That is, in the cathode active material formed by dry doping, a nanocomposite appeared at the end of the primary particle, and the structural stability was improved.

[0237] In Tables 9 and 10, Example 4 (Ca 1% dry-doped Na-NM5050, Na 0.98 Ca 0.01 [Ni 0.5 Mn 0.5 ]O2) had an O3 structure in the sintered body by dry doping, and the crystal structure and fine particle structure were different from those of Comparative Example 1. The electrochemical characteristics and cycle characteristics were evaluated by manufacturing a 2032 coin type half-cell. After performing 0.1 C and 0.2 C charge / discharge once each at 2.0 V - 4.0 V and 2.0 V - 4.3 V at 30 ℃, a 0.5 C 100-cycle evaluation was performed. It was confirmed that Example 4 with Ca dry doping at both 4.0 V and 4.3 V had improved cycle characteristics compared to Comparative Example 1. That is, as described above, the composite metal hydroxide was the same in Example 4 and Comparative Example 1, but it is believed that the stability of the sodium ion layer was improved by Ca added by dry doping during the process of manufacturing the sintered body, and the structural stability was improved by potassium ions filling the vacancy created by the loss of sodium ions during the charge / discharge process.

[0238]

[0239] Table 11 shows the results of evaluating the initial charge / discharge efficiency and 100 cycles of the half-cell according to the 4.0 V charge of Comparative Example 2 and Example 5. Table 12 shows the results of evaluating the initial charge / discharge efficiency and 100 cycles of the half-cell according to the 4.3 V charge of Comparative Example 2 and Example 5.

[0240] Classification Cathode 0.1 C Disch. Capacity (mAh / g) Efficiency 0.2 C Pacity (mAh / g) 0.2 C / 0.1 C 0.5 C Pacity (mAh / g) 0.5 C / 0.1 C Cycle 0.5 C Cycle Retention Comparative Example 2 Na-NFM402040 (layered) 144.5 96.8% 143.4 99.3% 141.0 97.6% 1008 6.4% Example 5 Na-NFM402040 (rock-salt nanocomposite) 146.5 95.1% 145.2 99.1% 142.4 97.2% 1009 0.5%

[0241] Classification Cathode 0.1 C Disch. Capacity (mAh / g) Efficiency 0.2 C Pacity (mAh / g) 0.2 C / 0.1 C 0.5 C Pacity (mAh / g) 0.5 C / 0.1 C Cycle 0.5 C Cycle Retention Comparative Example 2 Na-NFM402040 (layered) 201.09 1.8% 193.29 6.1% 184.99 2.0% 10064.1% Example 5 Na-NFM402040 (rock-salt nanocomposite) 200.59 1.0% 195.29 7.4% 187.19 3.3% 10075.2%

[0242] Fig. 21 is an SEM image of the composite metal hydroxide and the cathode active material of Comparative Example 2. Fig. 22 is an SEM image of the composite metal hydroxide and the cathode active material of Example 5. Fig. 23 is a TEM image of the cathode active material of Comparative Example 2 and the results showing the intensity ratio of the crystal planes using SAED. Fig. 24 is a TEM image of the cathode active material of Example 5 and the results showing the intensity ratio of the crystal planes using SAED. Fig. 25 is a TEM image of the cathode active material of Example 5, and is the result of confirming the inside of the primary particle existing on the surface of the secondary particle. Fig. 26 is an XRD analysis result of the cathode active materials of Comparative Example 2 and Example 5.

[0243] In Figures 21 to 25, the chemical formula is Na[Ni 0.40 Fe 0.20 Mn 0.40 ]For Comparative Example 2 and Example 5, which were manufactured using the same but different methods using O2, the electrochemical and cycle characteristics were confirmed due to the differences in the morphology of the composite metal hydroxide and the positive electrode active material, the shape and orientation of the primary particles, and the crystal structure.

[0244] Referring to Fig. 21, in Manufacturing Example 2, the thickness and shape of the primary particles constituting the composite metal hydroxide, which is a precursor, were irregular, and the primary particles were randomly aggregated and formed regardless of the center of the secondary particles. In addition, the shape and orientation of the primary particles of the composite metal hydroxide of Manufacturing Example 2 were also observed in the sintered body, which is the cathode active material, and it was confirmed that the orientation of the primary particles constituting the cathode active material was random.

[0245] On the other hand, referring to Fig. 22, in the case of Example 5, the primary particles in the precursor composite metal hydroxide were provided in a columnar shape that was elongated in one direction, and the manufactured primary particles were aligned toward the center of the secondary particles, showing high orientation. In addition, in Example 5, the columnar shape of the primary particles was maintained in the positive electrode active material obtained after calcining the composite metal hydroxide, and the orientation toward the center of the secondary particles was also maintained.

[0246] Comparative Example 2 produced a complex metal hydroxide by continuously adding a transition metal compound to a co-precipitation reactor, but Example 5 synthesized a seed precursor with an average particle size of 3.5 μm through a first co-precipitation reaction, and then additionally performed a second co-precipitation reaction to produce a complex metal hydroxide with an average particle size of 10 μm. In this way, Example 5 induced the formation of primary particles with high orientation on the surface of the seed precursor in the second co-precipitation reaction, thereby producing the primary particles constituting the secondary particles as a whole having a columnar structure and having an orientation toward the center of the secondary particles.

[0247] In Comparative Example 2 in Fig. 23, I(006) / I(003) is 0.71, which is I(006) <I(003)으로 나타났고, I(0-14) / I(0-11)은 0.76으로 I(006)<I(003), I(0-14)<I(0-11)로 나타났다. 도 24에서 실시예 5는 I(006) / I(003)은 1.28로 I(006)> It appeared as I(003), and I(0-14) / I(0-11) was 1.91, showing that I(006)>I(003), I(0-14)>I(0-11). That is, both Comparative Example 2 and Example 5 had an O3 structure, but Comparative Example 1 consisted of only a layered structure, whereas Example 5 had a mixed rock salt structure and a layered structure, confirming that there was a difference in microstructure from Comparative Example 1.

[0248] Referring to Fig. 25, Example 5 confirmed that both a nanoscale layered structure (indicated by the solid line area) and a nanoscale rock salt structure (indicated by the dotted line area) were present, and that a nanocomposite was formed by mixing these structures. In the lower right drawing of Fig. 25, a diffraction point representing a rock salt structure is indicated by a solid circle.

[0249] Referring to Fig. 26, Comparative Example 2 and Example 5 exhibited the same (003) and (104) peaks in the XRD peaks, and exhibited an O3-type layered structure. Example 5 was a positive electrode active material wet-doped with Mg, and it was confirmed that the positive electrode active material maintained the O3-type layered structure overall, similar to the positive electrode active material without doping.

[0250]

[0251] Referring to Tables 11 and 12, 2032 coin type half-cells were evaluated for the cathode active materials of Comparative Example 2 and Example 5. After performing 0.1 C and 0.2 C charge / discharge once each under the conditions of 2.0 V - 4.0 V, 30 ℃, 100 cycle evaluations were performed at 0.5 C. In Example 5, it was confirmed that the orientation of the primary particles was improved by using the seed co-precipitation method, and the structural stability of the secondary particles was improved by being provided in a columnar shape, thereby improving the cycle characteristics compared to Comparative Example 1. In addition, when 0.1 C and 0.2 C charge / discharge once each under the conditions of 30 ℃ at a high voltage of 2.0 V - 4.3 V, 0.1 C and 0.2 C were performed, and then 100 cycle evaluations were performed at 0.5 C, both the electrochemical characteristics and cycle characteristics were excellent. That is, as in Example 5, the structural stability of the cathode active material was improved by the co-precipitation reaction using seeds, and as a result, excellent cycle characteristics were observed not only at 4.0 V but also at a high voltage of 4.3 V.

[0252]

[0253] Table 13 shows the results of evaluating the initial charge / discharge efficiency and 100 cycles of the half-cells according to the 4.0 V charge of Comparative Example 2 and Examples 6 to 8. Table 15 shows the results of evaluating the initial charge / discharge efficiency and 100 cycles of the half-cells according to the 4.3 V charge of Comparative Example 2 and Examples 6 to 8.

[0254] Classification Cathode 0.1 C Disch. Capacitance (mAh / g) Efficiency 0.2 C Pacity (mAh / g) 0.2 C / 0.1 C 0.5 C Pacity (mAh / g) 0.5 C / 0.1 C Cycle 0.5 C Cycle Retention Comparative Example 2 Na-NFM 40 20 40 (layered) 144.5 96.8% 143.4 99.3% 141.0 97.6% 1008 6.4% Example 6 Mg 3% wet-doped Na-NFM 40 20 40 143.9 94.1% 143.1 99.4% 140.3 97.5% 1009 2.8% Example 7 Ti 3% wet-doped Na-NFM402040145.393.9%143.798.9%140.296.5%10094.0%Example 8Ca 1% dry-doped Na-NFM402040145.594.5%144.399.2%141.997.5%10093.9%

[0255] Classification Cathode 0.1 C Disch. Capacitance (mAh / g) Efficiency 0.2 C Pacity (mAh / g) 0.2 C / 0.1 C 0.5 C Pacity (mAh / g) 0.5 C / 0.1 C Cycle 0.5 C Cycle Retention Comparative Example 2 Na-NFM 40 20 40 (layered) 201.09 1.8% 193.29 6.1% 184.99 2.0% 100 64.1% Example 6 Mg 3% wet-doped Na-NFM 40 20 40 20 4.39 0.0% 197.59 6.7% 189.19 2.6% 100 74.0% Example 7 Ti 3% wet-doped Na-NFM402040196.190.3%191.697.7%184.794.2%10072.8%Example 8Ca 1% dry-doped Na-NFM402040197.792.5%192.997.6%186.294.2%8269.8%

[0256] Figure 27 is a SEM image of the composite metal hydroxide and the cathode active material of Example 6. Figure 28 is a TEM image of the cathode active material of Example 6 and the results showing the intensity ratio of crystal planes using SAED. Figure 29 is a TEM image of the cathode active material of Example 6, showing the results of confirming the inner side of the primary particle existing inside the secondary particle.

[0257] Example 6 was manufactured by manufacturing a cathode active material in the same manner as Comparative Example 2, but adding 3 mol% of Mg by wet doping during the process of manufacturing a complex metal hydroxide as a precursor.

[0258] Comparing Fig. 27 and Fig. 21, it was confirmed that Example 6 exhibited excellent columnar orientation of the primary particles in the composite metal hydroxide. That is, even in the case of a composite metal hydroxide containing more Fe, when Mg was added by wet doping, it was confirmed that the primary particles were manufactured in the form of columns extending in one direction by forming a chelate with Ni, Mn, and Fe, and that the secondary particles were manufactured to have a high orientation toward the center during the process of forming the secondary particles. In addition, in the case of Example 6, it was confirmed that the shape and orientation of the primary particles of the composite metal hydroxide were also shown in the positive electrode active material after sintering. That is, by adding a heterogeneous element such as Mg by wet doping as in Example 6, the morphology such as the shape and orientation of the primary particles of the composite metal hydroxide can be controlled, and the morphology of the composite metal hydroxide controlled in this way was similarly reflected in the positive electrode active material.

[0259] Referring to Figure 28, Example 6 showed that I(006) / I(003) was 1.13, so I(006)>I(003), and I(0-14) / I(0-11) was 3.04, so I(0-14)>I(0-11). That is, Example 6 had an O3 structure, but showed differences in microstructure from Comparative Example 2.

[0260] Referring to Fig. 29, Example 6 confirmed both the layered structure (indicated by the solid line area) and the rock salt structure (indicated by the dotted line area), and confirmed that these structures formed a nanocomposite mixed at the nanoscale. In the lower right drawing of Fig. 29, the diffraction points representing the rock salt structure are indicated by solid circles.

[0261] Referring to Tables 13 and 14, in the evaluation of 2032 coin type half-cells manufactured using Comparative Example 2 and Example 6, when 0.1 C and 0.2 C charge / discharge were performed once each under the conditions of 2.0 V - 4.0 V, 30 ℃, and then 0.5 C 100 cycles were evaluated, it was confirmed that Example 6 had improved initial charge / discharge efficiency and cycle characteristics due to wet doping of Mg. In addition, when evaluated at a high voltage of 2.0 V - 4.3 V under the same conditions, Example 6 showed superior initial charge / discharge efficiency and cycle characteristics compared to Comparative Example 2. That is, Example 6 confirmed that the shape and orientation of primary particles in a composite metal hydroxide were controlled by wet doping of Mg, and that the morphology of these primary and secondary particles was reflected in the cathode active material after sintering, thereby improving the structural stability against reversible insertion and deintercalation of sodium ions due to charge and discharge.

[0262]

[0263] Figure 30 is a SEM image of the composite metal hydroxide and the cathode active material of Example 7. Figure 31 is a TEM image of the cathode active material of Example 7 and the results showing the intensity ratio of crystal planes using SAED. Figure 32 is a TEM image of the cathode active material of Example 7, showing the results of confirming the inner side of the primary particle existing inside the secondary particle.

[0264] Example 7 was prepared by wet doping a composite metal hydroxide using Ti instead of Mg in Example 6. As a result of wet doping during the co-precipitation reaction using Ti as a heterogeneous element, the columnar shape and orientation of the primary particles constituting the composite metal hydroxide were improved, and these characteristics were also reflected in the cathode material, which is a sintered body.

[0265] Referring to Figure 31, Example 7 showed that I(006) / I(003) was 1.34, so I(006)>I(003), and I(0-14) / I(0-11) was 1.22, so I(0-14)>I(0-11). That is, Example 7 had an O3 structure, but had a difference in crystal structure from Comparative Example 2.

[0266] Referring to Fig. 32, Example 7 confirmed both the layered structure (indicated by the solid line area) and the rock salt structure (indicated by the dotted line area), and confirmed that these structures formed a nanocomposite mixed at the nanoscale. In the lower right drawing of Fig. 32, the diffraction points representing the rock salt structure are indicated by solid circles.

[0267] Referring to Tables 13 and 14, in the evaluation of 2032 coin type half-cells manufactured using Comparative Example 2 and Example 7, when 0.1 C and 0.2 C charge / discharge were performed once each under the conditions of 2.0 V - 4.0 V, 30 ℃, and then 0.5 C 100 cycles were evaluated, it was confirmed that Example 7 had improved initial charge / discharge efficiency and cycle characteristics due to wet doping of Ti. In addition, even at a high voltage of 2.0 V - 4.3 V under the same conditions, Example 7 showed superior initial charge / discharge efficiency and cycle characteristics compared to Comparative Example 2. That is, it was confirmed that Example 7, similar to Example 6, improved the structural stability of the cathode active material by controlling the morphology from the composite metal hydroxide through wet doping of Ti and reflecting it to the sintered body.

[0268] Figure 33 is a SEM image of the composite metal hydroxide and the cathode active material of Example 8. Figure 34 is a TEM image of the cathode active material of Example 8 and the results showing the intensity ratio of crystal planes using SAED. Figure 35 is a TEM image of the cathode active material of Example 8, showing the results of confirming the inner side of the primary particle existing in the center of the secondary particle.

[0269] Example 8 produced a cathode active material by dry doping with Ca, and as shown in FIG. 33, the composite metal hydroxide exhibited a morphology similar to that of Comparative Example 2. On the other hand, when the produced composite metal hydroxide was mixed with a sodium compound and a potassium compound and sintered, it was confirmed that the primary particle orientation of the produced sintered body, the cathode active material, was improved compared to Comparative Example 2. That is, by dry doping with Ca, sodium ions were substituted with potassium ions in the sodium layer, thereby improving structural stability, and as a result, the primary particles in the produced sintered body, the cathode active material, were arranged in a columnar shape and exhibited high orientation toward the center of the secondary particles.

[0270] Referring to Figure 34, Example 8 showed that I(006) / I(003) was 1.23, so I(006)>I(003), and I(0-14) / I(0-11) was 2.39, so I(0-14)>I(0-11). That is, Example 8 had an O3 structure, but had a difference in crystal structure from Comparative Example 2.

[0271] Referring to Fig. 35, Example 8 confirmed both the layered structure (indicated by the solid line area) and the rock salt structure (indicated by the dotted line area), and confirmed that these structures formed a nanocomposite mixed at the nanoscale. In the lower right drawing of Fig. 35, the diffraction points representing the rock salt structure are indicated by solid circles.

[0272] Referring to Tables 13 and 14, in the evaluation of 2032 coin type half-cells manufactured using Comparative Example 2 and Example 8, 0.1 C and 0.2 C charge / discharge were performed once each at 30 ℃ in the voltage ranges of 2.0 V - 4.0 V and 2.0 V - 4.3 V, respectively, and then 0.5 C 100 cycle evaluation was performed. Example 8 confirmed that the initial charge / discharge efficiency and cycle characteristics were improved by dry doping of Ca. That is, Example 8 confirmed that the structural stability of the cathode active material was improved by dry doping of Ca.

[0273]

[0274] Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering its technical spirit or essential characteristics. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims below rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

Claims

1. In a cathode active material for a sodium secondary battery, including a secondary particle composed of a group of a plurality of primary particles, The above primary particle is a cathode active material for a sodium secondary battery including a nanocomposite in which a rock salt (Fm3m) structure and a layered (R-3m) structure are mixed at the nanoscale.

2. In a cathode active material for a sodium secondary battery, including a secondary particle composed of a group of a plurality of primary particles, The primary particle includes a first primary particle provided at the center of the secondary particle and a second primary particle provided at the surface of the secondary particle, The above first primary particle is composed of a1, which is the average length of the major axis of the first primary particle, and a2, which is the average length of the minor axis perpendicular to a1, wherein a1 is equal to or greater than a2, A cathode active material for a sodium secondary battery, wherein the second primary particle is composed of b1, which is an average length of the long axis of the second primary particle, and b2, which is an average length of the short axis perpendicular to b1, wherein b1 is provided to be larger than b2.

3. In paragraph 1 or 2, A cathode active material for a sodium secondary battery, wherein the diffraction peak intensities of the (0-14) plane, (0-11) plane, (006) plane, and (003) plane obtained from the SAED electron diffraction image during TEM analysis are I(0-14) > I(0-11) and I(006) > I(003).

4. In paragraph 2, A positive electrode active material for a sodium secondary battery, wherein the surface portion of the secondary particle is within 20% of the average diameter of the secondary particle in the direction from the outermost surface of the secondary particle toward the center of the secondary particle.

5. In paragraph 2, At least some of the primary particles provided on the surface of the secondary particles are provided in a rod shape, The primary particle in the above rod shape is provided with a short axis length that is a short length passing through the center of the rod shape, and a long axis length that is provided longer than the short axis length so as to be perpendicular to the short axis length. A positive electrode active material for a sodium secondary battery, wherein the major axis length is 1.5 to 25 times the minor axis length, and the major axis length is provided in a direction toward the center of the secondary particle.

6. In paragraph 2, The above primary particles include oriented particles formed in the form of a columnar structure having a short axis and a long axis, and the oriented particles include oriented particles having an a-axis and a c-axis, and the length in the a-axis direction is provided to be longer than the length in the c-axis direction. Among the above-mentioned oriented particles, the length in the a-axis direction of the primary particle provided at the center of the secondary particle is provided longer than the length in the a-axis direction of the primary particle provided at the surface of the secondary particle. The above c-axis corresponds to the [001] direction in the SAED pattern obtained by observing the above-mentioned oriented particles with a transmission electron microscope, and the above-mentioned a-axis is perpendicular to the above-mentioned c-axis and is provided parallel to the long axis of the above-mentioned oriented particles. A positive electrode active material for a sodium secondary battery.

7. In paragraph 6, The above cathode active material is prepared by mixing and calcining a complex metal hydroxide as a precursor with a sodium compound. A positive electrode active material for a sodium secondary battery, wherein the above-mentioned oriented particles are provided before calcining the above-mentioned composite metal hydroxide.

8. In paragraph 1 or 2, The above cathode active material is prepared by mixing and calcining a complex metal hydroxide as a precursor with a sodium compound. The above complex metal hydroxide is a cathode active material for a sodium secondary battery, which is manufactured by a co-precipitation reaction using one or more transition metal compounds.

9. In paragraph 1 or 2, A cathode active material for a sodium secondary battery, wherein the average diameter of the secondary particles is 2 μm to 20 μm.

10. In paragraph 1 or 2, A cathode active material for a sodium secondary battery having an O3 crystal structure and represented by the following chemical formula 1: [Chemical Formula 1] [Na 1-x A1 x ][Ni y TM z A2 1-y-z ]O2 (In the above chemical formula 1, TM is at least one of Mn and Fe, A1 is selected from the group consisting of Li, Ca and combinations thereof, A2 is selected from the group consisting of Mg, Ti, Li, V, Sb, Mo, W, Zr, Sn, Y, B, Al, Co and combinations thereof, 0≤x≤0.1, 0.2≤y≤0.7, 0≤z≤0.8.) 11. In paragraph 10, The above chemical formula 1 is prepared by mixing and calcining a complex metal hydroxide, which is a precursor containing nickel (Ni) and a transition metal (TM), with a sodium compound, The above A1 is provided by dry doping, and the above A2 is provided by dry doping or wet doping, The above dry doping includes dry mixing the above complex metal hydroxide and sodium compound and then calcining them. The above wet doping includes introducing a compound including A2 together with a nickel compound including Ni and a transition metal compound including TM in the process of manufacturing the complex metal hydroxide by a co-precipitation reaction. A positive electrode active material for a sodium secondary battery, wherein the above A1 is substituted at the Na site and the above A2 is substituted at the Ni site or the TM site.

12. A method for manufacturing a positive electrode active material for a sodium secondary battery according to paragraph 1 or 2, A coprecipitation reaction step in which a nickel compound containing nickel (Ni) and a transition metal compound containing a transition metal (TM) are placed in a coprecipitation reactor and a precursor complex metal hydroxide is manufactured through a coprecipitation reaction for 30 to 60 hours; A calcination step of mixing the above complex metal hydroxide with a sodium compound and heat-treating it; and A method for manufacturing a cathode active material for a sodium secondary battery, comprising a quenching step of rapidly cooling after the above heat treatment is completed.

13. In paragraph 12, A method for producing a cathode active material for a sodium secondary battery, comprising, in the above coprecipitation reaction step, removing a solution remaining inside the coprecipitation reactor to the outside of the coprecipitation reactor during the process of performing the coprecipitation reaction.

14. In paragraph 12, The above complex metal hydroxide comprises secondary particles in which a plurality of primary particles are aggregated, wherein the primary particles comprise oriented particles in the form of a rod having a short axis and a long axis, The above-mentioned oriented particle includes an oriented particle having an a-axis and a c-axis, and the length in the a-axis direction is provided to be longer than the length in the c-axis direction, A method for producing a cathode active material for a sodium secondary battery, wherein the oriented particles of the above composite metal hydroxide are maintained in the cathode active material produced after the sintering step.

15. In paragraph 13, A method for manufacturing a positive electrode active material for a sodium secondary battery, wherein the c-axis corresponds to the [001] direction in an SAED pattern obtained by observing the oriented particles with a transmission electron microscope, and the a-axis is perpendicular to the c-axis and parallel to the long axis of the oriented particles.

16. In paragraph 13, The concentration of the complex metal hydroxide, which is a precursor manufactured in the above co-precipitation reaction step, is 0.3 kg. 전구체 / L 용액 A method for manufacturing a positive electrode active material for a sodium secondary battery.

17. In paragraph 13, A method for manufacturing a positive electrode active material for a sodium secondary battery, wherein the temperature in the above-mentioned sintering step is 730°C to 850°C and the time is 15 hours to 30 hours.

18. In paragraph 13, A method for manufacturing a cathode active material for a sodium secondary battery, wherein, in the above quenching step, rapid cooling is performed from 35°C to 20°C at a rate of 5°C / min to 16°C / min while maintaining a vacuum state in the chamber.

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