Positive electrode active material for lithium secondary battery, method of manufacturing the same, and lithium secondary battery

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery, the positive electrode active material comprising: a first positive electrode active material including a lithium nickel-cobalt-aluminum composite oxide, the first positive electrode active material being formed by agglomeration of a plurality of primary particles, at least some of which are arranged radially; and a second positive electrode active material including a lithium nickel-cobalt-aluminum-manganese composite oxide, the second positive electrode active material being formed by agglomeration of a plurality of primary particles, the average particle size of the secondary particles of the first positive electrode active material being larger than the average particle size of the secondary particles of the second positive electrode active material.

Description

[Technical Field]

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

[0002] Lithium secondary batteries, which have high energy density yet are easy to carry, are primarily used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, active research has been conducted into using high-energy-density lithium secondary batteries as power sources for hybrid and electric vehicles, or as power sources for power storage.

[0003] Various positive electrode active materials have been investigated to realize lithium secondary batteries suitable for such applications, and among these, lithium nickel oxides, lithium nickel manganese cobalt composite oxides, lithium nickel cobalt aluminum composite oxides, and lithium cobalt oxides are the most commonly used positive electrode active materials.

[0004] Recently, high-nickel cathode active materials have been widely used to achieve higher capacity. Furthermore, many cathode active materials have been developed that combine large and small particles of different particle sizes in the right ratio to increase energy density. However, these materials can cause cracks to form within the particles during the charge-discharge process over long periods of cycling. These cracks can induce side reactions between the cathode active material and the electrolyte, resulting in gas generation, which reduces safety, and electrolyte depletion, which reduces battery performance. Therefore, there is a need for the development of cathode active materials that can achieve both high capacity and long life. Summary of the Invention [Problem to be solved by the invention]

[0005] Provided are a positive electrode active material that has high capacity, high initial charge / discharge efficiency, and excellent life characteristics, a method for producing the same, and a lithium secondary battery including the same. [Means for solving the problem]

[0006] In one embodiment, there is provided a positive electrode active material for a lithium secondary battery, comprising: a first positive electrode active material comprising a lithium nickel-cobalt-aluminum-based composite oxide, the first positive electrode active material being in the form of secondary particles formed by agglomeration of a plurality of primary particles, at least a portion of which are radially arranged; and a second positive electrode active material comprising a lithium nickel-cobalt-aluminum-manganese-based composite oxide, the second positive electrode active material being in the form of secondary particles formed by agglomeration of a plurality of primary particles, the average particle size of the secondary particles of the first positive electrode active material being larger than the average particle size of the secondary particles of the second positive electrode active material.

[0007] In another embodiment, there is provided a method for producing a positive electrode active material for a lithium secondary battery, the method including: mixing a first positive electrode active material precursor, which includes a nickel-cobalt-aluminum composite hydroxide and is in the form of secondary particles formed by aggregating a plurality of primary particles, at least a portion of which are radially arranged; a second positive electrode active material precursor, which includes a nickel-cobalt-manganese composite hydroxide and is in the form of secondary particles formed by aggregating a plurality of primary particles; and a lithium source, followed by heat treatment, wherein the average particle size of the first positive electrode active material precursor is larger than the average particle size of the second positive electrode active material precursor.

[0008] In another embodiment, a lithium secondary battery is provided that includes a positive electrode containing the positive electrode active material, a negative electrode, and an electrolyte. [Effects of the Invention]

[0009] The positive electrode active material for a lithium secondary battery according to one embodiment exhibits high capacity, high initial charge / discharge efficiency, and excellent life characteristics. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a schematic diagram showing the shape of a plate-shaped primary particle according to one embodiment. [Figure 2] FIG. 10 is a diagram for explaining the definition of a radiation type in secondary particles according to an embodiment. [Figure 3]FIG. 2 is a schematic diagram illustrating a cross-sectional structure of a secondary particle according to one embodiment. [Figure 4] 1 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. [Figure 5] FIG. 1 is a cross-sectional view schematically illustrating an all-solid-state secondary battery according to an embodiment. [Figure 6] FIG. 1 is a cross-sectional view schematically illustrating an all-solid-state secondary battery according to an embodiment. [Figure 7] 1 is a graph showing the initial charge / discharge capacity at room temperature and the pellet density of the positive electrode active material for the batteries of Example 1 and Comparative Examples 1 to 6. [Figure 8] 1 is a graph showing the initial discharge capacity and 50-cycle capacity retention rate at high temperature for the batteries of Example 1 and Comparative Examples 1 to 6. [Figure 9] 1 is a scanning electron microscope (SEM) image of the separated granules of Example 1. [Figure 10] 1 is an SEM image of the separated small particles of Comparative Example 2. [Figure 11] 1 is a graph showing the contents of Co, Al, and Mn as a result of inductively coupled plasma emission spectrometry (ICP) for the small granules of Example 1 and the small granules of Comparative Example 2. [Figure 12] 1 is an SEM image of a cross section of the first lithium nickel-based composite oxide particles produced in Reference Example 1, cut with a focused ion beam (FIB). [Figure 13] 10 is an SEM image of a cross section of the third lithium nickel-based composite oxide particles produced in Reference Example 3, cut with an FIB. [Figure 14] 1 is an SEM image of the surface of the first lithium nickel-based composite oxide particles produced in Reference Example 1. [Figure 15] 1 is an SEM image of the surface of second lithium nickel composite oxide particles produced in Reference Example 2. [Figure 16] 1 is an SEM image of the surface of particles corresponding to large particles in the positive electrode active material of Example 1. [Figure 17]1 is an SEM image of the surface of particles corresponding to small particles of the positive electrode active material of Example 1. [Figure 18] 1 is an SEM image of the surface of particles corresponding to large particles in the positive electrode active material of Comparative Example 1. [Figure 19] 1 is an SEM image of the surface of particles corresponding to small particles of the positive electrode active material of Comparative Example 1. [Figure 20] 1 shows SEM images (top row) of the positive electrode active materials prepared in Example 1, Comparative Example 2, and Comparative Example 6, and images (bottom row) showing Al distribution as a result of energy dispersive X-ray spectroscopy (EDS) analysis of the SEM images (top row) of the positive electrode active materials prepared in Example 1, Comparative Example 2, and Comparative Example 6. [Figure 21] 21 is an enlarged SEM image (left side) of the portion shown in the white square box of Comparative Example 2 in FIG. 20, and an image (right side) showing the Al distribution by EDS. [Figure 22] 21 is an enlarged SEM image (left side) of the portion shown in the white square box of Comparative Example 6 in FIG. 20, and an image (right side) showing the Al distribution by EDS. [Figure 23] 10 is a transmission electron microscope (TEM) image of a cross section of a second positive electrode active material of Comparative Example 6. [Figure 24] This is an enlarged image of the yellow square box in Figure 23. [Figure 25] 1 is a TEM image of a cross section of a second positive electrode active material of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] Although specific embodiments are described below in detail so that those skilled in the art can easily implement the present invention, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0012] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0013] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0014] It should be understood that the terms "comprise," "comprise," or "have" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possible presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0015] In the drawings, the thickness of multiple layers and regions is exaggerated to clearly show them, and similar parts are designated by the same reference numerals throughout the specification. When a layer, film, region, plate, or other part is said to be "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part between them. Conversely, when a part is said to be "directly on" the other part, it means that there is no other part between them.

[0016] Furthermore, the term "layer" as used herein includes not only shapes formed on the entire surface when observed in a plan view, but also shapes formed on a portion of the surface.

[0017] The average particle size can be measured by methods well known to those skilled in the art, such as by using a particle size analyzer or by using a transmission electron microscope image or a scanning electron microscope image. Alternatively, the average particle size can be measured using dynamic light scattering, and the data can be analyzed to count the number of particles in each particle size range, followed by calculation to obtain the average particle size value. Unless otherwise defined, the average particle size can refer to the diameter (D50) of particles that make up 50% of the cumulative volume in a particle size distribution. Furthermore, unless otherwise defined, the average particle size can be determined by measuring the size (diameter or major axis length) of approximately 20 randomly selected particles in a scanning electron microscope image to obtain a particle size distribution, and then taking the diameter (D50) of particles that make up 50% of the cumulative volume in the particle size distribution as the average particle size.

[0018] Here, "or" is not to be construed in an exclusive sense; for example, "A or B" is to be construed as including A, B, A+B, etc.

[0019] The term "metal" is understood to include general metals, transition metals, and semimetals (metalloids).

[0020] positive electrode active material According to one embodiment, a positive electrode active material for a lithium secondary battery includes a first positive electrode active material and a second positive electrode active material. The first positive electrode active material includes a lithium nickel-cobalt-aluminum composite oxide and is formed by agglomeration of a plurality of primary particles, at least a portion of which are in the form of radially arranged secondary particles. The second positive electrode active material includes a lithium nickel-cobalt-aluminum-manganese composite oxide and is formed by agglomeration of a plurality of primary particles in the form of secondary particles. The average particle size of the secondary particles of the first positive electrode active material is larger than the average particle size of the secondary particles of the second positive electrode active material. The first positive electrode active material may be described as large particles, large particles, or large particles, and the second positive electrode active material may be described as small particles, small particles, or small particles. This positive electrode active material can achieve high capacity, high initial charge / discharge efficiency, and excellent room-temperature and high-temperature life.

[0021] The lithium nickel-cobalt-aluminum composite oxide in the first positive electrode active material refers to an oxide containing lithium, nickel, cobalt, and aluminum, and optionally further containing other elements, and may be represented as Ni-Co-Al or NCA. The lithium nickel-cobalt-aluminum-manganese composite oxide in the second positive electrode active material refers to an oxide containing lithium, nickel, cobalt, aluminum, and manganese, and optionally further containing other elements, and may be represented as Ni-Co-Al-Mn or NCAM. The nickel-cobalt-manganese hydroxide in the precursor of the second positive electrode active material in the manufacturing method of the positive electrode active material described below refers to an hydroxide containing nickel, cobalt, and manganese, and optionally further containing other elements, and may be represented as Ni-Co-Mn precursor or NCM precursor.

[0022] The cathode active material can be prepared by mixing a first cathode active material precursor (NCA precursor) and a second cathode active material precursor (NCM precursor) with a lithium source and co-firing the mixture. During the co-firing process, the Al component of the first cathode active material precursor, which is in the form of large, radiative secondary particles, migrates or diffuses into the second cathode active material precursor, which is in the form of small, secondary particles, to form the second cathode active material as NCAM. Conversely, the Mn component of the second cathode active material precursor does not diffuse into the first cathode active material precursor, so that the first cathode active material remains as NCA without becoming NCAM.

[0023] The second cathode active material prepared in this manner has a different shape and composition distribution than a cathode active material prepared simply using an NCAM composition precursor, or an NCAM cathode active material prepared by post-treating an NCM cathode active material with an Al precursor and then coating or doping it with Al, and has been confirmed to have better capacity and lifespan characteristics.

[0024] In addition, cathode active materials prepared by conventional methods, in which first and second cathode active material precursors are calcined separately and then mixed together, rather than co-calcined, also differ from the cathode active material according to one embodiment in terms of shape, composition distribution, etc., and have problems such as low pellet density, reduced battery volume capacity, and poor life characteristics due to different thermalization rates between large and small particles. Even if the second cathode active material is doped or coated with Al to enhance structural stability, the addition of Al raw material has been found to cause a decrease in capacity. The shape, composition distribution, and other characteristics of the cathode active material according to one embodiment will be described in detail below, and the manufacturing method thereof will also be described in detail below.

[0025] First positive electrode active material The first positive electrode active material includes a lithium nickel-cobalt-aluminum composite oxide, which can be represented by Chemical Formula 1 below. [Chemical formula 1] Li a1 Ni x1 Co y1 Al z1 M 1 w1 O2-b1 X b1

[0026] In Chemical Formula 1, 0.9 ≦ a1 ≦ 1.2, 0.7 ≦ x1 < 1, 0 < y1 < 0.3, 0 < z1 < 0.3, 0 ≦ w1 < 0.3, 0.9 ≦ x1 + y1 + z1 + w1 ≦ 1.1, and 0 ≦ b1 ≦ 0.1, and M 1 is one or more elements selected from the group consisting of B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0027] In Chemical Formula 1, for example, 0.7 ≦ x1 ≦ 0.98, 0.01 ≦ y1 ≦ 0.29, 0.01 ≦ z1 ≦ 0.29, 0 ≦ w1 ≦ 0.28 may hold, 0.8 ≦ x1 ≦ 0.98, 0.01 ≦ y1 ≦ 0.19, 0.01 ≦ z1 ≦ 0.19, 0 ≦ w1 ≦ 0.18 may hold, or 0.9 ≦ x1 ≦ 0.98, 0.01 ≦ y1 ≦ 0.09, 0.01 ≦ z1 ≦ 0.09, 0 ≦ w1 ≦ 0.08 may hold.

[0028] The first positive electrode active material is in the form of secondary particles in which a plurality of primary particles are aggregated, and the secondary particles can be spherical, ellipsoidal, polygonal, amorphous, etc. The first positive electrode active material is large particles, and the average particle diameter of the secondary particles can be 9 μm to 25 μm, for example, 9 μm to 20 μm, or 10 μm to 18 μm. Here, the average particle diameter of the secondary particles is obtained by selecting any about 20 particles of the large particles from the SEM image of the positive electrode active material, measuring their particle diameters (diameter, or major diameter, or length of the long axis), obtaining a particle size distribution, and taking the diameter (D50) of the particles with a cumulative volume of 50% in the particle size distribution as the average particle diameter.

[0029] The average particle size of the primary particles constituting the secondary particles of the first positive electrode active material may be less than 200 nm, e.g., 50 nm to less than 200 nm, 100 nm to less than 200 nm, 50 nm to 190 nm, or 50 nm to 180 nm. When the average particle size of the primary particles satisfies this range, the lithium diffusion path is shortened, reducing resistance and improving charge / discharge efficiency. Here, the average particle size of the primary particles refers to the size of the primary particles observed from the surface of the secondary particles. It can be obtained by randomly selecting approximately 20 primary particles from an SEM image of the surface of the secondary particles, measuring their particle sizes (diameter, major axis, or length of the major axis), and then calculating the arithmetic average.

[0030] The secondary particles of the first positive electrode active material are characterized by at least some of the primary particles being radially arranged. In this case, the degree of lithium diffusion is increased, improving initial charge / discharge efficiency and ensuring high capacity. Furthermore, since uniform expansion and contraction is possible during lithium insertion and desorption, the problem of cracking of the positive electrode active material during charge / discharge is alleviated, improving battery life characteristics and safety. Furthermore, when the first positive electrode active material is in the form of secondary particles in which at least some of the primary particles are radially arranged, it is favorable for the Al component of the first positive electrode active material precursor to diffuse into the second positive electrode active material precursor in a method for manufacturing a positive electrode active material according to an embodiment, thereby enabling the manufacture of a positive electrode active material with improved capacity characteristics, initial charge / discharge efficiency, and life characteristics.

[0031] The radial structure will now be described in detail.

[0032] At least some of the primary particles may have a plate shape. Figure 1 is a schematic diagram showing the plate shape of primary particles. Referring to Figure 1, the primary particles may have various detailed shapes while basically having a plate structure, such as (A) a polygonal nanoplate shape such as a hexagon, (B) a nanodisk shape, or (C) a rectangular parallelepiped shape.

[0033] In Figure 1, "a" refers to the length of the major axis of the primary particle, "b" refers to the length of the contraction, and "t" refers to the thickness. Here, the length of the major axis a refers to the maximum length based on the widest surface of the primary particle. The thickness t can be said to be the maximum length of the surface that is approximately perpendicular to the widest surface of the primary particle. The direction that includes the length of the major axis a and the length of the contraction b is defined as the plane direction, and the direction in which the thickness t is defined is defined as the thickness direction.

[0034] The thickness t of the primary particle may be smaller than the major axis length a and the contraction length b, which are the lengths in the planar direction. The major axis length a of the planar direction may be longer than or equal to the contraction length b.

[0035] The primary particles being radially arranged may mean, for example, that the major axes of the primary particles are arranged in a radial direction. Figure 2 is a diagram illustrating the definition of "radial." In one embodiment, the radial arrangement structure means that the thickness direction (t) of the primary particles is perpendicular to the direction R from the center of the secondary particles to the surface or forms an angle of ±5° with the perpendicular direction, as shown in Figure 2.

[0036] When at least a portion of the primary particles are arranged radially, the surface of the secondary particles can have a relatively large number of lithium diffusion paths between the primary particles. The lithium-transferable crystal planes are exposed to the outside, improving lithium diffusivity and ensuring high initial efficiency and high capacity. Furthermore, when the primary particles are arranged radially, the pores exposed on the surface of the secondary particles can further promote lithium diffusion toward the center of the secondary particles. Furthermore, the radially arranged primary particles enable uniform expansion and contraction during lithium insertion and deintercalation, and the pores present in the direction of the Miller index (001) plane, which is the direction of particle expansion during lithium deintercalation, provide a buffering effect. This reduces the likelihood of cracks occurring during contraction and expansion of the positive electrode active material. The internal pores further mitigate volumetric changes, reducing cracks that occur between primary particles during charge and discharge. This ultimately improves the lifespan of lithium secondary batteries and reduces resistance increase.

[0037] For example, the secondary particles may include an interior portion having an irregular porous structure and an exterior portion having a radially oriented structure surrounding the interior portion.

[0038] The irregular porous structure refers to a structure having primary particles and pores, and the pore size, shape, and position are not regular. That is, primary particles arranged internally may be arranged irregularly, unlike primary particles arranged externally. Here, "external" may refer to, for example, a region extending from 30 to 50% of the total distance from the outermost surface of the secondary particle, e.g., 40% of the total distance from the outermost surface, or a region extending from the outermost corner of the secondary particle to a depth of about 3 μm. Furthermore, "internal" may refer to a region extending from 50 to 70% of the total distance from the center of the secondary particle, e.g., 60% of the total distance from the center of the secondary particle, or the remaining region excluding a region extending from the outermost corner of the secondary particle to a depth of about 3 μm.

[0039] In addition, the pores present inside the secondary particles may be larger in size than the pores present outside. For example, the size of the pores present inside may be 150 nm to 1 μm, and the size of the pores present outside may be less than 150 nm. When the pore size inside is larger than the pores outside, the lithium diffusion distance from the inside of the positive electrode active material is shorter than that of secondary particles with the same pore size inside and outside, which has the advantage of facilitating lithium insertion from the outside and reducing volume changes that occur during charge and discharge. Here, the pore size refers to the diameter when the pores are spherical or circular, and the length of the major axis when the pores are elliptical, etc. The pore size may be a value obtained by measuring the size of approximately 20 pores randomly from an SEM image of the cross section of the secondary particles and then calculating the arithmetic average of the measured pore sizes.

[0040] The secondary particles may have open pores on their surfaces. The size of the open pores may be less than about 150 nm, for example, 10 to 148 nm. The open pores are pores in which a portion of the wall of the pores is not closed, formed by spaces between radially arranged plate-like primary particles, and are pores that are deeply connected from the surface toward the center of the secondary particles. Such open pores may be connected to the outside and serve as passages for materials to enter and exit. The open pores may extend from the surface toward the center of the secondary particles and may be formed to an average depth of 150 nm or less, for example, 0.001 to 100 nm, for example, 1 to 50 nm, from the surface of the secondary particles. The size and depth of the open pores may be measured using the BJH (Barrett, Joyner, and Halenda) method, which derives nitrogen adsorption or desorption content.

[0041] Figure 3 is a schematic diagram showing the cross-sectional structure of a secondary particle of a positive electrode active material. Referring to Figure 3, the secondary particle 11 includes an outer portion 14 in which plate-shaped primary particles 13 are radially arranged, and an inner portion 12 in which the primary particles 13 are irregularly arranged. The inner portion 12 may have more voids between the primary particles than the outer portion. The pore size and porosity in the inner portion may be larger and more irregular than the pore size and porosity in the outer portion. Arrows in Figure 3 indicate the direction of lithium ion migration.

[0042] The secondary particles have a porous structure inside, which reduces the diffusion distance of lithium ions to the interior, and the primary particles are radially arranged outside, which facilitates lithium ion intercalation on the surface. Furthermore, the small size of the primary particles facilitates lithium transport paths between crystal grains. Furthermore, the small size of the primary particles and the pores between the primary particles mitigate volumetric changes that occur during charge and discharge, minimizing stress caused by volumetric changes during charge and discharge. This positive electrode active material can reduce the resistance of lithium secondary batteries and improve their capacity and life characteristics.

[0043] The first positive electrode active material may be contained in an amount of 60% to 95% by weight, for example, 70% to 90% by weight, based on 100% by weight of the positive electrode active material for the lithium secondary battery. When the first positive electrode active material is contained within the above content range, it is possible to produce a positive electrode active material having an optimal composition while increasing the pellet density of the positive electrode active material and the energy density of the positive electrode.

[0044] Second positive electrode active material The second positive electrode active material is in the form of secondary particles in which a plurality of primary particles are aggregated, is a small particle, and the average particle diameter of the secondary particles may be 2 μm to 8 μm, for example, 2.5 μm to 7 μm, or 3 μm to 6 μm.

[0045] The second positive electrode active material contains a lithium nickel-cobalt-aluminum-manganese-based composite oxide, and this compound can be represented by the following Chemical Formula 2. [Chemical Formula 2] Li a2 Ni x2 Co y2 Al z2 Mn w2 M 2 v2 O 2-b2 X b2

[0046] In Chemical Formula 2, 0.9 ≦ a2 ≦ 1.2, 0.7 ≦ x2 < 1, 0 < y2 < 0.3, 0 < z2 < 0.3, 0 < w2 < 0.3, 0 ≦ v2 < 0.3, 0.9 ≦ x2 + y2 + z2 + w2 + v2 ≦ 1.1, and 0 ≦ b2 ≦ 0.1, and M 2 is one or more elements selected from the group consisting of B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0047] In Chemical Formula 2, for example, 0.7≦x2≦0.979, 0.01≦y2≦0.289, 0.001≦z2≦0.289, 0.01≦w2≦0.289, 0≦v2≦0.279 may be satisfied; 0.8≦x2≦0.979, 0.01≦y2≦0.189, 0.001≦z2≦0.189, 0.01≦w2≦0.189, 0≦v2≦0.179 may be satisfied; or 0.9≦x2≦0.979, 0.01≦y2≦0.089, 0.001≦z2≦0.089, 0.01≦w2≦0.089, 0≦v2≦0.079 may be satisfied.

[0048] The second cathode active material is made from an NCM precursor and has an NCAM composition by transferring an Al component from the first cathode active material during a calcination process, and has a different shape and composition distribution from a cathode active material made from an NCAM precursor as described above. For example, the second cathode active material may have a higher aluminum content in the surface layer of the secondary particles than in the interior of the secondary particles.

[0049] The "interior" of a secondary particle in the second positive electrode active material may refer to a region extending from the center of the secondary particle to approximately 70% of the length of the radius, and the "surface layer" of the secondary particle may refer to a region surrounding the interior, extending from the outermost surface of the secondary particle to a depth equivalent to 30% of the length of the radius.

[0050] The content of elements such as Al in the interior or surface layer of the secondary particles of the second positive electrode active material may be measured by TEM-EELS (Transmission Electron Microscope-Electron Energy Loss Spectroscopy) analysis of a cross section of the secondary particles cut with a focused ion beam (FIB), etc. Also, the aluminum content may refer to the at% content of aluminum relative to 100 at% of all metals excluding lithium.

[0051] For example, the aluminum content relative to the total metal excluding lithium in the surface layer of the secondary particles of the second positive electrode active material may be 0.2 at% to 2 at%. The aluminum content relative to the total metal excluding lithium in the interior of the secondary particles may be 0 at% to 0.6 at%, and the Al content in the surface layer may be higher than the Al content in the interior.

[0052] In addition, in the second positive electrode active material according to one embodiment, the aluminum content in the surface layer of the secondary particles in the portion that contacts the first positive electrode active material may be higher than the aluminum content in the portion that does not contact the first positive electrode active material. This is understood to be due to the transfer of Al components from the first positive electrode active material, and is a feature that distinguishes this from a case where an NCAM precursor is used as the small particles or a case where Al is separately coated or doped.

[0053] For example, the aluminum content relative to the total metal excluding lithium in the surface layer of the secondary particles of the second positive electrode active material in the portion in contact with the first positive electrode active material may be 0.8 at% to 2.0 at%, e.g., 0.8 at% to 1.8 at%, or 0.9 at% to 1.6 at%, and the aluminum content relative to the total metal excluding lithium in the portion not in contact with the first positive electrode active material may be less than 0.8 at%, e.g., 0 at% to 0.7 at%, or 0.1 at% to 0.6 at%.

[0054] In other words, the second positive electrode active material according to one embodiment can be said to include a high-Al-concentration region and a low-Al-concentration region in the surface layer of the secondary particle. The aluminum content of the high-Al-concentration region relative to the total metal excluding lithium may be 0.8 at% to 2.0 at%, for example, 0.8 at% to 1.8 at%, or 0.9 at% to 1.6 at%. The aluminum content of the low-Al-concentration region relative to the total metal excluding lithium may be less than 0.8 at%, for example, 0 at% to 0.7 at%, or 0.1 at% to 0.6 at%.

[0055] Furthermore, the difference between the aluminum content in the high-Al-concentration region and the aluminum content in the low-Al-concentration region may be 0.3 at % to 2.0 at %, for example, 0.4 at % to 1.8 at %, or 0.5 at % to 1.5 at %.

[0056] Another well-known method involves doping or coating the lithium-metal composite oxide with aluminum by mixing it with an aluminum source and heat-treating it. However, this method results in unreacted aluminum source material, e.g., aluminum oxide such as Al2O3, remaining in the final cathode active material. Furthermore, uneven Al doping on the particle surfaces can result in high Al concentrations (exceeding 2 at.%) in some areas of the surface, resulting in reduced capacity. In contrast, the cathode active material according to one embodiment does not add an additional aluminum source material during the sintering process. Therefore, no unreacted aluminum source material, such as aluminum oxide, is present on the outermost surfaces of the secondary particles of the first and second cathode active materials in the final cathode active material. Furthermore, even in the high-Al-content regions of the surface layer of the second cathode active material, the Al content remains below 2 at. The difference in Al content between the high- and low-Al-concentration regions is also small, at 2 at.% or less. As a result, the second positive electrode active material according to one embodiment has structural stability and performance improvement effects due to Al doping, while also effectively suppressing problems such as capacity reduction that occur when adding an Al raw material during firing.

[0057] The second positive electrode active material may be included in an amount of 5 to 40 wt %, for example, 10 to 30 wt %, based on 100 wt % of the positive electrode active material for a lithium secondary battery. When the second positive electrode active material is included in this content range, the pellet density of the positive electrode active material can be increased, and the energy density of the positive electrode can be increased, while a positive electrode active material having an optimal composition can be produced.

[0058] Method for producing positive electrode active material The method for producing the positive electrode active material will be described in detail below.

[0059] In one embodiment, there is provided a method for producing a positive electrode active material for a lithium secondary battery, the method including: mixing a first positive electrode active material precursor, which includes a nickel-cobalt-aluminum composite hydroxide and is in the form of secondary particles formed by aggregating a plurality of primary particles, at least a portion of which are radially arranged; a second positive electrode active material precursor, which includes a nickel-cobalt-manganese composite hydroxide and is in the form of secondary particles formed by aggregating a plurality of primary particles; and a lithium source; and heat treating the mixture; wherein the average particle size of the first positive electrode active material precursor is larger than the average particle size of the second positive electrode active material precursor.

[0060] This preparation method involves mixing a large-particle radiant secondary particle NCA precursor and a small-particle secondary particle NCM precursor with a lithium source and co-firing them. During the co-firing process, the large-particle Al component diffuses or migrates to the small particles, forming the small particles with an NCAM composition. This allows for the production of a cathode active material that combines large-particle radiant secondary particle NCA and small-particle NCAM. This is believed to be possible because the large-particle Al component diffuses faster than the small-particle Mn component in the co-firing temperature range, and because the large-particle precursor takes on the radiant secondary particle form, the Al component is more easily transferred to the small particles. The final cathode active material prepared in this manner exhibits high capacity, high initial charge / discharge efficiency, and excellent life characteristics.

[0061] The manufacturing method can significantly improve volumetric capacity compared to existing methods in which large and small particles are manufactured by separately firing them and then mixing them. It can also further improve initial discharge capacity, volumetric capacity, and energy density compared to methods in which large and small particles are individually fired and then doped or coated with Al, resulting in a mixture of large and small particles. Furthermore, the method according to one embodiment can improve life characteristics compared to using large and small particles with the same components, even when co-firing is applied, and can also improve initial discharge capacity and energy density compared to methods in which Al is separately doped or coated after co-firing. In the manufacturing method of a positive electrode active material according to one embodiment, an appropriate amount of aluminum is introduced into the large and small particles, ensuring structural stability and alleviating the problem of capacity reduction due to the addition of aluminum raw material, even without mixing aluminum raw material during or after co-firing.

[0062] The nickel-cobalt-aluminum composite hydroxide, which is the first positive electrode active material precursor, can be specifically represented by the following Chemical Formula 11. [Chemical formula 11] Ni x11 Co y11 Al z11 M 11 w11 (OH)2

[0063] In the above formula 11, 0.7≦x11<1, 0 <y11<0.3、0<z11<0.3、0≦w11<0.3、0.9≦x11+y11+z11+w11≦1.1であり、M 11 is one or more elements selected from the group consisting of B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr.

[0064] The first positive electrode active material precursor may be formed by agglomeration of a plurality of primary particles, at least some of which may be arranged in a radial pattern as secondary particles. The average particle size of the secondary particles may be 9 μm to 25 μm, for example, 9 μm to 20 μm or 10 μm to 18 μm. Here, the average particle size of the secondary particles may be determined by randomly selecting about 20 particles from an SEM image of the first positive electrode active material precursor, measuring their particle sizes (diameter, major axis, or length of the major axis), obtaining a particle size distribution, and then determining the diameter (D50) of the particles that make up 50% of the cumulative volume in the particle size distribution as the average particle size.

[0065] The first positive electrode active material precursor can be prepared by a co-precipitation reaction. Specifically, a composite metal raw material is prepared by mixing metal raw materials, such as a nickel raw material, and a complexing agent and a pH adjuster are added to the composite metal raw material to control the pH of the mixture, thereby producing a nickel-based composite hydroxide of the desired composition. The complexing agent adjusts the reaction rate of precipitate formation in the co-precipitation reaction and can be, for example, ammonium hydroxide (NH4OH) or citric acid. The pH adjuster can be, for example, sodium hydroxide (NaOH), sodium carbonate (Na2CO3), or sodium oxalate (Na2CO4). The pH of the mixture can be adjusted to a range of, for example, 10 to 13.

[0066] The coprecipitation reaction can be carried out in several stages, for example, two, three, or four stages. In each stage, the complexing agent concentration, the metal raw material feeding rate, the pH adjustment range, the reaction temperature, the reaction time, or the stirring power can be adjusted. By adjusting these parameters, a cathode active material precursor can be produced in the form of secondary particles in which at least some of the primary particles are radially arranged, and secondary particles with different internal and external shapes can be produced.

[0067] For example, a first cathode active material precursor having a radial structure can be prepared by the following method. The method for preparing the first cathode active material precursor includes a first step, a second step, and a third step for sequentially forming a core, an intermediate layer, and a shell. In the first step, a complexing agent, a pH adjuster, and a metal source are introduced into a reactor and reacted. The complexing agent concentration may be 0.1M to 0.7M, and the introduction rate may be 6mL / min to 12mL / min. The metal source concentration may be 0.1M to 3.5M, and the introduction rate may be 50mL / min to 100mL / min. Then, in the second step, a complexing agent, a pH adjuster, and a metal source are further introduced. The complexing agent concentration may be 0.3M to 1.0M, and the introduction rate may be 8mL / min to 15mL / min. The metal source concentration may be 0.1M to 3.5M, and the introduction rate may be 60mL / min to 120mL / min. Then, in the third step, the concentrations and input rates of the complexing agent and metal source are further increased or maintained the same to prevent a decrease in particle growth rate. In this case, the concentration of the complexing agent may be 0.35M to 1.0M, and the input rate may be 12mL / min to 20mL / min. The concentration of the metal source may be 0.1M to 3.5M, and the input rate may be 70mL / min to 150mL / min. In the first to third steps, the pH may be adjusted to between 10 and 12.

[0068] The nickel-cobalt-manganese composite hydroxide, which is the second positive electrode active material precursor, can be specifically represented by the following Chemical Formula 12. [Chemical formula 12] Ni x12 Co y12 Mn w12 M 12 v12 (OH)2

[0069] In the above formula 12, 0.7≦x12<1, 0 <y12<0.3、0<w12<0.3、0≦v12<0.3、0.9≦x12+y12+w12+v12≦1.1であり、M 12 is one or more elements selected from the group consisting of B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr.

[0070] The second positive electrode active material precursor may be in the form of secondary particles formed by agglomeration of a plurality of primary particles. The average particle size of the secondary particles may be 2 μm to 8 μm, for example, 2.5 μm to 7 μm, or 3 μm to 6 μm. Here, the average particle size of the secondary particles may be determined by randomly selecting about 20 particles from an SEM image of the second positive electrode active material precursor, measuring their particle sizes (diameter, major axis, or length of the major axis), obtaining a particle size distribution, and then taking the diameter (D50) of the particles that make up 50% of the cumulative volume in the particle size distribution as the average particle size.

[0071] The second positive electrode active material precursor can be produced by a general co-precipitation reaction.

[0072] The mixing weight ratio of the first positive electrode active material precursor to the second positive electrode active material precursor may be 60:40 to 95:5, or 70:30 to 90:10.

[0073] The lithium source may be, for example, Li2CO3, LiOH, a hydrate thereof, or a combination thereof. The lithium source may be mixed into the first positive electrode active material precursor and the second positive electrode active material precursor in an amount of 90 to 120 molar parts per 100 molar parts of the total metal.

[0074] The heat treatment may be performed at, for example, 600° C. to 1000° C. or 700° C. to 900° C. Within the temperature range, a first positive electrode active material and a second positive electrode active material each having an optimal composition may be prepared.

[0075] For example, the heat treatment may include a temperature rise step and a temperature maintenance step, with the temperature rise time being set to be longer than the temperature maintenance time. For example, the temperature rise time may be 6 to 16 hours, and the temperature maintenance time may be 1 to 9 hours, with the temperature rise time being longer than the temperature maintenance time. The temperature rise time in the heat treatment may be, for example, 6 to 15 hours, 6 to 14 hours, 6 to 13 hours, or 7 to 12 hours, and the temperature maintenance time may be 2 to 9 hours, or 3 to 8 hours. The ratio of (temperature rise time):(temperature maintenance time) may be 1.1:1 to 10:1, for example, 1.1:1 to 8:1, 1.1:1 to 6:1, 1.1:1 to 5:1, or 1.1:1 to 4:1.

[0076] positive electrode In one embodiment, a positive electrode for a lithium secondary battery is provided, the positive electrode for the lithium secondary battery including the positive electrode active material. The positive electrode for the lithium secondary battery includes a current collector and a positive electrode active material layer disposed on the current collector. The positive electrode active material layer includes the positive electrode active material and may further include a binder and / or a conductive material.

[0077] The binder serves to firmly adhere the positive electrode active material particles to each other and to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylate styrene-butadiene rubber, epoxy resin, and nylon.

[0078] The content of the binder in the positive electrode active material layer may be about 0.1 wt % to 5 wt % based on the total weight of the positive electrode active material layer.

[0079] The conductive material is used to impart conductivity to the electrodes, and any material that does not cause a chemical change in the constructed battery and is electronically conductive can be used. Examples of such a conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials containing copper, nickel, aluminum, silver, or the like in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof.

[0080] The content of the conductive material in the positive electrode active material layer may be 0.1 wt % to 5 wt % based on the total weight of the positive electrode active material layer.

[0081] The positive electrode current collector may be made of aluminum foil, but is not limited thereto.

[0082] Lithium secondary battery In one embodiment, a lithium secondary battery is provided, including a positive electrode containing the positive electrode active material, a negative electrode, and an electrolyte. Here, the lithium secondary battery can be understood as a broader concept including lithium ion batteries using a non-aqueous electrolyte, lithium metal batteries using lithium metal as the negative electrode, and all-solid-state secondary batteries in which a solid electrolyte layer is interposed between the positive electrode and the negative electrode.

[0083] Lithium-ion battery As an example, a lithium ion battery will be described that uses the above-mentioned positive electrode active material and a non-aqueous electrolyte solution as the electrolyte.

[0084] 4 is a schematic diagram illustrating a lithium secondary battery according to an embodiment. Referring to FIG. 4, the lithium secondary battery 100 according to the embodiment includes a battery cell including a positive electrode 114, a negative electrode 112 facing the positive electrode 114, a separator 113 disposed between the positive electrode 114 and the negative electrode 112, and a lithium secondary battery electrolyte impregnated in the positive electrode 114, the negative electrode 112, and the separator 113; a battery container 120 including the battery cell; and a sealing member 140 sealing the battery container 120.

[0085] negative electrode A negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer disposed on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder and / or a conductive material.

[0086] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0087] The material capable of reversibly intercalating / deintercalating lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite, such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite. Examples of the amorphous carbon include soft or hard carbon, mesophase pitch carbide, and calcined coke.

[0088] The lithium metal alloy may be an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0089] As the substance capable of doping and undoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. As the Si-based negative electrode active material, silicone, silicone-carbon composite, SiO x (0 < x < 2), Si-Q alloy (where Q is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof, and is not Si), as the Sn-based negative electrode active material, Sn, SnO2, Sn-R alloy (where R is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof, and is not Sn), etc. can be mentioned, and also, at least one of these can be mixed with SiO2 and used. As the elements Q and R, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and those selected from the group consisting of combinations thereof can be used.

[0090] As an example, the negative electrode active material can include silicon-carbon composite particles. The average particle size (D50) of the silicon-carbon composite particles can be, for example, from 0.5 μm to 20 μm. The average particle size (D50) is measured by a particle size analyzer and means the diameter of particles with a cumulative volume of 50% by volume in the particle size distribution. With respect to 100% by weight of the silicon-carbon composite particles, silicon may be contained at 10% to 60% by weight, and carbon may be contained at 40% to 90% by weight. The silicon-carbon composite particles can include, for example, a core containing silicon particles and a carbon coating layer located on the surface of the core. The average particle size (D50) of the silicon particles in the core can be from 10 nm to 1 μm, or from 10 nm to 200 nm. The silicon particles may exist alone as silicon, or may exist in the form of a silicon alloy or an oxidized form. The oxidized form of silicon can be represented by SiO x (0 < x < 2). Also, the thickness of the carbon coating layer can be from about 5 nm to 100 nm.

[0091] As an example, the silicon-carbon composite particles can include a core containing silicon particles and crystalline carbon, and a carbon coating layer containing amorphous carbon located on the surface of the core. As an example, the amorphous carbon in the silicon-carbon composite particles may not exist in the core and may exist only in the carbon coating layer. The crystalline carbon can be artificial graphite, natural graphite, or a combination thereof, and the amorphous carbon can be formed from coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum heavy oil, or a polymer resin (such as a phenol resin, a furan resin, a polyimide resin, etc.). In that case, with respect to 100% by weight of the silicon-carbon composite particles, the content of the crystalline carbon can be from 10% to 70% by weight, and the content of the amorphous carbon can be from 20% to 40% by weight.

[0092] The core of the silicone-carbon composite particle may include a void in the center, and the radius of the void may be 30 to 50% of the radius of the silicone-carbon composite particle.

[0093] The silicone-carbon composite particles described above effectively suppress problems such as volume expansion, structural collapse, or particle crushing during charge and discharge, and can prevent the conductive path from being disconnected, thereby achieving high capacity and high efficiency, and are advantageous for use under high voltage and high-speed charging conditions.

[0094] The Si-based or Sn-based negative electrode active material may be mixed with a carbon-based negative electrode active material, and the weight ratio of the Si-based or Sn-based negative electrode active material to the carbon-based negative electrode active material may be 1:99 to 90:10.

[0095] The content of the negative electrode active material in the negative electrode active material layer may be 95 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0096] In one embodiment, the negative electrode active material layer may further include a binder and, optionally, a conductive material. The content of the binder in the negative electrode active material layer may be 1 wt % to 5 wt % based on the total weight of the negative electrode active material layer. When the conductive material is further included, the negative electrode active material layer may include 90 wt % to 98 wt % of the negative electrode active material, 1 wt % to 5 wt % of the binder, and 1 wt % to 5 wt % of the conductive material.

[0097] The binder serves to firmly adhere the negative electrode active material particles to each other and to the current collector. The binder may be a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0098] Examples of the non-water-soluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, ethylene propylene copolymers, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, and combinations thereof.

[0099] The water-soluble binder may be a rubber-based binder or a polymer resin binder. The rubber-based binder may be selected from styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymer resin binder may be selected from polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0100] When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound can be further included as a thickener to impart viscosity. The cellulose-based compound can be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal can be sodium, potassium, or lithium. The amount of the thickener used can be 0.1 to 3 parts by weight per 100 parts by weight of the negative electrode active material.

[0101] The conductive material is used to impart conductivity to the electrodes, and any material that does not cause a chemical change in the constructed battery and is electronically conductive can be used. Examples of such a conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and conductive materials containing mixtures thereof.

[0102] The negative electrode current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0103] electrolyte The electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0104] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate. Examples of non-aqueous organic solvents include carbonates, esters, ethers, ketones, alcohols, and aprotic solvents. Examples of carbonate solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, etc. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. Examples of the ketone solvent include cyclohexanone, etc. In addition, examples of the alcohol solvent include ethyl alcohol and isopropyl alcohol, and examples of the aprotic solvent include nitriles such as R-CN (where R is a C2 to C20 linear, branched, or cyclic hydrocarbon group that may contain a double bond, an aromatic ring, or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes.

[0105] The non-aqueous organic solvents may be used alone or in combination of one or more thereof. When one or more thereof are used in combination, the mixing ratio may be appropriately adjusted depending on the desired battery performance, which is widely understood by those skilled in the art.

[0106] In addition, in the case of the carbonate-based solvent, a cyclic carbonate and a chain carbonate may be mixed and used. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent.

[0107] The non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent in addition to the carbonate-based solvent, and the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of about 1:1 to about 30:1.

[0108] The aromatic hydrocarbon solvent may be an aromatic hydrocarbon compound represented by the following formula I:

[0109] [ka]

[0110] In the above formula I, R 4 ~R 9 are the same or different and are selected from the group consisting of hydrogen, halogen, alkyl groups having 1 to 10 carbon atoms, haloalkyl groups having 1 to 10 carbon atoms, and combinations thereof.

[0111] Specific examples of the aromatic hydrocarbon solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, or combinations thereof.

[0112] The electrolyte may further contain vinylene carbonate or an ethylene carbonate-based compound of the following formula II as a life-enhancing additive to improve battery life.

[0113] [ka]

[0114] In the above formula II, R 10 and R 11 are the same or different and are selected from the group consisting of hydrogen, halogen, cyano, nitro, and fluorinated alkyl groups having 1 to 5 carbon atoms; 10 and R 11At least one of R is selected from the group consisting of a halogen group, a cyano group, a nitro group, and a fluorinated alkyl group having 1 to 5 carbon atoms, with the proviso that R 1 0 and R 11 Ding is not all hydrogen.

[0115] Representative examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, etc. When such a life-improving additive is further used, the amount used can be appropriately adjusted.

[0116] The lithium salt is a substance that dissolves in a non-aqueous organic solvent, acts as a source of lithium ions in the battery, enables basic operation of a lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode.

[0117] Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, and LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (where x and y are natural numbers, for example, integers of 1 to 20), lithium difluoro(bisoxalato)phosphate, LiCl, LiI, LiB(C2O4)2 (lithium bis(oxalato)borate, LiBOB), and lithium difluoro(oxalato)borate (LiDFOB).

[0118] The concentration of the lithium salt is preferably in the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within this range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively.

[0119] Separator The separator 113 separates the positive electrode 114 and the negative electrode 112 and provides a path for lithium ions to move. Any separator commonly used in lithium ion batteries can be used. A separator that has low resistance to ion movement in the electrolyte and excellent wettability with the electrolyte can be used. For example, the separator can include glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, and can be in the form of a non-woven or woven fabric. For example, polyolefin-based polymer separators such as polyethylene and polypropylene are commonly used in lithium ion batteries. Separators coated with ceramic components or polymer materials can also be used to ensure heat resistance or mechanical strength, and can be selectively used in a single-layer or multi-layer structure.

[0120] All-solid-state secondary battery In one example, an all-solid-state secondary battery will be described in which the above-mentioned positive electrode active material is used, a solid electrolyte is used as the electrolyte, and a solid electrolyte layer is interposed between the positive electrode and the negative electrode.

[0121] 5 is a cross-sectional view of an all-solid-state secondary battery according to an embodiment. Referring to FIG. 5, the all-solid-state secondary battery 100′ may have a structure in which an electrode assembly including a stack of an anode 400 including an anode current collector 401 and an anode active material layer 403, a solid electrolyte layer 300, and a cathode 200 including a cathode active material layer 203 and a cathode current collector 201 is housed in a battery case. The all-solid-state secondary battery 100′ may further include an elastic layer 500 on the outer surface of at least one of the cathode 200 and the anode 400. Although FIG. 5 shows one electrode assembly including the anode 400, the solid electrolyte layer 300, and the cathode 200, two or more electrode assemblies may be stacked to fabricate an all-solid-state secondary battery.

[0122] positive electrode The positive electrode for the all-solid-state secondary battery may further contain a solid electrolyte in addition to the positive electrode active material, binder, and conductive material described above.

[0123] solid electrolyte The solid electrolyte may be an inorganic solid electrolyte such as a sulfide-based solid electrolyte or an oxide-based solid electrolyte.

[0124] In one embodiment, the solid electrolyte may be a sulfide-based solid electrolyte having excellent ionic conductivity. Examples of the sulfide-based solid electrolyte particles include Li2S-P2S5, Li2S-P2S5-LiX (X is a halogen element, for example, I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S n (m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q(p, q are integers, and M is P, Si, Ge, B, Al, Ga, or In), or a combination thereof.

[0125] For example, such a sulfide-based solid electrolyte can be obtained by mixing Li2S and P2S5 in a molar ratio of 50:50 to 90:10 or 50:50 to 80:20, followed by selective heat treatment. Within this mixing ratio range, a sulfide-based solid electrolyte with excellent ionic conductivity can be produced. Additional components, such as SiS2, GeS2, and B2S3, can also be added to further improve ionic conductivity.

[0126] Mechanical milling and solution methods can be used to mix sulfur-containing raw materials to produce sulfide-based solid electrolytes. Mechanical milling involves placing the starting materials in a ball mill reactor and vigorously stirring them to finely mix the starting materials. When using the solution method, the starting materials are mixed in a solvent to obtain a solid electrolyte as a precipitate. Furthermore, when heat-treated after mixing, the crystals of the solid electrolyte may become even harder, thereby improving ionic conductivity. For example, a sulfide-based solid electrolyte may be produced by mixing sulfur-containing raw materials and heat-treating them two or more times. In this case, a sulfide-based solid electrolyte with high ionic conductivity and robustness can be produced.

[0127] For example, sulfide-based solid electrolyte particles according to one embodiment can be manufactured by a first heat treatment in which sulfur-containing raw materials are mixed and fired at 120°C to 350°C, and a second heat treatment in which the result of the first heat treatment is mixed and fired at 350°C to 800°C. The first and second heat treatments can be performed in an inert gas or nitrogen atmosphere, respectively. The first heat treatment can be performed for 1 hour to 10 hours, and the second heat treatment can be performed for 5 hours to 20 hours. The first heat treatment can crush small raw materials, and the second heat treatment can synthesize the final solid electrolyte. By performing these two or more heat treatments, a high-performance sulfide-based solid electrolyte with high ionic conductivity and rigidity can be obtained, and such a solid electrolyte can be suitable for mass production. The temperature of the first heat treatment can be, for example, 150°C to 330°C, or 200°C to 300°C, and the temperature of the second heat treatment can be, for example, 380°C to 700°C, or 400°C to 600°C.

[0128] For example, the sulfide-based solid electrolyte particles may include argyrodite-type sulfide. The argyrodite-type sulfide may be, for example, Li a M b P c S d A e (wherein a, b, c, d, and e are each 0 to 12, M is Ge, Sn, Si, or a combination thereof, and A is F, Cl, Br, or I). 7-x PS 6-x A x (wherein x is 0.2 or more and 1.8 or less, and A is F, Cl, Br, or I). The ajirodite-type sulfide can be specifically represented by the chemical formula Li3PS4, Li7P3S 11 , Li7PS6, Li6PS5Cl, Li6PS5Br, Li 5.8 PS 4.8 Cl 1.2 , Li 6.2 PS 5.2 Br 0.8 etc.

[0129] The sulfide-based solid electrolyte particles containing the azirodite-type sulfide have high ionic conductivity close to that of typical liquid electrolytes at room temperature, in the range of 10 to 10 S / cm, and can form a tight bond between the positive electrode active material and the solid electrolyte without causing a decrease in ionic conductivity, thereby forming a tight interface between the electrode layer and the solid electrolyte layer. All-solid-state secondary batteries containing the same can improve battery performance, such as rate characteristics, coulombic efficiency, and life characteristics.

[0130] The azirodite-type sulfide-based solid electrolyte can be prepared by mixing, for example, lithium sulfide and, optionally, lithium halide. After mixing, the mixture can be heat-treated. The heat treatment can include, for example, two or more heat treatment steps. Here, preparing the azirodite-type sulfide-based solid electrolyte can include, for example, a first heat treatment in which raw materials are mixed and fired at 120°C to 350°C, and a second heat treatment in which the result of the first heat treatment is mixed again and fired at 350°C to 800°C.

[0131] The sulfide-based solid electrolyte particles may have an average particle size (D50) of, for example, 0.1 μm to 5.0 μm, with small particles ranging from 0.1 μm to 1.9 μm and large particles ranging from 2.0 μm to 5.0 μm. The average particle size of the sulfide-based solid electrolyte particles may be measured using an electron microscope image. For example, the particle sizes (diameters or major axis lengths) of about 20 particles may be measured using a scanning electron microscope image to obtain a particle size distribution, from which D50 may be calculated.

[0132] The solid electrolyte may include an oxide-based inorganic solid electrolyte in addition to a sulfide-based material. The oxide-based inorganic solid electrolyte may be, for example, Li 1+x Ti 2-x Al(PO4)3(LTAP)(0≦x≦4), Li 1+x+y Al x Ti 2-x Si y P 3-y O 12(0 < x < 2, 0 ≤ y < 3), BaTiO3, Pb(Zr, Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT) (0 ≤ x < 1, 0 ≤ y < 1), PB(Mg3Nb 2 / 3 )O3 - PbTiO3 (PMN - PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), Li 1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0 ≤ x ≤ 1, 0 ≤ y ≤ 1), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), Li2O, LiAlO2, Li2O - Al2O3 - SiO2 - P2O5 - TiO2 - GeO2 - based ceramics, Garnet - based ceramics Li 3+x La3M2O 12 (M = Te, Nb, or Zr; x is an integer from 1 to 10), or mixtures thereof can be included.

[0133] The solid electrolyte is in particulate form, and the average particle size (D50) can be 5.0 μm or less, for example, 0.1 μm to 5.0 μm, 0.5 μm to 5.0 μm, 0.5 μm to 4.0 μm, 0.5 μm to 3.0 μm, 0.5 μm to 2.0 μm, or 0.5 μm to 1.0 μm. Such a solid electrolyte can effectively penetrate between the cathode active materials and is excellent in contact with the cathode active materials and connectivity between the solid electrolyte particles.

[0134] The solid electrolyte may be included in an amount of 0.1 wt % to 35 wt %, for example, 1 wt % to 35 wt %, 5 wt % to 30 wt %, 8 wt % to 25 wt %, or 10 wt % to 20 wt %, based on the total weight of the positive electrode active material layer. Furthermore, the positive electrode active material and the solid electrolyte may be included in an amount of 65 wt % to 99 wt % and 1 wt % to 35 wt %, based on the total weight of the positive electrode active material and the solid electrolyte in the positive electrode active material layer. For example, the positive electrode active material may be included in an amount of 80 wt % to 90 wt %, and the solid electrolyte may be included in an amount of 10 wt % to 20 wt %. When the solid electrolyte is included in the positive electrode in such an amount, the efficiency and lifespan characteristics of the all-solid-state battery can be improved without reducing the capacity.

[0135] negative electrode The negative electrode for the all-solid-state secondary battery can be, for example, the same negative electrode as that described for the lithium-ion battery.

[0136] Alternatively, as another example, the negative electrode for the all-solid-state secondary battery may be a deposition-type negative electrode, which does not include a negative electrode active material when the battery is assembled, but in which lithium metal or the like is deposited or attached to the negative electrode during battery charging, and this serves as the negative electrode active material.

[0137] FIG. 6 is a schematic cross-sectional view of an all-solid-state secondary battery including a deposition-type anode. Referring to FIG. 6, the deposition-type anode 400′ may include a current collector 401 and a negative electrode coating layer 405 disposed on the current collector. An all-solid-state secondary battery including this deposition-type anode 400′ begins initial charging without the presence of a negative electrode active material. During charging, high-density lithium metal is deposited or attached between the current collector 401 and the negative electrode coating layer 405 or on the negative electrode coating layer 405, forming a lithium metal layer 404, which can serve as the negative electrode active material. Thus, the deposition-type anode 400′ in an all-solid-state secondary battery that has been charged at least once may include, for example, a current collector 401, a lithium metal layer 404 disposed on the current collector, and a negative electrode coating layer 405 disposed on the lithium metal layer. The lithium metal layer 404 refers to a layer where lithium metal is deposited during the charging process of the battery, and may be called a metal layer, a lithium layer, a lithium electrodeposition layer, or a negative electrode active material layer.

[0138] The anode coating layer 405 may also be referred to as a lithium deposition inducing layer or an anode catalyst layer, and may include a metal, a carbon material, or a combination thereof that acts as a catalyst.

[0139] The metal may be a lithophilic metal, such as gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, zinc, or a combination thereof, or may consist of one of these or various types of alloys. When the metal is in particulate form, the average particle size (D50) may be about 4 μm or less, for example, 10 nm to 4 μm.

[0140] The carbon material may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The crystalline carbon may be, for example, natural graphite, artificial graphite, mesophase carbon microbeads, or a combination thereof. The amorphous carbon may be, for example, carbon black, activated carbon, acetylene black, denka black, ketjen black, or a combination thereof.

[0141] When the anode coating layer 405 includes both the metal and the carbon material, the weight ratio of the metal to the carbon material may be, for example, 1:10 to 2:1. In this case, the deposition of lithium metal may be effectively promoted, thereby improving the characteristics of the all-solid-state secondary battery. The anode coating layer 405 may include, for example, a carbon material supporting a catalytic metal, or a mixture of metal particles and carbon material particles.

[0142] For example, the negative electrode coating layer 405 may include the metal and amorphous carbon, which can effectively promote deposition of lithium metal.

[0143] The negative electrode coating layer 405 may further include a binder, for example, a conductive binder, and may further include common additives such as a filler, a dispersant, and an ion conductive agent.

[0144] The thickness of the negative electrode coating layer 405 may be, for example, 100 nm to 20 μm, or 500 nm to 10 μm, or 1 μm to 5 μm.

[0145] For example, the deposition-type negative electrode 400′ may further include a thin film on the surface of the current collector, i.e., between the current collector and the negative electrode coating layer. The thin film may include an element capable of forming an alloy with lithium. The element capable of forming an alloy with lithium may be, for example, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., and may be composed of one of these or various types of alloys. The thin film may further flatten the deposition morphology of the lithium metal layer 404, thereby further improving the characteristics of the all-solid-state secondary battery. The thin film may be formed by, for example, a vacuum deposition method, a sputtering method, a plating method, etc. The thickness of the thin film may be, for example, 1 nm to 500 nm.

[0146] The lithium metal layer 404 may include lithium metal or a lithium alloy, such as a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, or a Li-Si alloy.

[0147] The thickness of the lithium metal layer 404 may be 1 μm to 500 μm, 1 μm to 200 μm, 1 μm to 100 μm, or 1 μm to 50 μm. If the lithium metal layer 404 is too thin, it may be difficult for it to function as a lithium reservoir, and if it is too thick, the volume of the battery may increase, resulting in reduced performance.

[0148] When such a deposition-type anode is used, the anode coating layer 405 can protect the lithium metal layer 404 and suppress the deposition and growth of lithium deadlite, thereby suppressing short circuits and capacity reduction in the all-solid-state battery and improving its lifespan characteristics.

[0149] solid electrolyte layer The solid electrolyte layer 300 may include a sulfide-based solid electrolyte, an oxide-based solid electrolyte, etc. The sulfide-based solid electrolyte and the oxide-based solid electrolyte are the same as those described above, and therefore will not be described here.

[0150] Meanwhile, the average particle size (D50) of the solid electrolyte contained in the solid electrolyte layer 300 may be larger than the average particle size (D50) of the solid electrolyte contained in the cathode 200. In this case, the energy density of the all-solid-state secondary battery can be maximized while increasing lithium ion mobility, thereby improving overall performance. For example, the average particle size (D50) of the solid electrolyte contained in the cathode 200 may be 0.1 μm to 1.9 μm, or 0.1 μm to 1.0 μm, and the average particle size (D50) of the solid electrolyte contained in the solid electrolyte layer 300 may be 2.0 μm to 5.0 μm, or 2.0 μm to 4.0 μm, or 2.5 μm to 3.5 μm. When these particle size ranges are satisfied, the energy density of the all-solid-state secondary battery can be maximized while facilitating lithium ion transfer and reducing resistance, thereby improving overall performance of the all-solid-state secondary battery. Here, the average particle size (D50) of the solid electrolyte may be measured using a particle size analyzer using a laser diffraction method.

[0151] The solid electrolyte layer may further include a binder in addition to the solid electrolyte. The binder may be, but is not limited to, styrene butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, an acrylate-based polymer, or a combination thereof. Any binder commonly used in the art may be used. The acrylate-based polymer may be, for example, butyl acrylate, polyacrylate, polymethacrylate, or a combination thereof.

[0152] The solid electrolyte layer can be formed by adding a solid electrolyte to a binder solution, coating the solution on a substrate film, and drying. The solvent for the binder solution can be isobutyryl isobutyrate, xylene, toluene, benzene, hexane, or a combination thereof. The process for forming the solid electrolyte layer is well known in the art, so a detailed description thereof will be omitted.

[0153] The thickness of the solid electrolyte layer may be, for example, 10 μm to 150 μm.

[0154] The solid electrolyte layer may further include an alkali metal salt, an ionic liquid, and / or a conductive polymer.

[0155] The alkali metal salt may be, for example, a lithium salt. The content of the lithium salt in the solid electrolyte layer may be 1 M or more, for example, 1 M to 4 M. In this case, the lithium salt can improve the ion conductivity by increasing the lithium ion mobility in the solid electrolyte layer.

[0156] Examples of the lithium salt include LiSCN, LiN(CN)2, Li(CF3SO2)3C, LiC4F9SO3, LiN(SO2CF2CF3)2, LiCl, LiF, LiBr, LiI, LiB(C2O4)2, LiBF4, LiBF3(C2F5), lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LIODFB), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, LiN(SO2CF3)2), and lithium bis(fluorosulfonyl)imide (LiTFSI). The material may include bis(fluorosulfonyl)imide, LiFSI, LiN(SO2F)2), LiCF3SO3, LiAsF6, LiSbF6, LiClO4, or mixtures thereof.

[0157] The lithium salt may be an imide-based lithium salt, for example, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, LiN(SOCF)), or lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SOF)). The lithium salt may maintain or improve ionic conductivity by appropriately maintaining chemical reactivity with the ionic liquid.

[0158] The ionic liquid refers to a salt or a room-temperature molten salt that has a melting point below room temperature and is in a liquid state at room temperature and is composed of only ions.

[0159] The ionic liquid comprises: a) one or more cations selected from ammonium, pyrrolidinium, pyridinium, pyrimidinium, imidazolium, piperidinium, pyrazolium, oxazolium, pyridazinium, phosphonium, sulfonium, triazolium, and mixtures thereof; and b) BF4 - , PF6 - , AsF6 - , SbF6 - , AlCl4 - , HSO4 - , ClO4 - , CH3SO3 - , CF3CO2 - , Cl - , Br - , I - , BF4 - , SO4 - , CF3SO3 - , (FSO2)2N - , (C2F5SO2)2N - , (C2F5SO2)(CF3SO2)N - , and (CF3SO2)2N - The compound may contain one or more anions selected from the following:

[0160] The ionic liquid may be, for example, one or more selected from the group consisting of N-methyl-N-propylpyrrolidine bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(3-trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide.

[0161] The weight ratio of the solid electrolyte to the ionic liquid in the solid electrolyte layer may be 0.1:99.9 to 90:10, for example, 10:90 to 90:10, 20:80 to 90:10, 30:70 to 90:10, 40:60 to 90:10, or 50:50 to 90:10. A solid electrolyte layer satisfying this range can increase the electrochemical contact area with the electrode and maintain or improve ionic conductivity. This can improve the energy density, discharge capacity, rate characteristics, and the like of the all-solid-state secondary battery.

[0162] The all-solid-state secondary battery may be a unit cell having a structure of a positive electrode / solid electrolyte layer / negative electrode, a bi-cell having a structure of a negative electrode / solid electrolyte layer / positive electrode / solid electrolyte layer / negative electrode, or a stacked battery in which the structure of the unit battery is repeated.

[0163] The shape of the all-solid-state secondary battery is not particularly limited, and may be, for example, a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, or the like. The all-solid-state secondary battery can also be applied to large batteries used in electric vehicles and the like. For example, the all-solid-state secondary battery can also be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). The all-solid-state secondary battery can also be used in fields requiring large amounts of power storage, such as electric bicycles or power tools. The all-solid-state secondary battery can also be used in various fields such as portable electronic devices. [Example]

[0164] Examples of the present invention and comparative examples are described below. The following examples are illustrative of the present invention, and the present invention is not limited to the following examples.

[0165] Reference Example 1: Preparation of first lithium nickel-based composite oxide 1. Preparation of nickel-based composite hydroxide A first nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH)2) was synthesized. Nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and sodium aluminum sulfate (NaAl(SO4)2·12H2O) were dissolved in distilled water as a solvent in a molar ratio of 94.5:4:1.5 to prepare a mixed metal source solution. Ammonia water (NH4OH) and sodium hydroxide (NaOH) were also prepared as a precipitant to form the complex compound.

[0166] [1st stage: 2.5kW / m 3 , NH4OH 0.40M, pH 10.5-11.5, reaction time 6 hours] First, ammonia water with a concentration of 0.40 M was placed in the reactor. The stirring power was 2.5 kW / m 3 The reaction was initiated at a reaction temperature of 50°C by adding the metal raw material mixed solution and complexing agent (NH4OH) at rates of 85 ml / min and 10 ml / min, respectively. The reaction was carried out for 6 hours while adding NaOH to maintain the pH. As a result of the reaction, it was confirmed that the average size of the obtained core particles was in the range of approximately 6.5 μm to 7.5 μm, and the following two stages were carried out.

[0167] [2nd stage: 2.0kW / m 3 , NH4OH 0.45M, pH 10.5-11.5, reaction time 18 hours] While maintaining the reaction temperature at 50°C, the metal raw material mixed solution and the complexing agent were added at varying rates of 85 ml / min and 12 ml / min, respectively, until the concentration of the complexing agent reached 0.45 M. The reaction was continued for 18 hours while adding NaOH to maintain the pH. During this time, the stirring power was set to 2.0 kW / m, lower than the first stage. 3The reaction was carried out at a temperature lowered to 13.5 μm. After carrying out this reaction, it was confirmed that the average size of the product particles including the core and the intermediate layer was 13.5 μm to 14 μm, and the reaction was carried out in three stages as follows.

[0168] [3 stages: 1.5kW / m 3 , NH4OH 0.45M, pH 10.5-11.5, reaction time 14 hours] The reaction temperature was maintained at 50°C, and the addition rates of the metal raw material mixed solution and the complexing agent and the concentration of the complexing agent were the same as in the previous two stages. The reaction was carried out for 14 hours while adding NaOH to maintain the pH. The stirring power was 1.5 kW / m, lower than in the second stage. 3 The reaction was carried out at a temperature of 0.5°C.

[0169] [Post-process] After washing the resultant, it was dried with hot air at about 150°C for 24 hours to obtain the first nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH)2 was obtained.

[0170] 2.1 Preparation of lithium nickel composite oxide 100 moles of the first nickel-based composite hydroxide were mixed with 100 moles of LiOH, and the mixture was heated to 700°C in an oxygen atmosphere for 8 hours, and then the temperature was maintained for 7 hours to obtain a first lithium-nickel-based composite oxide (LiNi 0.945 Co 0.04 Al 0.015 O2) was produced.

[0171] The first lithium nickel-based composite oxide prepared in Reference Example 1 was confirmed to be in the form of secondary particles having an inner portion with an irregular porous structure and an outer portion with a radial array structure, and the average particle size (D50) of the secondary particles measured by a particle size distribution analyzer using laser diffraction was about 14 μm.

[0172] Reference Example 2: Preparation of second lithium nickel-based composite oxide 1. Preparation of second nickel-based composite hydroxide The second nickel-based composite hydroxide (Ni0.94 Co 0.04 Mn 0.02 (OH)2) was synthesized. Nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as a solvent in a molar ratio of 94:4:2 to prepare a mixed metal source solution. Ammonia water (NH4OH) and sodium hydroxide (NaOH) were also prepared as a precipitant to form the complex compound.

[0173] First, ammonia water with a concentration of 0.25M is placed in the reactor. The stirring power is 3.0kW / m 3 The reaction was initiated by adding the metal raw material mixed solution and complexing agent at a rate of 142 ml / min and 34 ml / min, respectively, at a reaction temperature of 50°C. The reaction was continued for 30 hours while adding NaOH to maintain the pH. The reaction was terminated when the average size of the resulting core particles reached 4 μm. The resulting product was washed and then dried with hot air at about 150°C for 24 hours to obtain the second nickel-based composite hydroxide (Ni 0.94 Co 0.04 Mn 0.02 (OH)2).

[0174] 2. Preparation of second lithium nickel composite oxide The second nickel transition metal composite hydroxide and LiOH were mixed in a molar ratio of 1:1 and heat-treated at 700°C for 10 hours in an oxygen atmosphere to obtain the second lithium nickel composite oxide (LiNi 0.94 Co 0.04 Mn 0.02 O2) was obtained.

[0175] The second lithium nickel-based composite oxide produced in Reference Example 2 was confirmed to be in the form of secondary particles formed by aggregation of multiple primary particles, and the average particle size (D50) of the secondary particles measured by a particle size distribution analyzer using laser diffraction was about 3.5 μm.

[0176] Reference Example 3: Preparation of third lithium nickel-based composite oxide 1. Production of third nickel-based composite hydroxide The third nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH)2) was synthesized. Nickel sulfate, cobalt sulfate, and aluminum nitrate (Al(NO3)3·9H2O) were dissolved in distilled water as a solvent in a molar ratio of 94.5:4:1.5 to prepare a mixed metal source solution. Ammonia water (NH4OH) and a sodium hydroxide (NaOH) aqueous solution were also prepared as a precipitant to form the complex compound.

[0177] After adding the diluted ammonia solution to the continuous reactor, the metal raw material mixed solution is continuously added, and sodium hydroxide solution is added to maintain the pH inside the reactor. The reaction is carried out slowly for about 80 hours, and once the reaction has stabilized, the overflowing product is collected. After washing, it is dried with hot air at about 150°C for 24 hours to obtain a tertiary nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH)2) was prepared.

[0178] 2. Production of third lithium nickel composite oxide 100 moles of the third nickel-based composite hydroxide are mixed with 100 moles of LiOH, and the mixture is heated to 730°C in an oxygen atmosphere for 5 hours and maintained at that temperature for 7 hours. This produces a non-radiative, secondary particle-form third lithium-nickel-based composite oxide (LiNi 0.945 Co 0.04 Al 0.015 The average particle size (D50) of the secondary particles measured by a particle size distribution analyzer using laser diffraction was about 15 μm.

[0179] Reference Example 4: Preparation of fourth lithium nickel-based composite oxide 1. Preparation of quaternary nickel-based composite hydroxide The fourth positive electrode active material precursor, a fourth nickel transition metal composite hydroxide (Ni 0.945 Co 0.04 Al 0.015Nickel sulfate, cobalt sulfate, and sodium aluminum sulfate were dissolved in distilled water as a solvent in a molar ratio of 94.5:4:1.5 to prepare a mixed solution of metal raw materials. Ammonia water (NH4OH) and sodium hydroxide (NaOH) were also prepared as a precipitant for forming a complex compound. Subsequently, a quaternary nickel transition metal composite hydroxide (Ni (OH)2) was synthesized by a method substantially similar to that of Reference Example 2. 0.945 Co 0.04 Al 0.015 (OH)2) was prepared.

[0180] 2. Preparation of quaternary lithium nickel composite oxide The quaternary nickel transition metal composite hydroxide and LiOH were mixed in a molar ratio of 1:1 and heat-treated at 700°C for 10 hours in an oxygen atmosphere to obtain the quaternary lithium nickel composite oxide (LiNi 0.945 Co 0.04 Al 0.015 The quaternary lithium nickel-based composite oxide was in the form of secondary particles formed by aggregation of a plurality of primary particles, and the average particle size (D50) of the secondary particles measured by a particle size distribution analyzer using laser diffraction was about 4 μm.

[0181] Example 1 1. Production of positive electrode active material The first nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH)2) 80 wt % and the second nickel-based composite hydroxide (Ni 0.94 Co 0.04 Mn 0.02 100 moles of LiOH was mixed with 20% by weight of (OH)2), and 100 moles of metals (first nickel-based composite hydroxide and second nickel-based composite hydroxide) were mixed together. This was heated to 700°C in an oxygen atmosphere for 8 hours, and then subjected to heat treatment at that temperature for 7 hours to produce the final positive electrode active material.

[0182] The first positive electrode active material was confirmed to be in the form of secondary particles with an inner part having an irregular porous structure and an outer part having a radial arrangement structure. The second positive electrode active material, which was contained at 20% by weight, was separated and analyzed by ICP (Inductively Coupled Plasma) emission spectroscopy, and the results showed that Ni 0.939 Co 0.039 Al 0.006 Mn 0.016 It was confirmed to be O2, and was confirmed to contain Al, unlike the second nickel-based composite hydroxide used as the raw material.

[0183] 2. Fabrication of the positive electrode 96 wt% of the obtained positive electrode active material, 2 wt% of polyvinylidene fluoride, 2 wt% of carbon nanotubes, and N-methylpyrrolidone solvent were mixed in a mixer to prepare a positive electrode slurry, which was then coated onto an aluminum foil to form a plate, dried at 135°C for 3 hours or more, and rolled to prepare a positive electrode.

[0184] 3. Battery manufacturing A unit cell was fabricated by placing a 16 μm thick separator made of porous polyethylene film between the fabricated positive electrode and the lithium metal counter electrode, and then inserted into a battery case and injected with electrolyte to fabricate a coin half cell. The electrolyte was a solution of 1.1 M LiPF6 dissolved in a solvent made by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:5.

[0185] Comparative Example 1 The fourth nickel-based composite hydroxide of Reference Example 4 was used instead of the second nickel-based composite hydroxide to prepare the first nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH)2) 80 wt% and quaternary nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 A positive electrode active material, a positive electrode, and a battery were prepared in substantially the same manner as in Example 1, except that 20 wt % of (OH)2) was mixed.

[0186] Comparative Example 2 A positive electrode active material, a positive electrode, and a battery were prepared in substantially the same manner as in Example 1, except that when adding 100 parts by mole of LiOH in the preparation of the positive electrode active material of Example 1, 0.15 parts by mole of alumina (Al2O3) was further added relative to 100 moles of the total metals of the first nickel-based composite hydroxide and the second nickel-based composite hydroxide.

[0187] Comparative Example 3 The first nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH)2), the third nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 A positive electrode active material, a positive electrode, and a battery were prepared in substantially the same manner as in Example 1, except that (OH)2) was used.

[0188] Comparative Example 4 A positive electrode and a battery were manufactured in substantially the same manner as in Example 1, except that a mixture of 80 wt % of the first lithium-nickel-based composite oxide prepared in Reference Example 1 and 20 wt % of the second lithium-nickel-based composite oxide prepared in Reference Example 2 was used as the positive electrode active material.

[0189] Comparative Example 5 A positive electrode and a battery were manufactured in substantially the same manner as in Example 1, except that a mixture of 80 wt % of the first lithium-nickel-based composite oxide prepared in Reference Example 1 and 20 wt % of the fourth lithium-nickel-based composite oxide prepared in Reference Example 4 was used as the positive electrode active material.

[0190] Comparative Example 6 The second nickel-based composite hydroxide of Reference Example 2 and LiOH were mixed in a molar ratio of 1:1, and 0.75 molar parts of alumina (Al2O3) were added to 100 molar parts of the total metals in the second nickel-based composite hydroxide. The mixture was heat-treated at 700°C for 10 hours in an oxygen atmosphere to obtain a fifth lithium-nickel-based composite oxide (LiNi 0.933 Co 0.04 Al 0.007 Mn 0.02 The 5th lithium nickel-based composite oxide was confirmed to be in the form of secondary particles formed by aggregation of a plurality of primary particles, and the average particle size (D50) of the secondary particles measured by a particle size distribution analyzer using laser diffraction was about 4.2 μm.

[0191] A positive electrode and a battery were manufactured in substantially the same manner as in Example 1, except that a mixture of 80 wt % of the first lithium-nickel-based composite oxide manufactured in Reference Example 1 and 20 wt % of the fifth lithium-nickel-based composite oxide was used as the positive electrode active material.

[0192] The positive electrode active material designs of Reference Examples 1 to 4, Example 1, and Comparative Examples 1 to 6 are briefly shown in Table 1 below.

[0193] [Table 1]

[0194] Evaluation example 1: Battery performance evaluation The coin half-cells prepared in Example 1 and Comparative Examples 1 to 6 were initially charged at 25°C with a constant current of 0.2 C up to an upper voltage limit of 4.25 V, with a 0.05 C cutoff, and then initially discharged at 0.2 C down to an end-of-discharge voltage of 3.0 V. The initial charge capacity (gray bars) and initial discharge capacity (black bars) are shown in Figure 7 and Table 2 below, and the ratio of the initial discharge capacity to the initial charge capacity is shown in Table 2 below as an efficiency.

[0195] Separately, the coin half-cells manufactured in Example 1 and Comparative Examples 1 to 6 were initially charged at a constant current of 1 C at a high temperature (45° C.) up to an upper limit voltage of 4.3 V, and then discharged at 1 C down to an end-of-discharge voltage of 3.0 V. This process was repeated 50 times. The ratio of the discharge capacity after 50 cycles to the initial discharge capacity (capacity retention rate) was calculated and is shown in Table 2 below and the dotted line graph (right vertical axis) in FIG. 8.

[0196] [Table 2]

[0197] While producing a positive electrode active material using only large particles or only small particles can achieve the best performance in terms of capacity and lifespan, the density of the positive electrode plate is low, preventing high capacity and high energy density. To overcome this problem, large particles and small particles have been produced and mixed together, as in Comparative Examples 4 and 5. However, in this case, the small particles participate in charging earlier than the large particles, resulting in a higher current being applied to the small particles than when the small particles are used alone, resulting in a shorter lifespan. To solve this problem, doping (or coating) the small particles with Al, as in Comparative Example 6, improves lifespan but reduces capacity.

[0198] Comparative Example 3, which has the same chemical composition as Example 1, including the nickel and cobalt content, is a conventional technique in which a large-particle NCA precursor in the form of non-radiative secondary particles is mixed with a small-particle NCM precursor and then calcined simultaneously, and exhibits a very low discharge capacity. Comparative Example 6, which is a conventional technique in which a large-particle NCA and small-particle NCM doped with Al are synthesized separately and then mixed, exhibits a higher discharge capacity than Comparative Example 3 and maintains a comparable lifespan.

[0199] In Example 1, the nickel and cobalt contents were similar to those of the comparative examples, and by mixing large-grained NCA precursors and small-grained NCM precursors in the form of radiating secondary particles and then firing them simultaneously, the capacity and lifespan were all improved compared to Comparative Examples 3 to 6 of the prior art.

[0200] In Comparative Example 1, the large and small particles all had the same composition as NCA, and the structural stability of the small particles was not improved, resulting in a reduced lifespan. In Comparative Example 2, in which Al was additionally doped (or coated) in Example 1, the formation of Al by-products and particle overgrowth were induced, resulting in a reduced pellet density and reduced volumetric capacity, as shown in Evaluation Examples 2 and 3 below.

[0201] Evaluation Example 2: Pellet Density Density (PD) evaluation The pellet densities (g / cc) of the positive electrode active materials prepared in Example 1 and Comparative Examples 1 to 6 were measured and are shown in Table 3 below and the dotted line graph in Figure 7. The pellet densities were obtained by placing 3 g of the positive electrode active material in a pellet manufacturing mold, maintaining it at 3.3 tons for 30 seconds, and then calculating the density from the pellet thickness and the mold diameter.

[0202] Evaluation example 3: Evaluation of volumetric capacity The volumetric capacity was calculated by multiplying the room temperature initial discharge capacity in Table 2 by the pellet density in Evaluation Example 2, and the results are shown in Table 3 below and in the bar graph (left vertical axis) in FIG.

[0203] [Table 3]

[0204] Referring to Table 3, Figures 7 and 8, it can be seen that Example 1, in which large NCA particles and small NCM particles were co-fired, had improved pellet density compared to Comparative Example 4, in which they were fired separately and then mixed. However, in Comparative Examples 1 and 5, in which the large and small particles had the same composition, the improvement in pellet density was small. These results demonstrate that co-firing the radial NCA large particle precursor and the NCM small particle precursor as in Example 1 further improved volumetric capacity compared to Comparative Examples 3 to 6, which are based on the prior art.

[0205] Evaluation example 4: Evaluation of small grain composition Large particles and small particles were separated from the final cathode active materials prepared in Example 1 and Comparative Example 2. The active materials were separated using a turbo classifier (Nisshin Engineering Inc.) with nitrogen as a carrier gas. FIG. 9 is an SEM image of the small particles separated in Example 1, and FIG. 10 is an SEM image of the small particles separated in Comparative Example 2. The two small particle cathode active materials were subjected to inductively coupled plasma (ICP) emission spectroscopy to measure the contents of cobalt, aluminum, and manganese, and the results are shown in FIG. 11.

[0206] If the aluminum added in Comparative Example 2 were doped equally into the large and small particles, the Al content of the 20% by weight small particles should be approximately 0.03 mol%, but the measured value was 1.2 mol%. This indicates that even assuming 0.6 mol% Al is received from the large NCA particles as in Example 1, the additional Al is doped more into the small particles than into the large particles. This is thought to lead to the formation of Al by-products and particle overgrowth, resulting in a decrease in volumetric capacity. In contrast, in Example 1, where no additional Al was added, the 20 wt% small NCM particles received Al from the 80 wt% large NCA particles, resulting in Al doping at a 0.6 mol% level. This Al doping of the small particles may be the reason for the improved lifespan compared to Comparative Example 4, where the small particles were simply mixed.

[0207] Evaluation example 5: Analysis of cross section of positive electrode active material Fig. 12 is an SEM image of a cross section obtained by cutting with a focused ion beam (FIB) the first lithium-nickel-based composite oxide particles produced in Reference Example 1. Fig. 13 is an SEM image of a cross section obtained by cutting with an FIB the third lithium-nickel-based composite oxide particles produced in Reference Example 3. It can be seen that, unlike the third lithium-nickel-based composite oxide particles, the first lithium-nickel-based composite oxide particles have primary particles that make up the secondary particles, which are small in size and have a long aspect ratio, and the primary particles are well oriented radially toward the surface of the secondary particles.

[0208] In light of this, it can be seen that Example 1 achieves better capacity than Comparative Example 3 by using such a first positive electrode active material with a radial structure that allows easy movement of lithium ions.

[0209] Evaluation example 6: Evaluation of primary particle size Fig. 14 is an SEM image of the surface of the first lithium-nickel composite oxide particle produced in Reference Example 1. Fig. 15 is an SEM image of the surface of the second lithium-nickel composite oxide particle produced in Reference Example 2.

[0210] FIG. 16 is an SEM image of the surface of a large particle of Example 1, and FIG. 17 is an SEM image of the surface of a small particle of Example 1.

[0211] FIG. 18 is an SEM image of the surface of a large particle of Comparative Example 1, and FIG. 19 is an SEM image of the surface of a small particle of Comparative Example 1.

[0212] 14 and 16, it can be seen that the size of the large primary particles in Example 1 in Fig. 16 is smaller than the size of the primary particles in Reference Example 1 in Fig. 14. Similarly, it can be seen that the size of the small primary particles in Example 1 in Fig. 17 is smaller than the size of the primary particles in Reference Example 2 in Fig. 15.

[0213] From this, as shown in Evaluation Example 2, it can be seen that when the two precursors are mixed and then fired simultaneously as in Example 1, the aggregation phenomenon between particles is suppressed, friction between particles is reduced, and pellet density is increased, compared to when the radial large-particle NCA precursor and the small-particle NCM precursor are fired separately and then mixed as in Comparative Example 4.

[0214] Conversely, the size of the large primary particles in Comparative Example 1 in Figure 18 is larger than the size of the primary particles in Reference Example 1 in Figure 14. Similarly, the size of the small primary particles in Comparative Example 1 in Figure 19 is larger than the size of the primary particles in the second lithium nickel-based composite oxide in Reference Example 2 in Figure 15.

[0215] As a result, when large-particle precursors and small-particle precursors with the same chemical composition are mixed and then co-fired, as in Comparative Example 1, the primary particles grow excessively. As a result, the lifespan of Comparative Example 1 is significantly shorter than that of Comparative Example 5, as in Evaluation Example 1, and the problem of particle aggregation is not resolved, as in Evaluation Example 2, and the pellet density is not improved.

[0216] Evaluation example 7: SEM-EDS evaluation To compare the production of small particles of NCAM by mixing a radiative NCA large particle precursor and a NCM small particle precursor and then co-firing them as in Example 1 with the production of small particles of NCAM by doping Al by separately adding Al2O3 as in Comparative Examples 2 and 6, the positive electrode active materials produced in Example 1, Comparative Example 2, and Comparative Example 6 were photographed with an SEM and the distribution of Al was confirmed with an EDS (Energy Dispersive X-ray Spectrometer). The results are shown in Figure 20.

[0217] First, referring to the image of Example 1 in Figure 20, it can be seen that Al is detected not only on the surface of the large particles but also on the surface of the small particles. This can be understood as being because the Al component contained in the large NCA particles is transferred to the small NCM particles during the firing process.

[0218] Furthermore, FIG. 20 confirms that Al is distributed more non-uniformly in Comparative Examples 2 and 6 than in Example 1. To clearly confirm this, the non-uniform portions indicated by the white square boxes in FIG. 20 are enlarged, FIG. 21 shows an enlarged image of the non-uniform portion in Comparative Example 2, and FIG. 22 shows an enlarged image of the non-uniform portion in Comparative Example 6. In FIG. 21, the contents (element %) of O, Ni, Co, Mn, and Al at points 1 to 3 on the surface of the small particles (second positive electrode active material) of Comparative Example 2 were analyzed, and the results are shown in Table 4. In FIG. 22, the contents (element %) of O, Ni, Co, Mn, and Al at points 1 to 4 on the surface of the small particles (second positive electrode active material) of Comparative Example 6 were analyzed, and the results are shown in Table 5.

[0219] [Table 4]

[0220] [Table 5]

[0221] From the results in Tables 4 and 5, it can be seen that when Al2O3 is added for doping, the Al content on the surface of the small particles is non-uniform, and only a portion of the surface layer is highly doped (or coated). From this, it can be understood that the reason for the low capacity of Comparative Examples 2 and 6 is due to the high concentration of Al-doped small particles.

[0222] Furthermore, SEM-EDS analysis results showed that no Mn component was detected on the surface of the large particles (first cathode active material; NCA) produced in Example 1. Aluminum diffuses more easily than manganese at the firing temperature, and the large-particle precursor is designed to be radiative, facilitating ion migration. As a result, in Example 1, it is understood that the aluminum in the large particles migrates to the small particles, while the manganese in the small particles does not migrate to the large particles.

[0223] Evaluation example 8: TEM-EELS evaluation Figure 23 is a TEM image of the cross section of the small particles of Comparative Example 6. For a clearer EDS analysis, the area enclosed by the yellow square box in Figure 23 is enlarged and shown in Figure 24. As a result of the analysis of Spot 1 in Figure 24, Al was detected, but Li was not. This indicates that Spot 1 is unreacted Al2O3. In Spot 2, Li and Ni were detected, indicating that it is a small particle active material.

[0224] From these results and the results of Evaluation Example 7, it can be seen that when the NCAM composition is prepared by adding Al2O3 as in Comparative Example 6, Al2O3 remains unreacted or small particles with a high Al content are formed, resulting in a decrease in capacity.

[0225] However, no such unreacted Al2O3 was found in Example 1. Figure 25 is a TEM image of a cross section of a small particle in Example 1. The contents (element %) of C, O, Al, Mn, Co, and Ni were measured by TEM-EELS analysis in Area 1 inside the particle and Areas 2 to 4 on the surface layer of the particle, and the results are shown in Table 6 below.

[0226] [Table 6]

[0227] Referring to Table 6, it can be seen that the Al content is high in Area 3 and Area 4, which are in contact with the large NCA on the surface of the small particles, and low in Area 2, which is not in contact with the large NCA. It can also be seen that the Al content is different between the center and the surface layer. This is understood to be because Al migrated from the large NCA and doped into the small NCM particles, forming NCAM small particles. This is because there are no small particles with excessive Al doping, and there is no unreacted Al2O3, which is why Example 1 has a high capacity and an improved lifespan.

[0228] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited to these, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the claims also fall within the scope of the present invention. [Explanation of symbols]

[0229] 11: Secondary particles 12: Inside the secondary particle 13: Primary particles 14: Outside of secondary particles 100: Lithium secondary battery 112: Negative electrode 113: Separator 114: Positive electrode 120:Battery container 140: Enclosure material 100': All-solid-state battery 200: Positive electrode 201: Positive electrode current collector 203: Positive electrode active material layer 300: Solid electrolyte layer 400: Negative electrode 401:Negative electrode current collector 403:Negative electrode active material layer 400': Deposition type negative electrode 404: Lithium metal layer 405: Negative electrode coating layer 500: Elastic layer

Claims

1. A positive electrode active material for a lithium secondary battery, a first positive electrode active material including a lithium nickel-cobalt-aluminum composite oxide, the first positive electrode active material being formed by aggregating a plurality of primary particles, at least a portion of which are arranged in a radial pattern as secondary particles; and A second positive electrode active material containing a lithium nickel-cobalt-aluminum-manganese composite oxide in the form of secondary particles formed by agglomeration of a plurality of primary particles. Including, A positive electrode active material for a lithium secondary battery, wherein the average particle size of the secondary particles of the first positive electrode active material is larger than the average particle size of the secondary particles of the second positive electrode active material.

2. the average particle size of the secondary particles of the first positive electrode active material is 9 μm to 25 μm; The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the average particle size of the secondary particles of the second positive electrode active material is 2 μm to 8 μm.

3. the second positive electrode active material has a higher aluminum content in the surface layer of the secondary particle than in the interior of the secondary particle; 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the interior refers to a region extending from the center of the secondary particle to a depth of approximately 70 length % of the radius, and the surface layer refers to a region surrounding the interior, extending from the outermost surface of the secondary particle to a depth equivalent to 30 length % of the radius.

4. the aluminum content relative to the total metal content excluding lithium in the surface layer of the secondary particle of the second positive electrode active material is 0.2 at % to 2 at %, 4. The positive electrode active material for a lithium secondary battery according to claim 3, wherein the content of aluminum relative to the total metal excluding lithium inside the secondary particles of the second positive electrode active material is 0 at % to 0.6 at %.

5. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein in a surface layer of the secondary particle of the second positive electrode active material, a content of aluminum in a portion in contact with the first positive electrode active material is higher than a content of aluminum in a portion not in contact with the first positive electrode active material.

6. 6. The positive electrode active material for a lithium secondary battery according to claim 5, wherein in the surface layer of the secondary particle of the second positive electrode active material, a content of aluminum relative to the total metal excluding lithium in a portion in contact with the first positive electrode active material is 0.8 at % to 2.0 at %, and a content of aluminum relative to the total metal excluding lithium in a portion not in contact with the first positive electrode active material is less than 0.8 at %.

7. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the second positive electrode active material includes, in a surface layer of the secondary particle, a high-concentration Al region in which the aluminum content relative to the total metal excluding lithium is 0.8 at % to 2.0 at %, and a low-concentration Al region in which the aluminum content relative to the total metal excluding lithium is less than 0.8 at %.

8. 8. The positive electrode active material for a lithium secondary battery according to claim 7, wherein a difference between the aluminum content in the low-Al-concentration region and the aluminum content in the high-Al-concentration region is 0.3 at % to 2.0 at %.

9. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the lithium nickel-cobalt-aluminum-manganese composite oxide of the second positive electrode active material is represented by the following chemical formula 2: [Chemical formula 2] Li a2 Ni x2 Co y2 Al z2 Mn w2 M 2 v2 O 2-b2 X b2 (In the above Chemical Formula 2, 0.9≦a2≦1.2, 0.7≦x2<1, 0<y2<0.3, 0<z2<0.3, 0<w2<0.3, 0≦v2<0.3, 0.9≦x2+y2+z2+w2+v2≦1.1, and 0≦b2≦0.1; M 2 is one or more elements selected from the group consisting of B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

10. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the lithium nickel-cobalt-aluminum composite oxide of the first positive electrode active material is represented by the following chemical formula 1: [Chemical formula 1] Li a1 Ni x1 Co y1 Al z1 M 1 w1 O 2-b1 X b1 (In the above Chemical Formula 1, 0.9≦a1≦1.2, 0.7≦x1<1, 0<y1<0.3, 0<z1<0.3, 0≦w1<0.3, 0.9≦x1+y1+z1+w1≦1.1, and 0≦b1≦0.1; M 1 is one or more elements selected from the group consisting of B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

11. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the secondary particles of the first positive electrode active material have an average particle size of less than 200 nm.

12. 2 . The positive electrode active material for a lithium secondary battery according to claim 1 , wherein the secondary particles of the first positive electrode active material include an interior having an irregular porous structure and an exterior having a radial array structure surrounding the interior.

13. 2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein at least some of the primary particles in the secondary particles of the first positive electrode active material have a plate shape, the secondary particles include open pores on their surfaces, the open pores being formed by spaces between the plate-shaped primary particles arranged radially, and the open pores are pores connected from the surfaces toward the center of the secondary particles.

14. With respect to 100% by weight of the positive electrode active material for lithium secondary batteries, 60% to 95% by weight of a first positive electrode active material; and The positive electrode active material for a lithium secondary battery according to claim 1 , comprising 5 to 40 wt % of the second positive electrode active material.

15. A method for producing a positive electrode active material for a lithium secondary battery, comprising: a first positive electrode active material precursor comprising a nickel-cobalt-aluminum composite hydroxide, the first positive electrode active material precursor being formed by aggregating a plurality of primary particles, at least a portion of which are arranged in a radial pattern; a second positive electrode active material precursor containing a nickel-cobalt-manganese composite hydroxide and in the form of secondary particles formed by aggregation of a plurality of primary particles; and Lithium raw materials and heat treating the mixture; A method for producing a positive electrode active material for a lithium secondary battery, wherein the average particle size of the first positive electrode active material precursor is larger than the average particle size of the second positive electrode active material precursor.

16. The nickel-cobalt-aluminum composite hydroxide of the first positive electrode active material precursor is represented by the following chemical formula 11:

16. The method for producing a positive electrode active material for a lithium secondary battery according to claim 15, wherein the nickel-cobalt-manganese composite hydroxide of the second positive electrode active material precursor is represented by the following chemical formula 12: [Chemical formula 11] Ni x11 Co y11 Al z11 M 11 w11 (OH) 2 (In the above chemical formula 11, 0.7≦x11<1, 0<y11<0.3, 0<z11<0.3, 0≦w11<0.3, 0.9≦x11+y11+z11+w11≦1.1, and M 11 is one or more elements selected from the group consisting of B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, and Zr. [Chemical formula 12] Ni x12 Co y12 Mn w12 M 12 v12 (OH) 2 (In the chemical formula 12, 0.7≦x12<1, 0<y12<0.3, 0<w12<0.3, 0≦v12<0.3, 0.9≦x12+y12+w12+v12≦1.1, and M 12 is one or more elements selected from the group consisting of B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, and Zr.

17. the average particle size of the secondary particles of the first positive electrode active material precursor is 9 μm to 25 μm; The method for producing a positive electrode active material for a lithium secondary battery according to claim 15, wherein the average particle size of the secondary particles of the second positive electrode active material precursor is 2 μm to 8 μm.

18. 16. The method of claim 15, wherein a mixing weight ratio of the first positive electrode active material precursor to the second positive electrode active material precursor is 60:40 to 95:

5.

19. 16. The method for producing a positive electrode active material for a lithium secondary battery according to claim 15, wherein the method does not include a step of mixing the first positive electrode active material precursor, the second positive electrode active material precursor, and a lithium raw material and then heat-treating the mixture, and thereafter not mixing the aluminum raw material.

20. The method for producing a positive electrode active material for a lithium secondary battery according to claim 15, wherein the heat treatment is performed at a temperature in the range of 600°C to 1000°C.

21. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 14. a negative electrode, and electrolyte A lithium secondary battery comprising:

22. 22. The lithium secondary battery according to claim 21, wherein the electrolyte comprises a non-aqueous electrolytic solution.

23. the electrolyte includes a sulfide-based solid electrolyte, The lithium secondary battery according to claim 21, wherein the lithium secondary battery is an all-solid-state secondary battery.

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