Positive electrode, preparation method thereof, and all-solid-state rechargeable batteries

Abstract

The present invention relates to a positive electrode and an all-solid-state rechargeable battery comprising same, the positive electrode comprising: a first positive electrode active material, which comprises secondary particles containing a lithium nickel-based composite oxide and formed by agglomeration of a plurality of primary particles, wherein at least a portion of the primary particles has a radial arrangement structure, a first coating layer located on the surfaces of the secondary particles and containing boron, and a second coating layer located on the first coating layer and containing a sulfide-based solid electrolyte; a second positive electrode active material, which contains a lithium nickel-based composite oxide and is in the form of single-particles, and comprises a first coating layer located on the surfaces of the single-particles and containing boron, and a second coating layer located on the first coating layer and containing a sulfide-based solid electrolyte, and which has an average particle diameter (D50) smaller than an average particle diameter (D50) of the first positive electrode active material; and a solid electrolyte, which comprises core particles containing a sulfide-based solid electrolyte, and a third coating layer located on the surfaces of the core particles and containing a lithium-metal-phosphate.

Description

Cathode, method for manufacturing anode, and all-solid-state secondary battery

[0001] It relates to a cathode, its manufacturing method, and an all-solid-state secondary battery.

[0002] Lithium secondary batteries, which boast high energy density and portability, are primarily used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, research is also actively underway to utilize high-energy-density lithium secondary batteries as power sources for hybrid and electric vehicles, or as power storage devices.

[0003] Recently, active development has been conducted on all-solid-state secondary batteries that utilize solid electrolytes instead of liquid ones to address issues such as fire safety. However, solid electrolytes have several drawbacks: lower ionic conductivity compared to liquid electrolytes, resistance at the interface with solid particles such as the cathode active material within the battery, and the formation of a depletion layer due to the contact between solids, which reduces ionic conductivity. Therefore, the development of a cathode that can utilize such solid electrolytes is urgently needed, and research is also needed on ways to improve the overall performance of all-solid-state secondary batteries, including capacity, charge-discharge efficiency, resistance characteristics, and cycle life.

[0004] Provided are a cathode having high initial charge / discharge capacity and efficiency, high volumetric capacity, and excellent life characteristics, a method for manufacturing the same, and an all-solid-state secondary battery including the same.

[0005] In one embodiment, a first cathode active material comprising a lithium nickel-based composite oxide, a secondary particle formed by agglomeration of a plurality of primary particles and at least a portion of the primary particles having a radial arrangement structure, a first coating layer positioned on the surface of the secondary particle and containing boron, and a second coating layer positioned on the first coating layer and containing a sulfide-based solid electrolyte; a first coating layer comprising a lithium nickel-based composite oxide in the form of a single particle and containing boron positioned on the surface of the single particle, and a second coating layer positioned on the first coating layer and containing a sulfide-based solid electrolyte, wherein the average particle diameter (D) of the first cathode active material 50 ) smaller than the average particle diameter (D 50 ) and a solid electrolyte including a core particle containing a sulfide-based solid electrolyte and a third coating layer located on the surface of the core particle and containing a lithium-metal-phosphate.

[0006] In another embodiment, (i) a first cathode active material precursor comprising a nickel-based composite hydroxide and in the form of secondary particles in which a plurality of primary particles are aggregated and at least a portion of the primary particles are radially arranged; a lithium nickel-based composite oxide comprising a single particle and having an average particle diameter (D) of the first cathode active material precursor 50 ) smaller than the average particle diameter (D 50) and a second cathode active material primary sintered product; a lithium raw material; and a boron raw material are mixed and subjected to a first heat treatment to obtain a boron-coated preliminary cathode active material, (ii) dry-mixing the boron-coated preliminary cathode active material and a sulfide-based solid electrolyte and performing a second heat treatment to obtain a final cathode active material, (iii) mixing core particles containing a sulfide-based solid electrolyte and a lithium-metal-phosphate and performing a third heat treatment at 200°C to 300°C to prepare a coated solid electrolyte, and (iv) mixing the final cathode active material and the coated solid electrolyte to produce a cathode.

[0007] In another embodiment, an all-solid-state secondary battery is provided, comprising the aforementioned positive electrode, the negative electrode, and a solid electrolyte layer positioned between the positive electrode and the negative electrode.

[0008] According to one embodiment, the cathode active material exhibits high capacity, high initial charge / discharge efficiency, high volumetric capacity, and excellent life characteristics.

[0009] Figure 1 is a schematic diagram showing the shape of a plate-shaped primary particle according to one implementation example.

[0010] Figure 2 is a drawing for explaining the definition of radiality in secondary particles according to one implementation example.

[0011] Figure 3 is a schematic diagram showing the cross-sectional structure of a secondary particle according to one implementation example.

[0012] Figures 4 and 5 are cross-sectional views schematically showing an all-solid-state secondary battery according to one embodiment.

[0013] Figure 6 is a graph showing the initial charge capacity (gray bar graph), initial discharge capacity (black bar graph), and initial charge / discharge efficiency (dotted line graph, right vertical axis) for the all-solid-state secondary batteries of Example 1 and Comparative Examples 1 to 5.

[0014] Figure 7 is a graph showing the capacity retention rate according to the number of cycles as a result of the life evaluation of the all-solid-state secondary batteries of Example 1 and Comparative Examples 1 to 4.

[0015] Figure 8 shows SEM images (top row) and EDS mapping images (bottom row) showing sulfur element for the final positive electrode active materials of Example 1, Comparative Example 3, and Comparative Example 4.

[0016] Figure 9 is a graph showing the particle size distribution for solid electrolytes manufactured in Comparative Example 1, Example 1, and Reference Example.

[0017] Below, specific implementation examples are described in detail so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in various different forms and is not limited to the implementation examples described herein.

[0018] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0019] Here, “combination of these” means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of the components.

[0020] It should be understood that the terms "include," "comprising," or "having" herein are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0021] To clearly illustrate various layers and regions in the drawings, their thicknesses are enlarged, and similar parts are designated by the same drawing reference numerals throughout the specification. When an element such as a layer, film, region, or plate is said to be "over" or "on" another element, this includes not only the case where it is "directly over" the other element, but also the case where there are other elements in between. Conversely, when an element is said to be "directly over" another element, it means that there are no other elements in between.

[0022] Also, here, “layer” includes not only the shape formed on the entire surface when observed in a plan view, but also the shape formed on a portion of the surface.

[0023] The average particle size can be measured by methods well known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with transmission electron microscope images or scanning electron microscope images. Alternatively, the average particle size can be obtained by measuring using dynamic light scattering, performing data analysis, counting the number of particles for each particle size range, and calculating from the counted number. Unless otherwise defined, the average particle size is the diameter (D) of the particles in the particle size distribution that have a cumulative volume of 50% by volume. 50 ) can mean. In addition, unless otherwise defined, the average particle size is obtained by measuring the size (diameter or length of major axis) of about 20 particles randomly in a scanning electron microscope image to obtain a particle size distribution, and the diameter (D) of the particle having a cumulative volume of 50% by volume in the particle size distribution 50 ) may be taken as the average particle diameter.

[0024] Here, “or” is not interpreted in an exclusive sense, for example, “A or B” is interpreted to include A, B, A+B, etc.

[0025] “Metal” is interpreted as a concept that includes common metals, transition metals, and metalloids (semi-metals).

[0026] anode

[0027] In one embodiment, a positive electrode is provided, which includes a first positive electrode active material, a second positive electrode active material, and a solid electrolyte. The first positive electrode active material includes a lithium nickel-based composite oxide, and includes secondary particles formed by agglomeration of a plurality of primary particles, at least a portion of which are radially arranged, a first coating layer positioned on the surface of the secondary particles and containing boron, and a second coating layer positioned on the first coating layer and containing a sulfide-based solid electrolyte. The second positive electrode active material includes a lithium nickel-based composite oxide in the form of a single particle, and includes a first coating layer positioned on the surface of the single particle and containing boron, and a second coating layer positioned on the first coating layer and containing a sulfide-based solid electrolyte, and an average particle diameter (D) of the first positive electrode active material 50 ) smaller than the average particle diameter (D 50 ) has. The solid electrolyte comprises a core particle containing a sulfide-based solid electrolyte and a third coating layer located on the surface of the core particle and containing lithium-metal-phosphate.

[0028] The above-mentioned positive electrode can be referred to as a positive electrode for a lithium secondary battery, and more specifically, as a positive electrode for an all-solid-state secondary battery. According to one embodiment, the positive electrode exhibits not only initial charge / discharge capacity and efficiency, but also a very high volumetric capacity and excellent lifespan characteristics.

[0029] The fact that the second cathode active material has a smaller average particle size than the first cathode active material means that the average particle size of the single particles of the second cathode active material is smaller than the average particle size of the secondary particles of the first cathode active material. The first cathode active material can be expressed as a counter or counter particle, and the average particle size of the secondary particles (D 50) may be 9 ㎛ to 25 ㎛, for example, 11 ㎛ to 18 ㎛, 12 ㎛ to 16 ㎛. The second positive electrode active material may be expressed as a particle or particles, and the average particle diameter (D of a single particle 50 ) may be 2 ㎛ to 7 ㎛, for example, 2 ㎛ to 6 ㎛, or 2 ㎛ to 5 ㎛. Here, the average particle diameter may be obtained by selecting 20 or so random particles from a scanning electron microscope image of the positive electrode active material, measuring the particle diameter (diameter, or major axis, or major axis length) thereof, and then obtaining a particle size distribution, and taking the size of particles having a cumulative volume of 50% by volume from the particle size distribution as the average particle diameter.

[0030] The solid electrolyte contained in the anode is in the form of particles, and its average particle diameter (D 50 ) may be about 0.1 ㎛ to 2 ㎛, for example, 0.5 ㎛ to 1.9 ㎛, 0.5 ㎛ to 1.5 ㎛, or 0.8 ㎛ to 1 ㎛, and the average particle diameter (D of the second positive electrode active material 50 ) may be less than or equal to.

[0031] With respect to the total of 100 wt% of the first positive electrode active material and the second positive electrode active material, the first positive electrode active material may be included in an amount of 60 wt% to 95 wt%, 70 wt% to 90 wt%, or 80 wt% to 90 wt%, and the second positive electrode active material may be included in an amount of 5 wt% to 40 wt%, 10 wt% to 30 wt%, or 10 wt% to 20 wt%. When the first positive electrode active material and the second positive electrode active material are mixed in the above weight ranges, the energy density of the positive electrode can be maximized.

[0032] In the positive electrode, the solid electrolyte may be included in an amount of 1 wt% to 35 wt%, for example, 5 wt% to 30 wt%, 10 wt% to 25 wt%, 10 wt% to 20 wt%, or 11 wt% to 15 wt%, based on 100 wt% of the total of the first positive electrode active material, the second positive electrode active material, and the solid electrolyte. When the sulfide-based solid electrolyte particles in the positive electrode satisfy the above range, the ionic conductivity can be improved while minimizing the capacity degradation of the positive electrode, thereby improving the overall performance of the all-solid-state secondary battery.

[0033] First positive electrode active material base material

[0034] The first cathode active material comprises a lithium nickel-based composite oxide, and comprises secondary particles in which at least two or more primary particles are aggregated, and at least a portion of the primary particles have a radial arrangement structure.

[0035] At least some of the above primary particles may have a plate shape. Fig. 1 is a schematic diagram showing the plate shape of the primary particles of the first positive electrode active material. Referring to Fig. 1, the primary particles according to one embodiment may have a basic plate structure but may also have various detailed shapes, such as (A) a polygonal nanoplate shape such as a hexagon, (B) a nanodisk shape, and (C) a rectangular parallelepiped shape. In Fig. 1, “a” refers to the length of the major axis of the primary particle, “b” refers to the length of the minor axis, and “t” refers to the thickness. Here, the major axis length (a) refers to the maximum length based on the widest surface of the primary particle. The thickness (t) may be said to be the maximum length of a surface that is approximately perpendicular to the widest surface of the primary particle. The direction in which the major axis length (a) and the minor axis length (b) are contained is defined as the surface direction, and the direction in which the thickness (t) is defined is defined as the thickness direction.

[0036] The thickness (t) of the primary particle may be smaller than the length of the major axis (a) and the length of the minor axis (b), which are lengths in the plane direction. Among the lengths in the plane direction, the length of the major axis (a) may be longer than or equal to the length of the minor axis (b).

[0037] In the first positive electrode active material, at least some of the primary particles may have a radial array structure, for example, the long axes of the primary particles may be arranged in a radial direction. Fig. 2 is a drawing for explaining the definition of radial in secondary particles according to one embodiment. In one embodiment, the radial array structure may mean that the thickness (t) direction of the primary particles is arranged perpendicular to the direction (R) from the center of the secondary particles toward the surface, or forms an angle of ±5° with the perpendicular direction, as shown in Fig. 2.

[0038] The average length of the primary particles constituting the secondary particles may be 0.01 μm to 5 μm, for example, 0.01 μm to 2 μm, 0.01 μm to 1 μm, 0.02 μm to 1 μm, 0.05 μm to 0.5 μm, or 150 nm to 500 nm. Here, the average length refers to the average length of the major axis length (a) in the plane direction when the primary particles are plate-shaped, and refers to the average particle diameter when the primary particles are spherical.

[0039] When the primary particles are plate-shaped, the average thickness of the primary particles may be, for example, 50 nm or more, 100 nm or more, 200 nm or more, 300 nm or more, 400 nm or more, 500 nm or more, 600 nm or more, 700 nm, 800 nm or more, or 900 nm or more, and may be, for example, 5 µm or less, 4 µm or less, 3 µm or less, 2 µm or less, 1 µm or less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, or 500 nm or less, and may be, for example, 100 nm to 200 nm. Additionally, in the primary particles, the ratio of the average thickness to the average length may be 1:1 to 1:10, for example, 1:1 to 1:8, 1:1 to 1:6, or 1:2 to 1:5.

[0040] Here, the length and thickness, etc. may be measured using an optical microscope such as a scanning electron microscope, and the average length may mean the arithmetic mean value of about 30 length data, and the average thickness may mean the arithmetic mean value of about 30 thickness data.

[0041] In this way, when the average length, average thickness, and the ratio of the average thickness to the average length of the primary particles satisfy the above-described ranges, and the primary particles are arranged radially, a relatively large number of lithium diffusion paths between grain boundaries can be provided on the surface, and a large number of crystal faces capable of lithium transfer are exposed to the outside, thereby improving lithium diffusion, thereby ensuring high initial efficiency and capacity. In addition, when the primary particles are arranged radially, the pores exposed on the surface can face toward the center of the secondary particles, thereby promoting lithium diffusion. In addition, uniform shrinkage and expansion are possible during lithium desorption and / or insertion due to the radially arranged primary particles, and the pores exist in the (001) direction, which is the direction in which the particles expand during lithium desorption, to provide a buffering effect. In addition, the size and arrangement of the primary particles reduce the probability of cracks occurring during shrinkage and expansion of the active material, and the internal pores further alleviate volume changes, thereby reducing cracks occurring between the primary particles during charge and discharge, thereby improving the life characteristics of the lithium secondary battery and reducing the phenomenon of resistance increase.

[0042] The first positive electrode active material may have an irregular porous structure in at least one of the inside and the outside of the secondary particle. The irregular porous structure refers to a structure having primary particles and pores, but the pore size, shape, location, etc. are not regular. For example, the secondary particle may have an inside including an irregular porous structure and an outside including a radially arranged structure as a region surrounding the inside. That is, the primary particles arranged inside may be arranged without regularity, unlike the primary particles arranged outside. The radially arranged structure refers to at least some of the primary particles being arranged radially.

[0043] Here, the term "outside" may mean a region of 30% to 50% in length from the outermost surface, for example, 40% in length from the outermost surface, among the total distance from the center of the secondary particle to the surface, or may mean a region from the outermost edge of the secondary particle to a depth of approximately 3 ㎛. In addition, the term "inside" may mean a region of 50% to 70% in length from the center, for example, 60% in length from the center, among the total distance from the center of the secondary particle to the surface, or may mean a remaining region excluding a region from the outermost edge of the secondary particle to a depth of approximately 3 ㎛.

[0044] The secondary particles of the first positive electrode active material may include an exterior oriented in a radial structure and an interior having an irregular porous structure, wherein the interior of the secondary particles may include pores larger in size than the pores present on the exterior. For example, the size of the pores present on the interior of the first positive electrode active material may be 150 nm to 1 ㎛, and the size of the pores present on the exterior may be less than 150 nm. In this case, when the pore size on the interior is larger than that on the exterior, compared to secondary particles having the same pore size on the interior and exterior, there is an advantage in that the lithium diffusion distance on the interior of the active material is shortened, lithium insertion from the exterior is facilitated, and volume changes occurring during charge and discharge are alleviated. Here, the pore size may refer to the diameter when the pore is spherical or circular, and may refer to the length of the major axis when the pore is elliptical, etc., and may be measured using a microscope such as a scanning electron microscope.

[0045] The secondary particles of the first positive electrode active material may have open pores on their surfaces. The size of the open pores may be less than about 150 nm, for example, 10 nm to 148 nm. The open pores are pores in which a portion of the pore wall is not closed, and are formed by spaces between the plate-shaped primary particles arranged radially, and are pores that are deeply connected from the surface of the secondary particle toward the center. These open pores may be connected to the outside and serve as passages through which substances can pass. The open pores may be formed to a depth of 150 nm or less on average, for example, 0.001 nm to 100 nm, for example, 1 nm to 50 nm, from the surface of the secondary particle. The size and depth of the above open pores may be measured by the BJH (Barrett, Joyner and Halenda) method, which is a method of deriving the content of nitrogen adsorption or desorption.

[0046] The secondary particles described above may have closed pores within them, and closed and / or open pores outside them. While the closed pores are unlikely to contain electrolytes, the open pores can contain electrolytes within them. The closed pores are formed with a structure in which all of their walls are closed, and thus can be considered independent pores that are not connected to other pores.

[0047] Fig. 3 is a schematic diagram showing the cross-sectional structure of the secondary particles of the first positive electrode active material. Referring to Fig. 3, the secondary particles (11) of the first positive electrode active material according to one embodiment contain an outer portion (14) having a structure in which primary particles (13) having a plate shape are arranged in a radial direction, and an inner portion (12) in which the primary particles (13) are arranged irregularly. In the inner portion (12), more empty spaces may exist between the primary particles than in the outer portion. In addition, the pore size and porosity in the inner portion are larger and irregular than those in the outer portion. In Fig. 3, arrows indicate the direction of movement of lithium ions.

[0048] The secondary particles have a porous structure on the inside, which reduces the diffusion distance of lithium ions to the inside, and the primary particles are arranged radially on the outside, which facilitates the insertion of lithium ions into the surface. In addition, the small size of the primary particles facilitates securing a lithium transfer path between the crystal grains. In addition, the small size of the primary particles and the pores between the primary particles alleviate the volume change that occurs during charge and discharge, thereby minimizing the stress due to the volume change during charge and discharge. Such a positive electrode active material can reduce the resistance of a lithium secondary battery and improve the capacity and life characteristics.

[0049] Meanwhile, in the secondary particle, a plurality of primary particles may be arranged toward one (1) center to form surface contact along the thickness direction of the primary particle, thereby forming a radial array structure. Alternatively, the secondary particle may have a multi-center radial array structure having multiple centers. In this way, when the secondary particle has a single-center or multi-center radial array structure, lithium is easily inserted / de-inserted to the center of the secondary particle.

[0050] The above secondary particles may include radial primary particles and non-radial primary particles. The content of the non-radial primary particles may be 40 wt% or less, for example, 0.01 wt% to 30 wt%, or 0.1 wt% to 20 wt%, based on 100 wt% of the total of the radial primary particles and the non-radial primary particles.

[0051] Second positive electrode active material base material

[0052] The second positive electrode active material is characterized by containing a lithium nickel-based composite oxide and having a single particle form. A single particle means that the particle exists alone without a grain boundary and is composed of a single particle, and may mean a single particle, a monolithic structure, a single-body structure, or a non-agglomerated particle in which the particles exist as an independent phase without being mutually aggregated in terms of morphology, and may be, for example, a single crystal. According to one embodiment, the positive electrode active material may exhibit improved life characteristics while implementing high capacity and high energy density by including the second positive electrode active material in the form of a single particle.

[0053] The shape of the second positive electrode active material is not particularly limited, and may have various shapes such as polyhedral, spherical, oval, plate-shaped, rod-shaped, and irregular.

[0054] lithium nickel-based composite oxide

[0055] The first positive electrode active material and the second positive electrode active material each contain a lithium nickel-based composite oxide. The nickel-based positive electrode active material can achieve high capacity and high energy density. The lithium nickel-based composite oxide of the first positive electrode active material and the lithium nickel-based composite oxide of the second positive electrode active material may be the same or different, and for example, each may be independently represented by the following chemical formula 5.

[0056] [Chemical Formula 5]

[0057] Li a5 Ni x5 M 5 y5 M 6 z5 O 2-b5 X b5

[0058] In the above chemical formula 5, 0.9≤a5≤1.2, 0.3≤x5<1, 0 <y5≤0.7, 0≤z5≤0.7, 0.9≤x5+y5+z5≤1.1, 및 0≤b5≤0.1이고, M 5 and M 6 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S.

[0059] For example, in the above chemical formula 5, 0.6≤x5<1, 0 <y5≤0.4, 0≤z5≤0.4일 수 있고, 또는 0.7<x5≤1, 0<y5≤0.3, 0≤z5≤0.3이거나, 0.8≤x5<1, 0<y5≤0.2, 0≤z5≤0.2이거나, 또는 0.9≤x5<1, 0<y5≤0.1, 0≤z5≤0.1일 수 있다.

[0060] The lithium nickel-based composite oxide of the first positive electrode active material and the lithium nickel-based composite oxide of the second positive electrode active material may each independently be a lithium nickel-cobalt-based composite oxide represented by the following chemical formula 6, as a specific example.

[0061] [Chemical Formula 6]

[0062] Li a6 Ni x6 Co y6 M 7 z6 O 2-b6 X b6

[0063] In the above chemical formula 6, 0.9≤a6≤1.8, 0.3≤x6<1, 0 <y6≤0.7, 0≤z6≤0.7, 0.9≤x6+y6+z6≤1.1, 및 0≤b6≤0.1이고 M7 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S.

[0064] The lithium nickel-based composite oxide of the first positive electrode active material and the lithium nickel-based composite oxide of the second positive electrode active material may each independently be, as a specific example, a lithium nickel-cobalt-manganese-based composite oxide, a lithium nickel-cobalt-aluminum-based composite oxide, or a lithium nickel-cobalt-aluminum-manganese-based composite oxide represented by the following chemical formula 7.

[0065] [Chemical Formula 7]

[0066] Li a7 Ni x7 Co y7 M 8 z7 M 9 w7 O 2-b7 X b7

[0067] In the above chemical formula 7, 0.9≤a7≤1.8, 0.3≤x7≤0.98, 0.01≤y7≤0.69, 0.01≤z7≤0.69, 0≤w7≤0.69, 0.9≤x7+y7+z7+w7≤1.1, and 0≤b7≤0.1, and M 8 is Al, Mn or a combination thereof, and M 8 is one or more elements selected from 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 F, P, and S.

[0068] For example, the first positive electrode active material may include a lithium nickel-cobalt-aluminum composite oxide, which means an oxide including lithium, nickel, cobalt, and aluminum, and optionally further including other elements, and may be expressed as Ni-Co-Al, or NCA.

[0069] The lithium nickel-cobalt-aluminum composite oxide of the first positive electrode active material can be represented by chemical formula 1.

[0070] [Chemical Formula 1]

[0071] Li a1 Ni x1 Co y1 Al z1 M 1 w1 O 2-b1 X b1

[0072] 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, 및 0≤b1≤0.1이고, M 1 is one or more elements selected from 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 F, P, and S.

[0073] In the above 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 be present, 0.8≤x1≤0.98, 0.01≤y1≤0.19, 0.01≤z1≤0.19, 0≤w1≤0.18 may be present, or 0.9≤x1≤0.98, 0.01≤y1≤0.09, 0.01≤z1≤0.09, 0≤w1≤0.08 may be present.

[0074] Also, as an example, the second positive electrode active material may include a lithium nickel-cobalt-aluminum-manganese composite oxide, which means an oxide including lithium, nickel, cobalt, aluminum, and manganese and optionally further including other elements, and may be expressed as Ni-Co-Al-Mn, or NCAM.

[0075] The lithium nickel-cobalt-aluminum-manganese composite oxide of the second positive electrode active material can be represented by chemical formula 2.

[0076] [Chemical Formula 2]

[0077] Li a2 Ni x2 Co y2 Al z2 Mn w2 M 2 v2 O 2-b2 X b2

[0078] 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, 및 0≤b2≤0.1이고, 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.

[0079] In the above 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 present, 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 present, and 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 present.

[0080] In the lithium nickel composite oxide, the content of nickel may be 30 mol% or more, for example, 40 mol% or more, 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more, or 90 mol% or more, and may be 99.9 mol% or less, or 99 mol% or less, based on 100 mol% of the metal excluding lithium.

[0081] In general, as the nickel content in the positive electrode active material increases, Ni 2+The mixing of cations occupying the lithium site may increase, which may actually reduce the capacity, or the diffusion of lithium ions may be hindered by impurities such as NiO, which may reduce the battery life, and the structural collapse or cracking of the positive electrode active material due to charge and discharge may increase side reactions with the electrolyte, which may reduce the battery life and cause safety issues. To solve this, when coating boron only on the surface of the active material using the conventional method, there was a problem that the boron acted as a resistor, which actually reduced the capacity and shortened the lifespan. On the other hand, according to one embodiment, even if a high-nickel system is used, the positive electrode active material is simultaneously coated with an appropriate amount of boron on the first positive electrode active material and the second positive electrode active material, thereby improving the problems caused by the high concentration of nickel, thereby implementing high capacity while improving the lifespan characteristics without deteriorating the initial discharge capacity.

[0082] First coating layer of positive electrode active material

[0083] According to one embodiment, a cathode active material includes a boron-containing first coating layer. The first coating layer may be described as a type of buffer layer or buffer layer, and may effectively suppress side reactions between a lithium nickel-based composite oxide and a sulfide-based solid electrolyte.

[0084] Previously, when coating boron on a positive electrode active material, it was common to use a method of mixing a boron source material into a lithium metal composite oxide in a wet or dry manner and then heat-treating it. However, in this case, there was a problem that boron acted as a resistor on the surface of the positive electrode active material, which actually worsened the capacity and lifespan. In particular, when mixing two types of positive electrode active materials, if each positive electrode active material is coated with boron and then mixed, the pellet density and initial discharge capacity of the entire positive electrode active material drop sharply, resulting in a significant drop in volumetric capacity and deterioration in lifespan characteristics. On the other hand, according to one embodiment, a positive electrode active material coated with a boron-containing compound can be obtained by mixing a first nickel-based composite hydroxide having radially oriented primary particles with a second lithium nickel-based composite oxide in the form of single particles and a lithium source material, and then adding the boron source material together and heat-treating the mixture. In this case, while obtaining a first lithium nickel-based composite oxide in which the primary particles are radially oriented, at the same time, an appropriate amount of boron is stably coated on the surfaces of the first positive electrode active material and the second positive electrode active material, so that boron no longer acts as a resistor, the structural stability of the positive electrode active material is secured, and problems due to contact between the positive electrode active material and the electrolyte are suppressed, so that the capacity characteristics and long-term life characteristics of the battery can be improved.

[0085] For example, nickel-based positive electrode active materials may experience structural collapse and cation mixing due to the formation of NiO and other ions on the surface with repeated charge and discharge, which may result in gas generation or deterioration of cycle life characteristics. In addition, the positive electrode active material may crack with repeated charge and discharge, which may increase side reactions between the positive electrode active material and the electrolyte, resulting in a decrease in battery capacity and deterioration of cycle life characteristics. However, according to one embodiment, an appropriate amount of a boron-containing compound is stably coated on the surfaces of the first positive electrode active material and the second positive electrode active material at the same time, and a first coating layer and a grain boundary boron coating portion or a boron-doped layer are simultaneously formed on the first positive electrode active material, thereby preventing the desorption of oxygen atoms from the surface of the positive electrode active material, suppressing structural collapse, and suppressing the deterioration of cracking due to repeated charge and discharge. In addition, single-particle forms such as the second positive electrode active material have difficulty in lithium diffusion into the particle, but in one embodiment, by coating a boron-containing compound on the surface, lithium diffusion can be facilitated, and oxygen atoms on the surface of the positive electrode active material can be effectively prevented from desorbing. Furthermore, the movement of lithium ions in an all-solid-state battery can be made smoother by the boron-containing compound present on the surface of the positive electrode active material, thereby improving the rate characteristics.

[0086] The first coating layer may be said to contain a boron-containing compound, for example, boron oxide, lithium boron oxide (lithium borate), or a combination thereof, for example, B2O2, B2O3, B4O3, B4O5, LiBO-2, Li3B7O 12 , Li6B4O9, Li3B 11 O 18 , Li2B4O7, Li3BO3, or a combination thereof.

[0087] The first coating layer may be present in the form of a continuous film on the surface of the secondary particles of the first positive electrode active material, or may be coated in the form of an island on the surface of the single particles of the second positive electrode active material.

[0088] The content of boron with respect to 100 mol% of the total metal excluding lithium in the entire positive electrode active material including the first positive electrode active material and the second positive electrode active material may be 0.01 mol% to 0.5 mol%, for example, 0.01 mol% to 0.4 mol%, 0.01 mol% to 0.3 mol%, or 0.1 mol% to 0.3 mol%. In addition, the content of boron with respect to 100 wt% of the total metal excluding lithium in the entire positive electrode active material may be 0.01 wt% to 0.5 wt%, for example, 0.01 wt% to 0.3 wt%, 0.01 wt% to 0.2 wt%, or 0.01 wt% to 0.1 wt%. The content of boron may be measured, for example, through ICP (Inductively Coupled Plasma) emission spectroscopy. When boron is coated with such a content, it does not act as a resistor and the battery capacity does not decrease, the diffusion of lithium ions into the positive electrode active material becomes easier, improving the initial charge / discharge efficiency, etc., and problems caused by repeated charge / discharge can be suppressed, thereby improving the long-life characteristics of the battery.

[0089] Meanwhile, the first positive electrode active material in the form of secondary particles including a radial structure may further include a grain boundary boron coating portion located on the surface of primary particles inside the secondary particles as well as a first coating layer located on the surface of the secondary particles. That is, in the first positive electrode active material, boron may be coated along the interface of the primary particles inside the secondary particles. Here, the inside of the secondary particles means the entire inside excluding the surface, for example, it may mean the entire inside from a depth of approximately 1 ㎛ from the outer surface, and it may also be expressed as a part that is not touched by distilled water when the positive electrode active material secondary particles are washed with distilled water. In this way, when a boron-containing compound is coated on the surface of the secondary particles and the inner grain boundary surface of the first positive electrode active material, boron does not act as a resistor and can effectively suppress the phenomenon of structural collapse or breakage of the positive electrode active material due to charge and discharge.

[0090] Here, the boron content present on the surface of the secondary particle may be higher than the boron content present at the internal grain boundary, for example, four times or more. That is, the weight of boron in the first coating layer may be four times or more the weight of boron in the grain boundary boron coating portion. For example, the ratio of the weight of boron in the first coating layer to the weight of boron in the grain boundary boron coating portion may be 70:30 to 98:2, for example, 75:25 to 97:3, or 80:20 to 95:5. In this case, boron may play a role in improving performance without acting as a resistor in the positive electrode active material, and may simultaneously improve the capacity characteristics and life characteristics of the lithium secondary battery.

[0091] For example, the boron content in the first coating layer may be 0.02 wt% to 0.5 wt%, 0.03 wt% to 0.4 wt%, 0.04 wt% to 0.3 wt%, or 0.05 wt% to 0.2 wt%, etc., with respect to 100 wt% of the first positive electrode active material. The boron content in the grain boundary boron coating portion may be 0.001 wt% to 0.05 wt%, 0.001 wt% to 0.04 wt%, 0.002 wt% to 0.03 wt%, or 0.003 wt% to 0.02 wt%, but is not limited thereto. When the boron contents in the first coating layer and the grain boundary boron coating portion are as such, both the capacity characteristics and the life characteristics of the lithium secondary battery can be improved. Here, the boron content may be measured through ICP emission spectroscopy analysis of the positive electrode active material, the boron content in the grain boundary boron coating portion may refer to the boron content remaining in the first positive electrode active material after washing, and the boron content of the first coating layer may refer to the difference between the boron content before washing and the boron content after washing.

[0092] According to one embodiment, the first positive electrode active material in the form of secondary particles containing a radial structure may further include a boron-doped layer positioned inside the primary particles exposed on the surface of the secondary particles. The boron-doped layer may be said to be positioned inside the secondary particles, and may be said to be positioned within a depth range of about 10 nm from the outer surface of the primary particles exposed on the surface of the secondary particles. If the outer surface of the primary particles exposed on the surface of the secondary particles is 0 nm, the doped layer may be said to exist in a depth range of 0 nm to 10 nm starting from the surface. In other words, the boron-doped layer may be said to be positioned within a depth range of 10 nm from the surface of the secondary particles. If the secondary particle surface is 0 nm, the doped layer may be said to exist in a depth range of 0 nm to 10 nm starting from the surface. Such a boron-doped layer can further enhance the structural stability of the positive electrode active material, and thus improve the life characteristics of a lithium secondary battery.

[0093] The above boron doping layer may be positioned, for example, within a depth range of 9 nm, within a depth range of 8 nm, within a depth range of 7 nm, within a depth range of 6 nm, within a depth range of 5 nm, within a depth range of 4 nm, within a depth range of 3 nm, or within a depth range of 2.5 nm from the outer surface of the primary particles exposed to the surface of the secondary particles. This boron doping layer is distinct from the first coating layer or the grain boundary boron coating portion, and is thought to contribute to the structural stability of the positive electrode active material.

[0094] Second coating layer of positive electrode active material

[0095] According to one embodiment, a cathode active material is characterized by having a second coating layer formed thereon containing a sulfide-based solid electrolyte. The second coating layer can be described as a sulfide-based solid electrolyte thermally complexed onto the surface of a cathode active material (specifically, a cathode active material having a first coating layer formed thereon). In the second coating layer, the sulfide-based solid electrolyte is not excessively aggregated or exists in the form of grown particles, but is uniformly distributed in a thin thickness, and can be said to maintain high ionic conductivity.

[0096] In the configuration of a positive electrode including a positive electrode active material and a sulfide-based solid electrolyte, when a second coating layer containing a sulfide-based solid electrolyte is formed on the outermost surface of positive electrode active material particles as in one embodiment and then mixed with the solid electrolyte to form a positive electrode, the resistance of the positive electrode is significantly reduced, and the initial charge / discharge capacity and efficiency of the all-solid-state secondary battery are improved simultaneously, and even the volumetric capacity and life characteristics can be improved. In addition, by forming a second coating layer on the positive electrode active material in a state where a boron-containing first coating layer, which serves as a type of buffer layer, is formed and heat-treated, a passivation layer is formed at the interface, so that adverse effects between the lithium nickel-based composite oxide and the sulfide-based solid electrolyte can be effectively blocked, and a good second coating layer having high ionic conductivity and no aggregation can be formed. According to one embodiment, a positive electrode active material can form a passivation layer on the surface of particles, thereby suppressing additional side reactions with solid electrolyte particles in the positive electrode, thereby improving the life characteristics of the battery. In addition, since the buffer layer function on the surface of the positive electrode active material particles is strengthened, the space charge layer can be better controlled, thereby improving the initial charge / discharge capacity and efficiency.

[0097] The thickness of the second coating layer in each of the first positive electrode active material and the second positive electrode active material may be approximately 100 nm to 2 μm, for example, 200 nm to 1 μm, 300 nm to 900 nm, or 400 nm to 800 nm. When the second coating layer has the above thickness range, high ionic conductivity can be achieved without increasing resistance.

[0098] The total amount of the sulfide-based solid electrolyte of the second coating layer of the first positive electrode active material and the sulfide-based solid electrolyte of the second coating layer of the second positive electrode active material may be 0.5 wt% to 3 wt%, for example, 0.5 wt% to 2 wt%, or 1 wt% to 1.5 wt%, based on 100 wt% of the total of the first positive electrode active material and the second positive electrode active material. When the second coating layer satisfies the above content range, the sulfide-based solid electrolyte does not aggregate on the surface of the positive electrode active material and can maintain high ionic conductivity. For example, when the content of the sulfide-based solid electrolyte of the second coating layer is excessive, the sulfide-based solid electrolyte particles may aggregate and grow into large particles with many grain boundaries, thereby increasing the resistance and decreasing the ionic conductivity, and ultimately reducing the capacity of the battery and deteriorating the life characteristics. On the other hand, when the content of the sulfide-based solid electrolyte of the second coating layer is too low, the second coating layer may not be formed effectively, and thus the effect of improving battery performance may not be obtained.

[0099] In addition, in one embodiment, with respect to 100 wt% of the total of the sulfide-based solid electrolyte of the second coating layer of the first positive electrode active material, the sulfide-based solid electrolyte of the second coating layer of the second positive electrode active material, and the solid electrolyte in the positive electrode, the combined amount of the sulfide-based solid electrolyte of the second coating layer of the first positive electrode active material and the sulfide-based solid electrolyte of the second coating layer of the second positive electrode active material may be 1 wt% to 20 wt%, for example, 3 wt% to 15 wt%, 5 wt% to 10 wt%, or 6 wt% to 9 wt%. This may be referred to as the weight ratio of the sulfide-based solid electrolyte thermally complexed on the surface of the positive electrode active material with respect to the total amount of the sulfide-based solid electrolyte present in the positive electrode, and when this ratio is appropriately adjusted within the above range, the capacity, efficiency, volumetric capacity, and lifespan characteristics of the battery may be improved simultaneously. For example, if the thermal compounding ratio is excessive, sulfide-based solid electrolytes may grow or aggregate on the surface of the positive electrode active material particles, resulting in decreased ionic conductivity and increased resistance. Conversely, if the thermal compounding ratio is too low, it may be difficult to achieve the increased effectiveness of thermal compounding.

[0100] The type or component of the sulfide-based solid electrolyte included in the second coating layer is not particularly limited. For example, the sulfide-based solid electrolyte may be Li2S-P2S5, Li2S-P2S5--LiX (wherein 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, Li2S-P2S5-Z. m S n (m, n are integers, Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MOq (p, q are integers, and M is P, Si, Ge, B, Al, Ga or In), or a combination thereof.

[0101] Such sulfide-based solid electrolytes can be obtained, for example, by mixing Li2S and P2S5 in a molar ratio of 50:50 to 90:10, or 50:50 to 80:20, and optionally heat-treating them. Within the above mixing ratio range, a sulfide-based solid electrolyte having excellent ionic conductivity can be produced. Here, the ionic conductivity can be further improved by further including other components such as SiS2, GeS2, and B2S3.

[0102] Methods for mixing sulfur-containing raw materials for manufacturing sulfide-based solid electrolytes can be either mechanical milling or solution milling. Mechanical milling involves placing starting materials in a ball mill reactor and vigorously stirring them to finely atomize and mix them. Using the solution milling method, the starting materials are mixed in a solvent to obtain a solid electrolyte as a precipitate. Furthermore, heat treatment after mixing can solidify the crystals of the solid electrolyte and improve ionic conductivity. The heat treatment can be performed at a temperature ranging from 400°C to 600°C, for example, from 450°C to 500°C, or from 460°C to 490°C, for 5 to 30 hours, 10 to 24 hours, or 15 to 20 hours. Heat treatment under the above conditions can maximize ionic conductivity. For example, a sulfide-based solid electrolyte can be manufactured by mixing sulfur-containing raw materials and heat-treating them twice or more, in which case a sulfide-based solid electrolyte with high ionic conductivity and strength can be manufactured.

[0103] According to one embodiment, a sulfide-based solid electrolyte can be manufactured through, for example, a first heat treatment in which sulfur-containing raw materials are mixed and calcined at 120°C to 350°C, and a second heat treatment in which the first heat treatment result is mixed and calcined at 350°C to 800°C. The first heat treatment and the second heat treatment can each be performed in an inert gas atmosphere. The first heat treatment can be performed for 1 to 10 hours, and the second heat treatment can be performed for 5 to 20 hours. The first heat treatment can have the effect of milling small raw materials, and the second heat treatment can synthesize the final solid electrolyte. Through two or more such heat treatments, a high-performance sulfide-based solid electrolyte with high ionic conductivity and strength can be obtained, and such a solid electrolyte can be said to be suitable for mass production. The temperature of the first heat treatment may be, for example, 150°C to 330°C, or 200°C to 300°C, and the temperature of the second heat treatment may be, for example, 380°C to 700°C, or 400°C to 600°C.

[0104] For example, the sulfide-based solid electrolyte may include an argyrodite-type sulfide. The argyrodite-type sulfide-based solid electrolyte has an ionic conductivity of 10, which is the ionic conductivity of a typical liquid electrolyte at room temperature. -4 10 inland -2 It has a high ionic conductivity close to the S / cm range and can form a close bond between the positive electrode active material and the solid electrolyte.

[0105] The argyrodite-type sulfide-based solid electrolyte may include, for example, a compound represented by the chemical formula 21 below.

[0106] [Chemical Formula 21]

[0107] (Li a M 1 b M 2 c )(P d M 3 e)(S f M 4 g )X h

[0108] In the above chemical formula 21, 4≤a≤8, and M 1 is Mg, Ca, Cu, Ag, or a combination thereof, and 0≤b<0.5, and M 2 is Na, K, or a combination thereof, 0≤c<0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, and 0 <d<4, 0≤e<1 이고, M 4 is N,O,SO n , or a combination thereof, and 1.5≤n≤5, 3≤f≤12, 0≤g<2, and X is F, Cl, Br, I, or a combination thereof, and 0≤h≤2.

[0109] For example, in chemical formula 21, a halide element (X) may be included as an essential element, in which case 0 <h≤2로 표시될 수 있다. 일 예로 화학식 21에 M 1 Elements may be required, in which case 0 <b<0.5로 표시될 수 있다. 화학식 21에서 M 3 can be understood as an element substituted in place of P and 0 <e<1일 수 있다. 화학식 21에서 M 4 is substituted in the S position, for example, 0 <g<2일 수 있으며 S의 비율인 f는 예를 들어 3≤f≤7일 수 있다. M 4 Go SO n If SO n It can be, for example, S4O6, S3O6, S2O3, S2O4, S2O5, S2O6, S2O7, S2O8, SO4, or SO5, and can be, for example, SO4.

[0110] For example, in chemical formula 21, a+b+c+h=7, d+e=1, and f+g+h=6.

[0111] As a specific example, argyrodite-type sulfide-based solid electrolyte particles include Li3PS4 and Li7P3S. 11, Li7PS6, Li6PS5Cl, Li6PS5Br, Li 5.8 PS 4.8 Cl 1.2 , Li 6.2 PS 5.2 Br 0.8 , Li 5.75 PS 4.75 Cl 1.25 , (Li 5.69 Cu 0.06 )PS 4.75 Cl 1.25 , (Li 5.72 Cu 0.03 )PS 4.75 Cl 1.25 , (Li 5.69 Cu 0.06 )P(S 4.70 (SO4) 0.05 )Cl 1.25 , (Li 5.69 Cu 0.06 )P(S 4.60 (SO4) 0.15 )Cl 1.25 , (Li 5.72 Cu 0.03 )P(S 4.725 (SO4) 0.025 )Cl 1.25 , (Li 5.72 Na 0.03 )P(S 4.725 (SO4) 0.025 )Cl 1.25 , Li 5.75 P(S 4.725 (SO4) 0.025 )Cl 1.25 , or combinations thereof, but are not limited thereto.

[0112] An argyrodite-type sulfide-based solid electrolyte can be manufactured, for example, by mixing lithium sulfide and phosphorus sulfide, and optionally, lithium halide. After mixing these, a heat treatment may be performed. The heat treatment may include, for example, two or more heat treatment steps. Here, manufacturing an argyrodite-type sulfide-based solid electrolyte may include, for example, a first heat treatment of mixing raw materials and calcining at 120°C to 350°C, and a second heat treatment of mixing the resultant of the first heat treatment again and calcining at 350°C to 800°C.

[0113] In the second coating layer, the sulfide-based solid electrolyte may be in the form of particles, and the average particle diameter (D) of the particles 50 ) may be, for example, 0.1 ㎛ to 1.5 ㎛, 0.3 ㎛ to 1 ㎛, or 0.8 ㎛ to 1 ㎛. The average particle diameter may be measured from an electron microscope image, and for example, a particle size distribution is obtained by measuring the size (diameter or length of the major axis) of about 20 particles in an SEM image, where D 50 It may be calculated. When the particle size of the sulfide-based solid electrolyte satisfies the above range, a second coating layer having a thin and uniform thickness can be formed. The size of the sulfide-based solid electrolyte of the second coating layer may be smaller than or equal to the sulfide-based solid electrolyte particles mixed in the positive electrode.

[0114] solid electrolyte

[0115] According to one embodiment, a positive electrode includes a solid electrolyte in addition to the first positive electrode active material and the second positive electrode active material described above, and the solid electrolyte is characterized by including core particles containing a sulfide-based solid electrolyte and a third coating layer located on the surface of the core particles and containing a lithium-metal-phosphate.

[0116] The sulfide-based solid electrolyte, which is the core particle of the above solid electrolyte, may include, for example, an argyrodite-type sulfide. Since the general information on the sulfide-based solid electrolyte and its manufacturing method, and the information on the argyrodite-type sulfide-based solid electrolyte and its manufacturing method are as described above, a detailed description thereof will be omitted.

[0117] The lithium metal phosphate of the third coating layer may refer to an oxide containing lithium and a metal other than lithium. Here, the metal is a concept including general metals, transition metals, and metalloids. In the lithium metal phosphate, the metal may be, for example, one or more elements selected from the group consisting of Al, B, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ta, V, W, and Zr.

[0118] The lithium metal phosphate may be amorphous. According to one embodiment, when an amorphous lithium metal phosphate is coated on the sulfide-based solid electrolyte-containing core particle and heat-treated, the resulting solid electrolyte can exhibit higher ionic conductivity, lower interfacial resistance with other solid particles such as a cathode active material within the battery, prevent agglomeration of solid electrolyte particles, improve ionic conductivity, and enhance capacity characteristics, life characteristics, etc.

[0119] In the third coating layer, the lithium-metal-phosphate may be in the form of particles, and its average particle diameter (D 50) may be, for example, 0.01 ㎛ to 1.0 ㎛, 0.01 ㎛ to 0.9 ㎛, 0.01 ㎛ to 0.8 ㎛, or 0.01 ㎛ to 0.5 ㎛. The average particle diameter of the lithium-metal-phosphate may be smaller than the particle diameter of the sulfide-based solid electrolyte particles. When a lithium-metal-phosphate having such a particle diameter range is used, it can be evenly coated on the surface of the sulfide-based solid electrolyte particles, and the ionic conductivity of the solid electrolyte can be sufficiently increased and the moisture stability can be improved.

[0120] The above lithium-metal-phosphate may exist in the form of a film or island on the surface of the core particle.

[0121] In a solid electrolyte according to one embodiment, the lithium-metal-phosphate may be included in an amount of 0.01 wt% to 3 wt% based on 100 wt% of the solid electrolyte, for example, 0.01 wt% to 2 wt%, 0.01 wt% to 1 wt%, 0.01 wt% to 0.8 wt%, or 0.1 wt% to 1.0 wt%. When the content of the lithium-metal-phosphate is such as this, the solid electrolyte can exhibit an appropriate particle size distribution without particle agglomeration while implementing high ionic conductivity. In particular, when the content of the lithium-metal-phosphate satisfies the range of 0.01 wt% to 0.8 wt% based on 100 wt% of the solid electrolyte, the lithium-metal-phosphate may be evenly coated on the surface of the sulfide-based solid electrolyte particles, and thus the ionic conductivity and moisture stability of the solid electrolyte may be further improved, and the efficiency and life characteristics of the battery may be further improved.

[0122] According to one embodiment, a solid electrolyte is formed in a form in which a lithium-metal-phosphate is coated on the surface of core particles containing a sulfide-based solid electrolyte, and the solid electrolyte has sufficiently high crystallinity to realize excellent ionic conductivity, and at the same time, has an appropriate particle size distribution without particle agglomeration. As the crystallinity of the solid electrolyte increases or the crystal size increases, the half-width of the main peak in X-ray diffraction analysis may decrease, and the solid electrolyte according to one embodiment may have a half-width of the main peak of 0.160 or less. Here, the main peak refers to the peak with the highest diffraction intensity in X-ray diffraction analysis. The half-width of the main peak in the X-ray diffraction analysis of the solid electrolyte according to one embodiment may be, for example, 0.159 or less, or 0.155 or less. It is known that when the half-width decreases, that is, when the crystallinity increases, the ionic conductivity improves. For example, it is understood that when the crystal size increases, the crystal grain boundaries decrease, which improves the ionic conductivity.

[0123] In general, sulfide-based solid electrolytes have particles that are clumped together or have a large particle size immediately after synthesis, and when they are subjected to processes such as pulverization to adjust the particle size to a particle size that can be used in a battery, the crystallinity is reduced and the ionic conductivity decreases. According to one embodiment, the solid electrolyte coats core particles containing the sulfide-based solid electrolyte with lithium-metal-phosphate and heat-treats them at a specific temperature range, thereby increasing the crystallinity and adjusting the half width of the main peak to 0.160 or less, and at the same time, having an even particle size distribution without clumping or growth of the particles, so that the ionic conductivity can be further improved.

[0124] The average particle size (D) of the solid electrolyte contained in the anode 50) may be 0.1 ㎛ to 5 ㎛, for example, 0.1 ㎛ to 3 ㎛, 0.1 ㎛ to 2 ㎛, 0.5 ㎛ to 1.9 ㎛, or 0.8 ㎛ to 1 ㎛. The size of the sulfide-based solid electrolyte particles included in the positive electrode may be larger than or equal to the particles of the sulfide-based solid electrolyte of the second coating layer of the positive electrode active material, and may be smaller than the size of the solid electrolyte included in the solid electrolyte layer described later. By appropriately adjusting the size of the sulfide-based solid electrolyte included in the positive electrode, the capacity and energy density of the positive electrode can be increased and the ionic conductivity can be improved. The average particle diameter of the solid electrolyte may be measured by a microscope image, for example, a particle size distribution is obtained by measuring the sizes of about 20 particles in a scanning electron microscope image, and here D 50 It may have been calculated.

[0125] According to one embodiment, a solid electrolyte is characterized by having a uniform particle size distribution without particle agglomeration. For example, in the particle size distribution for the solid electrolyte, the (D90-D10) / D50 value may be greater than 1 and less than or equal to 5, for example, 1.1 to 4.0, 1.1 to 3.0, or 1.1 to 2.0. The (D90-D10) / D50 value may indicate the degree of peak width in a particle size distribution graph for the solid electrolyte, specifically, in which the horizontal axis represents the particle size (㎛) and the vertical axis represents the cumulative volume % of the particles, and a smaller value may be interpreted as having a uniform particle size because the peak width of the graph is narrower. Here, D10 means the diameter of a particle having a cumulative volume of 10% by volume in the particle size distribution, D50 means the diameter of a particle having a cumulative volume of 50% by volume in the particle size distribution, and D90 means the diameter of a particle having a cumulative volume of 90% by volume in the particle size distribution.

[0126] The D10 of the above solid electrolyte may be, for example, 0.05 ㎛ to 0.7 ㎛, 0.05 ㎛ to 0.6 ㎛, 0.1 ㎛ to 0.5 ㎛, or 0.2 ㎛ to 0.4 ㎛. In addition, the D90 of the above solid electrolyte may be, for example, 0.9 ㎛ to 5.0 ㎛, 1.0 ㎛ to 4.0 ㎛, 1.0 ㎛ to 3.0 ㎛, or 1.2 ㎛ to 2.0 ㎛. When the solid electrolyte has such a particle size distribution, it is possible to improve the performance of the battery by implementing high energy density while implementing excellent ionic conductivity.

[0127] The ionic conductivity of the solid electrolyte at 25°C may be 2.9 mS / cm or more, for example, 2.9 mS / cm to 5.0 mS / cm, 3.0 mS / cm to 4.5 mS / cm, or 3.0 mS / cm to 4.0 mS / cm. The ionic conductivity may be measured through electrochemical impedance spectroscopy (EIS).

[0128] Binders and Challengers

[0129] According to one embodiment, the positive electrode may include a current collector and a positive electrode active material layer positioned on the current collector, wherein the positive electrode active material layer includes the first positive electrode active material, the second positive electrode active material, and the solid electrolyte described above, and optionally may further include a binder and / or a conductive material.

[0130] The binder serves to adhere the positive electrode active material particles well to each other and also to adhere the positive electrode active material well to the current collector, and representative examples thereof 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, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0131] The content of the binder may be approximately 0.1 wt% to 5 wt%, or 0.1 wt% to 3 wt%, based on 100 wt% of the entire positive electrode active material layer.

[0132] The conductive material is used to provide conductivity to the electrode, and any material that does not cause a chemical change and is electronically conductive can be used in the battery to be constructed. Examples of conductive materials that can be used include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof.

[0133] The content of the conductive agent may be 0.1 wt% to 5 wt%, or 0.1 wt% to 3 wt%, based on 100 wt% of the total positive electrode active material layer.

[0134] Aluminum foil or stainless steel (SUS) can be used as the current collector of the positive electrode, but is not limited thereto.

[0135] Anode density and volumetric capacity

[0136] According to one embodiment, the positive electrode can have a high density and can realize high specific capacity and energy density. The plate density of the positive electrode can be, for example, 3.5 g / cc or more, or 3.8 g / cc or more, for example, 3.8 g / cc to 4.0 g / cc. In addition, the positive electrode according to one embodiment can realize a high volumetric capacity, for example, the volumetric capacity of the positive electrode can be 700 mAh / cc or more, 770 mAh / cc or more, or 780 mAh / cc or more, for example, 700 mAh / cc to 800 mAh / cc, 750 mAh / cc to 800 mAh / cc, 770 mAh / cc to 800 mAh / cc, etc.

[0137] Method for manufacturing anode

[0138] In one embodiment, (i) a first cathode active material precursor comprising a nickel-based composite hydroxide and in the form of secondary particles in which a plurality of primary particles are aggregated and at least a portion of the primary particles are radially arranged; (ii) a lithium nickel-based composite oxide comprising a single particle and having an average particle diameter (D) of the first cathode active material precursor 50 ) smaller than the average particle diameter (D 50 ) and a second cathode active material primary sintered product; a lithium raw material; and a boron raw material are mixed and subjected to a first heat treatment to obtain a boron-coated preliminary cathode active material, (ii) dry-mixing the boron-coated preliminary cathode active material and a sulfide-based solid electrolyte and performing a second heat treatment to obtain a final cathode active material, (iii) mixing core particles containing a sulfide-based solid electrolyte and a lithium-metal-phosphate and performing a third heat treatment at 200°C to 300°C to prepare a coated solid electrolyte, and (iv) mixing the final cathode active material and the coated solid electrolyte to produce a cathode.

[0139] In step (i), a first nickel-based composite hydroxide and a lithium raw material react through a first heat treatment process to form a first lithium nickel-based composite oxide, and a boron-containing compound is coated on the surface and internal grain boundaries of secondary particles to manufacture a first cathode active material, and a second lithium nickel-based composite oxide in the form of a single particle is re-heat treated to coat the surface with boron to manufacture a second cathode active material. That is, a preliminary cathode active material can be manufactured by mixing a first cathode active material on which a first coating layer is formed through step (i) and a second cathode active material on which a first coating layer is formed.

[0140] In the step (i) above, the first lithium nickel-based composite oxide and the second lithium nickel-based composite oxide are not manufactured separately, coated, and then mixed, but the first nickel-based composite hydroxide, the second lithium nickel-based composite oxide, the lithium raw material, and the boron raw material are mixed and fired simultaneously. This method for manufacturing a cathode active material is not only simple and efficient, but also has high productivity. For example, the second lithium nickel-based composite oxide has good thermal conductivity in the form of single particles, so that the firing time can be shortened, thereby increasing production volume. In addition, the simultaneous firing method can reduce the number of firings, thereby significantly reducing costs. In addition, the pellet density and initial discharge capacity of the final cathode active material are improved, so that the volumetric capacity of the battery is significantly improved, and both the initial charge / discharge efficiency and the cycle life characteristics of the battery can be improved.

[0141] In the past, when coating boron on a positive electrode active material, a method was generally used in which a lithium raw material was mixed with a nickel-based composite hydroxide, heat-treated, to produce a lithium nickel-based composite oxide, and then wet or dry mixing the boron raw material therein and heat-treating again. However, in this case, there was a problem that the boron attached to the surface of the positive electrode active material acted as a resistor, which rather reduced the capacity and lifespan. In addition, when boron-coating was performed on only one of the first positive electrode active material and the second positive electrode active material and then mixed, or when boron-coating was performed on each of the first positive electrode active material and the second positive electrode active material separately and then mixed to produce the positive electrode active material, there were problems in that the pellet density and energy density were lower, the initial discharge capacity was lower, and the initial charge / discharge efficiency and lifespan characteristics were lower than those of the positive electrode active material manufactured according to one embodiment. On the other hand, the cathode active material manufactured according to one embodiment has a high pellet density and a high initial discharge capacity, so that the capacity per volume of the battery can be significantly increased, the initial charge / discharge efficiency can be high, and the room temperature and high temperature life characteristics can be improved.

[0142] In the above manufacturing method, the first nickel-based composite hydroxide, which is a precursor of the first positive electrode active material, may be formed by agglomerating a plurality of primary particles, and at least a portion of the primary particles may be in the form of secondary particles arranged radially. The average particle diameter of the secondary particles may be 10 ㎛ to 25 ㎛, for example, 11 ㎛ to 20 ㎛, or 12 ㎛ to 18 ㎛. Here, the average particle diameter of the secondary particles is obtained by selecting arbitrarily 20 or so particles from an SEM image of the first positive electrode active material precursor, measuring the particle diameter (diameter, or major axis, or major axis length) thereof, and then obtaining a particle size distribution, and in the particle size distribution, the diameter (D) of the particles having a cumulative volume of 50 vol% 50 ) may be taken as the average particle diameter.

[0143] The first cathode active material precursor can be prepared by a coprecipitation reaction. That is, a composite metal raw material is prepared by mixing metal raw materials such as nickel raw materials, and a complexing agent and a pH adjusting agent are added thereto to control the pH of the mixture while performing a coprecipitation reaction, thereby producing a nickel-based composite hydroxide of a desired composition. The complexing agent serves to control the reaction rate of precipitate formation in the coprecipitation reaction, and may be, for example, ammonium hydroxide (NH4OH) or citric acid. The pH adjusting agent may be, for example, sodium hydroxide (NaOH), sodium carbonate (Na2CO3), sodium oxalate (Na2C2O4), or the like. The pH of the mixture may be adjusted to, for example, a range of 10 to 13.

[0144] The above-described coprecipitation reaction can proceed in multiple stages, for example, in two, three, or four stages. In each stage, the concentration of the complexing agent, the rate of introduction of the metal raw material, the pH control range, the reaction temperature, the reaction time, or the stirring power can be adjusted differently. Through such adjustment, it is possible to manufacture a positive electrode active material precursor in the form of secondary particles in which at least a portion of the primary particles are radially arranged, and also to manufacture secondary particles with different internal and external shapes.

[0145] For example, a first positive electrode active material precursor having a radial structure can be manufactured, for example, by the following method. The method for manufacturing the first positive electrode active material precursor can include a first process, a second process, and a third process for forming a core, an intermediate layer, and a shell in that order. In the first process, a complexing agent, a pH adjusting agent, and a metal raw material are introduced into a reactor and reacted. At this time, the concentration of the complexing agent may be 0.1 M to 0.7 M, and the input amount may be 6 mL / min to 12 mL / min. The concentration of the metal raw material may be 0.1 M to 3.5 M, and the input amount may be 50 mL / min to 100 mL / min. Subsequently, in the second process, a complexing agent, a pH adjusting agent, and a metal raw material are further introduced, and at this time, the concentration of the complexing agent may be 0.3 M to 1.0 M, and the input amount may be 8 mL / min to 15 mL / min. The concentration of the metal raw material may be 0.1 M to 3.5 M and the input amount may be 60 mL / min to 120 mL / min. In the third process, the concentration and input amount of the complexing agent and the metal raw material may be further increased or maintained the same so as not to decrease the particle growth rate. At this time, the concentration of the complexing agent may be 0.35 M to 1.0 M and the input amount may be 12 mL / min to 20 mL / min. The concentration of the metal raw material may be 0.1 M to 2.5 M and the input amount may be 70 mL / min to 150 mL / min. In the first to third processes, the pH may be controlled between 10 and 12.

[0146] The first nickel-based composite hydroxide can be represented, for example, by the chemical formula 11 below.

[0147] [Chemical Formula 11]

[0148] Ni x11 M 11 y11 M 12 z11 (OH)2

[0149] In the above chemical formula 11, 0.3≤x11≤1, 0≤y11≤0.7, 0≤z11≤0.7, 0.9≤x11+y11+z11≤1.1, and M 11 and M 12 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr.

[0150] As a more specific example, the first nickel-based composite hydroxide may be a nickel-cobalt-aluminum hydroxide represented by the chemical formula 12 below.

[0151] [Chemical Formula 12]

[0152] Ni x12 Co y12 Al z12 M 13 w12 (OH)2

[0153] In the above chemical formula 12, 0.7≤x12<1, 0 <y12<0.3, 0<z12<0.3, 0≤w12<0.3, 0.9≤x12+y12+z12+w12≤1.1이고, M 13 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr.

[0154] In the first nickel-based composite hydroxide, at least some of the primary particles may have a plate shape. In this case, the secondary particles may have a radial arrangement structure in which the long axes of the plate primary particles are directed toward the surfaces of the secondary particles.

[0155] The second lithium nickel-based composite oxide in the form of single particles may be manufactured by mixing the second nickel-based composite hydroxide and a lithium raw material, heat-treating the mixture, and then optionally performing a process such as pulverization. Here, the heat treatment may be performed, for example, at 800°C to 1100°C, or 800°C to 1000°C, for about 1 to 25 hours or about 5 to 20 hours in an oxidizing gas atmosphere. The pulverization is performed to obtain a single particle form, is distinct from crushing, and may be performed using a device such as a jet mill. The second nickel-based composite hydroxide may be the same as or different from the first nickel-based composite hydroxide described above, and may be represented by Chemical Formula 11 or Chemical Formula 12. For example, the second lithium nickel-based composite oxide may be represented by Chemical Formula 2 described above. The average particle diameter (D) of the single particles containing the second lithium nickel-based composite oxide 50 ) may be 2 μm to 8 μm, for example 2 μm to 5 μm.

[0156] The mixing ratio of the first nickel-based composite hydroxide and the second lithium nickel-based composite oxide may be a weight ratio of 60:40 to 95:5, for example, 70:30 to 90:10. In this case, a cathode active material having high pellet density and energy density, high capacity, and excellent life characteristics can be manufactured.

[0157] The lithium raw material may be, for example, Li2CO3, LiOH, LiF, a hydrate or an anhydrate thereof, or a combination thereof. In addition, the lithium raw material may be mixed so that the molar ratio of lithium to the total metal in the first nickel-based composite hydroxide is 0.8 to 1, or 0.8 to 0.995, or 0.9 to 0.995. By adjusting the molar ratio of lithium within the above range, a preliminary positive electrode active material in which a first coating layer is effectively formed can be obtained.

[0158] The above boron raw material is a compound containing boron, for example, H3BO3, HBO2, B2O3, C6H5B(OH)2, (C6H5O)3B, [CH3(CH2)3O]3B, (C3H7O)3B, C3H9B3O6, C 13 H 19 BO3, or a combination thereof.

[0159] The content of the above boron raw material may be 0.01 mol part to 0.5 mol part based on 100 mol parts of the total amount of metals excluding lithium in the first nickel-based composite hydroxide and the second lithium nickel-based composite oxide, for example, 0.01 mol part to 0.3 mol part, or 0.1 mol part to 0.3 mol part. When the content of the boron raw material satisfies the above range, boron may not act as a resistor in the positive electrode active material and may play a role in improving the performance of the lithium secondary battery, thereby improving the capacity and life characteristics. When the content of the boron raw material becomes excessive, boron may act as a resistor in the positive electrode active material, thereby reducing the capacity and life characteristics of the battery.

[0160] The first heat treatment can be performed, for example, at a temperature of 650°C to 850°C, or 690°C to 780°C. In addition, the first heat treatment can be performed for 5 to 25 hours, for example, 5 to 20 hours. In this case, a high-capacity, high-energy-density positive electrode active material including a first positive electrode active material and a second positive electrode active material stably coated with a boron-containing compound can be manufactured. In a conventional coating method of mixing a lithium nickel-based composite oxide and a boron raw material and performing heat treatment, it is common to perform heat treatment at a much lower temperature, for example, 600°C or lower, but in one embodiment, heat treatment is performed at a higher temperature, 650°C to 850°C, which is different from this. By heat-treating in this temperature range, a first lithium nickel-based composite oxide in the form of secondary particles with a radial structure can be obtained while simultaneously coating it with a boron-containing compound, and at the same time, a surface of a second lithium nickel-based composite oxide in the form of single particles can be coated with a boron-containing compound, and the cathode active material thus manufactured can simultaneously improve the initial discharge capacity, initial efficiency, and life characteristics without the resistance-increasing effect caused by boron, and can improve the capacity per volume of the battery by increasing the pellet density.

[0161] In one embodiment, the first heat treatment comprises a temperature-raising step and a temperature-holding step, and the temperature-raising time may be set longer than the temperature-holding time. For example, the temperature-raising time may be 6 to 16 hours, and the temperature-holding time may be 1 to 9 hours, and the temperature-raising time may be longer than the temperature-holding time.

[0162] In the first heat treatment, the temperature raising time may be, for example, 6 to 15 hours, 6 to 14 hours, 6 to 13 hours, or 7 to 12 hours, and the temperature holding time may be, for example, 2 to 9 hours, or 3 to 8 hours.

[0163] Additionally, the ratio of (heating time):(temperature holding time) can be from 1.1:1 to 10:1, for example from 1.1:1 to 8:1, from 1.1:1 to 6:1, from 1.1:1 to 5:1, or from 1.1:1 to 4:1.

[0164] By controlling the first heat treatment profile in this way, a first positive electrode active material in the form of a high-efficiency radial secondary particle can be effectively manufactured, and an appropriate amount of a boron-containing compound can be stably coated on the first positive electrode active material and the second positive electrode active material.

[0165] (ii) In step (ii), the boron-coated preliminary positive electrode active material can be expressed as a positive electrode active material having a first coating layer formed thereon, and by dry-mixing this with a sulfide-based solid electrolyte and then performing a second heat treatment, the positive electrode active material and the sulfide-based solid electrolyte can be thermally complexed, and a second coating layer containing a sulfide-based solid electrolyte can be formed on the surface of the first coating layer.

[0166] (ii) The sulfide-based solid electrolyte mixed in step (ii) has an average particle diameter (D 50 ) may be 0.1 ㎛ to 1.5 ㎛, for example, 0.3 ㎛ to 1 ㎛, or 0.8 ㎛ to 1 ㎛. When the particle size of the sulfide-based solid electrolyte satisfies the above range, a second coating layer having a thin and uniform thickness may be formed. The size of the sulfide-based solid electrolyte of the second coating layer may be smaller than or equal to the size of the sulfide-based solid electrolyte particles mixed in the positive electrode.

[0167] (ii) The content of the sulfide-based solid electrolyte mixed in step (ii) may be 0.5 parts by weight to 3 parts by weight with respect to 100 parts by weight of the boron-coated preliminary positive electrode active material, for example, 0.5 parts by weight to 2 parts by weight, or 1 part by weight to 1.5 parts by weight.

[0168] In addition, with respect to the total of 100 wt% of the sulfide-based solid electrolyte mixed in step (ii) and the sulfide-based solid electrolyte particles of step (iii), the content of the sulfide-based solid electrolyte mixed in step (ii) may be 1 wt% to 20 wt%, for example, 3 wt% to 15 wt%, 5 wt% to 10 wt%, or 6 wt% to 9 wt%.

[0169] In this way, by appropriately adjusting the content of the sulfide-based solid electrolyte that is thermally complexed in step (ii), the resistance of the positive electrode can be significantly reduced while simultaneously improving the capacity, efficiency, and life characteristics of the battery.

[0170] (ii) The sulfide-based solid electrolyte mixed in step may be, for example, an argyrodite-type sulfide-based solid electrolyte. Since the overall details of the sulfide-based solid electrolyte and the argyrodite-type are the same as those described in the anode section, a detailed description thereof will be omitted.

[0171] The second heat treatment can be performed at, for example, 200°C to 300°C, and can be performed at, for example, 210°C to 290°C, 220°C to 280°C, 230°C to 270°C, or 240°C to 260°C. When the second heat treatment is performed in the above temperature range, a second coating layer having a solid and good shape can be formed, and the sulfide-based solid electrolyte can be prevented from agglomerating in the second coating layer and high ionic conductivity can be realized.

[0172] In step (iii), coating of the solid electrolyte to be injected into the anode is performed.

[0173] In general, solid electrolytes must exhibit excellent ion conductivity and high energy density within a battery, possessing an appropriate particle size distribution. Furthermore, they must exhibit excellent particle flowability, i.e., high-density electrode plates and electrolyte membranes. Simultaneously, the solid electrolyte must maintain high crystallinity to exhibit enhanced ionic conductivity. Sulfide-based solid electrolytes are among the most promising solid electrolytes for high ionic conductivity. However, immediately after synthesis at high temperatures, the particles are highly agglomerated or have large particle sizes, requiring pulverization. However, pulverization reduces ionic conductivity, and heat treatment to increase ionic conductivity can cause the particles to re-agglomerate and grow. In one embodiment, to address these issues, pulverized sulfide-based solid electrolyte particles are coated with lithium-metal-phosphate and heat-treated at a temperature ranging from 200°C to 300°C. This method enhances the crystallinity of the solid electrolyte, thereby enhancing ionic conductivity. Simultaneously, particle agglomeration and growth are suppressed, resulting in an appropriate particle size distribution. These solid electrolytes also have high moisture stability and can improve the capacity characteristics, initial charge / discharge efficiency, and life characteristics of batteries.

[0174] For example, if the third heat treatment is performed at a temperature below 200℃, the crystallinity may not increase sufficiently, and thus high ionic conductivity may not be achieved. If the heat treatment is performed at a temperature exceeding 300℃, agglomeration and growth of particles may occur, and thus an appropriate particle size distribution may not be achieved, and thus crystallinity may decrease. In addition, the higher the heat treatment temperature, the more coating agent is required, and this may cause a problem in that the ionic conductivity decreases.

[0175] The third heat treatment can be performed in an inert gas atmosphere, such as He, Ar, or N2. Furthermore, the heat treatment can be performed with the maximum temperature retention time set to 1 to 10 hours, for example, 1 to 8 hours, or 2 to 7 hours. When heat-treated under these conditions, the solid electrolyte produced can exhibit excellent ionic conductivity while achieving an appropriate particle size distribution.

[0176] The lithium-metal-phosphate may be mixed in an amount of 0.01 to 3 parts by weight based on 100 parts by weight of the sulfide-based solid electrolyte-containing core particles, for example, 0.01 to 2 parts by weight, 0.01 to 1 part by weight, 0.01 to 0.8 parts by weight, or 0.1 to 0.75 parts by weight. When mixed in this content range, the solid electrolyte produced may exhibit high ionic conductivity and have an appropriate particle size distribution without particle agglomeration. In particular, when 0.01 to 0.8 parts by weight of the lithium-metal-phosphate is mixed based on 100 parts by weight of the core particles, the ionic conductivity of the solid electrolyte may be further improved as an appropriate amount of lithium-metal-phosphate is evenly coated on the surface of the core particles.

[0177] Since the core particles containing a sulfide-based solid electrolyte and the lithium-metal-phosphate are as described above, a detailed description thereof is omitted.

[0178] As a specific example, the step (iii) above may be to mix sulfur-containing raw materials and perform heat treatment to synthesize a sulfide-based solid electrolyte, pulverize the synthesized sulfide-based solid electrolyte to prepare core particles, mix the core particles with lithium-metal-phosphate, and perform a third heat treatment at 200°C to 300°C to obtain a solid electrolyte in which a third coating layer containing lithium-metal-phosphate is formed on the surface of the core particles.

[0179] Step (iii) above is a more specific example, in which sulfur-containing raw materials are mixed, first fired at 120°C to 350°C, and second fired at 350°C to 800°C to manufacture a sulfide-based solid electrolyte, and the manufactured sulfide-based solid electrolyte is pulverized to obtain an average particle size (D 50 ) may be obtained by obtaining core particles having a diameter of 0.1 ㎛ to 2.0 ㎛, mixing the obtained core particles and lithium-metal-phosphate, and performing a third heat treatment at 200°C to 300°C, thereby obtaining a solid electrolyte in which a third coating layer containing lithium-metal-phosphate is formed on the surface of the core particles. Through this method, a solid electrolyte having very high ionic conductivity, a uniform particle size distribution, and little side reaction can be provided.

[0180] In one embodiment, mixing core particles and lithium-metal-phosphate and performing a third heat treatment can be considered a type of dry coating method. Unlike other oxide-based inorganic solid electrolytes or positive electrode active materials, sulfide-based solid electrolytes are difficult to wet coat and are vulnerable to high-temperature heat treatment, and are materials that require design of demanding coating conditions. In addition, wet coating methods generally use alcohol-based solvents or alkoxide-based raw materials, which may cause local carbon components to remain after coating, which may adversely affect conductivity, etc. In the method for manufacturing a positive electrode according to one embodiment, step (iii) has different conditions from those for coating other types of solid electrolyte particles, and is also distinguished from general wet coating.

[0181] Step (iv) may be defined as a process for manufacturing a positive electrode by mixing the final positive electrode active material manufactured in step (ii) and the coated solid electrolyte manufactured in step (iii). In this step, the solid electrolyte may be mixed in an amount of 1 wt% to 35 wt% based on a total of 100 wt% of the final positive electrode active material and the solid electrolyte, and may be included in an amount of, for example, 5 wt% to 30 wt%, 10 wt% to 25 wt%, 10 wt% to 20 wt%, or 11 wt% to 15 wt%. When the solid electrolyte in the positive electrode satisfies the above range, the ionic conductivity can be improved while minimizing the capacity degradation of the positive electrode, thereby improving the overall performance of the all-solid-state secondary battery.

[0182] (iv) In step 1, the solid electrolyte mixed inside the anode is in the form of particles, and its average particle diameter (D 50 ) may be 0.1 ㎛ to 5 ㎛, for example, 0.1 ㎛ to 3 ㎛, 0.1 ㎛ to 2 ㎛, 0.5 ㎛ to 1.9 ㎛, or 0.8 ㎛ to 1.5 ㎛. The size of the sulfide-based solid electrolyte particles included in the positive electrode may be larger than or equal to the sulfide-based solid electrolyte used in step (ii), and may be smaller than the size of the solid electrolyte included in the solid electrolyte layer described below.

[0183] (iv) The step may be to prepare a positive electrode composition by mixing the final positive electrode active material and the sulfide-based solid electrolyte, apply the positive electrode composition onto a positive electrode current collector, and then dry and press to prepare a positive electrode. At this time, a binder and / or a conductive material may be further added to the positive electrode composition.

[0184] All-solid-state secondary battery

[0185] In one example, an all-solid-state secondary battery is provided that includes the aforementioned positive electrode. The all-solid-state secondary battery includes the aforementioned positive electrode, the negative electrode, and a solid electrolyte layer positioned between the positive electrode and the negative electrode.

[0186] FIG. 4 is a cross-sectional view of an all-solid-state secondary battery according to an embodiment. Referring to FIG. 4, the all-solid-state secondary battery (100) may have a structure in which an electrode assembly in which a negative electrode (400) including a negative electrode current collector (401) and a negative electrode active material layer (403), a solid electrolyte layer (300), and a positive electrode (200) including a positive electrode active material layer (203) and a positive electrode current collector (201) are laminated is housed in a battery case. The all-solid-state secondary battery (100) may further include an elastic layer (500) on the outer side of at least one of the positive electrode (200) and the negative electrode (400). Although FIG. 4 illustrates one electrode assembly including the negative electrode (400), the solid electrolyte layer (300), and the positive electrode (200), an all-solid-state secondary battery may be manufactured by laminating two or more electrode assemblies.

[0187] cathode

[0188] The negative electrode (400) may include a current collector (401) and a negative electrode active material layer (403) positioned 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.

[0189] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0190] The material capable of reversibly intercalating / deintercalating the lithium ions may include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0191] As the above lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0192] As the material capable of doping and dedoping the lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material is silicon, a silicon-carbon composite, SiOx(0 <x<2), Si-Q 합금(상기 Q는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소(Si를 제외함), 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합에서 선택됨), 또는 이들의 조합일 수 있다. 상기 Sn계 음극 활물질로는 Sn, SnO2, Sn계 합금 또는 이들의 조합일 수 있다.

[0193] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the composite may include secondary particles (cores) in which silicon primary particles are assembled and an amorphous carbon coating layer (shell) positioned on the surface of the secondary particles. The amorphous carbon may also be positioned between the silicon primary particles, such that, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0194] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles and an amorphous carbon coating layer positioned on the surface of the core.

[0195] The above Si-based negative electrode active material or Sn-based negative electrode active material can be used in a mixture with a carbon-based negative electrode active material.

[0196] The content of the negative active material in the above negative active material layer may be 95 wt% to 99 wt% with respect to the total weight of the negative active material layer.

[0197] In one embodiment, the negative electrode active material layer further includes a binder and may optionally further include 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. In addition, when the negative electrode active material layer further includes a conductive material, 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.

[0198] The above binder serves to adhere the negative electrode active material particles well to each other and also to adhere the negative electrode active material well to the current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0199] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0200] The above-mentioned aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoroelastomer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0201] When using an aqueous binder as the above-mentioned negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li.

[0202] The above dry binder is a polymeric material capable of being fiberized, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0203] The conductive material is used to provide conductivity to the electrode, and any material that does not cause chemical changes and is electronically conductive can be used in the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metal-based materials in the form of metal powder or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0204] The negative electrode current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and a combination thereof.

[0205] precipitation cathode

[0206] As an example, the negative electrode for an all-solid-state secondary battery may be a precipitation-type negative electrode, unlike the above-mentioned one. The precipitation-type negative electrode may refer to a negative electrode that does not include a negative electrode active material when the battery is assembled, but in which lithium metal or the like is precipitated or deposited on the negative electrode when the battery is charged, and this acts as a negative electrode active material.

[0207] Fig. 5 is a schematic cross-sectional view of an all-solid-state secondary battery including a precipitation-type negative electrode. Referring to Fig. 5, the precipitation-type negative electrode (400') may include a current collector (401) and a negative electrode coating layer (405) positioned on the current collector. An all-solid-state secondary battery including such a precipitation-type negative electrode (400') starts initial charging in a state in which no negative electrode active material is present, and during charging, high-density lithium metal is precipitated or deposited between the current collector (401) and the negative electrode coating layer (405) or on the negative electrode coating layer (405) to form a lithium metal layer (404), which may function as a negative electrode active material. Accordingly, in an all-solid-state secondary battery that has been charged more than once, the precipitation-type negative electrode (400') may include, for example, a current collector (401), a lithium metal layer (404) positioned on the current collector, and a negative electrode coating layer (405) positioned on the metal layer. The lithium metal layer (404) refers to a layer in which lithium metal or the like is precipitated during the charging process of the battery, and may be referred to as a metal layer, a lithium layer, a lithium deposition layer, or a negative electrode active material layer.

[0208] The cathode coating layer (405) may be referred to as a lithium electrodeposition induction layer or a cathode catalyst layer, and may include a lithium-philic metal, a carbon material, or a combination thereof.

[0209] The above-mentioned lithium-philic metal may include, for example, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, zinc, or a combination thereof, and may be composed of one type of these or may be composed of several types of alloys. When the lithium-philic metal is present in the form of particles, its average particle diameter (D 50 ) may be about 4 ㎛ or less, for example, 10 nm to 4 ㎛, 10 nm to 1 ㎛, 10 nm to 600 nm. As an example, the lithium-philic metal may be in the form of nanoparticles having an average particle size of several to several hundred nanometers.

[0210] 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.

[0211] When the negative electrode coating layer (405) includes both a lithium-philic metal and a carbon material, the mixing ratio of the metal and the carbon material may be, for example, a weight ratio of 1:10 to 2:1. In this case, the precipitation of lithium metal can be effectively promoted and the characteristics of the all-solid-state secondary battery can be improved. The negative electrode coating layer (405) may include, for example, a carbon material loaded with a lithium-philic metal, or may include a mixture of lithium-philic metal particles and carbon material particles.

[0212] The cathode coating layer (405) may include, for example, a lithium-philic metal and amorphous carbon, in which case the precipitation of lithium metal can be effectively promoted.

[0213] Supported compounds

[0214] In one embodiment, the negative electrode coating layer may include a compound in which a lithium-philic metal is supported on a carbon material. The supported compound is distinguished from a simple mixture of a lithium-philic metal and a carbon material. When the negative electrode coating layer includes a supported compound, the lithium metal layer described below can be formed more uniformly, and the reversibility of lithium precipitation and dissociation can be improved, thereby improving the life characteristics of the all-solid-state secondary battery. Here, the lithium-philic metal is the same as described above, and the carbon material can be, for example, amorphous carbon.

[0215] The amorphous carbon material may be, for example, a single particle, or an assembly having the form of secondary particles assembled from primary particles. When the amorphous carbon material is a single particle, the average particle size may be 100 nm or less, for example, a nano-size of 10 nm to 100 nm. When the amorphous carbon material is an assembly, the particle size of the primary particles may be 20 nm to 100 nm, and the particle size of the secondary particles may be 1 μm to 20 μm.

[0216] In one embodiment, the particle size of the primary particles of the amorphous carbon material in the assembly shape may be 20 nm or more, 30 nm or more, 40 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, or 90 nm or more, and may be 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 40 nm or less, or 30 nm or less. The shape of the primary particles may be spherical, elliptical, plate-like, and a combination thereof, and in one embodiment, the shape of the primary particles may be spherical, elliptical, and a combination thereof.

[0217] In one embodiment, the particle size of the secondary particles of the amorphous carbon material in the assembly shape may be 1 µm or more, 3 µm or more, 5 µm or more, 7 µm or more, 10 µm or more, or 15 µm or more, and may be 20 µm or less, 15 µm or less, 10 µm or less, 7 µm or less, 5 µm or less, or 3 µm or less.

[0218] The lithium-philic metal may be included in an amount of 3 wt% to 40 wt% based on 100 wt% of the compound in which the lithium-philic metal is supported on the carbon material, for example, 3 wt% to 30 wt%, 4 wt% to 25 wt%, 5 wt% to 20 wt%, or 5 wt% to 15 wt%. The carbon material may be included in an amount of 60 wt% to 97 wt% based on 100 wt% of the compound in which the lithium-philic metal is supported on the carbon material, for example, 70 wt% to 97 wt%, 75 wt% to 96 wt%, 80 wt% to 95 wt%, or 85 wt% to 95 wt%. When the contents of the lithium-philic metal and the carbon material satisfy the above ranges, a uniform lithium metal layer can be effectively formed during charging.

[0219] In one embodiment, the carbon material and the lithium-philic metal may be chemically bonded via sulfur. That is, the carbon material and the lithium-philic metal may not be simply physically mixed, but may be chemically bonded to each other. In this case, the bonding strength between the carbon material and the lithium-philic metal is excellent, and the problem of the carbon material and the lithium-philic metal separating from each other during the mixing process can be effectively prevented. In addition, the phenomenon of the lithium-philic metal agglomerating is prevented, so that it can be uniformly dispersed within the negative electrode coating layer, thereby uniformly distributing the current within the negative electrode and inducing uniform deposition of the lithium metal.

[0220] When carbon materials and a lithiophilic metal are chemically bonded via sulfur, peaks related to the bonding of the lithiophilic metal and sulfur can be identified in the X-ray photoelectron spectroscopy (XPS) spectrum. For example, when the lithiophilic metal contains Ag, a peak can be identified in the S2p spectrum obtained by XPS analysis in the range of 160 eV to 162 eV, which is the Ag-S bond energy.

[0221] A composite in which carbon material and a lithium-philic metal are chemically bonded via sulfur can be manufactured by mixing carbon material and sulfur-containing raw materials in a dry or wet manner, optionally heat-treating them, then supporting the lithium-philic metal and heat-treating the mixture.

[0222] A method for supporting a lithiophilic metal may be, for example, a method of mixing a mixture of a carbon material and a sulfur-containing raw material, a lithiophilic metal compound, and a reducing agent in a solvent. The solvent may include, for example, water, ethanol, glycerol, benzene, xylene, or a combination thereof, and the reducing agent may include NaBH4, ascorbic acid, trisodium citrate, ethylene glycol, or a combination thereof. The lithiophilic metal compound may be a nitrate, sulfate, perchlorate, or the like containing a lithiophilic metal, and may include, for example, AgNO3, Ag2SO4, AgClO4, or a combination thereof.

[0223] The heat treatment after supporting the lithium-philic metal can usually be carried out at a temperature at which the sulfur-containing raw material can be decomposed and removed, for example, at 100°C to 500°C, 150°C to 500°C, 200°C to 450°C, or 200°C to 400°C. Specifically, when a thiol compound is used as the sulfur-containing raw material, the heat treatment can be carried out at 100°C to 400°C. The heat treatment can be carried out in an atmosphere of nitrogen, argon, or a combination thereof for about 2 to 20 hours.

[0224] The thickness of the cathode coating layer may be, for example, 100 nm to 40 μm, or 500 nm to 30 μm, or 1 μm to 20 μm. When the cathode coating layer satisfies the above thickness range, a lithium metal layer of uniform thickness can be effectively formed during charging.

[0225] The cathode coating layer may further include a binder, for example, a conductive binder. The cathode coating layer may also further include additives such as fillers, dispersants, and ionic conductive agents.

[0226] The binder of the cathode coating layer may include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0227] Non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0228] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoroelastomer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0229] When using an aqueous binder as the cathode binder, a cellulose-based compound capable of imparting viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li.

[0230] The dry binder is a polymeric material capable of being fiberized, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0231] The binder may be included in an amount of 0.1 to 5 wt%, 0.1 to 3 wt%, or 0.5 to 2 wt%, based on 100 wt% of the cathode coating layer.

[0232] lithium metal layer

[0233] According to one embodiment, the negative electrode is a type of precipitation-type negative electrode, and an all-solid-state secondary battery including the same starts initial charging in a state in which no negative electrode active material is present, and during charging, a high-density lithium metal is precipitated or deposited between the negative electrode current collector and the negative electrode coating layer, or on the negative electrode coating layer, to form a lithium metal layer, which can function as the negative electrode active material. Therefore, an all-solid-state secondary battery that has been charged at least once may include, for example, a negative electrode current collector, a lithium metal layer positioned on the negative electrode current collector, and a negative electrode coating layer positioned on the lithium metal layer. The lithium metal layer means a layer in which lithium ions are precipitated as lithium metal during the charging process of the battery, and may be expressed as a metal layer, a lithium layer, a lithium deposition layer, or a negative electrode active material layer.

[0234] The lithium metal layer may include lithium metal or a lithium alloy. The lithium alloy may be, for example, 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.

[0235] The thickness of the lithium metal layer may be, for example, 1 μm to 500 μm, 5 μm to 500 μm, 5 μm to 400 μm, 5 μm to 300 μm, or 10 μm to 200 μm. If the thickness of the lithium metal layer is too thin, it may be difficult to perform the role of a lithium storage tank, and if it is too thick, the battery volume may increase and the performance may deteriorate.

[0236] In one embodiment, a lithium metal layer having a uniform thickness and flatness can be formed by applying a compound in which the aforementioned lithium-philic metal is supported on a carbon material to the negative electrode coating layer. Therefore, according to one embodiment, the lithium metal layer formed during charging may have a very uniform thickness and a small thickness deviation. For example, the deviation in the thickness of the lithium metal layer may be 40% or less, 30% or less, 20% or less, 15% or less, 10% or less, or 5% or less. Here, the deviation in the thickness of the lithium metal layer may mean that the thickness of the lithium metal layer is measured at about 10 points in an electron microscope image of the negative electrode cross-section, the arithmetic mean is calculated, and then the absolute value of the difference between one data and the arithmetic mean is divided by the arithmetic mean and multiplied by 100. Also, for example, the thickness of the lithium metal layer may be 5 ㎛ to 80 ㎛, and the standard deviation of the thickness may be 0.1 ㎛ to 20 ㎛, 0.1 ㎛ to 15 ㎛, 0.1 ㎛ to 10 ㎛, 0.1 ㎛ to 5 ㎛, and 0.1 ㎛ to 3 ㎛. Similarly, the standard deviation of the thickness of the lithium metal layer may be calculated by measuring the thickness at about 10 points in an electron microscope photograph. The fact that the deviation or standard deviation of the thickness of the lithium metal layer satisfies the above range means that the lithium metal is well deposited in the form of a film with a uniform thickness, and accordingly, the electrochemical characteristics of the all-solid-state secondary battery may be improved.

[0237] etc

[0238] Meanwhile, the negative electrode according to one embodiment may further include a thin film on the surface of the negative electrode current collector, that is, between the negative electrode current collector and the negative electrode coating layer, or between the negative electrode current collector and the lithium metal 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 include, for example, Al, Ag, Au, Bi, Cu, Ge, In, Mg, Ni, Pd, Pt, Si, Sn, Zn, or a combination thereof. The thin film may further flatten the deposition morphology of the lithium metal layer and assist in forming a lithium metal layer with a uniform thickness. The thin film may be formed by, for example, a vacuum deposition method, a sputtering method, a plating method, or the like. The thickness of the thin film may be, for example, 1 nm to 500 nm.

[0239] negative current collector

[0240] The negative electrode current collector may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li) or an alloy thereof, and may be in the form of a foil or a sheet. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0241] solid electrolyte layer

[0242] The solid electrolyte layer (300) may include an inorganic solid electrolyte, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, etc. The sulfide-based solid electrolyte is substantially the same as that described in the positive electrode section, so a detailed description thereof is omitted.

[0243] Oxide-based solid electrolytes include, for example, Li 1+x Ti 2-x Al(PO4)3(LTAP)(0≤x≤4), Li 1+x+y Al x Ti2-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-GeO2계 세라믹스, 가넷(Garnet)계 세라믹스 Li 3+x La3M2O 12 (M= Te, Nb, or Zr; x is an integer from 1 to 10), or mixtures thereof.

[0244] A halide-based solid electrolyte contains a halogen element as a main component, and may mean that the ratio of the halide element to all elements constituting the solid electrolyte is 50 mol% or more, 70 mol% or more, 90 mol% or more, or 100 mol%. For example, the halide-based solid electrolyte may not contain a sulfur element.

[0245] The halide-based solid electrolyte may contain lithium element, a metal element other than lithium, and a halogen element. The metal element other than lithium may be Al, As, B, Bi, Ca, Cd, Co, Cr, Fe, Ga, Hf, In, Mg, Mn, Ni, Sb, Sc, Sn, Ta, Ti, Y, Zn, Zr, or a combination thereof. The halogen element may be F, Cl, Br, I, or a combination thereof, and may be Cl, Br, or a combination thereof. The halide-based solid electrolyte may contain, for example, Li a M1X6 (M is Al, As, B, Bi, Ca, Cd, Co, Cr, Fe, Ga, Hf, In, Mg, Mn, Ni, Sb, Sc, Sn, Ta, Ti, Y, Zn, Zr, or a combination thereof, X is F, Cl, Br, I, or a combination thereof, and 2≤a≤3) can be represented. The halide-based solid electrolyte is, for example, Li2ZrCl6, Li 2.7 Y 0.7 Zr 0.3 Cl6, Li 2.5 Y 0.5 Zr 0.5 Cl6, Li 2.5 In 0.5 Zr 0.5 Cl6, Li2In 0.5 Zr 0.5 Cl6, Li3YBr6, Li3YCl6, Li3YBr2Cl4, Li3YbCl6, Li 2.6 Hf 0.4 Yb 0.6 Cl6, or combinations thereof, but is not limited thereto.

[0246] Meanwhile, the average particle diameter (D) of the solid electrolyte included in the solid electrolyte layer (300) 50 ) is the average particle diameter (D) of the solid electrolyte contained in the positive electrode (200). 50) may be larger than that. In this case, the overall performance can be improved by increasing the mobility of lithium ions while maximizing the energy density of the all-solid-state secondary battery. For example, the average particle diameter (D) of the sulfide-based solid electrolyte particles included in the positive electrode (200) 50 ) may be 0.1 ㎛ to 1.9 ㎛, or 0.1 ㎛ to 1.0 ㎛, and the average particle diameter (D) of the solid electrolyte included in the solid electrolyte layer (300) 50 ) may be 2.0 ㎛ to 5.0 ㎛, or 2.0 ㎛ to 4.0 ㎛, or 2.5 ㎛ to 3.5 ㎛. When this particle size range is satisfied, the energy density of the all-solid-state secondary battery can be maximized while the transfer of lithium ions is facilitated, thereby suppressing the resistance and improving the overall performance of the all-solid-state secondary battery. Here, the average particle diameter (D of the solid electrolyte 50 ) may be measured using a particle size analyzer using laser diffraction.

[0247] The solid electrolyte layer (300) may further include a binder in addition to the solid electrolyte. At this time, the binder may be styrene butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, an acrylate polymer, or a combination thereof, but is not limited thereto, and any binder used in the relevant technical field may be used. The acrylate polymer may be, for example, butyl acrylate, polyacrylate, polymethacrylate, or a combination thereof.

[0248] The solid electrolyte layer (300) can be formed by adding a solid electrolyte to a binder solution, coating the same on a substrate film, and drying the same. The solvent of the binder solution may be isobutyryl isobutyrate, xylene, toluene, benzene, hexane, or a combination thereof. Since the solid electrolyte layer formation process is widely known in the art, a detailed description thereof will be omitted.

[0249] The thickness of the solid electrolyte layer (300) may be, for example, 10 μm to 800 μm.

[0250] The solid electrolyte layer (300) may further include an alkali metal salt, and / or an ionic liquid, and / or a conductive polymer.

[0251] The above 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 may improve ion conductivity by enhancing the lithium ion mobility of the solid electrolyte layer.

[0252] The lithium salt may be applied without limitation on type, and may include, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiSCN, LiN(CN)2, lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, or a combination thereof.

[0253] For example, the lithium salt may be an imide-based lithium salt such as LiTFSI, LiFSI, LiBETI, or a combination thereof. The imide-based lithium salt can maintain or improve ionic conductivity by appropriately maintaining chemical reactivity with the ionic liquid.

[0254] Ionic liquids are salts or molten salts that are composed only of ions and are liquid at room temperature, with a melting point below room temperature.

[0255] The ionic liquid comprises a) one or more cations selected from ammonium, pyrrolidinium, pyridinium, pyrimidinium, imidazolium, piperidinium, pyrazolium, oxazolium, pyridazinium, phosphonium, sulfonium, trizolium, 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 - It may be a compound containing one or more anions selected from among.

[0256] The ionic liquid may be, for example, one or more selected from the group consisting of N-methyl-N-propylpyrrolidinium 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.

[0257] In the solid electrolyte layer, the weight ratio of the solid electrolyte to the ionic liquid 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 the above range can maintain or improve ionic conductivity by improving the electrochemical contact area with the electrode. Accordingly, the energy density, discharge capacity, rate characteristics, etc. of the all-solid-state secondary battery can be improved.

[0258] The all-solid-state secondary battery may be a unit cell having a structure of positive electrode / solid electrolyte layer / negative electrode, a bi-cell having a structure of negative electrode / solid electrolyte layer / positive electrode / solid electrolyte layer / negative electrode, or a laminated battery in which the structure of the unit cell is repeated.

[0259] The shape of the above-mentioned all-solid-state secondary battery is not particularly limited, and may be, for example, coin-shaped, button-shaped, sheet-shaped, stacked, cylindrical, flat, etc. In addition, the above-mentioned all-solid-state secondary battery can be applied to large-scale batteries used in electric vehicles, etc. For example, the above-mentioned all-solid-state secondary battery can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). In addition, it can be used in fields requiring a large amount of power storage, and for example, it can be used in electric bicycles or power tools, etc. In addition, the above-mentioned all-solid-state secondary battery can be used in various fields such as portable electronic devices.

[0260] Hereinafter, examples and comparative examples of the present invention are described. The following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0261] Example 1

[0262] 1. Manufacturing of the first nickel-based composite hydroxide

[0263] Through the coprecipitation method described below, the first nickel-based composite hydroxide (Ni), which is a precursor of the first positive electrode active material, 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 at a molar ratio of 94.5:4:1.5 to prepare a mixed solution of metal raw materials. In addition, ammonia water (NH4OH) and sodium hydroxide (NaOH) were prepared as a precipitant to form a complex compound.

[0264] [Step 1: 2.5 kW / ㎥, NH4OH 0.40 M, pH 10.5~11.5, reaction time 6 hours]

[0265] First, ammonia water with a concentration of 0.40 M was added to the reactor. The reaction was initiated by adding a mixed solution of metal raw materials and a complexing agent (NH4OH) at a rate of 85 ml / min and 10 ml / min, respectively, at a stirring power of 2.5 kW / ㎥ and a reaction temperature of 50°C. 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 second step was carried out as follows.

[0266] [Step 2: 2.0 kW / ㎥, NH4OH 0.45 M, pH 10.5~11.5, reaction time 18 hours]

[0267] While maintaining the reaction temperature at 50℃, the metal raw material mixture solution and complexing agent were introduced at a rate of 85 ml / min and 12 ml / min, respectively, so that the concentration of the complexing agent became 0.45 M. The reaction was continued for 18 hours while adding NaOH to maintain the pH. At this time, the stirring power was lowered to 2.0 kW / ㎥, which was lower than in step 1, and the reaction was conducted. By conducting this reaction, it was confirmed that the average size of the product particles containing the core and the intermediate layer was 13.5 ㎛ to 14 ㎛, and the following 3 steps were performed.

[0268] [Step 3: 1.5 kW / ㎥, NH4OH 0.45 M, pH 10.5~11.5, reaction time 14 hours]

[0269] While maintaining the reaction temperature at 50℃, the mixing speed of the metal raw material solution and the complexing agent and the concentration of the complexing agent were the same as in the second step. The reaction was conducted for 14 hours while adding NaOH to maintain the pH. At this time, the stirring power was lowered to 1.5 kW / ㎥, which was lower than in the second step, to proceed with the reaction. After washing the obtained result, it was dried with hot air at about 150℃ for 24 hours to obtain the first nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH)2) was obtained.

[0270] 2. Manufacturing of a second nickel-based composite oxide

[0271] Nickel-based composite hydroxide (Ni), a precursor of the second cathode active material, was prepared through a co-precipitation method. 0.94 Co 0.04 Al 0.01 Mn 0.01 (OH)2) was synthesized. As metal raw materials, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), sodium aluminum sulfate (NaAl(SO4)2·12H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as a solvent at a molar ratio of 94:4:1:1 to prepare a mixed solution. The subsequent synthesis was carried out in the same manner as in the preparation of the first nickel-based composite hydroxide.

[0272] The manufactured second nickel-based composite hydroxide and lithium hydroxide were mixed in a molar ratio of 1:1 and heat-treated at 850°C in an oxygen atmosphere. The average particle size (D) of the obtained product was measured through an airflow impact crusher. 50 ) is pulverized to about 3 ㎛ to obtain a second lithium nickel composite oxide (LiNi) in the form of single particles. 0.94 Co 0.04 Al 0.1 Mn 0.01 O2) was obtained.

[0273] 3. Preparation of mixed cathode active material and formation of first coating layer

[0274] A first nickel-based composite hydroxide and a second lithium nickel-based composite oxide were mixed in a weight ratio of 7:3, LiOH was mixed so that the molar ratio of Li / (Ni+Co+Al)=0.96 in the relationship between the first nickel-based composite hydroxide and LiOH was satisfied, boric acid was mixed so that boron was 0.125 mol% with respect to 100 mol% of the total metal excluding lithium in the mixture, and the mixture was put into a kiln, heated to 700°C for 8 hours in an oxygen atmosphere, and a first heat treatment was performed for 7 hours to obtain a mixed preliminary cathode active material.

[0275] In the obtained mixed preliminary positive electrode active material, the first positive electrode active material is a first lithium nickel-based composite oxide (Li 0.96 Ni 0.945 Co 0.04 Al 0.015 O2) and the average particle size (D 50) was identified as a secondary particle with a size of approximately 13.8 ㎛. As a result of SEM analysis of the cross-section of the secondary particle, it was confirmed to be a secondary particle form containing an interior with an irregular porous structure and an exterior with a radial array structure. In addition, the mass spectrometry result of ToF-SIMS confirmed that the first cathode active material was evenly coated with lithium boron oxide such as LiBO2 on the surface of the secondary particle. In addition, the ICP emission spectroscopy analysis result measured that the boron content with respect to 100 wt% of the cathode active material before washing was 540 ppm, and the boron content with respect to 100 wt% of the cathode active material after washing was 30 ppm. The boron detected even after washing was confirmed to be coated on the internal grain boundaries of the secondary particle. The boron removed during the washing process corresponds to the component coated on the surface of the secondary particle and is confirmed to be 540-30 = 510 ppm. Accordingly, the ratio of the boron weight in the first coating layer to the boron weight in the grain boundary boron coating portion is calculated to be approximately 94:6. Furthermore, as a result of performing TEM-EELS analysis from the surface to the inside of the cross-section of the secondary particle, it was confirmed that a boron-doped layer was formed in a region corresponding to a depth of 2 nm to 5 nm from the outermost surface. In other words, it can be seen that a boron-doped layer was formed in the inside of the primary particle exposed on the surface of the secondary particle.

[0276] The second cathode active material is a second lithium nickel composite oxide (LiNi 0.94 Co 0.04 Al 0.1 Mn 0.01 O2) and the average particle diameter (D) as a result of SEM analysis 50 ) is confirmed to be in the form of a single particle of approximately 3 ㎛. In addition, the results of SEM-EDS analysis and ToF-SIMS mass analysis confirmed that lithium boron oxide such as LiBO2 was evenly coated on the surface of the single particle. A boron-containing first coating layer was formed on the surface of the positive electrode active material by the boric acid added during the manufacture of the mixed positive electrode active material, so a separate buffer layer was not coated.

[0277] 4. Preparation of solid electrolyte (Li6PS5Cl, Argyrodite)

[0278] An argyrodite-type sulfide-based solid electrolyte was synthesized using the method described below. Mixing of raw materials, pre- and post-heat treatment, and post-treatment were all performed in an argon-atmosphere glovebox. The raw materials were lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), and lithium chloride (LiCl) mixed in a molar ratio of 2.5:0.5:1 to prepare a mixed powder. After uniformly mixing the mixed powder using a Hansel mixer, it was calcined for the first time at 250°C for 5 hours in a tube furnace with argon gas flowing at a constant rate of 8 SLM.

[0279] The primary calcined powder was uniformly mixed again with a Hansel mixer and sieved, and then sieved at 500°C for 10 hours in a tube furnace with argon gas flowing at a constant rate of 8 SLM. The secondary calcined powder was pulverized and sieved to obtain sulfide-based solid electrolyte particles of Li6PS5Cl. The size (D) of the sulfide-based solid electrolyte particles thus obtained 50 ) was confirmed to be approximately 0.85 ㎛.

[0280] 5. Thermal complexation of positive electrode active materials

[0281] Through the method described below, the argyrodite-type sulfide-based solid electrolyte manufactured in step 4 was thermally complexed onto the surface of the positive electrode active material having the first coating layer manufactured in step 3.

[0282] 87.5 parts by weight of the positive electrode active material having the first coating layer formed and 1 part by weight of the argyrodite-type sulfide-based solid electrolyte prepared in step 4 were mixed using a Hansel mixer. The mixed powder was subjected to a second heat treatment at 250°C for 5 hours in a tube furnace through which argon gas flowed at a constant rate of 8 SLM. Through this, the sulfide-based solid electrolyte particles were evenly thermally complexed on the surface of the positive electrode active material, thereby preparing the final positive electrode active material having the second coating layer formed thereon. The SEM-EDS analysis of the thermally complexed positive electrode active material is described later in Evaluation Example 4 below.

[0283] 6. Coating of solid electrolyte

[0284] 100 parts by weight of the sulfide-based solid electrolyte manufactured in step 4 above and D as a coating agent 50 0.5 parts by weight of lithium zirconium phosphate (LZP; LiZr2(PO4)3), which is 0.15 ㎛ in size and amorphous according to X-ray diffraction analysis, was mixed using a Hansel mixer. The mixed powder was put into a tubular furnace through which argon gas flowed at a constant rate of 8 SLM and subjected to a third heat treatment at a maximum temperature of 250°C for 5 hours. Through this, a solid electrolyte was manufactured in which a third coating layer containing lithium zirconium phosphate was formed on the surface of core particles containing a sulfide-based solid electrolyte.

[0285] As a result of performing X-ray diffraction analysis on the manufactured solid electrolyte, it was confirmed that the lithium-zirconium-phosphate located on the surface of the core particle is in an amorphous state, as no peak corresponding to LZP was observed. In addition, the half width of the main peak was 0.152, which indicates that the crystal size increased and the crystallinity was enhanced. The change in particle size distribution of the solid electrolyte according to the coating and the effect of increasing ionic conductivity are described later in Evaluation Examples 5 and 6.

[0286] 7. Manufacturing of the anode

[0287] A positive electrode composition was prepared by mixing 88.5 wt% of the final positive electrode active material manufactured in step 5, 9.94 wt% of the coated solid electrolyte manufactured in step 6, 1 wt% of PVdF binder, 0.45 wt% of carbon nanotube conductive material, and 0.11 wt% of hydrogenated nitrile butadiene rubber (HNBR) as a dispersant in an isobutyryl isobutyrate (IBIB) solvent. This was applied to a positive electrode current collector, dried, and then rolled (hydrostatic pressing (WIP), 500 Mpa, 85°C, 30 min) to prepare a positive electrode.

[0288] 8. Manufacturing of precipitation-type cathode

[0289] Carbon black and 2-naphthalene thiol powders were mixed at a weight ratio of 10:1 and heat-treated at 90°C. The heat-treated product was poured into a water solvent, and AgNO3 and a reducing agent, NaBH4, were added and mixed. At this time, the AgNO3 content was 11 wt% with respect to 100 wt% of the total content of carbon black and AgNO3, and the content of NaBH4 was 22 wt% with respect to 100 wt% of AgNO3. The obtained product was heat-treated at 400°C for 4 hours under a nitrogen atmosphere to prepare a compound in the form of Ag supported on a carbon material. In the prepared Ag-C supported compound, the carbon material was 94.6 wt% with respect to the sum of the carbon material and Ag, the Ag content was 5.4 wt%, and the sulfur content was about 1.2 wt% with respect to 100 wt% of the Ag-C supported compound. Transmission electron microscopy (TEM) analysis of the manufactured Ag-C support compound confirmed that silver was uniformly dispersed in the carbon material. In addition, X-ray photoelectron spectroscopy (XPS) Sp2 spectrum measurement of the Ag-C support compound detected a peak corresponding to the Ag-S binding energy at approximately 161.8 eV.

[0290] The manufactured Ag-C support compound, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed in a water solvent at a weight ratio of 100:6:3 to prepare a negative electrode coating layer composition.

[0291] The manufactured negative electrode coating layer composition was coated on a stainless steel foil current collector having a thickness of 10 ㎛, and then vacuum-dried at 80°C to manufacture a deposition-type negative electrode having a negative electrode coating layer having a thickness of 12 ㎛ formed on the surface of the current collector.

[0292] 9. Manufacturing of all-solid-state secondary batteries

[0293] D 50 This argyrodite-type solid electrolyte of Li6PS5Cl with a particle size of approximately 3.0 μm was added to an IBIB solvent containing an acrylic binder and mixed to prepare a composition for forming a solid electrolyte layer. The composition was cast onto a release film and dried at room temperature to prepare a solid electrolyte layer.

[0294] The prepared positive electrode, negative electrode, and solid electrolyte layers were cut, a solid electrolyte layer was laminated on the positive electrode, and then a negative electrode was laminated on top of that. This was sealed in a pouch shape and subjected to high-temperature hydrostatic pressing at 80°C and 500 MPa for 30 minutes to manufacture an all-solid-state secondary battery.

[0295] Comparative Example 1

[0296] An all-solid-state secondary battery was manufactured in substantially the same manner as in Example 1, except that the sulfide-based solid electrolyte manufactured in Step 4 was used as a solid electrolyte in the manufacture of the positive electrode in Step 7, instead of forming a third coating layer on the solid electrolyte as in Step 6 of Example 1.

[0297] Comparative Example 2

[0298] In the process of manufacturing a positive electrode active material, a positive electrode active material having only a first coating layer formed without forming a second coating layer was used, and an all-solid-state secondary battery was manufactured in substantially the same manner as in Comparative Example 1, except that the positive electrode active material was mixed at 87.5 wt% and the solid electrolyte at 10.94 wt% in the manufacturing of the positive electrode.

[0299] Comparative Example 3

[0300] 87.5 parts by weight of the cathode active material in which the first coating layer was formed during the thermal compounding process of the cathode active material and 5 parts by weight of the manufactured argyrodite-type sulfide-based solid electrolyte were mixed, and an all-solid-state secondary battery was manufactured in substantially the same manner as Example 1, except that 92.5% by weight of the final cathode active material thermally compounded and 5.94% by weight of the sulfide-based solid electrolyte were mixed during the manufacture of the cathode.

[0301] Comparative Example 4

[0302] An all-solid-state secondary battery was manufactured in substantially the same manner as in Comparative Example 3, except that the second heat treatment was not performed in the thermal complexation process of the positive electrode active material.

[0303] Comparative Example 5

[0304] A positive electrode and an all-solid-state battery were manufactured in the same manner as in Comparative Example 1, except that the positive electrode active material was manufactured in the following manner. In the final positive electrode active material according to Comparative Example 5, both the first positive electrode active material and the second positive electrode active material contained a lithium nickel-based composite oxide in the form of non-radiative secondary particles, and the buffer layer corresponding to the first coating layer was Li2O·ZrO2 coated by a wet method, and the second coating layer (thermal composite) was not formed.

[0305] 1. Preparation of the first positive electrode active material according to Comparative Example 5

[0306] As metal raw materials, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and sodium aluminum sulfate (NaAl(SO4)2·12H2O) were dissolved in distilled water as a solvent at a molar ratio of 94.5:4:1.5 to prepare a mixed solution. To form a complex compound, ammonia water (NH4OH) and sodium hydroxide (NaOH) were prepared as a precipitant.

[0307] After introducing a diluted ammonia solution into a continuous reactor, a mixed solution of metal raw materials is continuously introduced, and sodium hydroxide is added to maintain the pH inside the reactor. The reaction proceeds slowly for approximately 80 hours, and when the reaction stabilizes, the overflowing product is collected and washed and dried to obtain the final precursor. Accordingly, nickel-based composite hydroxide (Ni) in the form of secondary particles in which the primary particles are not arranged radially is obtained. 0.945 Co 0.04 Al 0.015 (OH)2) is manufactured.

[0308] The obtained nickel-based composite hydroxide was washed and dried, and LiOH was mixed so that the molar ratio of the total metal and lithium was 1:0.98, and heat-treated at 730°C in an oxygen atmosphere for 8 hours, thereby obtaining secondary particles in the form of agglomerates of multiple primary particles and having an average particle diameter (D) of the secondary particles. 50 ) according to comparative example 5, the first positive electrode active material (LiNi) having a thickness of about 14 ㎛ 0.945 Co 0.04 Al 0.015 O2) was manufactured.

[0309] 2. Preparation of the second positive electrode active material according to Comparative Example 5

[0310] In the production of the first nickel-based composite hydrocarbon product of Comparative Example 5, the pH inside the reactor was maintained higher to produce a second nickel-based composite hydrocarbon product (Ni) with a size reduced to 4 μm. 0.945 Co 0.04 Al 0.01 Mn 0.1 (OH)2) was manufactured. The overflowing product was collected and washed and dried to obtain the final precursor. The second nickel-based composite hydroxide and LiOH were mixed so that the molar ratio of the entire metal except lithium and Li in the second nickel-based composite hydroxide was 1:0.98, and heat-treated at 700°C in an oxygen atmosphere for 8 hours, thereby obtaining secondary particles in the form of agglomerates of multiple primary particles and having an average particle diameter (D) of the secondary particles. 50) according to comparative example 5, the second positive electrode active material (LiNi) having a particle size of 4 ㎛ 0.945 Co 0.04 Al 0.01 Mn 0.01 O2) was manufactured.

[0311] 3. Preparation of mixed cathode active material according to Comparative Example 5

[0312] The first and second positive electrode active materials manufactured are each coated with a buffer layer using a wet method as follows. 2-Propanol from which moisture has been removed, a methanol solution containing 10% lithium methoxide, and zirconium isopropoxide are mixed in a molar ratio of 200:2:1, and the positive electrode active material is added and dispersed therein. The propanol is evaporated in a vacuum at 50°C while irradiating ultrasonic waves to prevent the positive electrode active material particles from agglomerating. The resultant is filtered and heat-treated at 350°C for 1 hour in an air atmosphere to obtain the first and second positive electrode active materials coated with a buffer layer, Li2O-ZrO2, respectively. The first and second positive electrode active materials coated with a buffer layer are mixed in a weight ratio of 7:3 to obtain a mixed positive electrode active material.

[0313] To aid understanding, the positive electrode active materials and positive electrode designs of Example 1 and Comparative Examples 1 to 5 are briefly presented in Table 1 below.

[0314] Cathode active material base material Cathode active material heat composite Amount of electrolyte added during anode manufacturing (wt%) Type of electrolyte added to anode Large particle heat treatment electrolyte (weight part) Example 1 Radial NCA single particle NCAMO 1.009.94 Li6PS5Cl / LZP Comparative Example 1 1.009.94 Li6PS5Cl Comparative Example 2 X010.94 Comparative Example 3 05.005.94 Comparative Example 4 X5.005.94 Comparative Example 5 Non-radial NCA polycrystalline NCAX 013.44

[0315] Reference example

[0316] Meanwhile, the solid electrolyte manufactured in step 4 of Example 1 was heat-treated at 250°C for 5 hours in a tube furnace through which argon gas flowed at a constant rate of 8 SLM to prepare a solid electrolyte according to a reference example.

[0317] Evaluation Example 1: Evaluation of the initial charge / discharge capacity of an all-solid-state secondary battery.

[0318] The all-solid-state secondary batteries manufactured in Example 1 and Comparative Examples 1 to 5 were charged at 45°C with a constant current of 0.1 C to an upper limit voltage of 4.25 V, charged at a constant voltage of 0.05 C, and then discharged at 0.1 C to an end-of-discharge voltage of 2.5 V to measure the initial charge-discharge capacity. The ratio of the initial discharge capacity to the initial charge capacity was calculated as efficiency, and the results are shown in Fig. 6 and Table 2.

[0319] Charge capacity (mAh / g)Discharge capacity (mAh / g)Efficiency (%)Example 1240.6206.085.6%Comparative example 1239.1205.185.8%Comparative example 2240.5199.783.0%Comparative example 3230.3199.786.7%Comparative example 4243.5201.982.9%Comparative example 5231.5184.279.6%

[0320] Referring to FIG. 6 and Table 2, it can be seen that in Example 1 and Comparative Examples 1 to 4, where the amount of solid electrolyte was reduced from 13.44 wt% to 10.94 wt% and the ratio of positive electrode active material was increased from 85 wt% to 87.5 wt% compared to Comparative Example 5, the charge and discharge capacity was high. This is understood to be because the first nickel-based composite oxide was manufactured in a radial shape to increase the capacity, and the second nickel-based composite active material was applied in a single particle shape, thereby facilitating the connectivity between the solid electrolyte within the positive electrode plate and the contact between the solid electrolyte and the positive electrode active material.

[0321] Comparative Example 1 is a case where the surface of the positive electrode active material in Comparative Example 2 was thermally composited with a sulfide-based solid electrolyte, and it was shown that the initial charge / discharge capacity was improved through this. In Example 1, a solid electrolyte coated with lithium-zirconium-phosphate was applied as the solid electrolyte in the positive electrode in Comparative Example 1 to further improve the ionic conductivity, and it was shown that the discharge capacity and charge / discharge efficiency of the all-solid-state secondary battery were greatly improved through this.

[0322] In addition, it can be seen that Comparative Example 3, which has a larger amount of thermal complexation than Comparative Example 1, has lower charge and discharge capacities. This is understood to be because, as in Evaluation Examples 4 to 6 described below, agglomeration of solid electrolyte particles occurs on the surface of the positive electrode active material, thereby deteriorating the contact between the positive electrode active material and the solid electrolyte.

[0323] However, in Comparative Example 4, where heat treatment was omitted during the thermal compounding process, unlike Comparative Example 3, no agglomeration of solid electrolyte particles on the surface of the positive electrode active material occurred due to heat treatment. In addition, Comparative Example 4 is understood to have a higher capacity than Comparative Example 2 due to the addition of a process of mixing the positive electrode active material and the solid electrolyte in a powder state in Comparative Example 2, which improved the contact between the positive electrode active material and the solid electrolyte.

[0324] In Example 1, as in Evaluation Example 4 described below, thermal complexation proceeds without aggregation of the solid electrolyte on the surface of the positive electrode active material, and as can be seen in Evaluation Example 6 described below, the ionic conductivity of the solid electrolyte on the surface of the positive electrode active material is further increased, and contact between the solid electrolyte and the positive electrode active material is facilitated, so that the discharge capacity and efficiency are greatly improved.

[0325] Evaluation Example 2: Evaluation of the initial volume capacity of an all-solid-state secondary battery

[0326] The positive electrodes prepared in Example 1 and Comparative Examples 1 to 5 were cut, sealed in a pouch shape, and subjected to hydrostatic pressing at a high temperature of 80°C and 500 MPa for 30 minutes to separately manufacture only the positive electrodes. The plate density was measured, which is shown in Table 3. The plate density was multiplied by the initial discharge capacity per weight in Table 2 to obtain the initial discharge capacity per volume, which is shown in Table 3.

[0327] Electrode Density (g / cc)Volume Capacity (mAh / cc)Example 13.81785Comparative Example 13.82784Comparative Example 23.68735Comparative Example 33.78755Comparative Example 43.79765Comparative Example 53.40626

[0328] Referring to Table 3, it can be seen that the plate density and volumetric capacity of Example 1 and Comparative Examples 1 to 4, in which the amount of solid electrolyte was reduced from 13.44 wt% to 10.94 wt% and the ratio of positive electrode active material was increased from 85 wt% to 87.5 wt%, were higher than in Comparative Example 5. This is understood to be because the first nickel-based composite oxide was manufactured in a radial shape to increase the capacity, the second nickel-based composite active material was applied in a single particle shape to increase the density of the plate, and sufficient electrolyte connectivity for ion conduction could be secured even when the amount of solid electrolyte was reduced.

[0329] In the case of Example 1, by using a single particle form as the second nickel-based composite active material, the density of the positive electrode within the positive electrode plate is improved, thereby increasing the plate density. In addition, by thermally complexing the solid electrolyte on the surface of the positive electrode active material, ion transfer from the positive electrode active material to the solid electrolyte is facilitated, and the ion conductivity of the electrolyte is improved by coating and heat treatment, thereby facilitating ion transfer in the positive electrode plate, thereby improving the initial discharge capacity and greatly improving the discharge capacity per volume. From this, it can be seen that if an all-solid-state secondary battery is manufactured according to one embodiment, high energy density can be implemented.

[0330] Evaluation Example 3: Evaluation of the Lifetime Characteristics of All-Solid-State Secondary Batteries

[0331] For the all-solid-state secondary batteries of Example 1 and Comparative Examples 1 to 5, after initial charging and discharging as in Evaluation Example 1, charging at 0.33C and discharging at 0.33C in a voltage range of 2.5 V to 4.25 V at 45°C were repeated 50 times, and the degree to which the discharge capacity after 50 times was maintained compared to the initial discharge capacity was evaluated, and the results are shown in Table 4 and Fig. 7.

[0332] Initial discharge capacity (mAh / cc) 50 cycles capacity retention rate (%) Example 178594% Comparative example 178490% Comparative example 273587% Comparative example 375584% Comparative example 476586% Comparative example 562687%

[0333] It can be confirmed that Example 1 has improved initial volume capacity and life characteristics compared to Comparative Examples 1 to 4. In addition, it can be seen that Example 1 has improved initial discharge capacity by more than 25% compared to Comparative Example 5, which is a conventional technique generally practiced, and life characteristics are also improved.

[0334] In the case of Example 1, in which a solid electrolyte coated with lithium-zirconium-phosphate was applied to the positive electrode in Comparative Example 1, in which performance was improved by thermal complexation with an appropriate content of the positive electrode active material, the ionic conductivity within the positive electrode was improved, so that the initial discharge capacity and efficiency of the battery were greatly improved, and it was found that the lithium-zirconium-phosphate coated on the solid electrolyte suppressed side reactions during the charge and discharge process, thereby improving the life characteristics.

[0335] Evaluation Example 4: Analysis of solid electrolyte distribution on the surface of the positive electrode active material using SEM-EDS.

[0336] The surfaces of the positive electrode active materials manufactured in Example 1, Comparative Example 3, and Comparative Example 4 were photographed by SEM, and the distribution of sulfur (S) was confirmed by EDS, which is shown in Fig. 8. Referring to Fig. 8, Example 1 was confirmed to have no particularly agglomerated parts in the SEM photograph, and the EDS mapping image confirmed that S was evenly and well dispersed in large and small particles. Comparing Comparative Example 3 and Comparative Example 4, it can be confirmed that in the case of Comparative Example 3, an excessive amount of solid electrolyte particles were agglomerated on the surface of the positive electrode active material due to heat treatment. This can also be confirmed through Evaluation Example 5 described below.

[0337] Evaluation Example 5: Evaluation of particle size distribution of solid electrolyte

[0338] The particle size distributions for the sulfide-based solid electrolyte prepared in step 4 of Example 1 (before coating, i.e., the solid electrolyte of Comparative Example 1), the solid electrolyte coated with lithium-zirconium-phosphate in step 6 of Example 1 (after coating and heat treatment), and the solid electrolyte of the reference example (heat treatment without coating) were analyzed and shown in Fig. 9. The particle size distributions were measured using a particle size analysis device that uses xylene from which moisture has been removed as a solvent and utilizes laser diffraction.

[0339] Also, the cumulative size of 10% by volume is D 10 , 50% of the cumulative size of D 50 , and 90% of the cumulative size is D 90 , and are shown in Table 5 below, and to compare the wideness of the particle size distribution (D 90 -D 10 ) / D 50 was calculated and shown as Span in Table 5.

[0340] MV (㎛) D10 D50 D90 Span Comparative Example 1 (Uncoated) 0.92 0.26 0.85 1.64 1.63 Example 1 (Coated and Heat Treated) 0.88 0.26 0.87 1.46 1.37 Reference Example (Heat Treated Without Coating) 4.0 7 0.37 1.14 12.89 10.94

[0341] Referring to Figure 9 and Table 5, as in the reference example, when only the solid electrolyte is heat-treated at 250℃ for 5 hours under the thermal complexing condition, rapid aggregation occurs and D 90 It can be confirmed that the Span increases significantly. Through this, it can be understood that when the amount of solid electrolyte used for coating the positive electrode active material is excessive, as in Comparative Examples 3 and 4, the solid electrolyte particles may leave the surface of the positive electrode active material and aggregate with each other during the heat treatment process, resulting in a decrease in performance.

[0342] On the other hand, the solid electrolyte coated with lithium-zirconium-phosphate and heat-treated does not have a wide particle size distribution or an increase in D90 due to aggregation, but rather, the fine particles grow and the D10 increases, so that the particle sizes of the solid electrolyte particles become more uniform, as shown in Fig. 9. In summary, when combined with the results of improved ionic conductivity in Evaluation Example 6 below, it is understood that the coated electrolyte of Example 1 has a decrease in grain boundaries contained in the particles due to the growth of fine particles without aggregation of the particles, thereby lowering the resistance.

[0343] Evaluation Example 6: Evaluation of the ionic conductivity of a solid electrolyte

[0344] Each of the sulfide-based solid electrolyte prepared in step 4 of Example 1 (before coating, i.e., the solid electrolyte of Comparative Example 1), the solid electrolyte coated with lithium-zirconium-phosphate in step 6 of Example 1 (after coating and heat treatment), and the solid electrolyte of the reference example (heat treatment without coating) was charged at 0.15 g and 40 kgf / cm 2 After pressurizing with a pressure of , a torque cell is manufactured. Electromagnetic interference (EIS) analysis was performed on the manufactured cells to calculate the ionic conductivity. EIS has an amplitude of approximately 10 mV and a frequency of 0.1 Hz to 10 6The experiments were conducted at Hz, air atmosphere, and 25℃. The resistance value was obtained from the arc of the Nyquist plot through EIS, and the ionic conductivity was calculated by considering the thickness and area of ​​the cell, etc., and the results are shown in Table 6 below.

[0345] Ionic Conductivity (mS / cm) Comparative Example 1 (Uncoated) 2.73 Example 1 (Coated and Heat Treated) 3.59 Reference Example (Heat Treated Without Coating) 1.95

[0346] Referring to Table 6, it can be seen that the ionic conductivity is greatly improved when the solid electrolyte is coated with lithium-zirconium-phosphate and then heat-treated as in Example 1. When the sulfide-based solid electrolyte is coated with lithium-metal-phosphate and then heat-treated, Ostwald ripening, in which small particles are integrated into large particles, is induced, which reduces the number of small particles and accordingly reduces the grain boundaries (grain boundaries) provided by the small particles, and increases the crystallinity of the solid electrolyte particles themselves. Since the ionic conductivity at grain boundaries is usually much lower than that of the bulk, it is understood that the solid electrolyte of Example 1 has greatly improved ionic conductivity as the number of grain boundaries is reduced.

[0347] However, it can be seen that the ionic conductivity is greatly reduced when only heat treatment is performed without coating, as in the reference example. In the case of the reference example where heat treatment was performed without coating, the solid electrolyte particles coagulate with each other and coagulate into large particles, so particles containing many particle boundaries are generated, which is understood to be the cause of the low ionic conductivity. In addition, it is thought that the thermal energy is consumed in particle coagulation, so the increase in crystallinity is minimal, and accordingly, the effect of improving ionic conductivity by the increase in crystallinity does not appear. In addition, in the case of Example 1, it is understood that the ionic conductivity of the solid electrolyte in the positive electrode is further improved compared to Comparative Example 1, the coagulation phenomenon between particles is reduced, and the resistance is reduced by having a uniform particle size distribution, and the initial discharge capacity, initial charge / discharge efficiency, and life characteristics are improved.

[0348] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the following claims also fall within the scope of the present invention.

[0349] [Explanation of symbols]

[0350] 11: Secondary particle 12: Inside the secondary particle

[0351] 13: Primary particle 14: External of secondary particle

[0352] 100': All-solid-state battery 200: Anode

[0353] 201: Cathode current collector 203: Cathode active material layer

[0354] 300: Solid electrolyte layer 400: Cathode

[0355] 401: Negative current collector 403: Negative active material layer

[0356] 400': Precipitation type cathode 404: Lithium metal layer

[0357] 405: Cathode coating layer 500: Elastic layer

Claims

1. A first cathode active material comprising a lithium nickel-based composite oxide, a secondary particle formed by agglomeration of a plurality of primary particles, at least a portion of the primary particles having a radial arrangement structure, a first coating layer located on the surface of the secondary particle and containing boron, and a second coating layer located on the first coating layer and containing a sulfide-based solid electrolyte; A first coating layer comprising a lithium nickel-based composite oxide in the form of single particles and containing boron located on the surface of the single particles, and a second coating layer located on the first coating layer and containing a sulfide-based solid electrolyte, and having an average particle diameter (D) of the first positive electrode active material 50 ) smaller than the average particle diameter (D 50 ) having a second positive electrode active material; and A positive electrode comprising a solid electrolyte comprising a core particle containing a sulfide-based solid electrolyte and a third coating layer located on the surface of the core particle and containing a lithium-metal-phosphate.

2. In paragraph 1, The average particle diameter (D) of the secondary particles of the first positive electrode active material 50 ) is 9 ㎛ to 25 ㎛, The average particle diameter (D) of the single particles of the second positive electrode active material 50 ) is 2 ㎛ to 7 ㎛, A positive electrode comprising the secondary particles of the first positive electrode active material having an interior having an irregular porous structure and an exterior having a radial array structure as a region surrounding the interior.

3. In paragraph 1, For a total of 100 wt% of the first positive electrode active material and the second positive electrode active material, The first positive electrode active material is included in an amount of 60 wt% to 95 wt%, and the second positive electrode active material is included in an amount of 5 wt% to 40 wt%. A positive electrode comprising 1 to 35 wt% of the sulfide-based solid electrolyte particles relative to 100 wt% of the total of the first positive electrode active material, the second positive electrode active material, and the sulfide-based solid electrolyte particles.

4. In paragraph 1, The first coating layer of the first positive electrode active material and the first coating layer of the second positive electrode active material each include boron oxide, lithium boron oxide, or a combination thereof, A positive electrode having a boron content of 0.01 wt% to 0.5 wt% based on 100 wt% of the total metal excluding lithium in the first positive electrode active material and the second positive electrode active material.

5. In paragraph 1, The first cathode active material further includes a grain boundary boron coating portion located on the surface of the primary particles inside the secondary particles, In the first positive electrode active material, The weight of boron in the first coating layer is at least four times the weight of boron in the grain boundary boron coating portion, or An anode having a ratio of the weight of boron in the first coating layer to the weight of boron in the grain boundary boron coating portion of 70:30 to 98:

2.

6. In paragraph 1, The first cathode active material further includes a boron-doped layer located inside the primary particle exposed on the surface of the secondary particle, An anode in which the boron doping layer is located within a depth range of 10 nm from the outer surface of the primary particle exposed on the surface of the secondary particle.

7. In paragraph 1, The second coating layer of the first positive electrode active material and the second coating layer of the second positive electrode active material each contain an argyrodite-type sulfide-based solid electrolyte, and their thicknesses are each 100 nm to 2 μm. The total amount of the sulfide-based solid electrolyte of the second coating layer of the first positive electrode active material and the sulfide-based solid electrolyte of the second coating layer of the second positive electrode active material is 0.5 wt% to 3 wt% based on 100 wt% of the total of the first positive electrode active material and the second positive electrode active material. A positive electrode, wherein the combined amount of the sulfide-based solid electrolyte of the second coating layer of the first positive electrode active material and the sulfide-based solid electrolyte of the second coating layer of the second positive electrode active material is 1 to 20 wt%, based on 100 wt% of the total of the sulfide-based solid electrolyte of the second coating layer of the first positive electrode active material, the sulfide-based solid electrolyte of the second coating layer of the second positive electrode active material, and the sulfide-based solid electrolyte particles in the positive electrode.

8. In paragraph 1, The nickel-based composite oxide of the first positive electrode active material is a lithium nickel-cobalt-aluminum composite oxide represented by the following chemical formula 1, The nickel-based composite oxide of the second positive electrode active material is a lithium nickel-cobalt-aluminum-manganese composite oxide represented by the following chemical formula 2: [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, 및 0≤b1≤0.1이고, M 1 is one or more elements selected from 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 F, P, and S, [Chemical Formula 2] Li a2 Ni x2 Co y2 Al z2 Mr 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, 및 0≤b2≤0.1이고, M 2 is one or more elements selected from 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 F, P, and S.

9. In paragraph 1, The sulfide-based solid electrolyte contained in the core particles of the above solid electrolyte includes argyrodite-type sulfide, In the lithium-metal-phosphate of the third coating layer included in the solid electrolyte, the metal is at least one element selected from the group consisting of Al, B, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ta, V, W, and Zr, The above lithium-metal-phosphate is amorphous, The content of lithium-metal-phosphate in the third coating layer is 0.01 wt% to 3 wt% with respect to 100 wt% of the solid electrolyte, The average particle diameter (D) of the above solid electrolyte 50 ) is 0.1 ㎛ to 2 ㎛, The above solid electrolyte has a (D90-D10) / D50 value in the particle size distribution of greater than 1 and less than or equal to 5, An anode having a half-width of the main peak of 0.160 or less in X-ray diffraction analysis of the above solid electrolyte. 10.(i) A first positive electrode active material precursor in the form of secondary particles containing a first nickel-based composite hydroxide and formed by agglomeration of a plurality of primary particles, at least a portion of the primary particles being radially arranged; Containing a second lithium nickel-based composite oxide, in the form of single particles, and having an average particle diameter (D) of the first cathode active material precursor 50 ) smaller than the average particle diameter (D 50 ) Primary sintered product of the second cathode active material; lithium raw materials; and A boron-coated preliminary positive electrode active material is obtained by mixing boron raw materials and performing a first heat treatment, (ii) Dry mixing of a boron-coated preliminary positive electrode active material and a sulfide-based solid electrolyte and performing a second heat treatment to obtain a final positive electrode active material, (iii) A coated solid electrolyte is prepared by mixing core particles containing a sulfide-based solid electrolyte and lithium-metal-phosphate and performing a third heat treatment at 200°C to 300°C, (iv) A method for manufacturing a positive electrode, comprising manufacturing a positive electrode by mixing a final positive electrode active material and a coated solid electrolyte.

11. In paragraph 10, The average particle diameter (D) of the secondary particles of the first cathode active material precursor 50 ) is 9 ㎛ to 25 ㎛, and the average particle diameter (D) of the single particles of the second positive electrode active material primary sintered product 50 ) is 2 ㎛ to 7 ㎛, A method for manufacturing a positive electrode, wherein the mixing weight ratio of the first positive electrode active material precursor and the second positive electrode active material primary sintered product is 60:40 to 95:

5.

12. In paragraph 10, The above lithium raw material is mixed so that the molar ratio of lithium to the total metal of the first nickel-based composite hydroxide is 0.8 to 0.995, The above boron raw materials are H3BO3, B2O3, C6H5B(OH)2, (C6H5O)3B, [CH3(CH2)3O]3B, C 13 H 19 Containing BO3, C3H9B3O6, (C3H7O)3B, or a combination thereof, The above boron raw material is mixed so that the content of boron is 0.01 mol part to 0.5 mol part with respect to 100 mol parts of the total metal excluding lithium in the first nickel-based composite hydroxide and the second lithium nickel-based composite oxide. A method for manufacturing an anode, wherein the first heat treatment is performed at a temperature of 650°C to 850°C for 5 to 25 hours.

13. In paragraph 10, The first heat treatment includes a temperature raising step and a temperature maintaining step, The heating time is longer than the temperature holding time, or The ratio of (heating time):(temperature holding time) is 1.1:1 to 10:1, A method for manufacturing an anode, wherein the heating time is 6 to 16 hours and the temperature holding time is 1 to 9 hours.

14. In paragraph 10, The content of the sulfide-based solid electrolyte mixed in the above step (ii) is 0.5 to 3 parts by weight based on 100 parts by weight of the boron-coated positive electrode active material. With respect to the total of 100 wt% of the sulfide-based solid electrolyte mixed in step (ii) and the sulfide-based solid electrolyte particles of step (iii), the content of the sulfide-based solid electrolyte mixed in step (ii) is 1 wt% to 20 wt%, A method for manufacturing an anode in which the second heat treatment is performed at 200°C to 300°C.

15. In paragraph 10, In the step (iii) above, 0.01 to 3 parts by weight of the lithium-metal-phosphate is mixed with 100 parts by weight of core particles containing a sulfide-based solid electrolyte, In the above step (iii), the sulfide-based solid electrolyte of the core particles contains argyrodite-type sulfide, and the average particle diameter (D) of the core particles 50 ) is 0.1 ㎛ to 2 ㎛, In the lithium-metal-phosphate, the metal is one or more elements selected from the group consisting of Al, B, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ta, V, W, and Zr, The above lithium-metal-phosphate is in particle form and has an average particle diameter (D 50 ) is 0.01 ㎛ to 1.0 ㎛, A method for manufacturing an anode, wherein the third heat treatment is performed in an inert gas atmosphere with the highest temperature maintenance time set to 1 to 10 hours.

16. In paragraph 10, Step (iii) above A sulfide-based solid electrolyte is manufactured by mixing sulfur-containing raw materials and calcining them for the first time at 120°C to 350°C and then calcining them for the second time at 350°C to 800°C. The manufactured sulfide solid electrolyte was pulverized to obtain an average particle size (D 50 ) to obtain core particles having a size of 0.1 ㎛ to 2.0 ㎛, The obtained core particles and lithium-metal-phosphate are mixed and subjected to a third heat treatment at 200°C to 300°C, A method for manufacturing a positive electrode, wherein the solid electrolyte is mixed in an amount of 1 to 35 wt% based on a total of 100 wt% of the final positive electrode active material and the solid electrolyte in step (iv).

17. The anode according to any one of paragraphs 1 to 9; cathode, and An all-solid-state secondary battery comprising a solid electrolyte layer positioned between the positive electrode and the negative electrode.

18. In paragraph 17, The above negative electrode comprises a negative electrode current collector, and a negative electrode coating layer positioned on the negative electrode current collector and containing a compound in which a lithium-philic metal is supported on a carbon material, In the above cathode coating layer, the lithium-philic metal includes Al, Ag, Au, Bi, Cu, Ge, In, Mg, Ni, Pd, Pt, Si, Sn, Zn, or a combination thereof, The above carbon material is an amorphous carbon material, An all-solid-state secondary battery, wherein the lithium-philic metal is included in an amount of 3 to 40 wt% and the carbon material is included in an amount of 60 to 97 wt% based on a total of 100 wt% of the lithium-philic metal and the carbon material in the cathode coating layer.

19. In paragraph 18, In the above cathode coating layer, the lithium-philic metal and the carbon material are chemically bonded via sulfur, The above lithium-philic metal includes Ag, An all-solid-state secondary battery, wherein the cathode coating layer has a peak at 160 eV to 162 eV corresponding to the Ag-S binding energy in the S2p spectrum measured by X-ray photoelectron spectroscopy.

20. In paragraph 18, The thickness of the above cathode coating layer is 100 nm to 40 ㎛, Further comprising a lithium metal layer formed by charging between the negative electrode current collector and the negative electrode coating layer, The thickness of the lithium metal layer is 5 ㎛ to 500 ㎛, An all-solid-state secondary battery wherein the thickness deviation of the lithium metal layer is 40% or less.

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