All-solid-state rechargeable battery

Abstract

The present invention relates to an all-solid-state rechargeable battery comprising a positive electrode, a negative electrode, and a solid-electrolyte layer located between the positive electrode and the negative electrode, the positive electrode comprising a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector and containing positive electrode active materials, wherein the positive electrode active materials comprise: a first positive electrode active material which contains a lithium nickel-based composite oxide and is in the form of a secondary particle which is formed by the aggregation of a plurality of primary particles and in which at least some of the primary particles are structured to be radially arranged; and a second positive electrode active material which contains a lithium nickel-based composite oxide and is in the form of a single particle, the first positive electrode active material comprising a first boron coating layer located on the surface of the secondary particle and a grain boundary boron coating located on the surfaces of the primary particles inside the secondary particle, the second positive electrode active material comprising a second boron coating layer located on the surface of the single particle, and the negative electrode comprising a negative electrode current collector and a negative electrode coating layer located on the negative electrode current collector and containing a compound having a lithium-philic metal supported on a carbon material.

Description

All-solid-state secondary battery

[0001] It is about all-solid-state secondary batteries.

[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, active research is 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 electrolytes. However, solid electrolytes have several drawbacks, including 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 cathode active materials that can be used with these solid electrolytes is urgently needed. Furthermore, the development of cathode active materials that can improve the overall performance, including capacity and longevity, of all-solid-state secondary batteries is also necessary.

[0004] Lithium metal anodes can be used as cathodes in all-solid-state secondary batteries. While this can increase energy density, it also suffers from the problem of lithium metal volume expansion. Furthermore, irreversible lithium dendrite growth on the cathode surface during charge and discharge can reduce reversible capacity and compromise safety due to battery short-circuiting. Therefore, research is being conducted on methods that do not use lithium metal itself as the anode, but instead precipitate lithium metal onto the cathode current collector during charging, thereby using this as the anode active material. However, these precipitated anodes have limitations, such as low initial charge / discharge efficiency and output characteristics, and the potential for battery short-circuiting.

[0005] Provides an all-solid-state secondary battery with high initial charge / discharge capacity and efficiency, excellent output characteristics, and excellent life characteristics.

[0006] In one embodiment, an all-solid-state secondary battery is provided, comprising a positive electrode, a negative electrode, and a solid electrolyte layer positioned between the positive electrode and the negative electrode, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material layer positioned on the positive electrode current collector and containing a positive electrode active material, wherein the positive electrode active material comprises a first positive electrode active material containing a lithium nickel-based composite oxide 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 have a radial arrangement structure, and a second positive electrode active material containing a lithium nickel-based composite oxide and in the form of single particles, wherein the first positive electrode active material comprises a first boron coating layer positioned on the surface of the secondary particles and a grain boundary boron coating portion positioned on the surface of the primary particles inside the secondary particles, and the second positive electrode active material comprises a second boron coating layer positioned on the surface of the single particles, and wherein the 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.

[0007] An all-solid-state secondary battery according to one embodiment has high initial charge / discharge capacity and efficiency, and excellent output characteristics and lifespan characteristics.

[0008] Figure 1 is a cross-sectional view schematically showing an all-solid-state secondary battery according to one embodiment.

[0009] Figure 2 is a schematic diagram showing the shape of a plate-shaped primary particle according to one embodiment.

[0010] Figure 3 is a drawing for explaining the definition of radiality in secondary particles according to one implementation example.

[0011] Figure 4 is a schematic diagram showing the cross-sectional structure of a secondary particle according to one implementation example.

[0012] Figure 5 is a transmission electron microscope (TEM) image of the Ag-C support compound manufactured in Example 1.

[0013] Figure 6 is a TEM image of the Ag / C mixture manufactured in Comparative Example 2.

[0014] Figure 7 is a scanning electron microscope (SEM) image of a cross-section of the first nickel-based composite hydroxide of Example 1.

[0015] Figure 8 shows the mass spectrum results of ToF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) for the positive electrode active material manufactured in Example 1.

[0016] Figure 9 is a TEM photograph of a primary particle exposed on the surface of a secondary particle in the first positive electrode active material of Example 1.

[0017] Figure 10 is a TEM-EELS (transmission electron microscopy - electron energy loss spectroscopy) analysis graph for a total of 10 points from point 1 to point 10 shown in Figure 9.

[0018] Figure 11 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 3.

[0019] Figure 12 is a graph showing voltage changes according to charge / discharge capacity for the all-solid-state secondary batteries of Example 1 and Comparative Example 1.

[0020] Figure 13 is a graph showing voltage changes according to charge / discharge capacity for the all-solid-state secondary batteries of Example 1 and Comparative Example 2.

[0021] Figure 14 is a graph showing the rate characteristic evaluation data for the all-solid-state secondary batteries of Example 1 and Comparative Examples 1 to 3, showing the ratio of the 1 / 3C discharge capacity to the 0.1C discharge capacity (black dotted line graph) and the ratio of the 1C discharge capacity to the 0.1C discharge capacity (red dotted line graph).

[0022] Figure 15 is a graph showing the life characteristic data for the all-solid-state secondary batteries of Example 1 and Comparative Examples 1 to 3, and showing the discharge capacity according to the number of cycles.

[0023] Below, specific implementation examples are described in detail to facilitate their implementation by those skilled in the art. However, the present invention may be implemented in various different forms and is not limited to the implementation examples described herein.

[0024] 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.

[0025] Here, “combination of these” means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of the components.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] Here, “or” is not interpreted in an exclusive sense, for example, “A or B” is interpreted to include A, B, A+B, etc.

[0031] “Metal” is interpreted as a concept that includes common metals, transition metals, and metalloids (semi-metals).

[0032] All-solid-state secondary battery

[0033] In one embodiment, an all-solid-state secondary battery is provided, comprising a positive electrode, a negative electrode, and a solid electrolyte layer positioned between the positive electrode and the negative electrode.

[0034] The positive electrode includes a positive electrode current collector and a positive electrode active material layer positioned on the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material. The positive electrode active material includes a first positive electrode active material containing a lithium nickel-based composite oxide and having a secondary particle form in which a plurality of primary particles are aggregated and at least a portion of the primary particles have a radial arrangement structure, and a second positive electrode active material containing a lithium nickel-based composite oxide and having a single particle form, wherein the first positive electrode active material includes a first boron coating layer positioned on a surface of the secondary particle and a grain boundary boron coating portion positioned on a surface of the primary particles inside the secondary particle, and the second positive electrode active material includes a second boron coating layer positioned on a surface of the single particle.

[0035] The above negative electrode includes a negative electrode current collector and a negative electrode coating layer positioned on the negative electrode current collector, and the negative electrode coating layer is characterized in that it contains a compound in which a lithium-philic metal is supported on a carbon material.

[0036] FIG. 1 is a cross-sectional view of an all-solid-state secondary battery according to an embodiment. Referring to FIG. 1, 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 collector (401) and a negative electrode coating layer (405), a solid electrolyte layer (300), and a positive electrode (200) including a positive electrode active material layer (203) and a positive electrode 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. 1 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.

[0037] In an all-solid-state secondary battery according to one embodiment, the negative electrode (400') may be referred to as a precipitation-type negative electrode. An all-solid-state secondary battery having a precipitation-type negative electrode starts initial charging in a state in which no negative electrode active material exists, and during charging, a 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 the negative electrode active material. Accordingly, in an all-solid-state secondary battery that has been charged at least 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, etc. is deposited during the charging process of the battery, and may be referred to as a metal layer, a lithium layer, a lithium electrodeposition layer, or a negative electrode active material layer.

[0038] The cathode will be described in detail later, but the anode will be explained first.

[0039] anode

[0040] The positive electrode (200) includes a positive electrode current collector (201) and a positive electrode active material layer (203) positioned on the positive electrode current collector, and the positive electrode active material layer (203) includes a positive electrode active material and may optionally include a solid electrolyte, a binder and / or a conductive material.

[0041] positive electrode active material

[0042] According to one embodiment, a cathode active material includes a first cathode active material and a second cathode active material. The first cathode active material includes a lithium nickel-based composite oxide, is formed by agglomerating a plurality of primary particles, and is in the form of secondary particles having a radial arrangement structure, and the first cathode active material is coated with a boron-containing compound, and is specifically characterized by including a first boron coating layer located on the surface of the secondary particles and a grain boundary boron coating portion located on the surface of the primary particles inside the secondary particles. The second cathode active material includes a lithium nickel-based composite oxide, is in the form of a single particle, and includes a second boron coating layer located on the surface of the single particle.

[0043] These positive electrode active materials for lithium secondary batteries have high pellet density and high initial discharge capacity, resulting in a very high capacity per volume, high initial charge / discharge efficiency, and excellent output and life characteristics.

[0044] Here, the boron coating layer, boron coating portion, etc. mean something containing the boron element, and may mean something containing a boron-containing compound, for example.

[0045] 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 was coated with boron and then mixed, the pellet density and initial discharge capacity of the entire positive electrode active material dropped 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 (precursor) with primary particles oriented radially, 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.

[0046] For example, nickel-based positive electrode active materials may experience structural collapse and cation mixing due to the formation of NiO, etc. on the surface with repeated charge and discharge, which may cause 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 boron coating layer and a grain boundary boron coating portion 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 cracking phenomenon due to repeated charge and discharge. Furthermore, the boron-containing compound present on the surface of the positive electrode active material may facilitate the movement of lithium ions in the all-solid-state battery, thereby improving the rate characteristics.

[0047] First positive electrode active material

[0048] The first cathode active material includes a secondary particle including a lithium nickel-based composite oxide, and a first boron coating layer positioned on the surface of the secondary particle. The first boron coating layer includes a boron-containing compound, and the boron-containing compound may include, for example, boron oxide, lithium boron oxide (lithium borate), or a combination thereof, for example, B2O2, B2O3, B4O3, B4O5, LiBO2, Li3B7O 12 , Li6B4O9, Li3B 11 O 18 , Li2B4O7, Li3BO3, or a combination thereof.

[0049] The first boron coating layer may be present in the form of a continuous film on the surface of the secondary particle or may be coated in the form of an island.

[0050] The content of boron based on 100 mol% of the total metal excluding lithium in the entire 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 based on 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, and suppressing problems caused by repeated charge / discharge, which can improve the long-life characteristics of the battery.

[0051] According to one embodiment, a first positive electrode active material includes not only a first boron coating layer located on the surface of a secondary particle, but also a grain boundary boron coating layer located on the surface of primary particles inside the secondary particle. That is, in the first positive electrode active material, boron may be coated along the interface of the primary particles inside the secondary particle. Here, the inside of the secondary particle means the entire inside excluding the surface, for example, it may mean the entire inside from a depth of about 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 particle is washed with distilled water. In this way, when a boron-containing compound is coated on the surface of the secondary particle and the inner grain boundary surface of the first positive electrode active material, boron does not act as a resistor, and the phenomenon of structural collapse or breakage of the positive electrode active material due to charge and discharge can be effectively suppressed.

[0052] 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 boron coating layer may be four times or more than the weight of boron in the grain boundary boron coating portion. For example, the ratio of the boron weight in the first boron coating layer to the boron weight 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.

[0053] For example, the boron content in the first boron 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 boron coating layer and the grain boundary boron coating portion are as described above, 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, and the boron content in the grain boundary boron coating portion may mean the difference between the boron content of the first positive electrode active material before washing and the boron content after washing.

[0054] According to one embodiment, the first positive electrode active material may further include a boron-doped layer located inside the primary particles exposed on the surface of the secondary particles. The boron-doped layer may be said to be located inside the secondary particles, and may be said to be located 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 within 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 located 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 within 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.

[0055] The 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 boron coating layer or the grain boundary boron coating portion, and is thought to contribute to the structural stability of the positive electrode active material.

[0056] Meanwhile, the first positive electrode active material includes 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.

[0057] At least some of the above primary particles may have a plate shape. Fig. 2 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. 2, "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 the 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.

[0058] The thickness (t) of the above 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).

[0059] In the above 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. 3 is a drawing for explaining the definition of radial in secondary particles according to one embodiment. In one embodiment, the radial array structure means 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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 ㎛.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] Fig. 4 is a schematic diagram showing the cross-sectional structure of the secondary particles of the first positive electrode active material. Referring to Fig. 4, the secondary particles (11) of the first positive electrode active material according to one embodiment include an outer portion (14) having a structure in which primary particles (13) having a plate shape are arranged radially, 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. 4, arrows indicate the direction of movement of lithium ions.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] The average particle diameter of the first positive electrode active material (D 50 ) may be 9 ㎛ to 25 ㎛, for example, 9 ㎛ to 20 ㎛, or 10 ㎛ to 15 ㎛, etc. For example, the first positive electrode active material may be expressed as a large particle or a large particle, and the second positive electrode active material described below may be expressed as a small particle or a small particle. When the average particle diameter of the first positive electrode active material satisfies the above range, the capacity of the positive electrode active material for a lithium secondary battery can be increased and the pellet density and energy density can be further increased. The average particle diameter of the first positive electrode active material is obtained by measuring the particle size in a scanning electron microscope image, for example, to obtain a particle size distribution, and here, D 50 It may have been calculated.

[0074] Second positive electrode active material

[0075] 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.

[0076] 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.

[0077] The average particle size of the second positive electrode active material may be 0.5 μm to 8 μm. For example, it may be 0.5 μm to 7 μm, 0.5 μm to 6 μm, 0.5 μm to 5 μm, or 1 μm to 4 μm. In this case, the pellet density and energy density of the positive electrode active material for a lithium secondary battery can be further increased. The average particle size of the second positive electrode active material is obtained by measuring the particle size in a scanning electron microscope image, for example, to obtain a particle size distribution, where D 50 It may have been calculated.

[0078] The second cathode active material includes a second boron coating layer located on the surface of the single particle, and the second boron coating layer includes a boron-containing compound. The boron-containing compound may include, 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. The single particle structure makes it difficult for lithium to diffuse into the interior of the particle, but by coating the surface with a boron-containing compound, the diffusion of lithium can be facilitated and the desorption of oxygen atoms on the surface of the positive electrode active material can be effectively prevented.

[0079] The second boron coating layer may be present in the form of a continuous film on the surface of the single particle or in the form of an island.

[0080] The first positive electrode active material may be included in an amount of 60 to 95 wt% and the second positive electrode active material may be included in an amount of 5 to 40 wt%, based on a total of 100 wt% of the first positive electrode active material and the second positive electrode active material. For example, the first positive electrode active material may be included in an amount of 70 to 90 wt% and the second positive electrode active material may be included in an amount of 10 to 30 wt%. When the particles and the small particles are mixed in such a content range, a high energy density battery can be realized.

[0081] In the lithium nickel-based 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 99.9 mol% or less, or 99 mol% or less, based on 100 mol% of the metal excluding lithium. For example, the content of nickel in the lithium nickel-based composite oxide may be higher than the content of each of the other metals, such as cobalt, manganese, and aluminum. When the content of nickel satisfies the above range, the positive electrode active material may exhibit excellent battery performance while implementing a high capacity.

[0082] 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 may each be independently represented by chemical formula 1.

[0083] [Chemical Formula 1]

[0084] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0085] In the above chemical formula 1, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, 0≤z1≤0.7, 0.9≤x1+y1+z1≤1.1, and 0≤b1≤0.1, and M 1 and M2 are each independently Al, B, Ba, Ca, Ce, Co, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, Zr or a combination thereof, and X is F, P, S or a combination thereof.

[0086] In the above chemical formula 1, 0.4≤x1≤1, 0≤y1≤0.6, and 0≤z1≤0.6, or 0.5≤x1≤1, 0≤y1≤0.5, and 0≤z1≤0.5, or 0.6≤x1≤1, 0≤y1≤0.4, and 0≤z1≤0.4, or 0.7≤x1≤1, 0≤y1≤0.3, and 0≤z1≤0.3, or 0.8≤x1≤1, 0≤y1≤0.2, and 0≤z1≤0.2, or 0.9≤x1<1, 0 <y1≤0.1, 및 0≤z1≤0.1일 수 있다.

[0087] 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 be independently represented, for example, by the chemical formula 2 below.

[0088] [Chemical Formula 2]

[0089] Li a2 Ni x2 Co y2 M 3 z2 O 2-b2 X b2

[0090] In the above chemical formula 2, 0.9≤a2≤1.8, 0.3≤x2<1, 0 <y2≤0.7, 0≤z2≤0.7, 0.9≤x2+y2+z2≤1.1, 및 0≤b2≤0.1이고 M 3 is Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, Zr or a combination thereof, and X is F, P, S or a combination thereof.

[0091] In the above chemical formula 2, 0.3≤x2≤0.99, 0.01≤y2≤0.7, and 0≤z2≤0.7, or 0.4≤x2≤0.99, 0.01≤y2≤0.6, and 0≤z2≤0.6, or 0.5≤x2≤0.99, 0.01≤y2≤0.5, and 0≤z2≤0.5, or 0.6≤x2≤0.99, 0.01≤y2≤0.4, and 0≤z2≤0.4, or 0.7≤x2≤0.99, 0.01≤y2≤0.3, and 0≤z2≤0.3, or 0.8≤x2≤0.99, 0.01≤y2≤0.2, and 0≤z2≤0.2, or 0.9≤x2≤0.99, 0.01≤y2≤0.1, and 0≤z2≤0.1.

[0092] 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 be independently represented, for example, by the chemical formula 3 below.

[0093] [Chemical Formula 3]

[0094] Li a3 Ni x3 Co y3 M 4 z3 M 5 w3 O 2-b3 X b3

[0095] In the above chemical formula 3, 0.9≤a3≤1.8, 0.3≤x3≤0.98, 0.01≤y3≤0.69, 0.01≤z3≤0.69, 0≤w3≤0.69, 0.9≤x3+y3+z3+w3≤1.1, and 0≤b3≤0.1, and M 4 is Al, Mn or a combination thereof, and M 5 is B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sr, Ti, V, W, Zr or a combination thereof, and X is F, P, S or a combination thereof.

[0096] In the above chemical formula 3, 0.4≤x3≤0.98, 0.01≤y3≤0.59, 0.01≤z3≤0.59, and 0≤w3≤0.59, or 0.5≤x3≤0.98, 0.01≤y3≤0.49, 0.01≤z3≤0.49, and 0≤w3≤0.49, or 0.6≤x3≤0.98, 0.01≤y3≤0.39, 0.01≤z3≤0.39, and 0≤w3≤0.39, or 0.7≤x3≤0.98, 0.01≤y3≤0.29, 0.01≤z3≤0.29, and 0≤w3≤0.29, or 0.8≤x3≤0.98, 0.01≤y3≤0.19, 0.01≤z3≤0.19, and 0≤w3≤0.19, or 0.9≤x3≤0.98, 0.01≤y3≤0.09, 0.01≤z3≤0.09, and 0≤w3≤0.09.

[0097] 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.

[0098] According to one embodiment, a cathode active material can have a high pellet density and realize high specific capacity and energy density. The pellet density of the cathode active material may be, for example, 3.5 g / cc or more, or 3.6 g / cc to 3.8 g / cc. In addition, the specific capacity of the cathode active material may be 214 mAh / g or more. An all-solid-state secondary battery using such a cathode active material can exhibit a high energy density. For example, the volumetric capacity of a cathode using the cathode active material may be 700 mAh / cc or more, for example, 700 mAh / cc to 800 mAh / cc, 750 mAh / cc to 800 mAh / cc, 760 mAh / cc to 800 mAh / cc, etc.

[0099] Method for manufacturing positive electrode active material

[0100] A method for manufacturing a positive electrode active material according to one embodiment includes mixing and heat-treating a first nickel-based composite hydroxide in the form of secondary particles in which a plurality of primary particles are aggregated and at least a portion of the primary particles have a radial arrangement structure; a second lithium nickel-based composite oxide in the form of single particles; a lithium raw material; and a boron raw material. Through the heat-treating process, the first nickel-based composite hydroxide and the lithium raw material react to form a first lithium nickel-based composite oxide, and a boron-containing compound is coated on the surface and internal grain boundaries of the secondary particles, thereby manufacturing a first positive electrode active material. The second lithium nickel-based composite oxide in the form of single particles is re-heat-treated, thereby coating the boron-containing compound on the surface, thereby manufacturing a second positive electrode active material.

[0101] A method for manufacturing a cathode active material according to one embodiment is not to manufacture a first lithium nickel-based composite oxide and a second lithium nickel-based composite oxide separately, coat them separately, and then mix them, but to synthesize a cathode active material by mixing, for example, a precursor of a first cathode active material, a second cathode active material, a lithium raw material, and a boron raw material, and simultaneously firing them, so that the manufacturing method is simple and efficient, and the pellet density and initial discharge capacity of the final cathode active material are improved, so that the capacity per volume of the battery is significantly improved, and both the initial charge / discharge efficiency and the life characteristics of the battery can be improved.

[0102] Previously, when coating a positive electrode active material with boron, a common method involved mixing a lithium source with a nickel-based composite hydroxide, heat-treating it, and then mixing the boron source into the resulting lithium-nickel composite oxide, either wet or dry, and heat-treating it again. However, this method presented a problem: the boron attached to the surface of the positive electrode active material acted as a resistor, reducing capacity and lifespan.

[0103] In addition, when only one of the first positive electrode active material and the second positive electrode active material is mixed after being coated with boron, or when the first positive electrode active material and the second positive electrode active material are individually coated with boron and then mixed to manufacture the positive electrode active material, there are problems in that the pellet density and energy density are low, the initial discharge capacity is low, and the initial charge / discharge efficiency and life characteristics are inferior compared to the positive electrode active material manufactured according to one embodiment. On the other hand, the positive electrode 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 is significantly increased, the initial charge / discharge efficiency is high, and the room temperature and high temperature life characteristics can be improved.

[0104] In the above manufacturing method, the first nickel-based composite hydroxide (precursor of the first positive electrode active material) may be in the form of secondary particles in which at least a portion of the primary particles are radially arranged, and may be manufactured by a coprecipitation method, etc. Metal raw materials such as nickel raw materials are mixed to prepare a composite metal raw material, 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 manufacturing a nickel-based composite hydroxide having 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), etc. The pH of the mixture may be adjusted to, for example, a range of 10 to 13.

[0105] 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.

[0106] 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 3.5 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.

[0107]

[0108] The first nickel-based composite hydroxide can be represented, for example, by the chemical formula 11 below.

[0109] [Chemical Formula 11]

[0110] Ni x11 M 11 y11 M 12 z11 (OH)2

[0111] 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.

[0112] The average particle size (D) of the first nickel-based composite hydroxide 50 ) may be, for example, 9 μm to 25 μm, or 10 μm to 20 μm. This may be measured by a particle size analyzer using laser diffraction.

[0113] The description of the radial array structure in the first nickel-based composite hydroxide is the same as described above. For example, the secondary particles of the first nickel-based composite hydroxide may include an interior having an irregular porous structure and an exterior having a radial array structure as a region surrounding the interior. The interior of the secondary particles has a porous structure, which has the effect of reducing the diffusion distance of lithium ions to the interior, and the exterior has the advantage of being able to produce a first nickel-based composite oxide in which lithium ions can be easily inserted and deintercalated because the primary particles are arranged radially.

[0114] 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.

[0115] 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. The second lithium nickel-based composite oxide may be represented by Chemical Formula 1 or Chemical Formula 2 described above. The average particle diameter (D) of the second lithium nickel-based composite oxide 50 ) may be 0.5 ㎛ to 8 ㎛, for example, 1 ㎛ to 5 ㎛.

[0116] 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.

[0117] The lithium raw material may be, for example, Li2CO3, LiOH, LiF, a hydrate thereof, or a combination thereof, and may be mixed in an amount of 0.9 molar parts to 1.1 molar parts, or 0.9 molar parts to 1.05 molar parts, or 0.95 molar parts to 1.05 molar parts, based on 1 molar part of the total metal in the first nickel-based composite hydroxide.

[0118] 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, C13 H 19 BO3, or a combination thereof.

[0119] 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.

[0120] In the above manufacturing method, the heat treatment can be performed at a temperature of, for example, 650°C to 850°C, or 690°C to 780°C. In addition, the 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, the 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 having 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 having a monolithic structure can be coated with a boron-containing compound, and the cathode active material thus manufactured can simultaneously improve 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.

[0121] In one embodiment, the heat treatment includes 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.

[0122] In the above heat treatment, the temperature elevation time may be, for example, 6 hours to 15 hours, 6 hours to 14 hours, 6 hours to 13 hours, or 7 hours to 12 hours, and the temperature holding time may be 2 hours to 9 hours, or 3 hours to 8 hours.

[0123] 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.

[0124] By controlling the heat treatment profile in this way, a high-efficiency radial secondary particle-shaped first positive electrode active material 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.

[0125] bookbinder

[0126] 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.

[0127] 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.

[0128] Challenge

[0129] 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.

[0130] 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.

[0131] Aluminum foil may be used as the positive electrode current collector, but is not limited thereto.

[0132] solid electrolyte

[0133] The cathode active material layer may further include a solid electrolyte in addition to the cathode active material. The solid electrolyte may be an inorganic solid electrolyte, such as a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a halide-based solid electrolyte.

[0134] In one embodiment, the solid electrolyte may be a sulfide-based solid electrolyte having excellent ion conductivity. The sulfide-based solid electrolyte particles include, for example, 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 MO q (p, q are integers, and M is P, Si, Ge, B, Al, Ga or In), or a combination thereof.

[0135] 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.

[0136] 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.

[0137] According to one embodiment, sulfide-based solid electrolyte particles 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 or nitrogen 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 robustness 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.

[0138] For example, the sulfide-based solid electrolyte particles may include argyrodite-type sulfides. The argyrodite-type sulfide-based solid electrolyte particles have 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 approaching the S / cm range, can form a close bond between a positive electrode active material and a solid electrolyte without causing a decrease in ionic conductivity, and can further form a close interface between an electrode layer and a solid electrolyte layer. An all-solid-state secondary battery including the same can have improved battery performance, such as rate characteristics, Coulombic efficiency, and cycle life characteristics.

[0139] The argyrodite-type sulfide-based solid electrolyte particles may include, for example, a compound represented by the chemical formula 21 below.

[0140] [Chemical Formula 21]

[0141] (Li a M 1 b M 2 c )(P d M 3 e )(S f M 4 g )X h

[0142] 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.

[0143] 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.

[0144] For example, in chemical formula 21, a+b+c+h=7, d+e=1, and f+g+h=6.

[0145] 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.

[0146] An argyrodite-type sulfide-based solid electrolyte can be manufactured, for example, by mixing lithium sulfide and phosphorus sulfide, optionally a 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.

[0147] The average particle diameter (D) of the above sulfide-based solid electrolyte particles 50 ) may be, for example, 0.1 ㎛ to 5.0 ㎛, may be small particles of 0.1 ㎛ to 1.9 ㎛, or may be large particles of 2.0 ㎛ to 5.0 ㎛. The average particle diameter of the sulfide-based solid electrolyte particles may be measured by an electron microscope image, and for example, a particle size distribution is obtained by measuring the size (diameter or length of major axis) of about 20 particles in a scanning electron microscope image, where D 50 It may have been calculated.

[0148] The above solid electrolyte may include an oxide-based inorganic solid electrolyte in addition to a sulfide-based material. The above oxide-based inorganic solid electrolyte may include, for example, Li 1+x Ti 2-x Al(PO4)3(LTAP)(0≤x≤4), Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 <x<2, 0≤y<3), BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT)(0≤x<1, 0≤y<1), PB(Mg3Nb 2 / 3)O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 <x<2, 0<y<3), Li 1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0≤x≤1, 0≤y≤1), lithium lanthanum titanate (Li x La y TiO3, 0 <x<2, 0<y<3), Li2O, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-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.

[0149] The solid electrolyte may further include, for example, a halide-based solid electrolyte. The 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.

[0150] 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.

[0151] The above solid electrolyte is in particle form and has an average particle diameter (D 50) may be 5.0 μm or less, for example, 0.1 μm to 5.0 μm, 0.5 μm to 5.0 μm, 0.5 μm to 4.0 μm, 0.5 μm to 3.0 μm, 0.5 μm to 2.0 μm, or 0.5 μm to 1.0 μm. Such a solid electrolyte can effectively penetrate between positive electrode active materials, and has excellent contact with the positive electrode active material and connectivity between solid electrolyte particles.

[0152] With respect to the total 100 wt% of the positive electrode active material layer, the solid electrolyte may be included in an amount of 0.1 wt% to 35 wt%, for example, 1 wt% to 35 wt%, 5 wt% to 30 wt%, 8 wt% to 25 wt%, or 10 wt% to 20 wt%. In addition, with respect to the total weight of the positive electrode active material and the solid electrolyte in the positive electrode active material layer, 65 wt% to 99 wt% of the positive electrode active material and 1 wt% to 35 wt% of the solid electrolyte may be included, for example, 80 wt% to 90 wt% of the positive electrode active material and 10 wt% to 20 wt% of the solid electrolyte may be included. When the solid electrolyte is included in the positive electrode in such an amount, the efficiency and life characteristics of the all-solid-state battery can be improved without reducing the capacity.

[0153] cathode

[0154] According to one embodiment, a negative electrode includes 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. Such a negative electrode may be referred to as a precipitation-type negative electrode. A 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 serves as a negative electrode active material.

[0155] cathode coating layer

[0156] The cathode coating layer may also be referred to as a lithium electrodeposition induction layer or a cathode catalyst layer. The cathode coating layer is characterized by comprising a compound in which a lithiophilic metal is supported on a carbon material, which is distinct from a compound in which a lithiophilic metal and a carbon material are simply mixed.

[0157] The lithiophilic metal may include, for example, Al, Ag, Au, Bi, Cu, Ge, In, Mg, Ni, Pd, Pt, Si, Sn, Zn, or a combination thereof, and may be composed of one of these or an alloy of two or more thereof. The average particle size (D) of the lithiophilic metal 50 ) may be about 900 nm or less, and may be, for example, 5 nm to 900 nm, 5 nm to 500 nm, 10 nm to 200 nm, 10 nm to 100 nm, or 20 nm to 80 nm. When the average particle diameter of the lithium-philic metal satisfies the above range, the uniformity of the particle size increases and it is appropriately dispersed in the negative electrode coating layer, thereby effectively inducing precipitation of the lithium metal.

[0158] The carbon material of the cathode coating layer may be, for example, an amorphous carbon material, and the amorphous carbon material may include, for example, carbon black, activated carbon, acetylene black, Denka black, Ketjen black, furnace black, or a combination thereof. An example of carbon black is Super P (Timcal).

[0159] 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.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] 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, selectively heat-treating them, then supporting the lithium-philic metal and heat-treating them.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] The binder of the cathode coating layer may include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0171] 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.

[0172] 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.

[0173] When using an aqueous 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.

[0174] 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.

[0175] 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.

[0176] negative current collector

[0177] 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.

[0178] lithium metal layer

[0179] 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 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 collector, a lithium metal layer positioned on the negative electrode 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.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] etc

[0184] 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.

[0185] solid electrolyte layer

[0186] The solid electrolyte layer (300) may include a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, etc. Details on this are omitted as they are the same as those described in the anode section.

[0187] 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 the average particle size of the solid electrolyte (200). 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 size (D) of the solid electrolyte 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.

[0188] 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.

[0189] 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.

[0190] The thickness of the solid electrolyte layer (300) may be, for example, 10 μm to 300 μm.

[0191] The solid electrolyte layer may further include an alkali metal salt, and / or an ionic liquid, and / or a conductive polymer.

[0192] 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.

[0193] 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.

[0194] 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.

[0195] 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.

[0196] 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.

[0197] 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.

[0198] 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.

[0199] 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.

[0200] 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-sized 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.

[0201] 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.

[0202] Example 1 (supported carbon, integral LiBO2BL coating)

[0203] 1. Manufacturing of the first nickel-based composite hydroxide

[0204] 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.

[0205] [Step 1: 2.5 kW / ㎥, NH4OH 0.40 M, pH 10.5~11.5, reaction time 6 hours]

[0206] 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.

[0207] [Step 2: 2.0 kW / ㎥, NH4OH 0.45 M, pH 10.5~11.5, reaction time 18 hours]

[0208] 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.

[0209] [Step 3: 1.5 kW / ㎥, NH4OH 0.45 M, pH 10.5~11.5, reaction time 14 hours]

[0210] While maintaining the reaction temperature at 50°C, the addition rate of the metal raw material mixture solution and the complexing agent, as well as the concentration of the complexing agent, were the same as in Step 2. The reaction was continued for 14 hours, with NaOH added to maintain the pH. At this time, the stirring power was lowered to 1.5 kW / ㎥, which was lower than in Step 2, to proceed with the reaction.

[0211] [Post-processing]

[0212] After washing the above result, it was dried with hot air at about 150℃ for 24 hours to obtain the first nickel-based composite hydroxide (Ni 0.945 Co0.04 Al 0.015 (OH)2) was obtained.

[0213] 2. Manufacturing of a second lithium nickel-based composite oxide

[0214] 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) is 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) are dissolved in distilled water as a solvent in a molar ratio of 94:4:1:1 to prepare a mixed solution. The subsequent synthesis is the same as the production of the first nickel-based composite hydroxide.

[0215] Nickel-based composite hydroxide and lithium hydroxide prepared by the above method 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 crushed to about 3 ㎛ to obtain a single particle of lithium nickel-based composite oxide (LiNi 0.94 Co 0.04 Al 0.1 Mn 0.01 A second positive electrode active material (O2) was obtained.

[0216] 3. Preparation of mixed cathode active materials

[0217] A first nickel-based composite hydroxide and a second lithium nickel-based composite oxide are mixed in a weight ratio of 7:3, LiOH is mixed so that the molar ratio of Li / (Ni+Co+Al)=0.98 is satisfied in the relationship between the first nickel-based composite hydroxide and LiOH, boric acid is mixed so that boron is 0.125 molar parts for 100 molar parts of the total metal excluding Li in the mixture, and the mixture is put into a kiln, and the mixture is heated to 700°C for 8 hours in an oxygen atmosphere and heat-treated for 7 hours to obtain a mixed cathode active material.

[0218] In the obtained final 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 is a secondary particle form with a radial structure, the surface and internal grain boundaries of which are coated with boron, and the average particle diameter (D 50 ) is confirmed to be approximately 13.8 ㎛. The second positive electrode active material is a second lithium nickel composite oxide (LiNi 0.94 Co 0.04 Al 0.1 Mn 0.01 O2) and is in the form of single particles, the surface of which is coated with a boron-containing compound, and the average particle diameter (D 50 ) is confirmed to be approximately 3 ㎛.

[0219] 4. Positive electrode active material buffer layer coating

[0220] A boron-containing buffer layer is formed on the surface by the boric acid added during the manufacturing of the mixed cathode active material, so a separate buffer layer is not coated.

[0221] 5. Manufacturing of the anode

[0222] A positive electrode composition is prepared by mixing 84.9 wt% of a positive electrode active material, 13.61 wt% of a manufactured solid electrolyte, 1 wt% of a PVdF binder, 0.35 wt% of a carbon nanotube conductive material, and 0.14 wt% of hydrogenated nitrile butadiene rubber (HNBR) as a dispersant in an isobutyryl isobutyrate (IBIB) solvent.

[0223] The manufactured positive electrode composition is applied to the positive electrode current collector, dried, and then rolled (hydrostatic pressing (WIP), 500 Mpa, 85°C, 30 min) to prepare the positive electrode.

[0224] 6. Manufacturing of the cathode

[0225] 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. Figure 5 is a TEM image of the Ag-C support compound manufactured in Example 1, and it can be seen that silver is uniformly dispersed in the carbon material.

[0226] 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.

[0227] 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.

[0228] 7. Manufacturing of all-solid-state secondary batteries

[0229] Argyrodite-type solid electrolyte of Li6PS5Cl (D 50 =3㎛) was added to an IBIB solvent containing an acrylic binder and mixed to prepare a composition for forming a solid electrolyte layer. The composition includes 98.5 wt% of the solid electrolyte and 1.5 wt% of the binder. The composition was cast on a release film and dried at room temperature to prepare a solid electrolyte layer.

[0230] The prepared positive electrode, negative electrode, and solid electrolyte layer are cut, a solid electrolyte layer is laminated on the positive electrode, and then the negative electrode is laminated on top of that. This is 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.

[0231] Comparative Example 1 (Carbon support, wet Li2O·ZrO2BL coating)

[0232] A positive electrode active material and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1, except that the positive electrode active material buffer layer was coated in the following manner.

[0233] 4. Positive active material buffer layer coating (Comparative Example 1)

[0234] In Example 1, the mixed positive electrode active material was manufactured without adding boric acid. The method for forming a buffer layer on the manufactured positive electrode active material is a wet coating 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 amount of zirconium was designed to be 0.25 molar parts per 100 molar parts of metals excluding lithium in the positive electrode active material. The solvent was evaporated in a vacuum at 50°C while irradiating ultrasonic waves to prevent agglomeration of the positive electrode active material particles. The resultant was filtered and heat-treated at 350°C for 1 hour in an air atmosphere to obtain a final positive electrode active material coated with a buffer layer containing Li2CO3, LiOH, and ZrO2.

[0235] Comparative Example 2 (Mixed Carbon, Integral LiBO2BL Coating)

[0236] A positive electrode active material and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1, except that the negative electrode was manufactured in the following manner.

[0237] 7. Manufacturing of the cathode (Comparative Example 2)

[0238] Carbon black with a primary particle size of about 30 nm and an average particle size (D 50 ) is prepared by mixing silver (Ag) having a diameter of approximately 60 nm in a weight ratio of 3:1, and adding 0.25 g of the Ag / C mixture to 2 g of an NMP solution containing 7 wt% of polyvinylidene fluoride binder and mixing to prepare a negative electrode coating layer composition. This is applied onto a negative electrode current collector and then dried to prepare a deposition-type negative electrode in which a negative electrode coating layer is formed on the current collector.

[0239] Fig. 6 is a TEM image of the Ag / C mixture manufactured in Comparative Example 2. Unlike Fig. 5, it can be seen that silver is clumped in some areas of the carbon material.

[0240] Comparative Example 3 (Mixed Carbon, Wet Li2O·ZrO2BL Coating)

[0241] A positive electrode active material and an all-solid-state secondary battery were manufactured in substantially the same manner as in Comparative Example 1, except that the negative electrode was manufactured as in Comparative Example 2.

[0242] To aid understanding, the positive electrode active material and negative electrode design of Example 1 and Comparative Examples 1 to 3 are briefly shown in Table 1 below.

[0243] Cathode coating layer Cathode active material coating Example 1 Ag-C support compound integrated LiBO2 Comparative example 1 Wet Li2O·ZrO2 Comparative example 2 Ag / C mixture integrated LiBO2 Comparative example 3 Wet Li2O·ZrO2

[0244]

[0245] Experimental Example 1: Analysis of the positive electrode active material of Example 1

[0246] Figure 7 is an SEM photograph of a cross-section of the first nickel-based composite hydroxide of Example 1. It can be seen that there is a region in the center where pores are formed, and the surface area surrounding this has primary particles radially oriented toward the surface of the secondary particles.

[0247] Figure 8 shows the mass spectrum results of ToF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) analysis of the positive electrode active material manufactured in Example 1. The mass analysis results confirmed that the BO2 form was predominant. From these results, it is understood that the boron-containing compound coated on the surface of the positive electrode active material is mainly composed of LiBO2.

[0248] Hereinafter, the grain boundary boron coating portion of the first positive electrode active material of Example 1 is analyzed. The first positive electrode active material and the second positive electrode active material were prepared by separating them from the final positive electrode active material manufactured in Example 1. The separation of the active materials was performed using a turbo classifier (Nisshin Engineering Inc.) and nitrogen as a transport gas. The boron content of each of the separated first positive electrode active material and the second positive electrode active material was measured by ICP (Inductively Coupled Plasma) emission spectrometry. Thereafter, 10 g each of the first positive electrode active material and the second positive electrode active material was added to 100 g of distilled water, stirred for 30 minutes, and filtered. Through this washing process, all boron present on the surface or near-surface region of the positive electrode active material is removed. After drying the recovered positive electrode active material at 130℃ for 24 hours, ICP emission spectroscopy is performed again to measure the amount of boron remaining in the positive electrode active material, which is expressed as the amount of boron existing within the positive electrode active material, i.e., at the grain boundaries. This refers to the amount of boron in the grain boundary boron coating. In addition, the amount of boron removed through the washing process, which is calculated by subtracting the amount of boron before washing from the amount of boron after washing, is expressed as the amount of boron existing on the surface of the positive electrode active material.

[0249] In Table 1 below, the unit ppm is 10 -4 It means weight% and refers to the content of boron for 100 weight% of each positive electrode active material.

[0250] Boron before washing (ppm)Internal grain boundary boron (ppm)Surface boron (ppm)Example 1 First positive electrode active material 54030 (grain boundary boron coating part) 510 (first boron coating layer)Example 1 Second positive electrode active material 3500350 (second boron coating layer)

[0251] Referring to Table 2, it can be seen that the second positive electrode active material in the form of a single particle of Example 1 did not have a boron coating inside the particle, whereas the first positive electrode active material of Example 1 had boron coating not only on the surface but also on the internal grain boundaries. The boron coating content on the surface of the first positive electrode active material is about 0.0510 wt% with respect to 100 wt% of the first positive electrode active material, and the boron coating content on the internal grain boundaries is about 0.003 wt% with respect to 100 wt% of the first positive electrode active material, and the weight ratio between these is about 94:6.

[0252] Hereinafter, the boron-doped layer of the first positive electrode active material of Example 1 will be examined. Fig. 9 is a TEM image of the primary particles exposed on the surface of the secondary particles of the first positive electrode active material, i.e., the primary particles at the outermost edge of the secondary particles. Electron energy loss spectroscopy (EELS) was performed on a total of 10 points from point 1 to point 10 indicated in Fig. 9, and the results are shown in Fig. 10. In Fig. 10, for example, ① represents the analysis graph at point 1, and ② represents the analysis graph at point 2. Referring to the lower graph of Fig. 10, since cobalt was detected from point 4, the starting point of the surface of the positive electrode active material can be said to be approximately point 4. Referring to the upper graph of Fig. 10, boron was detected at points 3 to 8, where the point 3 position is understood to be the first boron coating layer existing on the surface of the positive electrode active material, and the boron detected at points 4 to 8 is understood to be a very thin boron doping layer existing inside the positive electrode active material.

[0253] Evaluation Example 1: Evaluation of the initial charge / discharge capacity of an all-solid-state secondary battery.

[0254] The all-solid-state secondary batteries manufactured in Example 1 and Comparative Examples 1 to 3 were charged at 45°C with a constant current of 0.1 C to 4.25 V and a constant voltage of 0.05 C to measure the initial charge capacity, and discharged at 0.1 C to 2.5 V to measure the initial discharge capacity. The ratio of the initial discharge capacity to the initial charge capacity was calculated as efficiency and is shown in Table 3 and Figure 11 below.

[0255] In addition, the voltage according to the charge / discharge capacity of Example 1 and Comparative Example 1 was compared and shown in Fig. 12, and the voltage according to the charge / discharge capacity of Example 1 and Comparative Example 2 was compared and shown in Fig. 13.

[0256] Charge capacity (mAh / g)Discharge capacity (mAh / g)Efficiency (%)Example 1242.0202.183.5%Comparative example 1231.6193.783.7%Comparative example 2241.0199.382.7%Comparative example 3237.1195.282.3%

[0257] Referring to Table 3 and Fig. 11, it can be seen that Example 1 and Comparative Examples 2, which applied an integrated positive electrode active material in which a boron-containing buffer layer was formed during the synthesis of the positive electrode active material without a separate buffer layer coating process, showed significantly improved initial charge capacity and initial discharge capacity compared to Comparative Examples 1 and 3, which applied a positive electrode active material in which a zirconium buffer layer was wet-coated using an expensive metal alkoxide raw material in an organic solvent, which is a conventional technology. In addition, it can be seen that Example 1, which applied an Ag-C supported compound negative electrode coating layer, showed better performance in terms of initial charge / discharge capacity and efficiency compared to Comparative Example 2, which applied an Ag / C mixture negative electrode coating layer.

[0258] Referring to Fig. 12, among the cases where an Ag-C support compound was applied to the cathode coating layer, it can be seen that in the case of Example 1, which used a cathode active material in which a zirconium buffer layer was formed by a wet method, the resistance during charge and discharge was greatly improved, thereby improving the capacity.

[0259] Referring to Fig. 13, among the cases in which a cathode active material forming an integral boron buffer layer was applied, it can be seen that the resistance at the end of discharge of the battery of Example 1 in which an Ag-C support compound was applied to the cathode coating layer was further improved compared to Comparative Example 2 in which an Ag / C mixture was applied to the cathode coating layer.

[0260] Evaluation Example 2: Evaluation of Rate Characteristics of All-Solid-State Secondary Battery

[0261] The all-solid-state secondary batteries manufactured in Example 1 and Comparative Examples 1 to 3 were charged to 4.25 V at a constant current of 0.1 C at 45°C, charged to a constant voltage of 0.05 C, and then discharged to a final voltage of 2.5 V at a constant current. The discharge capacities when the discharge C-rate was set to 0.1 C, 1 / 3 C, and 1 C are shown in Table 4. In addition, the ratio of the 1 / 3 C discharge capacity to the 0.1 C discharge capacity and the ratio of the 1 C discharge capacity to the 0.1 C discharge capacity are shown in Fig. 14.

[0262] 0.1C discharge (mAh / g)0.33C discharge (mAh / g)1C discharge (mAh / g)Example 1202188173Comparative example 1194177162Comparative example 2199184169Comparative example 3195178160

[0263] According to Table 4, it can be seen that Example 1 and Comparative Example 2, which applied a cathode active material forming an integral boron buffer layer, have higher capacities at high rates than Comparative Examples 1 and 3, which applied a cathode active material forming a zirconium buffer layer by a wet method. Among them, it can be seen that Example 1, which applied an Ag-C support compound to the cathode coating layer, has an even higher capacity at high rates.

[0264] Referring to Figure 14, it can be seen that the case of Example 1, which used a cathode active material having an integral boron buffer layer formed thereon and a Ag-C support compound cathode coating layer, has the best rate characteristics indicating the output characteristics of the battery.

[0265] Evaluation Example 3: Evaluation of the Lifetime Characteristics of All-Solid-State Secondary Batteries

[0266] For the all-solid-state secondary batteries manufactured in Example 1 and Comparative Examples 1 to 3, initial charging and discharging were performed as in Evaluation Example 1, and then charging at 0.33 C and discharging at 0.33 C in a voltage range of 2.5 V to 4.25 V at 45°C were repeated 100 times, and the ratio of the discharge capacity at 100 cycles to the initial discharge capacity was shown in Figure 15.

[0267] Referring to Figure 15, it can be seen that Example 1 and Comparative Example 2, which applied a positive electrode active material forming an integral boron buffer layer, are advantageous in terms of lifespan, and among them, Example 1, which applied an Ag-C support compound to the negative electrode coating layer rather than an Ag / C mixture, can secure higher lifespan characteristics.

[0268] 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.

[0269] [Explanation of symbols]

[0270] 11: Secondary particle 12: Inside the secondary particle

[0271] 13: Primary particle 14: External of secondary particle

[0272] 100': All-solid-state battery 200: Anode

[0273] 201: Cathode current collector 203: Cathode active material layer

[0274] 300: Solid electrolyte layer 400: Cathode

[0275] 401: Negative current collector 403: Negative active material layer

[0276] 400': Precipitation type cathode 404: Lithium metal layer

[0277] 405: Cathode coating layer 500: Elastic layer

Claims

1. An all-solid-state secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer positioned between the positive electrode and the negative electrode, The above positive electrode includes a positive electrode current collector and a positive electrode active material layer positioned on the positive electrode current collector and containing a positive electrode active material, The above positive electrode active material is a first positive electrode active material containing a lithium nickel-based composite oxide and formed by agglomeration of a plurality of primary particles, and at least a portion of the primary particles are in the form of secondary particles having a radial arrangement structure, and It includes a second positive electrode active material in the form of a single particle containing a lithium nickel-based composite oxide, The first cathode active material includes a first boron coating layer located on the surface of the secondary particle and a grain boundary boron coating portion located on the surface of the primary particles inside the secondary particle. The second positive electrode active material includes a second boron coating layer located on the surface of the single particle, An all-solid-state secondary battery, wherein the 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.

2. In paragraph 1, An all-solid-state secondary battery, wherein the first boron coating layer, the grain boundary boron coating portion, and the second boron coating layer each include boron oxide, lithium boron oxide, or a combination thereof.

3. In paragraph 1, An all-solid-state secondary battery in which the content of boron is 0.01 wt% to 0.5 wt% based on 100 wt% of the total metal excluding lithium in the entire positive electrode active material.

4. In paragraph 1, An all-solid-state secondary battery, wherein the weight of boron in the first boron coating layer in the first positive electrode active material is at least four times the weight of boron in the grain boundary boron coating portion.

5. In paragraph 1, An all-solid-state secondary battery, wherein the ratio of the weight of boron in the first boron coating layer and the weight of boron in the grain boundary boron coating portion in the first positive electrode active material is 70:30 to 98:

2.

6. In paragraph 1, An all-solid-state secondary battery in which, with respect to 100 wt% of the first positive electrode active material, the boron content in the first boron coating layer is 0.02 wt% to 0.5 wt%, and the boron content in the grain boundary boron coating portion is 0.001 wt% to 0.05 wt%.

7. In paragraph 1, An all-solid-state secondary battery, wherein the first cathode active material further includes a boron-doped layer located inside the primary particle exposed on the surface of the secondary particle.

8. In paragraph 7, An all-solid-state secondary battery, wherein the boron doping layer is located within a depth range of 10 nm from the outer surface of the primary particle exposed to the surface of the secondary particle.

9. In paragraph 1, 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 are the same or different and are each independently represented by the chemical formula 1: An all-solid-state secondary battery: [Chemical Formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In the above chemical formula 1, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, 0≤z1≤0.7, 0.9≤x1+y1+z1≤1.1, and 0≤b1≤0.1, and M 1 and M 2 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, and X is one or more elements selected from F, P, and S.

10. In paragraph 1, In the first positive electrode active material, at least some of the primary particles have a plate shape, An all-solid-state secondary battery wherein the average length of the plate-shaped primary particles is 150 nm to 500 nm, the average thickness is 100 nm to 200 nm, and the ratio of the average thickness to the average length is 1:2 to 1:

5.

11. In paragraph 1, The average particle diameter (D) of the first positive electrode active material 50 ) is 9 ㎛ to 25 ㎛, The average particle diameter (D) of the second positive electrode active material 50 ) is an all-solid-state secondary battery having a particle size of 0.5 ㎛ to 8 ㎛.

12. In paragraph 1, The above positive electrode active material layer further includes a sulfide-based solid electrolyte, An all-solid-state secondary battery, wherein the positive electrode active material is included in an amount of 65 to 99 wt% and the sulfide-based solid electrolyte is included in an amount of 1 to 35 wt%, based on a total of 100 wt% of the positive electrode active material and the sulfide-based solid electrolyte in the positive electrode active material layer.

13. In paragraph 1, In the 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 all-solid-state secondary battery that is an amorphous carbon material.

14. In paragraph 1, 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.

15. In paragraph 1, An all-solid-state secondary battery in which the lithium-philic metal and the carbon material in the cathode coating layer are chemically bonded via sulfur.

16. In paragraph 15, An all-solid-state secondary battery, wherein the cathode coating layer has a peak corresponding to the binding energy of a lithium-philic metal and sulfur in a spectrum measured by X-ray photoelectron spectroscopy.

17. In paragraph 15, 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.

18. In paragraph 1, An all-solid-state secondary battery wherein the thickness of the cathode coating layer is 100 nm to 40 ㎛.

19. In paragraph 1, An all-solid-state secondary battery further comprising a lithium metal layer formed by charging between the negative electrode current collector and the negative electrode coating layer.

20. In paragraph 19, 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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