Positive electrode and all-solid-state rechargeable batteries

Abstract

The present invention relates to a positive electrode and all-solid-state rechargeable batteries comprising same. The positive electrode includes a positive electrode current collector and a first positive electrode active material layer and a second positive electrode active material layer on the positive electrode current collector. The first positive electrode active material layer includes: a positive electrode active material that includes core particles containing a lithium nickel-based composite oxide and a boron coating layer on the core particles; and a first solid electrolyte containing an argyrodite-type sulfide including Li, P, S, and a halogen element. The second positive electrode active material layer includes: a positive electrode active material that includes core particles containing a lithium nickel-based composite oxide and a boron coating layer on the core particles; and a second solid electrolyte containing an argyrodite-type sulfide including Li, P, S, and a halogen element. The first solid electrolyte and the second solid electrolyte differ in the molar ratio of at least one among Li, P, S, and the halogen element.

Description

Anode and all-solid-state secondary batteries

[0001] This relates to positive electrodes and all-solid-state secondary batteries.

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

[0003] Recently, active development has been underway for all-solid-state secondary batteries using solid electrolytes instead of liquid electrolytes to address issues such as fire safety. However, solid electrolytes have problems such as lower ionic conductivity compared to liquid electrolytes, resistance occurring at the interface with solid particles like the positive electrode active material within the battery, and degraded ionic conductivity performance due to the formation of a depletion layer caused by the junction of solids. Consequently, there is a need for research on methods to improve the overall performance of all-solid-state secondary batteries using such solid electrolytes, including capacity, charge / discharge efficiency, resistance characteristics, and lifespan characteristics.

[0004] We provide a positive electrode and an all-solid-state secondary battery that have high initial charge / discharge capacity and efficiency, and excellent rate characteristics and lifespan characteristics.

[0005] In one embodiment, the positive electrode comprises a positive electrode current collector, and a first positive electrode active material layer and a second positive electrode active material layer located on the positive electrode current collector, wherein the first positive electrode active material layer comprises a positive electrode active material comprising a core particle containing a lithium nickel-based composite oxide and a boron coating layer located on the core particle, and a first solid electrolyte containing an azirodite-type sulfide containing Li, P, S and a halogen element, and the second positive electrode active material layer comprises a positive electrode active material comprising a core particle containing a lithium nickel-based composite oxide and a boron coating layer located on the core particle, and a second solid electrolyte containing an azirodite-type sulfide containing Li, P, S and a halogen element, wherein the molar ratio of at least one of Li, P, S and a halogen element in the first solid electrolyte and the second solid electrolyte is different from each other.

[0006] In another embodiment, an all-solid-state secondary battery is provided, comprising the anode, the cathode, and a solid electrolyte layer located between the anode and the cathode.

[0007] A solid-state secondary battery according to one embodiment achieves high capacity and high energy density, while having high initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency, and excellent rate characteristics and life characteristics.

[0008] Figure 1 is a schematic diagram showing the shape of a plate-shaped primary particle.

[0009] Figure 2 is a diagram illustrating the definition of radial in secondary particles.

[0010] Figure 3 is a schematic diagram showing the cross-sectional structure of a secondary particle.

[0011] Figures 4 and 5 are schematic cross-sectional views of an all-solid-state secondary battery.

[0012] FIG. 6 is a particle size distribution curve for the first solid electrolyte and the second solid electrolyte of the seventh to ninth embodiments, and the solid electrolyte of the reference example.

[0013] FIG. 7 is a particle size distribution curve for the first solid electrolyte and the second solid electrolyte of the tenth to twelfth embodiments, and the solid electrolyte of the reference example.

[0014] FIG. 8 is a particle size distribution curve for the first solid electrolyte and the second solid electrolyte of the thirteenth to fifteenth embodiments, and the solid electrolyte of the reference example.

[0015] Specific embodiments are described below in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0016] The terms used herein are for describing exemplary embodiments only and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0017] Here, "combinations of these" refers to mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, etc.

[0018] The terms "include," "equip," or "have" used herein are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0019] In the drawings, thicknesses have been enlarged to clearly represent various layers and regions, and the same reference numerals have been used for similar parts throughout the specification. When a part such as a layer, film, region, or plate is described as being "on" or "on" another part, this includes not only cases where it is "immediately on" another part, but also cases where there is another part in between. Conversely, when a part is described as being "immediately on" another part, it means that there is no other part in between.

[0020] In addition, the term “layer” here includes not only shapes formed on the entire surface when viewed in a plan view, but also shapes formed on some surfaces.

[0021] The average particle size can be measured by methods widely known to those skilled in the art, for example, by measuring with a particle size analyzer, or by using transmission electron microscope or scanning electron microscope images. Alternatively, the average particle size value can be obtained by measuring using dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this. Unless otherwise defined, the average particle size is the diameter (D) of the particle at which the cumulative volume in the particle size distribution is 50 volume%. 50 It may mean ). In addition, unless otherwise defined, the average particle size is obtained by measuring the size (diameter or length of the major axis) of approximately 20 randomly selected particles from scanning electron microscope images to obtain a particle size distribution, and the diameter (D) of the particle with a cumulative volume of 50% in the said particle size distribution. 50 It may be that ) was taken as the average particle size.

[0022] Here, “or” is not interpreted in an exclusive sense; for example, “A or B” is interpreted to include A, B, A+B, etc.

[0023] The term “metal” is interpreted as a concept that includes ordinary metals, transition metals, and metalloids (semimetals).

[0024] [First Implementation Example]

[0025] anode

[0026] In one embodiment, a positive electrode is provided comprising a positive current collector, and a first positive active material layer and a second positive active material layer located on the positive current collector. The first positive active material layer comprises a positive active material comprising a core particle containing a lithium nickel-based composite oxide and a boron coating layer located on the core particle, and a first solid electrolyte containing an azirodite-type sulfide containing Li, P, S and a halogen element. The second positive active material layer comprises a positive active material comprising a core particle containing a lithium nickel-based composite oxide and a boron coating layer located on the core particle, and a second solid electrolyte containing an azirodite-type sulfide containing Li, P, S and a halogen element. Here, the first solid electrolyte and the second solid electrolyte have different compositions from each other, specifically, the molar ratio of at least one of Li, P, S and a halogen element is different from each other.

[0027] The above-mentioned anode may be described as a cathode for a lithium secondary battery or a cathode for an all-solid-state secondary battery. Additionally, the above-mentioned anode may be described as a multilayer cathode or a double-layer cathode comprising two or more layers of cathode active material.

[0028] The anode may, for example, include an anode current collector, a first anode active material layer located on the anode current collector, and a second anode active material layer located on the first anode active material layer. That is, the anode may be formed such that the anode current collector, the first anode active material layer, and the second anode active material layer are formed sequentially. As another example, the anode may include an anode current collector, a second anode active material layer located on the anode current collector, and a first anode active material layer located on the second anode active material layer, in which case the anode may be stacked in the order of the anode current collector, the second anode active material layer, and the first anode active material layer.

[0029] The first positive active material layer and the second positive active material layer may be in contact with each other, or another layer may exist between the first positive active material layer and the second positive active material layer. The positive active material layer close to the current collector may be in contact with the current collector, and the positive active material layer far from the positive current collector may be in contact with a separator or a solid electrolyte layer.

[0030] A multilayer cathode according to one embodiment is advantageous for realizing high capacity and high energy density by increasing the loading level and thickness of the cathode active material layer, and by appropriately selecting and applying different types of solid electrolytes to the cathode active material layer close to the current collector and the cathode active material layer far from the current collector, the capacity, energy density, charge / discharge efficiency, rate characteristics, and lifespan characteristics can be improved.

[0031] The thickness of each of the first positive active material layer and the second positive active material layer may be 15 μm to 100 μm, for example, 20 μm to 80 μm, 25 μm to 60 μm, or 30 μm to 50 μm. The thickness of the first positive active material layer and the second positive active material layer can be measured using a scanning electron microscope (SEM) on the cross-section of the positive electrode.

[0032] The ratio of the thickness of the first positive active material layer to the thickness of the second positive active material layer may be 20:80 to 80:20, for example, 30:70 to 70:30, 40:60 to 60:40, or 45:55 to 55:45.

[0033] The loading level of each of the first positive electrode active material layer and the second positive electrode active material layer is 10 mg / cm² 2 to 80 mg / cm² 2 It could be, for example, 10 mg / cm² 2 to 60 mg / cm² 2 , 15 mg / cm 2 to 40 mg / cm² 2 It could be.

[0034] The density of each of the first positive active material layer and the second positive active material layer may be 3.0 g / cc to 3.9 g / cc, for example, 3.2 g / cc to 3.8 g / cc, or 3.4 g / cc to 3.7 g / cc. In addition, the density of the entire positive active material layer including the first positive active material layer and the second positive active material layer may be 3.0 g / cc to 3.9 g / cc, for example, 3.2 g / cc to 3.8 g / cc, or 3.4 g / cc to 3.7 g / cc. When the first positive active material layer and the second positive active material layer, or the entire positive active material layer, satisfy the above density ranges, it is advantageous for realizing high capacity and high energy density. The density of the first positive active material layer and the second positive active material layer, and the density of the entire positive active material layer, refers to the ratio of weight to volume of each positive active material layer in the rolled positive electrode, and the cross-sectional area, thickness, and weight of each positive active material layer excluding the positive current collector can be measured, the volume can be calculated by multiplying the cross-sectional area and thickness, and the weight can be measured by dividing the volume.

[0035] The first solid electrolyte and the second solid electrolyte are each in the form of particles, and their average particle size (D 50The values ​​may be identical or different from each other and may each independently be 0.1 μm to 5 μm, for example, 0.1 μm to 3 μm, 0.1 μm to 2 μm, 0.1 μm to 1.9 μm, 0.1 μm to 1 μm, or 0.5 μm to 0.9 μm. When the particle sizes of the first solid electrolyte and the second solid electrolyte satisfy the above ranges, high capacity and high energy density can be achieved while increasing lithium ion conductivity within the anode. The average particle size (D) of the solid electrolyte 50 ) may be measured using a particle size analyzer utilizing laser diffraction.

[0036] The content of the first solid electrolyte may be 1% to 35% by weight with respect to 100% by weight of the first positive electrode active material layer, for example, 2% to 30% by weight, 5% to 25% by weight, 10% to 20% by weight, or 10% to 15% by weight. Additionally, the content of the second solid electrolyte may be 1% to 35% by weight with respect to 100% by weight of the second positive electrode active material layer, for example, 2% to 30% by weight, 5% to 25% by weight, 10% to 20% by weight, or 10% to 15% by weight. When the content of the first solid electrolyte and the second solid electrolyte satisfies the above ranges, high capacity and high energy density can be achieved while increasing lithium ion conductivity within the positive electrode.

[0037] The weight ratio of the first solid electrolyte and the second solid electrolyte in the entire anode may be 1:99 to 99:1, and for example, 10:90 to 90:10, 20:80 to 80:20, 30:70 to 70:30, 40:60 to 60:40, 50:50 to 99:1, 60:40 to 95:5, or 70:30 to 90:10. By appropriately adjusting the weight ratio of two types of solid electrolytes with different compositions within the anode, the capacity, efficiency, and lifespan characteristics of the battery can be improved.

[0038] A positive electrode according to one embodiment may be manufactured by (i) mixing the positive electrode active material, the first solid electrolyte, and optionally a binder and / or a conductive material to prepare a first positive electrode active material layer composition, (ii) mixing the positive electrode active material, the second solid electrolyte, and optionally a binder and / or a conductive material to prepare a second positive electrode active material layer composition, (iii) applying the first positive electrode active material layer composition onto a positive electrode current collector and drying it to form a first positive electrode active material layer, (iv) applying the second positive electrode active material layer composition onto the first positive electrode active material layer and drying it to form a second positive electrode active material layer, and (v) rolling (e.g., hydrostatic pressing).

[0039]

[0040] First solid electrolyte and second solid electrolyte with different compositions

[0041] In one embodiment, the composition of the first solid electrolyte included in the first positive electrode active material layer and the second solid electrolyte included in the second positive electrode active material layer are different from each other. Specifically, the first solid electrolyte and the second solid electrolyte have different molar ratios of at least one of Li, P, S, and halogen elements. The molar ratio refers to the ratio of the number of moles between constituent elements in the chemical formula of each solid electrolyte. The first solid electrolyte and the second solid electrolyte may also have different contents of at least one of Li, P, S, and halogen elements, where the content may refer to the molar percentage of a specific element relative to 100 mol% of each solid electrolyte. For example, the first solid electrolyte and the second solid electrolyte may have the same type of element but different compositions, for instance, the molar ratios of the elements may be different or the contents of a specific element may be different.

[0042] According to one embodiment, by applying a sulfide-based solid electrolyte with different compositions to a positive active material layer close to the positive current collector and a positive active material layer far from the positive current collector, the electron-to-ion conductivity ratio and density of the entire positive electrode can be improved, and the electrochemical performance of the battery, such as capacity, rate characteristics, and life characteristics, can be further enhanced. The physical properties of an azirodite-type sulfide-based solid electrolyte can vary depending on minute changes in composition, and by applying two or more types of sulfide-based solid electrolytes with different physical properties to each side of a positive electrode multilayer, a positive electrode with improved performance can be provided.

[0043] For example, the molar ratio of halogen elements in the second solid electrolyte may be higher than the molar ratio of halogen elements in the first solid electrolyte. For example, the molar content of halogen elements in the second solid electrolyte relative to 100 mol% of the second solid electrolyte may be higher than the molar content of halogen elements in the first sulfide-based solid electrolyte relative to 100 mol% of the first solid electrolyte. In this case, the second solid electrolyte may have softer (or softer) characteristics compared to the first solid electrolyte. The first solid electrolyte and the second solid electrolyte may have similar ionic conductivity but different degrees of hardness, and by applying these two types of solid electrolytes to the first and second positive active material layers, respectively, the ionic conductivity of the positive electrode can be increased, energy density can be increased, and capacity characteristics, rate characteristics, and lifespan characteristics can be improved simultaneously.

[0044] For example, the molar ratio of the halogen element in the second solid electrolyte may be 1.1 to 2.5 times the molar ratio of the halogen element in the first solid electrolyte, and for example, 1.2 to 2 times. In this case, the ionic conductivity of the anode can be increased while increasing the energy density, and the capacity characteristics, rate characteristics, and lifespan characteristics can be improved simultaneously. At this time, the weight ratio of the first solid electrolyte and the second solid electrolyte in the entire anode may be 60:40 to 99:1, for example, 70:30 to 99:1, 80:20 to 99:1, or 85:15 to 95:5.

[0045] For example, the molar ratio of halogen elements in the second solid electrolyte may be higher than the molar ratio of halogen elements in the first solid electrolyte, and the molar ratio of sulfur in the second solid electrolyte may be lower than the molar ratio of sulfur in the first solid electrolyte.

[0046] In one embodiment, the content of the halogen element in the first solid electrolyte may be 5 mol% to 10 mol% with respect to 100 mol% of the first solid electrolyte, for example, 6 mol% to 9 mol%, or 7 mol% to 8 mol%. The content of the halogen element in the second solid electrolyte may be 11 mol% to 15 mol% with respect to 100 mol% of the second solid electrolyte, for example, 11 mol% to 14 mol%, or 12 mol% to 13 mol%. When the content of each halogen element satisfies the above range, the ionic conductivity and energy density of the anode are improved, and the capacitance characteristics, rate characteristics, and lifetime characteristics can be improved simultaneously.

[0047] In one embodiment, the azirodite-type sulfide of the first solid electrolyte is represented by the following chemical formula 22, and the azirodite-type sulfide of the second solid electrolyte is represented by the following chemical formula 23, provided that the compositions may be different from each other.

[0048] [Chemical Formula 22]

[0049] (Li a2 M1 b2 M 2 c2 )(P d2 M 3 e2 )(S f2 M 4 g2 )X h2

[0050] In Chemical Formula 22, 4 ≤ a2 ≤ 8, and M 1 is Mg, Ca, Cu, Ag, or a combination thereof, 0 ≤ b2 < 0.5, and M 2 is Na, K, or a combination thereof, 0 ≤ c2 < 0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, 0 < d2 < 4, 0 ≤ e2 < 1, and M 4 is N, O, SO n , or a combination thereof, 1.5 ≤ n ≤ 5, 3 ≤ f2 ≤ 12, 0 ≤ g2 < 2, X is F, Cl, Br, I, or a combination thereof, and 0 < h2 ≤ 2.

[0051] [Chemical Formula 23]

[0052] (Li a3 M 1 b3 M 2 c3 )(P d3 M 3 e3 )(S f3 M 4 g3 )X h3

[0053] In Chemical Formula 23, 4 ≤ a3 ≤ 8, and M 1 is Mg, Ca, Cu, Ag, or a combination thereof, 0 ≤ b3 < 0.5, and M 2 is Na, K, or a combination thereof, 0 ≤ c3 < 0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, 0 < d3 < 4, 0 ≤ e3 < 1, and M 4 is N, O, SO n, or a combination thereof, 1.5≤n≤5, 3≤f3≤12, 0≤g3<2, and X is F, Cl, Br, I, or a combination thereof, and 0 <h3≤2이다.

[0054] In the above chemical formulas 22 and 23, a2≠a3, d2≠d3, f2≠f3, or h2≠h3. This means that the molar ratio of at least one of Li, P, S, and halogen elements in the first solid electrolyte and the second solid electrolyte is different from each other. In this case, the ionic conductivity of the anode can be increased while increasing the energy density, and the capacitance characteristics, rate characteristics, and lifetime characteristics can be improved simultaneously.

[0055] For example, a2≠a3, f2≠f3, and h2≠h3.

[0056] Also, (a2+b2+c2) and (a3+b3+c3) may not be equal to each other, for example, (a2+b2+c2) > (a3+b3+c3). Alternatively, a2 / (a2+b2+c2) ≠ a3 / (a3+b3+c3), b2 / (a2+b2+c2) ≠ b3 / (a3+b3+c3), or c2 / (a2+b2+c2) ≠ c3 / (a3+b3+c3).

[0057] Or d2+e2≠d3+e3 or d2 / (d2+e2)≠d3 / (d3+e3).

[0058] Alternatively, f2+g2≠f3+g3, or (f2+g2)>(f3+g3), or f2 / (f2+g2)≠f3 / (f3+g3).

[0059] or h2 ≠ h3 or h2 <h3일 수 있다.

[0060] For example, (a2+b2+c2)>(a3+b3+c3) or (f2+g2)>(f3+g3) and / or h2 <h3일 수 있다.

[0061] For example, (h2 x 1.1)≤h3≤(h2 x 2.5) can be satisfied, and for instance, (h2 x 1.2)≤h3≤(h2 x 2.0) can be satisfied.

[0062] As a specific example, the first solid electrolyte is Li6PS5X (where X is a halogen element), and the second solid electrolyte may have a molar ratio of at least one of Li, P, S and a halogen element that is different from that of the first solid electrolyte.

[0063] For example, the first solid electrolyte may be Li6PS5Cl and the second solid electrolyte may have a higher molar ratio of Cl than the first solid electrolyte. For example, the first solid electrolyte is Li6PS5Cl and the second solid electrolyte is Li 5.4 PS 4.4 Cl 1.6 , Li 5.5 PS 4.5 Cl 1.5 , Li 5.6 PS 4.6 Cl 1.4 , Li 5.7 PS 4.7 Cl 1.3 , Li 5.75 PS 4.75 Cl 1.25 , Li 5.8 PS 4.8 Cl 1.2 , (Li 5.34 Cu 0.06 )PS 4.4 Cl 1.6 , (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 , (Li5.72 Na 0.03 )P(S 4.725 (SO4) 0.025 )Cl 1.25 , or Li 5.75 P(S 4.725 (SO4) 0.025 )Cl 1.25 It could be.

[0064] As another example, the first solid electrolyte is Li 6.2 PS 5.2 Br 0.8 And the second solid electrolyte can be Li6PS5Br.

[0065] In one embodiment, the anode may have different types of halogen elements included in the first solid electrolyte and different types of halogen elements included in the second solid electrolyte. For example, the first solid electrolyte may contain Cl and the second solid electrolyte may contain Br, or conversely, the first solid electrolyte may contain Br and the second solid electrolyte may contain Cl. Alternatively, the first solid electrolyte may contain either Cl or Br, and the second solid electrolyte may contain both Cl and Br. When the types of halogen elements included in the first solid electrolyte and the second solid electrolyte are changed in this way, and the molar ratio of at least one of Li, P, S, and the halogen element is designed to be different, the electron-to-ion conductivity ratio and density of the entire anode can be improved, and the electrochemical performance of the battery, such as capacity, rate characteristics, and lifespan characteristics, can be further enhanced.

[0066] The azirodite-type sulfide-based solid electrolytes of the first solid electrolyte and the second solid electrolyte can each be prepared by mixing, for example, lithium sulfide, phosphorus sulfide, and lithium halide. After mixing these, heat treatment may be performed. The heat treatment may include, for example, two or more heat treatment steps. Here, preparing the azirodite-type sulfide-based solid electrolyte may include, for example, a first heat treatment in which raw materials are mixed and calcined at 120°C to 350°C, and a second heat treatment in which the result of the first heat treatment is mixed again and calcined at 350°C to 800°C.

[0067]

[0068] Cathode active material - Type A

[0069] The positive active material included in the first positive active material layer and the positive active material included in the second positive active material layer may be the same or different from each other, and each independently includes a core particle containing a lithium nickel-based composite oxide and a boron coating layer located on said core particle.

[0070]

[0071] Core particles of the positive electrode active material

[0072] The lithium nickel-based composite oxide of the above core particles can be represented, for example, by the following chemical formula 5.

[0073] [Chemical Formula 5]

[0074] Li a5 Ni x5 M 5 y5 M 6 z5 O 2-b5 X b5

[0075] In the above chemical formula 5, 0.9≤a5≤1.2, 0.3≤x5≤1, 0≤y5≤0.7, 0≤z5≤0.7, 0.9≤x5+y5+z5≤1.1, and 0≤b5≤0.1, and M 5 and M 6are distinct elements and each independently is one or more of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, T, Zn and Zr, and X is one or more of F, P and S.

[0076] For example, in the above chemical formula 5, 0.6≤x5≤1, 0≤y5≤0.4, 0≤z5≤0.4, or 0.7≤x5≤1, 0≤y5≤0.3, 0≤z5≤0.3, or 0.8≤x5≤1, 0≤y5≤0.2, 0≤z5≤0.2, or 0.9≤x5<1, 0 <y5≤0.1, 0≤z5≤0.1이거나, 0.9≤x5≤1, 0≤y5≤0.1, 0≤z5≤0.1일 수 있다.

[0077] The cathode active material containing the above lithium nickel-based composite oxide as a core particle can achieve high capacity and high energy density.

[0078] The nickel content in the above lithium-nickel composite oxide may be 30 mol% or more with respect to 100 mol% of metal excluding lithium, 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.

[0079] Generally, as the nickel content in the cathode active material increases, Ni 2+Increased cation mixing, where ions occupy lithium sites, can actually lead to a decrease in capacity, or impurities such as NiO can hinder the diffusion of lithium ions, thereby degrading battery life. Additionally, structural collapse or cracking of the cathode active material during charging and discharging can increase side reactions with the electrolyte, which can reduce battery life and raise safety concerns. According to one embodiment, even when using a high-nickel cathode active material, the problems associated with high nickel concentration can be improved by coating an appropriate amount of boron onto the cathode active material, selectively coating internal grain boundaries, or forming a boron doping layer. This allows for the realization of high capacity while simultaneously improving lifespan characteristics without a decrease in initial discharge capacity.

[0080]

[0081] Boron coating layer of positive electrode active material

[0082] A positive electrode active material according to one embodiment includes a boron coating layer located on the surface of a core particle. The boron coating layer can be described as a type of buffer layer or buffer layer and can effectively suppress side reactions between a lithium nickel-based composite oxide and a sulfide-based solid electrolyte.

[0083] The boron coating layer may be said to contain a boron-containing compound, and 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 It may include Li2B4O7, Li3BO3, or a combination thereof.

[0084] The boron coating layer may exist on the surface of the core particle as a continuous film or as an island.

[0085] The boron content of the above boron coating layer may be 0.01 mol% to 0.5 mol% with respect to 100 mol% of the total metal excluding lithium in the cathode active material, for example, 0.01 mol% to 0.4 mol%, 0.01 mol% to 0.3 mol%, or 0.1 mol% to 0.3 mol%. Additionally, the boron content may be 0.01 wt% to 0.5 wt% with respect to 100 wt% of the total metal excluding lithium in the cathode active material, 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 boron content may be measured, for example, through Inductively Coupled Plasma (ICP) emission spectroscopic analysis. When boron is coated with such a content, it does not act as a resistance and does not degrade battery capacity; furthermore, the diffusion of lithium ions into the positive electrode active material becomes easier, improving initial charge-discharge efficiency and suppressing problems caused by repeated charge-discharge cycles, thereby enhancing the long-life characteristics of the battery.

[0086] Meanwhile, the core particle may include a secondary particle formed by the aggregation of a plurality of primary particles. At least some of the primary particles constituting the secondary particle may be arranged radially, and the radial structure is described in detail below in the first positive electrode active material of the bimodal.

[0087] A positive electrode active material according to one embodiment may further include a grain boundary boron coating portion located on the surface of primary particles within the secondary particles, in addition to a boron coating layer located on the surface of secondary particles. That is, in the positive electrode active material, boron may be coated along the interface of primary particles within the secondary particles. When a boron-containing compound is coated on the surface of the secondary particles and on the internal grain boundary surface, the boron does not act as a resistor, and the structural collapse or breakage of the positive electrode active material due to charging and discharging can be effectively suppressed.

[0088] The boron content present on the surface of the secondary particles may be higher than the boron content present at the internal grain boundaries, for example, the weight of boron in the boron coating layer may be four times or more the weight of boron in the grain boundary boron coating portion. For example, the ratio of the weight of boron in the boron coating layer to the weight of boron in the grain boundary boron coating portion may be 70:30 to 98:2, for example, 75:25 to 97:3, or 80:20 to 95:5. In this case, boron does not act as a resistor in the cathode active material but can play a role in improving performance, and can simultaneously improve the capacity characteristics and lifespan characteristics of the lithium secondary battery.

[0089] For detailed information regarding the grain boundary boron coating, please refer to the bimodal boron coating layer below.

[0090] A positive electrode active material according to one embodiment may further include a boron doping layer formed in a layered form along the periphery surface of the secondary particle, located inside the primary particle exposed on the surface of the secondary particle. The boron doping layer may be said to be located inside the secondary particle and within a depth range of about 10 nm from the outer surface of the primary particle exposed on the surface of the secondary particle. Such a boron doping layer can further improve the structural stability of the positive electrode active material and, accordingly, improve the lifespan characteristics of the lithium secondary battery.

[0091] For detailed information on the boron doping layer, please refer to the boron coating layer of the bimodal below.

[0092]

[0093] Bimodal positive electrode active material

[0094] The positive active material of the first positive active material layer and the positive active material of the second positive active material layer each independently comprise: (i) a first positive active material comprising a lithium nickel-based composite oxide, a plurality of primary particles aggregated to form secondary particles in which at least a portion of the primary particles are arranged radially, and a boron coating layer located on the surface of the secondary particles; and (ii) a lithium nickel-based composite oxide, a single particle form, and a boron coating layer located on the surface of the single particle, wherein the average particle size (D) of the first positive active material 50 Average particle size (D) smaller than ) 50 It may include a second positive active material having ).

[0095] The first positive active material can be expressed as an opposite or an opposite, and the average particle size of the secondary particle (D 50 ) may be 9 μm to 25 μm, for example, 11 μm to 18 μm, or 12 μm to 16 μm. The second positive active material may be expressed as microparticles or microparticles, and the average particle size (D) of the single particles is 50 ) can be 2 μm to 8 μm, for example 2.5 μm to 7 μm, or 3 μm to 6 μm. Here, the average particle size (D 50 ) may be obtained by selecting approximately 20 random particles from a scanning electron microscope (SEM) image of the positive electrode active material, measuring their particle size (diameter, or major axis, or length of the major axis), obtaining a particle size distribution, and taking the size of the particle with a cumulative volume of 50% of the particle size distribution as the average particle size.

[0096] With respect to the total of 100 wt% of the first positive active material and the second positive active material, the first positive active material may be included in an amount of 60 wt% to 95 wt%, 70 wt% to 90 wt%, or 80 wt% to 90 wt%, and the second positive active material may be included in an amount of 5 wt% to 40 wt%, 10 wt% to 30 wt%, or 10 wt% to 20 wt%. When the first positive active material and the second positive active material are mixed within the above weight ranges, high capacity and lifespan characteristics can be achieved while maximizing the energy density of the positive.

[0097]

[0098] First positive active material of bimodal positive active material

[0099] The first cathode active material may include, for example, a lithium nickel-cobalt-aluminum-based composite oxide, which means an oxide comprising lithium, nickel, cobalt, and aluminum and optionally further comprising other elements, and may be expressed as Ni-Co-Al or NCA.

[0100] The lithium nickel-cobalt-aluminum composite oxide of the first positive electrode active material can be represented by Chemical Formula 1.

[0101] [Chemical Formula 1]

[0102] Li a1 Ni x1 Co y1 Al z1 M 1 w1 O 2-b1 X b1

[0103] In the above Chemical Formula 1, 0.9≤a1≤1.2, 0.7≤x1<1, 0 <y1<0.3, 0<z1<0.3, 0≤w1<0.3, 0.9≤x1+y1+z1+w1≤1.1, 및 0≤b1≤0.1이고, M 1is one or more of the elements B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more of the elements F, P, and S.

[0104] In the above chemical formula 1, for example, 0.7≤x1≤0.98, 0.01≤y1≤0.29, 0.01≤z1≤0.29, 0≤w1≤0.28, 0.8≤x1≤0.98, 0.01≤y1≤0.19, 0.01≤z1≤0.19, 0≤w1≤0.18, or 0.9≤x1≤0.98, 0.01≤y1≤0.09, 0.01≤z1≤0.09, 0≤w1≤0.08.

[0105] The first positive active material is in the form of secondary particles formed by the aggregation of multiple primary particles, and the secondary particles may be spherical, elliptical, polygonal, amorphous, etc.

[0106] The average particle size of the primary particles constituting the secondary particles of the first cathode active material may be less than 200 nm, for example, 50 nm or more and less than 200 nm, 100 nm or more and less than 200 nm, 50 nm or more and less than 190 nm, or 50 nm or more and less than 180 nm. When the average particle size of the primary particles satisfies the above range, the lithium diffusion path is shortened, thereby reducing resistance and improving charge / discharge efficiency. Here, the average particle size of the primary particles refers to the size of the primary particles observed on the surface of the secondary particles, and can be obtained by selecting approximately 20 random primary particles from an SEM image of the surface of the secondary particles, measuring their particle sizes (diameter or major axis, or length of the major axis), and calculating the arithmetic mean thereof.

[0107] The first positive electrode active material may be characterized in that at least a portion of the primary particles forming the secondary particles are arranged radially. In this case, the diffusivity of lithium is increased, which improves the initial charge-discharge efficiency and enables the securing of a high capacity. Additionally, uniform expansion and contraction are possible during the insertion and extraction of lithium, thereby improving the problem of the positive electrode active material breaking during charge-discharge, which can improve the lifespan characteristics and safety of the battery.

[0108] The radial structure is explained in detail below.

[0109] At least some of the primary particles may have a plate shape. FIG. 1 is a schematic diagram showing the plate shape of the primary particles. Referring to FIG. 1, the primary particles may have various detailed shapes while basically having a plate structure, such as (A) a polygonal nanoplate shape such as a hexagon, (B) a nanodisk shape, and (C) a rectangular parallelepiped shape.

[0110] In FIG. 1, “a” represents the length of the major axis of the primary particle, “b” represents the length of the minor axis, and “t” represents the thickness. Here, the length of the major axis (a) represents the maximum length based on the widest face of the primary particle. The thickness (t) can be defined as the maximum length of the plane that is approximately perpendicular to the widest face of the primary particle. The direction containing the length of the major axis (a) and the length of the minor axis (b) is defined as the plane direction, and the direction in which the thickness (t) is defined is defined as the thickness direction.

[0111] 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 the lengths in the plane direction. Among the lengths in the plane direction, the length of the major axis (a) may be longer or equal to the length of the minor axis (b).

[0112] The statement that the primary particles are arranged radially may mean, for example, that the major axis of the primary particles is arranged in a radial direction. FIG. 2 is a diagram for explaining the definition of radial. In one embodiment, the term "radial arrangement structure" means that, as shown in FIG. 2, the thickness (t) direction of the primary particles is arranged to be perpendicular to the direction (R) from the center of the secondary particles toward the surface, or to form an angle of ±5° with the perpendicular direction.

[0113] In this way, when at least some of the primary particles are arranged radially, the surface of the secondary particles can have relatively many lithium diffusion channels between the primary particles, and the crystal planes capable of lithium transfer are exposed to the outside, thereby improving lithium diffusion and enabling high initial efficiency and high capacity. Additionally, when the primary particles are arranged radially, the pores exposed on the surface of the secondary particles are oriented toward the center of the secondary particles, further promoting the diffusion of lithium. Furthermore, the radially arranged primary particles allow for uniform expansion and contraction during the insertion and extraction of lithium, and pores exist in the direction of the Miller index (001) plane, which is the direction in which the particles expand during lithium extraction, and this acts as a buffer. Accordingly, the probability of cracking occurring during the expansion and contraction of the positive electrode active material is reduced, and the internal pores further mitigate volume changes, thereby reducing cracks occurring between primary particles during charging and discharging, and ultimately improving the lifespan characteristics of the lithium secondary battery and reducing the phenomenon of resistance increase.

[0114] For example, the secondary particle may include an interior having an irregular porous structure and an exterior having a radially oriented structure as a region surrounding the interior.

[0115] The above irregular porous structure refers to a structure having primary particles and pores, wherein the pore size, shape, location, etc., are not regular. That is, the primary particles placed inside may be arranged without regularity, unlike the primary particles placed outside. The above radial arrangement structure may refer to a shape in which primary particles are arranged radially. Here, “outside” may refer, for example, to an area of ​​30% to 50% of the total distance from the center of the secondary particle to the surface, for example, from the outermost surface to 40% of the length, or may refer to an area from the outermost edge of the secondary particle to a depth of approximately 3 μm. In addition, "inside" may refer to the region from the center to 50% to 70% of the total distance from the center to the surface of the secondary particle, for example, from the center to 60% of the length, or the remaining region excluding the region from the outermost edge of the secondary particle to a depth of approximately 3 μm.

[0116] In addition, the pores existing inside the secondary particle may be larger than the pores existing outside. For example, the size of the pores existing inside may be 150 nm to 1 μm, and the size of the pores existing outside may be less than 150 nm. When the size of the internal pores is larger than that of the external pores in this way, compared to a secondary particle where the internal and external pore sizes are the same, there is an advantage of a shorter lithium diffusion distance within the cathode active material, easier insertion of lithium from the outside, and an effect of mitigating volume changes occurring during charging and discharging. Here, the pore size refers to the diameter when the pores are spherical or circular, and refers to the length of the major axis when the pores are elliptical, etc. The pore size may be a value calculated by arbitrarily measuring the size of about 20 pores in an SEM image of the cross-section of the secondary particle and calculating the arithmetic mean thereof.

[0117] The secondary particle may have open pores on its surface. 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 part of the pore wall is not closed, formed by the space between radially arranged plate-like primary particles, and are pores deeply connected from the surface of the secondary particle toward the center. These open pores may be connected to the outside and serve as a passage for substances to enter and exit. The open pores may be oriented toward the center from the surface of the secondary particle and may be formed to a depth of, on average, less than 150 nm, 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 open pores may be measured using the BJH (Barrett, Joyner and Halenda) method, which is a method derived through the adsorption or desorption content of nitrogen.

[0118] FIG. 3 is a schematic diagram showing the cross-sectional structure of a secondary particle of a positive electrode active material. Referring to FIG. 3, the secondary particle (11) includes an outer layer (14) having a structure in which primary particles (13) having a plate shape are arranged in a radial direction, and an inner layer (12) in which primary particles (13) are arranged irregularly. In the inner layer (12), there may be more empty spaces between the primary particles than in the outer layer. Also, the pore size and porosity in the inner layer are larger than the pore size and porosity in the outer layer, and the shape, etc., may be irregular. In FIG. 3, the arrow indicates the direction of movement of lithium ions.

[0119] The interior of the aforementioned secondary particles has a porous structure, which has the effect of reducing the diffusion distance of lithium ions to the interior, while the exterior has primary particles arranged radially, making it easy for lithium ions to be inserted into the surface. Additionally, the small size of the primary particles makes it easier to secure lithium transport pathways between the crystal grains. Furthermore, the small size of the primary particles and the pores between them mitigate volume changes that occur during charging and discharging, thereby minimizing stress caused by volume changes during charging and discharging. Such a cathode active material can reduce the resistance of a lithium secondary battery and improve capacity and lifespan characteristics.

[0120]

[0121] Second positive active material of bimodal positive active material

[0122] The second positive electrode active material contains a lithium nickel-based composite oxide and is characterized by being in the form of a single particle. A single particle refers to a particle that exists independently without grain boundaries within the particle and consists of a single particle. Morphologically, it may refer to a single particle, a monolith structure, a monolithic structure, or a non-aggregated particle existing in an independent phase where the particles are not mutually aggregated, and as an example, it may be a single crystal. The single particles may exist independently or may be aggregated together. For example, 2 to 10 single particles may be aggregated and in contact with each other. The positive electrode active material according to one embodiment can achieve high capacity and high energy density while exhibiting improved lifespan characteristics by including the second positive electrode active material in the form of a single particle.

[0123] The shape of the second positive active material is not particularly limited and can have various shapes such as polyhedral, spherical, elliptical, plate-shaped, rod-shaped, and irregular.

[0124] The second cathode active material may include, for example, a lithium nickel-cobalt-aluminum-manganese-based composite oxide, which means an oxide comprising lithium, nickel, cobalt, aluminum, and manganese and optionally further comprising other elements, and can be expressed as Ni-Co-Al-Mn or NCAM.

[0125] The lithium nickel-cobalt-aluminum-manganese-based composite oxide of the second positive electrode active material can be represented by Chemical Formula 2.

[0126] [Chemical Formula 2]

[0127] Li a2 Ni x2 Co y2 Al z2 Mn w2 M 2 v2 O 2-b2 X b2

[0128] In the above chemical formula 2, 0.9≤a2≤1.2, 0.7≤x2<1, 0 <y2<0.3, 0<z2<0.3, 0<w2<0.3, 0≤v2<0.3, 0.9≤x2+y2+z2+w2+v2≤1.1, 및 0≤b2≤0.1이고, M 2 is one or more of the elements B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Z, and X is one or more of the elements F, P, and S.

[0129] In the above chemical formula 2, for example, 0.7≤x2≤0.979, 0.01≤y2≤0.289, 0.001≤z2≤0.289, 0.01≤w2≤0.289, 0≤v2≤0.279, 0.8≤x2≤0.979, 0.01≤y2≤0.189, 0.001≤z2≤0.189, 0.01≤w2≤0.189, 0≤v2≤0.179, and 0.9≤x2≤0.979, 0.01≤y2≤0.089, 0.001≤z2≤0.089, 0.01≤w2≤0.089, 0≤v2≤0.079.

[0130]

[0131] Boron coating layer of bimodal positive electrode active material

[0132] Conventionally, when coating a positive electrode active material with boron, it was common practice to use a method of mixing a boron raw material into a lithium transition metal composite oxide in a wet or dry manner and then heat-treating it. However, in this case, there was a problem in that boron acted as a resistance on the surface of the positive electrode active material, thereby worsening the capacity and lifespan. In particular, when mixing two types of positive electrode active materials, if each positive electrode active material is coated with boron and then mixed, the pellet density and initial discharge capacity of the entire positive electrode active material drop sharply, resulting in a decrease in capacity per volume and deterioration of lifespan characteristics. On the other hand, according to one embodiment, as described below, a positive electrode active material coated with a boron-containing compound can be obtained through a method such as mixing a first nickel-based composite hydroxide in which primary particles are radially oriented, a second lithium nickel-based composite oxide in the form of a single particle, and a lithium raw material, while simultaneously adding a boron raw material and heat-treating it. In this case, a first lithium nickel-based composite oxide in which primary particles are radially oriented is obtained, and at the same time, an appropriate amount of boron is stably coated on the surface of the first and second positive active materials, so that boron no longer acts as a resistor, the structural stability of the positive active material is secured, and problems caused by contact between the positive active material and the electrolyte are suppressed, thereby improving the capacity characteristics and long-term life characteristics of the battery.

[0133] Nickel-based cathode active materials may experience structural collapse and cation mixing phenomena due to the formation of NiO and other elements on the surface during repeated charging and discharging cycles, which can lead to problems such as gas generation or deterioration of lifespan characteristics. Additionally, repeated charging and discharging can cause the cathode active material to break down, which increases adverse reactions between the cathode active material and the electrolyte, resulting in a decrease in battery capacity and deterioration of lifespan characteristics. However, according to one embodiment, an appropriate amount of a boron-containing compound is stably coated simultaneously on the surfaces of the first and second cathode active materials. Furthermore, a boron coating layer and a grain boundary boron coating portion or boron doping layer are simultaneously formed on the first cathode active material, thereby preventing the detachment of oxygen atoms from the surface of the cathode active material, suppressing structural collapse, and inhibiting the breakage phenomenon caused by repeated charging and discharging. Moreover, while it is difficult for lithium to diffuse into the interior of particles in single-particle forms such as the second cathode active material, in one embodiment, coating the surface with a boron-containing compound facilitates lithium diffusion and effectively prevents the detachment of oxygen atoms from the surface of the cathode active material. Furthermore, the movement of lithium ions within the all-solid-state battery can be made smoother by the boron-containing compound present on the surface of the positive electrode active material, and accordingly, the rate characteristics can be improved.

[0134] The above boron coating layer may be said to contain a boron-containing compound, and 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 It may include Li2B4O7, Li3BO3, or a combination thereof.

[0135] The above boron coating layer may exist in the form of a continuous film on the surface of the secondary particles of the first positive active material and also on the surface of the single particles of the second positive active material, or it may be coated in the form of an island.

[0136] The boron content relative to 100 mol% of the total metal excluding lithium in the entire cathode active material including the first cathode active material and the second cathode 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%. Additionally, the boron content relative to 100 wt% of the total metal excluding lithium in the entire cathode 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 boron content may be measured, for example, through ICP (Inductively Coupled Plasma) emission spectroscopic analysis. When boron is coated with such a content, it does not act as a resistance and does not degrade battery capacity; furthermore, the diffusion of lithium ions into the positive electrode active material becomes easier, improving initial charge-discharge efficiency and suppressing problems caused by repeated charge-discharge cycles, thereby enhancing the long-life characteristics of the battery.

[0137] Meanwhile, the first positive active material, which is in the form of a secondary particle including a radial structure, may further include a grain boundary boron coating portion located on the surface of the primary particles within the secondary particle, in addition to a boron coating layer located on the surface of the secondary particle. That is, in the first positive active material, boron may be coated along the interface of the primary particles within the secondary particle. Here, "inside of the secondary particle" refers to the entire interior excluding the surface; for example, it may refer to the entire interior starting from a depth of approximately 1 μm from the outer surface, or it may be described as the part that is not reached by distilled water when washing the secondary particles of the positive active material with distilled water. In this way, when a boron-containing compound is coated on the surface of the secondary particle and the internal grain boundary surface in the first positive active material, the boron does not act as a resistor, and the structural collapse or breakage of the positive active material due to charging and discharging can be effectively suppressed.

[0138] Here, the boron content present on the surface of the secondary particles may be higher than the boron content present at the internal grain boundaries, for example, it may be four times or more. That is, the weight of boron in the boron coating layer may be four times or more the weight of boron in the grain boundary boron coating portion. For example, the ratio of the weight of boron in the boron coating layer to the weight of boron in the grain boundary boron coating portion may be 70:30 to 98:2, for example, 75:25 to 97:3, or 80:20 to 95:5. In this case, boron does not act as a resistor in the cathode active material but can play a role in improving performance, and can simultaneously improve the capacity characteristics and lifespan characteristics of the lithium secondary battery.

[0139] For example, the boron content in the boron coating layer may be 0.02 wt% to 0.5 wt% with respect to 100 wt% of the first positive active material, 0.03 wt% to 0.4 wt%, 0.04 wt% to 0.3 wt%, or 0.05 wt% to 0.2 wt%, etc. The boron content in the grain boundary boron coating portion may be 0.001 wt% to 0.05 wt% with respect to 100 wt% of the first positive active material, 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 content in the boron coating layer and the grain boundary boron coating portion is such, both the capacity characteristics and lifespan characteristics of the lithium secondary battery can be improved. Here, the boron content may be measured through ICP emission spectroscopic analysis of the anode active material, the boron content in the grain boundary boron coating portion may refer to the boron content remaining in the first anode active material after washing, and the boron content of the boron coating layer may refer to the difference between the boron content before washing and the boron content after washing.

[0140] According to one embodiment, the first positive active material, which is in the form of a secondary particle containing a radial structure, may further include a boron doping layer formed in a layer form along the periphery surface of the secondary particle, located inside the primary particle exposed on the surface of the secondary particle. The boron doping layer may be said to be located inside the secondary particle and may be said to be located within a depth range of about 10 nm from the outer surface of the primary particle exposed on the surface of the secondary particle. If the outer surface of the primary particles exposed on the surface of the secondary particle is defined as 0 nm, the doping layer may be said to exist in a depth range of 0 nm to 10 nm starting from the surface. In other words, the boron doping layer may be said to be located within a depth range of 10 nm from the surface of the secondary particle. If the surface of the secondary particle is defined as 0 nm, the doping layer may be said to exist in a depth range of 0 nm to 10 nm starting from the surface. This boron-doped layer can further enhance the structural stability of the cathode active material, thereby improving the lifespan characteristics of the lithium secondary battery.

[0141] The boron doping layer may be located, for example, within a depth range of 9 nm, 8 nm, 7 nm, 6 nm, 5 nm, 4 nm, 3 nm, or 2.5 nm from the outer surface of the primary particles exposed on the surface of the secondary particles. This boron doping layer is distinct from the boron coating layer or the grain boundary boron coating portion and is thought to contribute to the structural stability of the cathode active material.

[0142]

[0143] Method for manufacturing bimodal positive electrode active material

[0144] A bimodal cathode active material according to one embodiment comprises: a first cathode active material precursor in the form of secondary particles containing a first nickel-based composite hydroxide, wherein a plurality of primary particles are aggregated and at least a portion of the primary particles are arranged radially; and a second lithium nickel-based composite oxide containing a single particle and having an average particle size (D) of the first cathode active material precursor. 50 Average particle size (D) smaller than ) 50 A second positive electrode active material primary calcined product having ); a lithium raw material; and a boron raw material can be mixed and subjected to a first heat treatment to be manufactured.

[0145] Through a first heat treatment process, a first nickel-based composite hydroxide and a 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 secondary particles to produce a first positive active material, and a second lithium nickel-based composite oxide in the form of single particles is re-heat-treated to coat boron on its surface to produce a second positive active material. That is, through the above method, a positive active material can be produced in which the first positive active material with a boron coating layer formed thereon and the second positive active material with a boron coating layer formed thereon are mixed.

[0146] The above manufacturing method involves not separately preparing the first lithium-nickel-based composite oxide and the second lithium-nickel-based composite oxide, coating them individually, and then mixing them, but rather mixing the first nickel-based composite hydroxide, the second lithium-nickel-based composite oxide, the lithium raw material, and the boron raw material and calcining them simultaneously. This method of manufacturing the cathode active material is not only simple and efficient but also highly productive. For example, thermal conductivity through the single-particle form of the second lithium-nickel-based composite oxide is advantageous, which can shorten the calcination time and increase production volume. Furthermore, the simultaneous calcination method reduces the number of calcination cycles, thereby significantly lowering costs. In addition, this method improves the pellet density and initial discharge capacity of the final cathode active material, significantly enhancing the capacity per unit volume of the battery, and improving both the initial charge / discharge efficiency and lifespan characteristics of the battery.

[0147] Conventionally, when coating a positive electrode active material with boron, a method was generally used in which a lithium nickel-based composite oxide was prepared by mixing a lithium raw material with a nickel-based composite hydroxide and heat-treating it, and then mixing a boron raw material into it in a wet or dry manner and heat-treating it again. However, in this case, the boron attached to the surface of the positive electrode active material acted as a resistor, which actually reduced the capacity and lifespan. Furthermore, when only one of the first positive electrode active material and the second positive electrode active material is boron-coated and then mixed, or when the first positive electrode active material and the second positive electrode active material are boron-coated individually and then mixed to prepare the positive electrode active material, there is a problem in that the pellet density and energy density are lower, the initial discharge capacity is lower, and the initial charge-discharge efficiency and lifespan characteristics are inferior compared to the positive electrode active material prepared according to one embodiment. On the other hand, the positive electrode active material prepared according to one embodiment has a high pellet density and a high initial discharge capacity, which significantly increases the capacity per unit volume of the battery, and can improve the initial charge-discharge efficiency and room temperature and high temperature lifespan characteristics.

[0148] In the above manufacturing method, the first nickel-based composite hydroxide, which is a precursor of the first cathode active material, may be in the form of secondary particles formed by the aggregation of a plurality of primary particles, wherein at least a portion of the primary particles are arranged radially. The average particle size of the secondary particles may be 10 μm to 25 μm, for example, 11 μm to 20 μm, or 12 μm to 18 μm. Here, the average particle size of the secondary particles is determined by selecting approximately 20 arbitrary particles from an SEM image of the first cathode active material precursor, measuring their particle sizes (diameter, or major axis, or length of the major axis), obtaining a particle size distribution, and determining the diameter (D) of the particle whose cumulative volume is 50 volume% in the particle size distribution. 50 It may be that ) was taken as the average particle size.

[0149] The first cathode active material precursor can be prepared by a co-precipitation reaction. That is, a complex metal raw material is prepared by mixing metal raw materials such as nickel raw materials, and a complexing agent and a pH adjuster are added to control the pH of the mixture while carrying out a co-precipitation reaction to produce a nickel-based complex hydroxide of a desired composition. The complexing agent plays a role in controlling the reaction rate of precipitate formation in the co-precipitation reaction and may be, for example, ammonium hydroxide (NH4OH) or citric acid. The pH adjuster may be, for example, sodium hydroxide (NaOH), sodium carbonate (Na2CO3), sodium oxalate (Na2C2O4), etc. The pH of the mixture may be adjusted to a range of, for example, 10 to 13.

[0150] The above co-precipitation reaction can proceed in multiple stages, for example, in two, three, or four stages. In each stage, the concentration of the complexing agent, the input rate of the metal raw material, the pH control range, the reaction temperature, the reaction time, or the stirring power can be controlled differently. Through such control, a cathode active material precursor in the form of secondary particles in which at least a portion of the primary particles are arranged radially can be produced, and secondary particles with different internal and external shapes can also be produced.

[0151] For example, a first cathode active material precursor with a radial structure can be manufactured in the following manner. The method for manufacturing the first cathode active material precursor may include a first process, a second process, and a third process for forming a core, an intermediate layer, and a shell in sequence. In the first process, a complexing agent, a pH adjuster, and a metal raw material are introduced into a reactor and reacted. At this time, the concentration of the complexing agent may be 0.1M to 0.7M and the input amount may be 6 mL / min to 12 mL / min. The concentration of the metal raw material may be 0.1M to 3.5M and the input amount may be 50 mL / min to 100 mL / min. Subsequently, in the second process, the complexing agent, the pH adjuster, and the metal raw material are further introduced, at which time the concentration of the complexing agent may be 0.3M to 1.0M and the input amount may be 8 mL / min to 15 mL / min. The concentration of the metal raw material may be 0.1M to 3.5M and the input amount may be 60 mL / min to 120 mL / min. Subsequently, in the third process, the concentration and input amount of the complexing agent and the metal raw material are further increased or maintained at the same level to prevent a decrease in the particle growth rate. At this time, the concentration of the complexing agent may be 0.35M to 1.0M and the input amount may be 12 mL / min to 20 mL / min. The concentration of the metal raw material may be 0.1M to 2.5M and the input amount may be 70 mL / min to 150 mL / min. In the first to third processes, the pH may be adjusted to between 10 and 12.

[0152] The first nickel-based complex hydroxide can be represented, for example, by the chemical formula 11 below.

[0153] [Chemical Formula 11]

[0154] Ni x11 M 11 y11 M 12 z11 (OH)2

[0155] 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 Each is independently one or more of the elements Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr.

[0156] As a more specific example, the first nickel-based complex hydroxide may be a nickel-cobalt-aluminum-based hydroxide represented by the chemical formula 12 below.

[0157] [Chemical Formula 12]

[0158] Ni x12 Co y12 Al z12 M 13 w12 (OH)2

[0159] In the above chemical formula 12, 0.7 ≤ x 12 < 1, 0 <y12<0.3, 0<z12<0.3, 0≤w12<0.3, 0.9≤x12+y12+z12+w12≤1.1이고, M 13 It is one or more of the elements B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr.

[0160] 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 axis of the plate primary particles is directed toward the surface of the secondary particles.

[0161] The second lithium-nickel-based composite oxide in the form of single particles may be manufactured by mixing the second nickel-based composite hydroxide with a lithium raw material, heat treating the mixture, and then optionally undergoing a process such as grinding. Here, the heat treatment may be carried out, for example, in an oxidizing gas atmosphere at 800°C to 1100°C or at 800°C to 1000°C for about 1 to 25 hours or about 5 to 20 hours. The grinding is performed to obtain a single-particle form and is distinct from crushing; it may be carried out using a device such as a jet mill.

[0162] The second nickel-based complex hydroxide is identical or different from the first nickel-based complex hydroxide described above and can be represented by Chemical Formula 11 or Chemical Formula 12. Alternatively, the second nickel-based complex hydroxide can be represented by Chemical Formula 13 below.

[0163] [Chemical Formula 13]

[0164] Ni x13 Co y13 Al z13 Mn w13 M 14 v13 (OH)2

[0165] In the above chemical formula 13, 0.7 ≤ x 13 < 1, 0 <y13<0.3, 0<z13<0.3, 0<w13<0.3, 0≤v13<0.3, 0.9≤x13+y13+z13+w13+v13≤1.1이고, M 14 It is one or more of the elements B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, T, Zn, and Zr.

[0166] For example, the second lithium nickel-based composite oxide may be represented by the aforementioned chemical formula 2.

[0167] Average particle size (D) of a single particle containing a second lithium nickel-based composite oxide 50 ) can be 2 μm to 8 μm, and for example, 2 μm to 5 μm.

[0168] 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 positive electrode active material can be manufactured that has high pellet density and energy density, achieves high capacity, and has excellent lifespan characteristics.

[0169] The above lithium raw material may be, for example, Li2CO3, LiOH, LiF, their hydrates or anhydrous states, or a combination thereof. Additionally, the lithium raw material may be mixed such that the molar ratio of lithium to the total metal in the first nickel-based composite hydroxide is 0.8 to 1, 0.8 to 0.995, 0.9 to 0.995, or 0.950 to 0.995. By adjusting the molar ratio of lithium to the above range, a preliminary cathode active material with a boron coating layer effectively formed can be obtained.

[0170] The above boron raw material is a compound containing boron, for example, H3BO3, HBO2, B2O3, C6H5B(OH)2, (C6H5O)3B, [CH3(CH2)3O]3B, (C3H7O)3B, C3H9B3O6, C 13 H 19 It may include BO3, or a combination thereof.

[0171] The content of the boron raw material may be 0.01 to 0.5 molar parts per 100 molar parts of the total amount of metal excluding lithium in the first nickel-based composite hydroxide and the second lithium-nickel-based composite oxide, for example, 0.01 to 0.3 molar parts, or 0.1 to 0.3 molar parts. When the content of the boron raw material satisfies the above range, boron does not act as a resistor in the cathode active material and can play a role in improving the performance of the lithium secondary battery, thereby increasing capacity and improving lifespan characteristics. If the content of the boron raw material becomes excessive, boron acts as a resistor in the cathode active material, which can reduce the capacity and lifespan of the battery.

[0172] The first heat treatment can be performed at a temperature of, for example, 650°C to 850°C or 690°C to 780°C. Additionally, the first heat treatment can be carried out for 5 to 25 hours, for example, 5 to 20 hours. In this case, a high-capacity, high-energy-density cathode active material comprising a first cathode active material and a second cathode active material stably coated with a boron-containing compound can be manufactured. In a conventional coating method, which involves mixing a lithium nickel-based composite oxide with a boron raw material and performing heat treatment, it was common to perform heat treatment at a much lower temperature, for example, 600°C or lower; however, one embodiment is distinguished in that heat treatment is performed at a higher temperature of 650°C to 850°C. By heat treating in this temperature range, a first lithium-nickel-based composite oxide in the form of secondary particles with a radial structure can be obtained while simultaneously being coated with a boron-containing compound, and a second lithium-nickel-based composite oxide in the form of single particles can also be coated with a boron-containing compound on its surface. Accordingly, the cathode active material produced can simultaneously improve initial discharge capacity, initial efficiency, and lifespan characteristics without the resistance increase effect caused by boron, and increase pellet density to improve the capacity per unit volume of the battery.

[0173] In one embodiment, the first heat treatment includes a heating step and a temperature holding step, and the heating time may be set longer than the temperature holding time. For example, the heating time may be 6 to 16 hours and the temperature holding time may be 1 to 9 hours, and the heating time may be longer than the temperature holding time.

[0174] In the first heat treatment, the heating time may be, for example, 6 to 15 hours, 6 to 14 hours, 6 to 13 hours, or 7 to 12 hours, and the temperature holding time may be 2 to 9 hours, or 3 to 8 hours.

[0175] In addition, the ratio of (heating time):(temperature holding time) may be 1.1:1 to 10:1, and for example, 1.1:1 to 8:1, 1.1:1 to 6:1, 1.1:1 to 5:1, or 1.1:1 to 4:1.

[0176] By controlling the first heat treatment profile in this way, a first positive active material in the form of high-efficiency radial secondary particles can be effectively manufactured, and an appropriate amount of boron-containing compound can be stably coated on the first positive active material and the second positive active material.

[0177]

[0178] Binder and conductive material of the positive electrode active material layer

[0179] The first positive active material layer and the second positive active material layer may each independently further include a binder and / or a conductive material.

[0180] The binder serves to adhere the positive active material particles well to each other and also to adhere the positive active material well to the current collector. Representative examples include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0181] The content of the binder may be 0.1% to 5% by weight or 0.1% to 3% by weight with respect to 100% by weight of the entire positive active material layer, approximately 0.1% to 5% by weight or 0.1% to 3% by weight with respect to 100% by weight of the first positive active material layer, and approximately 0.1% to 5% by weight or 0.1% to 3% by weight with respect to 100% by weight of the entire second positive active material layer.

[0182] A conductive material is used to impart conductivity to an electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples 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 in the form of metal powder or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or conductive materials comprising a mixture thereof.

[0183] The content of the conductive material may be 0.1% to 5% by weight or 0.1% to 3% by weight with respect to 100% by weight of the entire positive active material layer, approximately 0.1% to 5% by weight or 0.1% to 3% by weight with respect to 100% by weight of the first positive active material layer, and approximately 0.1% to 5% by weight or 0.1% to 3% by weight with respect to 100% by weight of the entire second positive active material layer.

[0184] For example, the first positive active material layer may comprise 55% to 99% by weight of the positive active material, 1% to 35% by weight of the first solid electrolyte, 0% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material, based on 100% by weight of the first positive active material layer. As a specific example, the first positive active material layer may comprise 69% to 94% by weight of the positive active material, 5% to 25% by weight of the first solid electrolyte, 0.5% to 3% by weight of the binder, and 0.5% to 3% by weight of the conductive material.

[0185] In addition, the second positive active material layer may comprise 55% to 99% by weight of the positive active material, 1% to 35% by weight of the first solid electrolyte, 0% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material, based on 100% by weight of the second positive active material layer. As a specific example, the second positive active material layer may comprise 69% to 94% by weight of the positive active material, 5% to 25% by weight of the first solid electrolyte, 0.5% to 3% by weight of the binder, and 0.5% to 3% by weight of the conductive material.

[0186] Aluminum foil or stainless steel (SUS) can be used as the current collector for the anode, but is not limited thereto.

[0187]

[0188] All-solid-state secondary battery

[0189] In one embodiment, an all-solid-state secondary battery is provided, comprising the aforementioned positive and negative electrodes and a solid electrolyte layer located between the positive and negative electrodes.

[0190] FIG. 4 is a cross-sectional view of an all-solid-state secondary battery according to one embodiment. Referring to FIG. 4, the all-solid-state secondary battery (100) may have a structure in which an electrode assembly is housed in a battery case, wherein the electrode assembly comprises a negative electrode (400) including a negative electrode current collector (401) and a negative electrode active material layer (403), a solid electrolyte layer (300), and a positive electrode (200) including a positive electrode active material layer (203) and a positive electrode current collector (201). 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).

[0191] FIG. 4 illustrates a single electrode assembly including a negative electrode (400), a solid electrolyte layer (300), and a positive electrode (200), but an all-solid-state secondary battery may be manufactured by stacking two or more electrode assemblies. The all-solid-state secondary battery may be in the form of a monocell having a structure of positive electrode / solid electrolyte layer / negative electrode, or a bicell having a structure of negative electrode / solid electrolyte layer / positive electrode / solid electrolyte layer / negative electrode, and may be a stacked battery in which a plurality of electrode assemblies are repeated.

[0192] The shape of all-solid-state secondary batteries is not particularly limited and can be, for example, coin-type, button-type, sheet-type, stacked-type, cylindrical-type, flat-type, etc. Furthermore, all-solid-state secondary batteries can be used in fields requiring large amounts of power storage, such as electric vehicles, motorcycles, electric bicycles, drones, ships, trains, and aircraft. In addition, all-solid-state secondary batteries can be used in various other fields, such as portable electronic devices and power tools.

[0193]

[0194] cathode

[0195] The cathode (400) may include a current collector (401) and a cathode active material layer (403) located on the current collector. The cathode active material layer may include a cathode active material and may further include a binder, a conductive material, and / or a solid electrolyte.

[0196] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0197] A material capable of reversibly intercalating / deintercalating the above lithium ions may be a carbon-based negative electrode active material, such as crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0198] As the above lithium metal alloy, an alloy of lithium with one or more metals selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0199] As a material capable of doping and undoping the above lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used, and the Si-based negative electrode active material may include silicon, a silicon-carbon composite, or SiO₂. x(0<x≤2), Si-Q 합금(상기 Q는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님), 상기 Sn계 음극 활물질로는 Sn, SnO2, Sn-R 합금(상기 R은 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Sn은 아님) 등을 들 수 있고, 또한 이들 중 적어도 하나와 SiO2를 혼합하여 사용할 수도 있다. 상기 원소 Q 및 R로는 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, 및 이들의 조합으로 이루어진 군에서 선택되는 것을 사용할 수 있다.

[0200] The silicon-carbon composite may be, for example, a silicon-carbon composite comprising a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. The amorphous carbon may be pitch carbon, soft carbon, hard carbon, mesophase pitch carbide, calcined coke, carbon fiber, or a combination thereof. In this case, the silicon content may be 10% to 50% by weight of the total weight of the silicon-carbon composite. Additionally, the content of the crystalline carbon may be 10% to 70% by weight of the total weight of the silicon-carbon composite, and the content of the amorphous carbon may be 20% to 40% by weight of the total weight of the silicon-carbon composite. Additionally, the thickness of the amorphous carbon coating layer may be 5nm to 100nm.

[0201] The average particle size (D50) of the silicon particles may be 10 nm to 20 µm, for example, 10 nm to 500 nm. The silicon particles may exist in an oxidized form, wherein the atomic content ratio of Si:O within the silicon particles indicating the degree of oxidation may be 99:1 to 33:67. The silicon particles are SiO x It can be a particle, and in this case, SiO x In this case, the range of x may be greater than 0 and less than 2. Here, the average particle size (D50) is measured by a particle size analyzer using laser diffraction and refers to the diameter of a particle with a cumulative volume of 50% in the particle size distribution.

[0202] The above Si-based negative electrode active material or Sn-based negative electrode active material may be used in combination with a carbon-based negative electrode active material. The mixing ratio of the Si-based negative electrode active material or Sn-based negative electrode active material and the carbon-based negative electrode active material may be 1:99 to 90:10 by weight.

[0203] The content of the negative electrode active material in the above negative electrode active material layer may be 95% to 99% by weight with respect to the total weight of the negative electrode active material layer.

[0204] In one embodiment, the negative active material layer further comprises a binder and optionally further comprises a conductive material. The content of the binder in the negative active material layer may be 1% to 5% by weight with respect to the total weight of the negative active material layer. Additionally, when further comprising a conductive material, the negative active material layer may comprise 90% to 98% by weight of the negative active material, 1% to 5% by weight of the binder, and 1% to 5% by weight of the conductive material.

[0205] The above binder serves to effectively bond the negative electrode active material particles to each other and also to effectively bond the negative electrode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof may be used.

[0206] Examples of the above-mentioned non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide imide, polyimide, or combinations thereof.

[0207] The above-mentioned water-based binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylenepropylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0208] When a water-based binder is used as the above-mentioned cathode binder, a cellulose-based compound capable of imparting viscosity may be further included. As this cellulose-based compound, one or more types such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K, or Li may be used as the alkali metal.

[0209] The above dry binder is a polymer material capable of fiberization, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0210] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fiber, carbon nanofiber, carbon nanotube; metal-based materials in the form of metal powder or metal fibers including copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0211] As the above-mentioned cathode current collector, a material selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof may be used.

[0212]

[0213] Precipitation type cathode

[0214] As an example, the negative electrode for an all-solid-state secondary battery may be a precipitation-type negative electrode, unlike the one described above. The precipitation-type negative electrode may refer to a negative electrode that does not contain a negative electrode active material during battery assembly, but in which lithium metal, etc. is precipitated or electrodeposited on the negative electrode during battery charging, and which acts as the negative electrode active material.

[0215] FIG. 5 is a schematic cross-sectional view of an all-solid-state secondary battery including a precipitation type negative electrode. Referring to FIG. 5, the precipitation type negative electrode (400') may include a current collector (401) and a negative electrode coating layer (405) located on the current collector. An all-solid-state secondary battery having such a precipitation type negative electrode (400') starts initial charging in a state where no negative electrode active material is present, and during charging, high-density lithium metal is precipitated or electrodeposited 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 can serve as a negative electrode active material. Accordingly, in an all-solid-state secondary battery that has undergone one or more charging cycles, the precipitation type negative electrode (400') may include, for example, a current collector (401), a lithium metal layer (404) located on the current collector, and a negative electrode coating layer (405) located on the lithium metal layer. The lithium metal layer (404) refers to a layer in which lithium metal, etc. is precipitated 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.

[0216] The negative electrode coating layer (405) may be a lithium electrodeposition inducing layer or a negative electrode catalyst layer, and may include a lithium-friendly metal, a carbon material, or a combination thereof.

[0217] The above-mentioned lithium-friendly metal may include, for example, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, zinc, or combinations thereof, and may be composed of one of these or may be composed of several types of alloys. When the lithium-friendly metal exists in the form of particles, its average particle size (D 50 ) can be about 4 μm or less, and for example, 10 nm to 4 μm, 10 nm to 1 μm, or 10 nm to 600 nm. As an example, the lithium-friendly metal may be in the form of nanoparticles having an average particle size of several to several hundred nanometers.

[0218] The carbon material may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The crystalline carbon may be, for example, natural graphite, artificial graphite, mesophase carbon micro beads, or a combination thereof. The amorphous carbon may be, for example, carbon black, activated carbon, acetylene black, Denka black, Ketjen black, or a combination thereof. As an example, the carbon material may be an amorphous carbon material.

[0219] When the negative electrode coating layer (405) includes both a lithium-friendly metal and a carbon material, the mixing ratio of the metal and the carbon material may be, for example, a weight ratio of 1:10 to 2:1. In this case, the precipitation of lithium metal can be effectively promoted and the characteristics of the all-solid-state secondary battery can be improved. The negative electrode coating layer (405) may include, for example, a carbon material supported with a lithium-friendly metal, or may include a mixture of lithium-friendly metal particles and carbon material particles.

[0220] The cathode coating layer (405) may include, for example, a lithium-friendly metal and amorphous carbon, and in this case, can effectively promote the precipitation of lithium metal.

[0221]

[0222] Supported compounds of precipitation-type cathodes

[0223] In one embodiment, the cathode coating layer may comprise a compound in which a lithium-friendly metal is supported on a carbon material. The supported compound is distinguished from a case where the lithium-friendly metal and the carbon material are simply mixed. When the cathode coating layer comprises the supported compound, the lithium metal layer described below can be formed more uniformly, and the reversibility of lithium precipitation and dissociation is improved, thereby improving the lifespan characteristics of the all-solid-state secondary battery. Here, the lithium-friendly metal is the same as described above, and the carbon material may be, for example, amorphous carbon.

[0224] The amorphous carbon material may be, for example, a single particle, or an assembly having a secondary particle form in which primary particles are assembled. 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 particle may be 20 nm to 100 nm, and the particle size of the secondary particle may be 1 µm to 20 µm.

[0225] In one embodiment, the particle size of the primary particles of the amorphous carbon material in the shape of an assembly 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, or a combination thereof.

[0226] In one embodiment, the particle size of the secondary particles of the amorphous carbon material in the shape of an assembly 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.

[0227] With respect to 100 wt% of the compound in which the lithium-friendly metal is supported on the carbon material, the lithium-friendly metal may be included in an amount of 3 wt% to 40 wt%, 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% with respect to 100 wt% of the compound in which the lithium-friendly 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 content of the lithium-friendly metal and the carbon material satisfies the above ranges, a uniform lithium metal layer can be effectively formed during charging.

[0228] In one embodiment, the carbon material and the lithium-friendly metal may be chemically bonded via sulfur. That is, the carbon material and the lithium-friendly metal may not be merely physically mixed but may be chemically bonded to each other. In this case, the bonding strength between the carbon material and the lithium-friendly metal is excellent, effectively preventing the problem of the carbon material and the lithium-friendly metal separating from each other during the mixing process. Furthermore, the aggregation of the lithium-friendly metal is prevented, allowing it to be uniformly dispersed within the cathode coating layer. Consequently, the current distribution within the cathode can be made uniform, and the uniform precipitation of lithium metal can be induced.

[0229] When a carbon material and a lithium-friendly metal are chemically bonded via sulfur, a peak associated with the bonding of the lithium-friendly metal and sulfur can be identified in the X-ray photoelectron spectroscopy (XPS) spectrum. For example, when the lithium-friendly metal contains Ag, a peak can be identified in the range of 160 eV to 162 eV, which is the Ag-S bonding energy, in the S2p spectrum obtained by XPS analysis.

[0230] A composite in which a carbon material and a lithium-friendly metal are chemically bonded via sulfur can be manufactured by mixing a carbon material and a sulfur-containing raw material in a dry or wet manner, selectively heat-treating the mixture, supporting a lithium-friendly metal, and then heat-treating the mixture.

[0231] A method for supporting a lithium-friendly metal may, for example, be a method of mixing a mixture of a carbon material and a sulfur-containing raw material, a lithium-friendly 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 lithium-friendly metal compound may be a nitrate, sulfate, perchlorate, etc. containing a lithium-friendly metal, and may include, for example, AgNO3, Ag2SO4, AgClO4, or a combination thereof.

[0232] Heat treatment after supporting a lithium-friendly metal can generally be carried out at a temperature where 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, heat treatment can be carried out at 100°C to 400°C. The heat treatment can be carried out for about 2 to 20 hours in an atmosphere of nitrogen, argon, or a combination thereof.

[0233] 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.

[0234] The cathode coating layer may further include a binder, for example, a conductive binder. Additionally, the cathode coating layer may further include additives such as fillers, dispersants, and ion conductive agents.

[0235] The binder of the cathode coating layer may include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0236] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide imide, polyimide, or combinations thereof.

[0237] The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylenepropylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0238] When a water-based binder is used as the cathode binder, a cellulose-based compound capable of imparting viscosity may be further included. As this cellulose-based compound, one or more types such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K, or Li may be used as the alkali metal.

[0239] The dry binder is a polymer material capable of fiberization, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0240] The binder may be included in an amount of 0.1 to 5 weight% with respect to 100 weight% of the cathode coating layer, 0.1 to 3 weight%, or 0.5 to 2 weight%.

[0241]

[0242] lithium metal layer of precipitation type cathode

[0243] According to one embodiment, the negative electrode is a type of precipitation type negative electrode (400'), and an all-solid-state secondary battery including the same is initially charged in a state where no negative electrode active material is present. During charging, high-density lithium metal is precipitated or electrodeposited between the negative electrode current collector and the negative electrode coating layer, or on the negative electrode coating layer, to form a lithium metal layer, which can serve as the negative electrode active material. Accordingly, an all-solid-state secondary battery that has undergone one or more charges may include, for example, a negative electrode current collector, a lithium metal layer located on the negative electrode current collector, and a negative electrode coating layer located on the lithium metal layer. The lithium metal layer refers to 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 electrodeposited layer, or a negative electrode active material layer.

[0244] 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.

[0245] 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 is difficult to perform the role of a lithium reservoir, and if it is too thick, the battery volume may increase and performance may deteriorate.

[0246] In one embodiment, a lithium metal layer with uniform thickness and flatness can be formed by applying a compound in which the aforementioned lithium-friendly metal is supported on a carbon material to the cathode coating layer. Accordingly, the lithium metal layer formed during charging according to one embodiment may have a very uniform thickness and a small thickness variation. For example, the variation 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 variation in the thickness of the lithium metal layer may mean calculating the arithmetic mean by measuring the thickness of the lithium metal layer at about 10 points in an electron microscope image of the cathode cross-section, dividing the absolute value of the difference between one data point and the arithmetic mean value by the arithmetic mean value, and then multiplying by 100. In addition, for example, the thickness of the lithium metal layer may be 5 μm to 80 μm, and the standard deviation of the thickness may be 0.1 μm to 20 μm, 0.1 μm to 15 μm, 0.1 μm to 10 μm, 0.1 μm to 5 μm, or 0.1 μm to 3 μm. Likewise, the standard deviation of the lithium metal layer thickness may be calculated by measuring the thickness at about 10 points in an electron microscope image. The fact that the deviation or standard deviation of the lithium metal layer thickness satisfies the above range means that the lithium metal has been well deposited in the form of a film of uniform thickness, and accordingly, the electrochemical characteristics of the all-solid-state secondary battery may be improved.

[0247]

[0248] Other components of precipitation type cathode

[0249] Meanwhile, the cathode according to one embodiment may further include a thin film on the surface of the cathode current collector, that is, between the cathode current collector and the cathode coating layer, or between the cathode 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 can further flatten the precipitation pattern of the lithium metal layer and help form a lithium metal layer of uniform thickness. The thin film may be formed by, for example, vacuum deposition, sputtering, plating, etc. The thickness of the thin film may be, for example, 1 nm to 500 nm.

[0250]

[0251] cathode current collector

[0252] The negative 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 alloys thereof, and may be in the form of a foil or a sheet. The thickness of the negative current collector may be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0253]

[0254] solid electrolyte layer

[0255] The solid electrolyte layer (300) may include a solid electrolyte and optionally a binder. The solid electrolyte may include an inorganic solid electrolyte and / or an organic solid electrolyte, and the inorganic solid electrolyte may include, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, etc.

[0256] In one embodiment, the average particle size (D) of the solid electrolyte included in the solid electrolyte layer. 50 ) is the average particle size (D) of the first solid electrolyte of the aforementioned first anode active material layer. 50 ) and the average particle size (D) of the second solid electrolyte of the aforementioned second positive active material layer 50 It may be larger than ). For example, the average particle size (D) of the solid electrolyte included in the solid electrolyte layer. 50 ) is 2.1 μm to 5 μm, and the average particle size (D) of the first solid electrolyte is 50 ) and the average particle size (D) of the second solid electrolyte 50 ) may each be 0.1 μm to 2 μm. When the size of the solid electrolyte in the solid electrolyte layer and the size of the solid electrolyte in the positive electrode active material layer are adjusted as described above, it is possible to maximize the capacity of the all-solid-state secondary battery while improving ion conductivity and enhancing rate characteristics and lifespan characteristics. The above average particle size may be measured using an electron microscope; for example, a particle size distribution is obtained by measuring the size (diameter or length of the major axis) of about 20 particles from a scanning electron microscope image of a battery cross-section, and here D 50 It could be that it was calculated.

[0257] For example, the solid electrolyte layer (300) may include a sulfide-based solid electrolyte, and specifically, may include an azirodite-type sulfide-based solid electrolyte.

[0258] The type or composition of sulfide-based solid electrolytes is not particularly limited. For example, sulfide-based solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiX (where X is a halogen element, e.g., I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Zm S n (m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p, q are integers, and M is P, Si, Ge, B, Al, Ga or In), or may include a combination thereof.

[0259] 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. Within the above mixing ratio range, a sulfide-based solid electrolyte having excellent ionic conductivity can be manufactured. Additionally, ionic conductivity may be further improved by including other components such as SiS2, GeS2, B2S3, etc.

[0260] Mechanical milling or a solution method can be applied as a mixing method for sulfur-containing raw materials to manufacture sulfide-based solid electrolytes. Mechanical milling is a method in which starting materials are placed in a ball mill reactor and vigorously stirred to finely atomize and mix the starting materials. When using the solution method, starting materials are mixed in a solvent to obtain a solid electrolyte as a precipitate. Additionally, if heat treatment is performed after mixing, the crystals of the solid electrolyte can become more robust and the ionic conductivity can be improved. The heat treatment can be carried out in a temperature range of 400°C to 600°C, for example, 450°C to 500°C or 460°C to 490°C, and can be carried out for 5 to 30 hours, 10 to 24 hours, or 15 to 20 hours. When heat treatment is performed under the above conditions, the ionic conductivity can be maximized. For example, a sulfide-based solid electrolyte can be manufactured by mixing sulfur-containing raw materials and heat-treating them two or more times, in which case a sulfide-based solid electrolyte with high ionic conductivity and robustness can be manufactured.

[0261] A sulfide-based solid electrolyte according to one embodiment can be manufactured, for example, by mixing sulfur-containing raw materials and calcining at 120°C to 350°C in a first heat treatment, and by mixing the results of the first heat treatment and calcining at 350°C to 800°C in a second heat treatment. The first heat treatment and the second heat treatment can each be carried out in an inert gas atmosphere. The first heat treatment can be performed for 1 to 10 hours, and the second heat treatment can be performed for 5 to 20 hours. Through the first heat treatment, the effect of milling small raw materials can be obtained, and through the second heat treatment, the final solid electrolyte can be synthesized. Through two or more such heat treatments, a high-performance sulfide-based solid electrolyte with high ion conductivity and robustness can be obtained, and such a solid electrolyte can be considered 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.

[0262] For example, the above sulfide-based solid electrolyte may include an azyrodite-type sulfide. The azyrodite-type sulfide-based solid electrolyte has an ionic conductivity of 10 at room temperature, which is the ionic conductivity of a typical liquid electrolyte. -4 to 10 -2 It has high ionic conductivity approaching the S / cm range and can form a tight bond between the positive active material and the solid electrolyte.

[0263] A azirodite-type sulfide-based solid electrolyte may include, for example, a compound represented by the chemical formula 21 below.

[0264] [Chemical Formula 21]

[0265] (Li a M 1 b M 2 c )(P d M 3 e)(S f M 4 g )X h

[0266] In the above chemical formula 21, 4≤a≤8, and M 1 is Mg, Ca, Cu, Ag, or a combination thereof, 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, 1.5≤n≤5, 3≤f≤12, 0≤g<2, X is F, Cl, Br, I, or a combination thereof, and 0≤h≤2.

[0267] For example, in Chemical Formula 21, a halide element (X) may be required to be included, in which case 0 <h≤2로 표시될 수 있다. 일 예로 화학식 21에 M 1 An element 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 the P position, 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 ga SO n In the case of SO n It can be, for example, S4O6, S3O6, S2O3, S2O4, S2O5, S2O6, S2O7, S2O8, SO4, or SO5, and as an example, it can be SO4.

[0268] For example, in chemical formula 21, a+b+c+h=7, d+e=1, and f+g+h=6.

[0269] As a specific example, azirodite-type sulfide-based solid electrolyte particles include Li3PS4 and Li7P3S 11, Li7PS6, Li6PS5Cl, Li6PS5Br, Li 6.2 PS 5.2 Br 0.8 , Li 5.4 PS 4.4 Cl 1.6 , Li 5.5 PS 4.5 Cl 1.5 , Li 5.6 PS 4.6 Cl 1.4 , Li 5.7 PS 4.7 Cl 1.3 , Li 5.75 PS 4.75 Cl 1.25 , Li 5.8 PS 4.8 Cl 1.2 , (Li 5.34 Cu 0.06 )PS 4.4 Cl 1.6 , (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 a combination thereof may be included, but is not limited thereto.

[0270] An azirodite-type sulfide-based solid electrolyte can be prepared by mixing, for example, lithium sulfide and phosphorus sulfide, and optionally lithium halide. After mixing these, heat treatment may be performed. The heat treatment may include, for example, two or more heat treatment steps. Here, preparing an azirodite-type sulfide-based solid electrolyte may include, for example, a first heat treatment in which raw materials are mixed and calcined at 120°C to 350°C, and a second heat treatment in which the result of the first heat treatment is mixed again and calcined at 350°C to 800°C.

[0271] The sulfide-based solid electrolyte included in the solid electrolyte layer (300) may be in the form of particles, and the average particle size (D) of the particles 50 ) may, for example, be 0.1 μm to 5 μm, 1 μm to 5 μm, 2.1 μm to 5 μm, or 2.5 μm to 4 μm. The above average particle size may be measured using electron microscope images, for example, by measuring the size (diameter or length of the major axis) of about 20 particles in an SEM image to obtain a particle size distribution, where D 50 It could be that it was calculated.

[0272] The above oxide-based solid electrolyte is, 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 may include a mixture thereof.

[0273] The above halide-based solid electrolyte contains a halogen element as a main component, and the ratio of the halide element to all elements constituting the solid electrolyte may be 50 mol% or more, 70 mol% or more, 90 mol% or more, or 100 mol%. As an example, the above halide-based solid electrolyte may not contain a sulfur element.

[0274] The halide-based solid electrolyte may contain a 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 for example, may be Cl, Br, or a combination thereof. The halide-based solid electrolyte is, for example, Li a It can be represented as 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). The above 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 It may include Cl6, or a combination thereof, but is not limited thereto.

[0275] Binder of the solid electrolyte layer

[0276] The solid electrolyte layer (300) may further include a binder in addition to the solid electrolyte. In this case, the binder may be styrene butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, acrylate-based polymer, or a combination thereof, but is not limited thereto, and any material used as a binder in the relevant technical field may be used. The acrylate-based polymer may be, for example, butyl acrylate, polyacrylate, polymethacrylate, or a combination thereof.

[0277] A solid electrolyte layer (300) can be formed by adding a solid electrolyte to a binder solution, coating the mixture onto a substrate film, and drying it. The solvent of the binder solution may be isobutyryl isobutyrate, xylene, toluene, benzene, hexane, or a combination thereof. Since the process for forming the solid electrolyte layer is widely known in the field, a detailed description will be omitted.

[0278] The thickness of the solid electrolyte layer (300) can be, for example, 10 μm to 800 μm.

[0279] Other components of the solid electrolyte layer

[0280] The solid electrolyte layer (300) may further include an alkali metal salt, and / or an ionic liquid, and / or a conductive polymer.

[0281] The above alkali metal salt may be, for example, a lithium salt. The content of the lithium salt in the above solid electrolyte layer may be 1 M or more, for example, 1 M to 4 M. In this case, the lithium salt can improve ion conductivity by improving the lithium ion mobility of the solid electrolyte layer.

[0282] Lithium salts may be applied without limitation of type and may include, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiSCN, LiN(CN)2, lithium bis(oxalate)borate (LiBOB), lithium difluoro(oxalate)borate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFBOP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, or combinations thereof.

[0283] For example, the above 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.

[0284] Ionic liquids are salts or room temperature molten salts that have a melting point below room temperature, are in a liquid state at room temperature, and consist only of ions.

[0285] 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.

[0286] The ionic liquid may be one or more of, for example, N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(3-trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolinium bis(trifluoromethylsulfonyl)amide, and 1-ethyl-3-methylimidazolinium bis(trifluoromethylsulfonyl)amide.

[0287] The weight ratio of the solid electrolyte to the ionic liquid in the solid electrolyte layer (300) may be 0.1:99.9 to 90:10, and 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 increasing 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.

[0288]

[0289] Examples and comparative examples of the present invention are described below. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0290] Example 1-1 (Li6PS5Cl 17 mg / cm² - Li 5.4 PS 4.4 Cl 1.6 17 mg / ㎠ (two-layer anode)

[0291] 1. Preparation of the first nickel-based complex hydroxide

[0292] The first nickel-based complex hydroxide (Ni), which is a precursor of the first positive electrode active material, is obtained through the coprecipitation method described below. 0.945 Co 0.04 Al 0.015 (OH)2) was synthesized. A mixed solution of metal raw materials was prepared by dissolving nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and sodium aluminum sulfate (NaAl(SO4)2·12H2O) in distilled water, the solvent, in a molar ratio of 94.5:4:1.5. In addition, water ammonia (NH4OH) and sodium hydroxide (NaOH) were prepared as a precipitating agent to form a complex.

[0293] [Stage 1: 2.5kW / m³, NH4OH 0.40M, pH 10.5~11.5, Reaction time 6 hours]

[0294] First, ammonia water with a concentration of 0.40 M was added to the reactor. The reaction was started at a stirring power of 2.5 kW / m³ and a reaction temperature of 50°C by adding the metal raw material mixed solution and the complexing agent (NH4OH) at rates of 85 ml / min and 10 ml / min, respectively. The reaction was carried out for 6 hours while adding NaOH to maintain the pH. As a result of the reaction, it was confirmed that the average size of the obtained core particles was in the range of approximately 6.5 µm to 7.5 µm, and the following two steps were performed.

[0295] [Stage 2: 2.0kW / m³, NH4OH 0.45M, pH 10.5~11.5, reaction time 18 hours]

[0296] While maintaining the reaction temperature at 50℃, the metal raw material mixed solution and the complexing agent were added at varying rates of 85 ml / min and 12 ml / min, respectively, so that the concentration of the complexing agent became 0.45 M. The reaction was carried out for 18 hours while adding NaOH to maintain the pH. During this time, the stirring power was lowered to 2.0 kW / m³, which is lower than that of the first step, to proceed with the reaction. After carrying out this reaction, it was confirmed that the average size of the product particles containing the core and intermediate layer was 13.5 μm to 14 μm, and the following three steps were performed.

[0297] [Stage 3: 1.5kW / ㎥, NH4OH 0.45M, pH 10.5~11.5, reaction time 14 hours]

[0298] While maintaining the reaction temperature at 50°C, the input rate and concentration of the metal raw material mixed solution and complexing agent were set identically to those in Step 2 above. The reaction was carried out for 14 hours while adding NaOH to maintain the pH. During this process, the stirring power was lowered to 1.5 kW / m³, lower than that of Step 2, to proceed with the reaction. After washing the obtained product, it was hot-air dried at approximately 150°C for 24 hours to produce a first nickel-based complex hydroxide (Ni) having a structure in which at least some of the primary particles constituting the secondary particles are arranged radially, in the form of secondary particles. 0.945 Co 0.04 Al 0.015 (OH)2) obtained.

[0299]

[0300] 2. Preparation of Second Lithium Nickel-Based Composite Oxides

[0301] Second nickel-based complex hydroxide (Ni), which is a precursor of the second positive electrode active material, obtained through the co-precipitation method 0.94 Co 0.04 Al 0.01 Mn 0.01(OH)2) was synthesized. As metal raw materials, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), sodium aluminum sulfate (NaAl(SO4)2·12H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water, a solvent, in a molar ratio of 94:4:1:1 to prepare a mixed solution. Subsequently, the synthesis proceeded in the same manner as the preparation of the first nickel-based complex hydroxide.

[0302] The prepared nickel-based composite hydroxide and lithium hydroxide were mixed such that the molar ratio of the total metal of the nickel-based composite hydroxide to the lithium of the lithium hydroxide was 1:1, and the mixture was heat-treated at 850°C in an oxygen atmosphere. The average particle size (D) of the product obtained through an air-flow impingement grinder 50 Grinding was performed so that the particle size was approximately 3 μm to obtain a single-particle form of the second lithium nickel-based composite oxide (LiNi 0.94 Co 0.04 Al 0.1 Mn 0.01 Obtained O2.

[0303]

[0304] 3. Preparation of mixed cathode active material

[0305] A first nickel-based composite hydroxide and a second lithium nickel-based composite oxide were mixed in a weight ratio of 7:3, LiOH was mixed to satisfy a molar ratio of Li / (Ni+Co+Al)=0.96 in the relationship between the first nickel-based composite hydroxide and LiOH, and boric acid was mixed so that boron was 0.125 mol% with respect to all elements excluding Li, O, and H in the mixture, and the mixture was fed into a calcination furnace, heated to 700°C over 8 hours in an oxygen atmosphere, and subjected to a first heat treatment for 7 hours to obtain a mixed cathode active material.

[0306] In the obtained mixed cathode active material, the first cathode active material is a first lithium nickel-based composite oxide (Li 0.96 Ni 0.945 Co 0.04 Al 0.015 Contains O2) and average particle size (D 50It was identified as a secondary particle with a diameter of approximately 13.8 μm. SEM analysis of the cross-section of the secondary particle revealed that it was in the form of a secondary particle containing an interior with an irregular porous structure and an exterior with a radial arrangement structure.

[0307] Mass spectrometry analysis of the first cathode active material by ToF-SIMS confirmed that lithium boron oxides, such as LiBO2, are evenly coated on the surface of the secondary particles. Additionally, inductively coupled plasma (ICP) emission spectroscopy analysis revealed that the boron content per 100 wt% of the cathode active material before washing was 540 ppm, and the boron content per 100 wt% of the cathode active material after washing was 30 ppm. The boron detected even after washing was confirmed to be coated on the internal grain boundaries of the secondary particles. The boron removed during the washing process corresponds to the component coated on the surface of the secondary particles and is confirmed to be 540 - 30 = 510 ppm. Accordingly, the ratio of the boron weight in the boron coating layer to the boron weight in the grain boundary boron coating portion is calculated to be approximately 94:6.

[0308] Furthermore, TEM-EELS analysis was performed on the cross-section of the secondary particle from the surface inward, and it was confirmed that a boron doping layer was formed in the region corresponding to a depth of 2 nm to 5 nm from the outermost surface. This boron layer is understood to exist within the primary particle exposed on the surface of the secondary particle, and to exist in a layered form along the periphery of the surface of the secondary particle.

[0309] The second positive electrode active material is a second lithium nickel-based composite oxide (LiNi 0.94 Co 0.04 Al 0.1 Mn 0.01 Contains O2, and SEM analysis results show an average particle size (D 50 It was confirmed to be in the form of a single particle with a particle size of about 3 μm. In addition, SEM-EDS analysis and ToF-SIMS mass spectrometry results confirmed that lithium boron oxides such as LiBO2 were evenly coated on the surface of the single particle.

[0310]

[0311] 4. Preparation of the first solid electrolyte (Li6PS5Cl, Argyrodite, 0.85㎛)

[0312] An azirodite-type sulfide-based solid electrolyte was synthesized through the process described below. Mixing of raw materials, pre-treatment, and post-treatment of heat treatment were all carried out in a glove box under an argon atmosphere. As raw materials, lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), and lithium chloride (LiCl) were mixed in a molar ratio of 2.5:0.5:1 to prepare a mixed powder. After uniformly mixing the mixed powder with a Henschel mixer, it was first calcined at 250°C for 5 hours in a tubular furnace where argon gas flowed at a constant speed of 8 SLM.

[0313] The powder from the first calcination was homogeneously mixed again using a Henschel mixer and sieved, then subjected to a second calcination at 500°C for 10 hours in a tubular furnace where argon gas flowed at a constant speed of 8 SLM. The powder from the second calcination was ground and sieved to obtain Li6PS5Cl sulfide-based solid electrolyte particles. The size of the first solid electrolyte particles obtained in this way (D 50 ) is confirmed to be approximately 0.85 µm.

[0314]

[0315] 5. Preparation of the second solid electrolyte (Li 5.4 PS 4.4 Cl 1.6 , Argyrodite, 0.8 µm)

[0316] A second sulfide-based solid electrolyte was prepared in substantially the same manner as the first sulfide-based solid electrolyte, except that lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), and lithium chloride (LiCl) were mixed as raw materials in a molar ratio of 1.9:0.5:1.6. The second solid electrolyte thus obtained has a composition of Li 5.4 PS 4.4 Cl 1.6 It is an azyrodite-type solid electrolyte and particle size (D 50) is confirmed to be about 0.8 µm.

[0317]

[0318] 6. Preparation of the first positive electrode active material layer

[0319] A first cathode composition was prepared by adding 85 wt% of a cathode active material with a boron coating layer, 13.44 wt% of an azirodite-type first solid electrolyte of Li6PS5Cl, 1 wt% of a PVdF binder, 0.4 wt% of a carbon nanotube conductive material, and 0.16 wt% of hydrogenated nitrile butadiene rubber (HNBR) as a dispersant to an isobutyryl isobutyrate (IBIB) solvent and mixing. This was applied to a cathode current collector at a loading level of 17 mg / cm² and dried to form a first cathode active material layer.

[0320]

[0321] 7. Preparation of the second positive electrode active material layer

[0322] 85 wt% of positive active material with a boron coating layer, Li 5.4 PS 4.4 Cl 1.6 A second cathode composition was prepared by adding 13.44 wt% of an azyrodite-type second solid electrolyte, 1 wt% of a PVdF binder, 0.4 wt% of a carbon nanotube conductive material, and 0.16 wt% of hydrogenated nitrile butadiene rubber (HNBR) as a dispersant to an isobutyryl isobutyrate (IBIB) solvent and mixing. This was applied to the first cathode active material layer at 17 mg / cm² 2 A second positive active material layer was formed by applying it at a loading level and drying it, and a positive was prepared by rolling (hydrostatic press; WIP; 500 Mpa, 85℃, 30 min).

[0323]

[0324] 8. Manufacturing of all-solid-state secondary batteries

[0325] Carbon black and 2-naphthalene thiol powder were mixed in a weight ratio of 10:1 and heat-treated at 90°C. The heat-treated product was added to a water solvent, and AgNO3 and a reducing agent, NaBH4, were added and mixed. At this time, the AgNO3 content was 11 wt% relative to the total content of carbon black and AgNO3 (100 wt%), and the NaBH4 content was 22 wt% relative to 100 wt% of AgNO3. The resulting product was heat-treated at 400°C for 4 hours under a nitrogen atmosphere to produce a compound in which Ag is supported on a carbon material. In the prepared Ag-C supported compound, the carbon material accounted for 94.6 wt% relative to the total amount of carbon material and Ag, the Ag content was 5.4 wt%, and the sulfur content was approximately 1.2 wt% relative to 100 wt% of the Ag-C supported compound. Transmission electron microscopy (TEM) analysis of the prepared Ag-C supported compound confirmed that silver is uniformly dispersed in the carbon material. In addition, X-ray photoelectron spectroscopy (XPS) analysis of the Ag-C supported compound revealed a Sp2 spectrum at approximately 161.8 eV corresponding to the Ag-S binding energy.

[0326] A cathode coating layer composition was prepared by mixing the manufactured Ag-C supported compound, styrene-butadiene rubber, and sodium carboxymethyl cellulose in a water solvent at a weight ratio of 100:6:3.

[0327] A precipitation type cathode was prepared by coating a stainless steel foil current collector with a thickness of 10 μm with the prepared cathode coating layer composition and vacuum drying it at 80°C to form a cathode coating layer with a thickness of 12 μm on the surface of the current collector.

[0328] Azirodite-type solid electrolyte of Li6PS5Cl (D 50A composition for forming a solid electrolyte layer was prepared by adding (=3㎛) to an IBIB solvent containing an acrylic binder and mixing. The composition contains 98.5 wt% of solid electrolyte and 1.5 wt% of binder. The composition was cast onto a release film and dried at room temperature to prepare a solid electrolyte layer.

[0329] A solid electrolyte layer was laminated on the anode, and then a cathode was laminated on top of it. This was sealed in a pouch form and subjected to hydrostatic pressing at a high temperature of 80°C at 500 MPa for 30 minutes to manufacture an all-solid-state secondary battery.

[0330]

[0331] Comparative Example 1-1 (Li6PS5Cl 34 mg / cm² thick film anode)

[0332] A positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1-1, except that when manufacturing the first positive electrode active material layer, 34 mg / cm² of the first positive electrode composition was applied to the positive electrode current collector and the second positive electrode active material layer was not applied.

[0333]

[0334] Comparative Example 1-2 (Li6PS5Cl 17 mg / cm² - 17 mg / cm² bilayer anode)

[0335] A positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1-1, except that a first solid electrolyte was used instead of a second solid electrolyte when manufacturing the second positive electrode active material layer.

[0336]

[0337] Comparative Examples 1-3 (Li 5.4 PS 4.4 Cl 1.6 34 mg / cm² thick film anode)

[0338] A positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1-1, except that a second positive electrode composition of 34 mg / cm² was applied without applying a first positive electrode active material layer on the positive electrode current collector.

[0339]

[0340] Comparative Examples 1-4 (Li 5.4 PS 4.4 Cl 1.6 17 mg / ㎠ - 17 mg / ㎠ (two-layer anode)

[0341] A positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1, except that a second solid electrolyte was used instead of a first solid electrolyte when manufacturing the first positive electrode active material layer.

[0342] To aid understanding, the anode design details of Example 1-1 and Comparative Examples 1-1 to 1-4 are briefly shown in Table 1 below.

[0343] First positive active material layer, second positive active material layer, double layer positive example 1-1Li6PS5ClLi 5.4 PS 4.4 Cl 1.6 Comparative Example 1-1Li6PS5ClX Comparative Example 1-2Li6PS5ClLi6PS5ClO Comparative Example 1-3Li 5.4 PS 4.4 Cl 1.6 X Comparative Example 1-4Li 5.4 PS 4.4 Cl 1.6 Li 5.4 PS 4.4 Cl 1.6 O

[0344] Evaluation Example 1-1: Evaluation of Initial Charge / Discharge Capacity of All-Solid State Secondary Battery

[0345] The all-solid-state secondary batteries prepared in Example 1-1 and Comparative Examples 1-1 to 1-4 were charged to 4.25V with a constant current of 0.1C at 45℃ and to 0.05C with a constant voltage to measure the initial charge capacity, and discharged to 2.5V with 0.1C to measure the initial discharge capacity. The ratio of discharge capacity to charge capacity was calculated as efficiency, and the results are shown in Table 2.

[0346] Charge Capacity (mAh / g) Discharge Capacity (mAh / g) Efficiency (%) Example 1-1 24 3.8 200 0.28 2.1 Comparative Example 1-1 22 7.1 174 77 6.9 Comparative Example 1-2 23 2.9 179 277 7.0 Comparative Example 1-3 21 8.1 170 878 3 Comparative Example 1-4 23 7.1 178 77 5.4

[0347] Referring to Table 2, it can be seen that Example 1-1 has improved initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency compared to Comparative Examples 1-1 to 1-4.

[0348] Evaluation Example 1-2: Evaluation of High Rate Characteristics

[0349] For the all-solid-state secondary batteries prepared in Example 1-1 and Comparative Examples 1-1 to 1-4, after performing initial charge and discharge as in Evaluation Example 1-1, the batteries were charged with a constant current of 0.1C to an upper limit voltage of 4.25V and with a constant voltage of 0.05C, and then discharged at 0.33C to a discharge cutoff voltage of 2.5V to measure the discharge capacity at 0.33C. Subsequently, the batteries were charged with a constant current of 0.1C to an upper limit voltage of 4.25V and with a constant voltage of 0.05C, and then discharged at 1.0C to a discharge cutoff voltage of 2.5V to measure the discharge capacity at 1.0C. The high-rate discharge characteristic (rate capability) was calculated from Equation 1 below, and the discharge capacity and high-rate discharge characteristic for each cycle are shown in Table 3.

[0350] [Equation 1]

[0351] High-rate discharge characteristic (%) = {(Discharge capacity at 1C) / (Discharge capacity at 0.1C)} x 100

[0352] Discharge Capacity (mAh / g) High Rate Discharge Characteristics (%) 0.1C 1.0C Example 1-1 200 16783 Comparative Example 1-1 1759 554 Comparative Example 1-2 179 12067 Comparative Example 1-3 171 3420 Comparative Example 1-4 179 7743

[0353] Referring to Table 3 above, it can be confirmed that Example 1-1 has significantly superior high-rate discharge characteristics compared to Comparative Examples 1-1 to 1-4.

[0354] Evaluation Example 1-3: Evaluation of Lifespan Characteristics of All-Solid State Secondary Batteries

[0355] For the all-solid-state secondary batteries prepared in Example 1-1 and Comparative Examples 1-1 to 1-4, after performing initial charge and discharge as in Evaluation Example 1, the life characteristics were evaluated by repeating the charging and discharging at 0.33C and 0.33C 100 times in a voltage range of 2.5V to 4.25V at 45℃. Table 4 below shows the initial discharge capacity (1-cycle discharge capacity), 100-cycle discharge capacity, and the capacity retention rate, which is the ratio of the latter to the former.

[0356] Single Discharge Capacity (mAh / g) 100 Discharge Capacity (mAh / g) Capacity Retention Rate (%) Example 1-11 65 14 789 Comparative Example 1-11 26 90 72 Comparative Example 1-21 38 10 173 Comparative Example 1-31 17 9 782 Comparative Example 1-41 26 10 280

[0357] Referring to Table 4 above, it can be seen that Example 1-1 has a further improved capacity retention rate at 100 cycles compared to Comparative Examples 1-1 to 1-4.

[0358]

[0359] [Second Implementation Example]

[0360] The second embodiment is substantially identical to the first embodiment above, except that the positive active material Type A is changed to the positive active material Type B. Except for the details regarding the positive active material Type B below, the details described in the first embodiment above can be applied in the same way.

[0361] In one embodiment, a positive electrode is provided comprising a positive current collector, and a first positive active material layer and a second positive active material layer located on the positive current collector. The first positive active material layer comprises a positive active material comprising a core particle containing a lithium nickel-based composite oxide and a Zr coating layer located on the core particle, and a first solid electrolyte containing an azirodite-type sulfide containing Li, P, S and a halogen element. The second positive active material layer comprises a positive active material comprising a core particle containing a lithium nickel-based composite oxide and a Zr coating layer located on the core particle, and a second solid electrolyte containing an azirodite-type sulfide containing Li, P, S and a halogen element. Here, the first solid electrolyte and the second solid electrolyte have different compositions from each other, specifically, the molar ratio of at least one of Li, P, S and a halogen element is different from each other.

[0362]

[0363] Cathode active material - Type B

[0364] The positive active material included in the first positive active material layer and the positive active material included in the second positive active material layer may be identical or different from each other, and each independently includes a core particle containing a lithium nickel-based composite oxide and a Zr coating layer located on said core particle.

[0365]

[0366] Core particles of the positive electrode active material

[0367] The lithium nickel-based composite oxide of the above core particles can be represented, for example, by the following chemical formula 5.

[0368] [Chemical Formula 5]

[0369] Li a5 Ni x5 M 5 y5 M 6 z5 O 2-b5 X b5

[0370] In the above chemical formula 5, 0.9≤a5≤1.2, 0.3≤x5≤1, 0≤y5≤0.7, 0≤z5≤0.7, 0.9≤x5+y5+z5≤1.1, and 0≤b5≤0.1, and M 5 and M 6 are distinct elements and each independently is one or more of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, T, Zn and Zr, and X is one or more of F, P and S.

[0371] For example, in the above chemical formula 5, 0.6≤x5≤1, 0≤y5≤0.4, 0≤z5≤0.4, or 0.7≤x5≤1, 0≤y5≤0.3, 0≤z5≤0.3, or 0.8≤x5≤1, 0≤y5≤0.2, 0≤z5≤0.2, or 0.9≤x5<1, 0 <y5≤0.1, 0≤z5≤0.1이거나, 0.9≤x5≤1, 0≤y5≤0.1, 0≤z5≤0.1일 수 있다.

[0372] The cathode active material containing the above lithium nickel-based composite oxide as a core particle can achieve high capacity and high energy density.

[0373] The nickel content in the above lithium-nickel composite oxide may be 30 mol% or more with respect to 100 mol% of metal excluding lithium, 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.

[0374]

[0375] Zr coating layer of the positive electrode active material

[0376] A positive electrode active material according to one embodiment includes a Zr coating layer located on the surface of a core particle. The Zr coating layer can be described as a type of buffer layer or buffer layer and can effectively suppress side reactions between a lithium nickel-based composite oxide and a sulfide-based solid electrolyte.

[0377] The above Zr coating layer may be characterized as being formed via a dry coating method. Such a Zr coating layer may contain a mixed phase of ZrO2 and Li6Zr2O7. That is, the Zr coating layer can be said to contain ZrO2, which has relatively high crystallinity, and Li6Zr2O7, which has lower crystallinity. The presence or absence of ZrO2 and Li6Zr2O7 can be determined, for example, through the Inverse FFT or FFT rotation pattern of HRTEM images of the surface of the cathode active material. A Zr coating layer containing ZrO2 and Li6Zr2O7 can facilitate the movement of lithium ions on the surface of the cathode active material core particles, improve the structural stability of the cathode active material, and improve interfacial resistance by reducing reactivity with sulfide-based solid electrolytes.

[0378] The Zr coating layer may further include amorphous regions. For example, the Zr coating layer may include a ZrO2 crystalline phase, a Li6Zr2O7 crystalline phase, and a Zr-containing amorphous region. Such a Zr coating layer can have a thin and uniform thickness while improving lithium ion conductivity and enhancing the lifespan characteristics of the cathode active material.

[0379] The Zr coating layer may be in the form of a continuous film or an island. The coating layer can be manufactured using a dry coating method described later, and thus the coating can be formed well with a uniform thickness on the surface of the positive active material without aggregation or localization. For example, the Zr coating layer may exist as a continuous and uniform film on the surface of secondary particles. In this case, the capacity and lifespan characteristics of the positive active material can be further improved.

[0380] The thickness of the Zr coating layer may be 5 nm to 300 nm, for example, 5 nm to 200 nm, 5 nm to 100 nm, 5 nm to 80 nm, or 10 nm to 50 nm. By having the Zr coating layer within the above thickness range, the electrochemical characteristics of the battery can be improved by suppressing the increase in resistance caused by the coating, effectively protecting the positive electrode active material, and improving ion conductivity.

[0381] According to one embodiment, the Zr coating layer may be formed with a uniform thickness without being locally present or aggregated on the surface of the core particle. For example, the deviation in the thickness of the Zr coating layer may be 20% or less, 10% or less, or 5% or less relative to the diameter of the positive active material, and may be 100 nm or less, 50 nm or less, or 30 nm or less. Here, the deviation in the coating layer thickness refers to the thickness of the coating layer within a single positive active material particle. The deviation in the coating layer thickness may mean, for example, measuring the thickness at about 10 points in an electron microscope image of a cross-section of a single positive active material particle, calculating the arithmetic mean, dividing the absolute value of the difference between one data point and the arithmetic mean value by the arithmetic mean value, and multiplying by 100. The fact that the deviation or standard deviation of the coating layer thickness satisfies the above range means that a coating layer of uniform thickness is formed in a good form on the surface of the positive active material particles, and accordingly, the structural stability of the positive active material is improved, side reactions with the solid electrolyte are effectively suppressed, and the increase in resistance or decrease in capacity caused by the coating can be minimized.

[0382] The Zr content of the Zr coating layer may be 0.1 to 0.6 molar parts with respect to 100 molar parts of the total metal excluding lithium in the lithium nickel-based composite oxide of the core particles, for example, 0.1 to 0.5 molar parts, or 0.1 to 0.4 molar parts. In addition, the Zr content of the Zr coating layer may be 0.1 to 6 wt% with respect to 100 wt% of the positive electrode active material, for example, 0.5 to 6 wt%, or 1 to 5.5 wt%. Alternatively, the Zr content of the Zr coating layer may be 0.1 to 10 at% with respect to 100 at% of the positive electrode active material, for example, 0.1 to 8 at%, 0.1 to 7 at%, 0.5 to 6.5 at%, or 1 to 6 at%.

[0383] When the Zr content of the Zr coating layer satisfies the above range, the Zr coating layer can adequately protect the positive electrode active material without acting as a resistor, and can exist well with a uniform thickness without aggregating or existing locally on the surface of the core particles; accordingly, lifespan characteristics can be effectively improved without degrading the capacity of the positive electrode active material. For example, if the Zr content is excessive, the coating layer becomes thick and may act as a resistive layer, which may reduce the charge / discharge capacity of the battery; conversely, if the Zr content is too low, it may not adequately perform the buffer function, which may degrade the lifespan characteristics of the positive electrode active material.

[0384]

[0385] Method for manufacturing positive electrode active material

[0386] A positive electrode active material according to one embodiment can be manufactured by dry mixing a core particle containing a lithium nickel-based composite oxide and a zirconium raw material and heat treating them.

[0387] The above method applies a dry coating method, which does not use organic solvents or expensive coating raw materials, and allows the use of existing equipment, making it economical, environmentally friendly, and capable of realizing mass production. According to the above method, a positive electrode active material with a coating layer containing ZrO2 and Li6Zr2O7 can be synthesized, and a coating layer of appropriate content and thickness can be synthesized in a good form, thereby enabling the production of a positive electrode active material with improved capacity and lifespan characteristics. For example, such a positive electrode active material has low reactivity with sulfide-based solid electrolyte particles and low interfacial resistance, so it can be applied to all-solid-state secondary batteries to improve capacity, rate, and lifespan characteristics.

[0388] The zirconium raw material is a compound containing the element zirconium, and any compound capable of dry mixing may be applied without limitation. The zirconium raw material may be, for example, a zirconium-containing oxide, a zirconium-containing sulfide, a zirconium-containing carbonate, a zirconium-containing hydroxide, etc., and may be, for example, zirconium oxide, zirconium sulfide, zirconium carbonate, zirconium hydroxide, or a combination thereof.

[0389] Zirconium raw material can be mixed in an amount of 0.1 to 0.6 molar parts per 100 molar parts of the total metal excluding lithium in the lithium nickel-based composite oxide, for example, 0.1 to 0.5 molar parts, or 0.1 to 0.4 molar parts. When zirconium raw material is introduced within the above range, a coating layer of appropriate content and thickness can be formed, which can sufficiently perform the role of protecting the positive electrode active material and can exist with a uniform thickness without aggregating or existing locally on the surface of the core particles. For example, if the content of zirconium raw material is excessive, the coating layer becomes thick and may act as a resistive layer, thereby reducing the charge / discharge capacity of the positive electrode active material; conversely, if the content of zirconium raw material is too low, it may not sufficiently perform the buffer role, which may reduce the lifespan characteristics of the positive electrode active material.

[0390] The zirconium raw material may be in the form of nanoparticles, for example. The zirconium raw material is in the form of particles, and the average particle size (D) of the particles 50 ) may be, for example, 10 nm to 500 nm, 10 nm to 500 nm, or 50 nm to 500 nm. As an example, the zirconium raw material is a particle containing zirconium oxide, and the average particle size (D) of the particle is 50 ) may be 10 nm to 500 nm. In this case, it may be advantageous for synthesizing a coating layer of appropriate thickness.

[0391] In one embodiment, mixing dry means mixing without a solvent and can be understood as a solid-state coating method. This is distinguished from wet coating or liquid coating.

[0392] According to the above method for manufacturing the positive electrode active material, a coating layer having a uniform thickness and containing a mixed phase of ZrO2 and Li6Zr2O7 can be formed on the surface of the core particles. The heat treatment temperature may be 420°C to 580°C, for example, 430°C to 570°C, 440°C to 560°C, 450°C to 550°C, or 460°C to 530°C. By heat treating within the above temperature range, it is possible to synthesize a Zr coating layer having an appropriate crystalline phase, and the Zr coating layer can sufficiently perform a buffer role without acting as a resistor, thereby improving the capacity and lifespan characteristics of the positive electrode active material. For example, if the heat treatment temperature is below 420°C, the Zr coating layer may not form an appropriate crystalline phase and may act only as a resistor, which may degrade the capacity characteristics of the positive electrode active material. If the above heat treatment temperature exceeds 580℃, the coating materials may aggregate or be coated only locally, reducing the buffer effect, and zirconium may be absorbed into the cathode active material, failing to act as a buffer and potentially degrading capacity and lifespan characteristics.

[0393] The above heat treatment can be carried out in an oxygen atmosphere, for example, for 5 to 25 hours, or for 10 to 20 hours. A good coating layer can be formed under these conditions.

[0394] In one embodiment, when the core particles and the zirconium raw material are mixed dry, a lithium raw material may be mixed together. The lithium raw material is a compound containing lithium and can be applied without limitation as long as it is capable of dry mixing. The lithium raw material may be, for example, Li2CO3, LiOH, hydrates thereof, or a combination thereof. In one embodiment, anhydrous lithium hydroxide may be used as the lithium raw material. The lithium raw material may be mixed in an amount of more than 1 mole and less than or equal to 4 moles per 1 mole of the zirconium raw material, for example, more than 1 mole and less than or equal to 3 moles, or more than or equal to 2 moles and less than or equal to 4 moles. When the lithium raw material is mixed together and heat-treated, it is advantageous for forming a lithium zirconium oxide, for example, a Li6Zr2O7 crystalline phase, in the coating layer, and it is advantageous for increasing lithium ion conductivity and obtaining a coating layer of appropriate thickness in a good form.

[0395]

[0396] Bimodal positive electrode active material

[0397] The positive active material of the first positive active material layer and the positive active material of the second positive active material layer each independently comprise: (i) a first positive active material comprising a lithium nickel-based composite oxide, a plurality of primary particles aggregated to form secondary particles in which at least a portion of the primary particles are arranged radially, and a Zr coating layer located on the surface of the secondary particles; and (ii) a lithium nickel-based composite oxide, a plurality of primary particles aggregated to form secondary particles, and a Zr coating layer located on the surface of the secondary particles, wherein the average particle size (D) of the first positive active material 50 Average particle size (D) smaller than ) 50 It may include a second positive active material having ).

[0398] The first positive active material can be expressed as an opposite or an opposite, and the average particle size of the secondary particle (D 50) can be 9 μm to 25 μm, for example, 11 μm to 18 μm, or 12 μm to 16 μm. The second positive electrode active material can be expressed as microparticles or microparticles, and the average particle size (D) of the secondary particles 50 ) can be 2 μm to 8 μm, for example 2.5 μm to 7 μm, or 3 μm to 6 μm. Here, the average particle size (D 50 ) may be obtained by selecting approximately 20 random particles from a scanning electron microscope (SEM) image of the positive electrode active material, measuring their particle size (diameter, or major axis, or length of the major axis), obtaining a particle size distribution, and taking the size of the particle with a cumulative volume of 50% of the particle size distribution as the average particle size.

[0399] With respect to the total of 100 wt% of the first positive active material and the second positive active material, the first positive active material may be included in an amount of 60 wt% to 95 wt%, 70 wt% to 90 wt%, or 80 wt% to 90 wt%, and the second positive active material may be included in an amount of 5 wt% to 40 wt%, 10 wt% to 30 wt%, or 10 wt% to 20 wt%. When the first positive active material and the second positive active material are mixed within the above weight ranges, high capacity and lifespan characteristics can be achieved while maximizing the energy density of the positive.

[0400]

[0401] First positive active material of bimodal positive active material

[0402] The first cathode active material may include, for example, a lithium nickel-cobalt-aluminum-based composite oxide, which means an oxide comprising lithium, nickel, cobalt, and aluminum and optionally further comprising other elements, and may be expressed as Ni-Co-Al or NCA.

[0403] The lithium nickel-cobalt-aluminum composite oxide of the first positive electrode active material can be represented by Chemical Formula 1.

[0404] [Chemical Formula 1]

[0405] Li a1 Ni x1 Co y1 Al z1 M 1 w1 O 2-b1 X b1

[0406] In the above Chemical Formula 1, 0.9≤a1≤1.2, 0.7≤x1<1, 0 <y1<0.3, 0<z1<0.3, 0≤w1<0.3, 0.9≤x1+y1+z1+w1≤1.1, 및 0≤b1≤0.1이고, M 1 is one or more of the elements B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more of the elements F, P, and S.

[0407] In the above chemical formula 1, for example, 0.7≤x1≤0.98, 0.01≤y1≤0.29, 0.01≤z1≤0.29, 0≤w1≤0.28, 0.8≤x1≤0.98, 0.01≤y1≤0.19, 0.01≤z1≤0.19, 0≤w1≤0.18, or 0.9≤x1≤0.98, 0.01≤y1≤0.09, 0.01≤z1≤0.09, 0≤w1≤0.08.

[0408] The first positive active material is in the form of secondary particles formed by the aggregation of multiple primary particles, and the secondary particles may be spherical, elliptical, polygonal, amorphous, etc.

[0409] The average particle size of the primary particles constituting the secondary particles of the first cathode active material may be less than 200 nm, for example, 50 nm or more and less than 200 nm, 100 nm or more and less than 200 nm, 50 nm or more and less than 190 nm, or 50 nm or more and less than 180 nm. When the average particle size of the primary particles satisfies the above range, the lithium diffusion path is shortened, thereby reducing resistance and improving charge / discharge efficiency. Here, the average particle size of the primary particles refers to the size of the primary particles observed on the surface of the secondary particles, and can be obtained by selecting approximately 20 random primary particles from an SEM image of the surface of the secondary particles, measuring their particle sizes (diameter or major axis, or length of the major axis), and calculating the arithmetic mean thereof.

[0410] The first positive active material is characterized by having at least a portion of the primary particles forming the secondary particles arranged radially. In this case, the diffusivity of lithium is increased, which improves the initial charge-discharge efficiency and enables the securing of a high capacity. Additionally, uniform expansion and contraction are possible during the insertion and extraction of lithium, thereby improving the problem of the positive active material breaking during charging and discharging, which can improve the lifespan characteristics and safety of the battery. Furthermore, when the first positive active material is in the form of secondary particles in which at least a portion of the primary particles are arranged radially, in the method for manufacturing the positive active material according to one embodiment, the Al component is advantageous for diffusing from the precursor of the first positive active material to the precursor of the second positive active material, and as a result, a positive active material with improved capacity characteristics, initial charge-discharge efficiency, and lifespan characteristics can be manufactured.

[0411] The above radial structure is substantially the same as that described above, so a detailed explanation is omitted.

[0412]

[0413] Second positive active material of bimodal positive active material

[0414] The second cathode active material may include, for example, a lithium nickel-cobalt-aluminum-manganese-based composite oxide, which means an oxide comprising lithium, nickel, cobalt, aluminum, and manganese and optionally further comprising other elements, and can be expressed as Ni-Co-Al-Mn or NCAM.

[0415] A positive electrode active material according to one embodiment can be manufactured by a method of mixing an NCA precursor, which is a first positive electrode active material precursor, and an NCM precursor, which is a second positive electrode active material precursor, with a lithium raw material and simultaneously calcining them. In the above simultaneous calcination process, the Al component of the first positive electrode active material precursor, which is in the form of a radial secondary particle, moves or diffuses into the second positive electrode active material precursor, which is in the form of a secondary particle, thereby making the second positive electrode active material into NCAM, while conversely, the Mn component of the second positive electrode active material precursor does not diffuse into the first positive electrode active material precursor, so the first positive electrode active material does not become NCAM and remains as NCA.

[0416] It is confirmed that the second cathode active material produced in this manner differs in shape and compositional distribution from the cathode active material produced by simply using an NCAM compositional precursor, or from the NCAM cathode active material produced by post-processing with an Al raw material after manufacturing an NCM cathode active material to coat or dope it with Al, and also exhibits superior capacity and lifespan characteristics.

[0417] In addition, the cathode active material manufactured by the conventional method of calcining the first cathode active material precursor and the second cathode active material precursor separately and then mixing them, rather than calcining them simultaneously, differs from the cathode active material according to one embodiment in terms of shape and compositional distribution, and has problems such as reduced volumetric capacity of the battery due to low pellet density and low lifespan characteristics due to different degradation rates between large and small particles, and even if structural stability is improved by separately doping or coating the second cathode active material with Al, there is a problem of capacity reduction due to the addition of Al raw materials.

[0418] The lithium nickel-cobalt-aluminum-manganese-based composite oxide of the second positive electrode active material can be represented by Chemical Formula 2.

[0419] [Chemical Formula 2]

[0420] Li a2 Ni x2 Co y2 Al z2 Mn w2 M 2 v2 O 2-b2 X b2

[0421] In the above chemical formula 2, 0.9≤a2≤1.2, 0.7≤x2<1, 0 <y2<0.3, 0<z2<0.3, 0<w2<0.3, 0≤v2<0.3, 0.9≤x2+y2+z2+w2+v2≤1.1, 및 0≤b2≤0.1이고, M 2 is one or more of the elements B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Z, and X is one or more of the elements F, P, and S.

[0422] In the above chemical formula 2, for example, 0.7≤x2≤0.979, 0.01≤y2≤0.289, 0.001≤z2≤0.289, 0.01≤w2≤0.289, 0≤v2≤0.279, 0.8≤x2≤0.979, 0.01≤y2≤0.189, 0.001≤z2≤0.189, 0.01≤w2≤0.189, 0≤v2≤0.179, and 0.9≤x2≤0.979, 0.01≤y2≤0.089, 0.001≤z2≤0.089, 0.01≤w2≤0.089, 0≤v2≤0.079.

[0423] For example, the second cathode active material may have a higher aluminum content in the “surface layer of the secondary particle” than in the “inside of the secondary particle.” The inside of the secondary particle may refer to an area extending from the center of the secondary particle to approximately 80% of the radius, and the surface layer of the secondary particle refers to an area surrounding the interior, extending from the outermost surface of the secondary particle to a depth corresponding to 20% of the radius. The outermost surface refers to the surface of the secondary particle excluding the coating layer and can be understood as the boundary between the secondary particle and the Zr coating layer. That is, the secondary particle of the second cathode active material may be said to include an interior, a surface layer surrounding the interior, and a Zr coating layer located on the surface layer. Both the interior and the surface layer of the secondary particle are composed of a plurality of primary particles.

[0424] The Al content in the interior or surface layer of the secondary particle can be measured through TEM-EELS (Transmission Electron Microscope - Electron Energy Loss Spectroscopy) analysis of a cross-section cut by a focused ion beam (FIB) or the like. Additionally, the Al content may refer to the at% content of aluminum relative to 100 at% of the total metals excluding lithium in the lithium nickel-cobalt-aluminum-manganese composite oxide.

[0425] For example, the Al content in the surface layer of the secondary particle is 0.2 at% to 2.0 at% with respect to 100 at% of the total metal excluding lithium in the second positive active material, and the Al content in the interior of the secondary particle is 0 at% to 0.6 at% with respect to 100 at% of the total metal excluding lithium in the second positive active material, and the Al content in the surface layer may be higher than the Al content in the interior.

[0426] In addition, according to one embodiment, the second positive active material may have a higher aluminum content in the portion in contact with the first positive active material in the surface layer of the secondary particles than in the portion not in contact with the first positive active material. This is understood to be because the second positive active material received Al components from the first positive active material during the first heat treatment process, and it is also a characteristic that distinguishes it from cases where an NCAM precursor is used as a fine particle or where Al is separately coated or doped.

[0427] For example, in the surface layer of the secondary particles of the second positive active material, the content of aluminum relative to the total metal excluding lithium in the portion in contact with the first positive active material may be 0.8 at% to 2.0 at%, for example, 0.8 at% to 1.8 at%, or 0.9 at% to 1.6 at%. The content of aluminum relative to the total metal excluding lithium in the portion not in contact with the first positive active material may be less than 0.8 at%, for example, 0 at% to 0.7 at%, or 0.1 at% to 0.6 at%.

[0428] In other words, the second cathode active material according to one embodiment may be said to include a high-concentration Al region and a low-concentration Al region in the surface layer of the secondary particle. In the high-concentration Al region, the content of aluminum relative to the total metal excluding lithium may be 0.8 at% to 2.0 at%, for example, 0.8 at% to 1.8 at%, or 0.9 at% to 1.6 at%. In the low-concentration Al region, the content of aluminum relative to the total metal excluding lithium may be less than 0.8 at%, for example, 0 at% to 0.7 at%, or 0.1 at% to 0.6 at%.

[0429] In addition, the difference between the aluminum content in the high concentration Al region and the aluminum content in the low concentration Al region may be 0.3 at% to 2.0 at%, for example, 0.4 at% to 1.8 at%, or 0.5 at% to 1.5 at%.

[0430] It is a well-known method of separately doping or coating with Al by mixing aluminum raw materials and heat treating them after manufacturing a lithium transition metal composite oxide. However, in this case, unreacted Al raw materials, such as aluminum oxide (e.g., Al2O3), remain in the final cathode active material, and Al is unevenly doped on the particle surface, resulting in a high concentration of Al doping exceeding 2 at% in some parts of the surface, which causes a problem of reduced capacity. In contrast, the cathode active material according to one embodiment does not add a separate Al raw material during the calcination process. Accordingly, unreacted Al raw materials, such as aluminum oxide, do not exist on the outermost surface of the secondary particles of the first and second cathode active materials in the final cathode active material. Furthermore, even in the region with a high Al content in the surface layer of the second cathode active material, the Al content is 2 at% or less, and the difference in Al content between the high-concentration Al region and the low-concentration Al region is also small, at 2 at% or less. Accordingly, the second cathode active material according to one embodiment has structural stability and performance enhancement effects due to Al doping, and problems such as capacity reduction caused by adding Al raw material during calcination can be effectively suppressed.

[0431]

[0432] Method for manufacturing bimodal positive electrode active material

[0433] A bimodal positive electrode active material according to one embodiment comprises: (i) a first positive electrode active material precursor in the form of secondary particles comprising a nickel-based composite hydroxide and formed by the aggregation of a plurality of primary particles, wherein at least a portion of the primary particles are arranged radially; and a secondary particle in the form of a nickel-based composite hydroxide and a plurality of primary particles aggregated, wherein the average particle size (D) of the first positive electrode active material precursor. 50 Average particle size (D) smaller than ) 50 A second positive active material precursor having ) and a lithium raw material can be mixed and subjected to a first heat treatment to obtain a preliminary positive active material, and (ii) the preliminary positive active material and a zirconium raw material can be dry-mixed and subjected to a second heat treatment to produce a preliminary positive active material.

[0434] (i) In step (i), the first positive active material precursor may include, for example, a nickel-cobalt-aluminum-based composite hydroxide, and the second positive active material precursor may include, for example, a nickel-cobalt-manganese-based composite hydroxide.

[0435] Steps (i) and (ii) can be described as a method of mixing a counter-proportion NCA radial secondary particle precursor and a micro-proportion NCM secondary particle precursor with a lithium raw material, simultaneous calcining, and then dry-coating zirconium. During the simultaneous calcination process, the Al component of the counter-proportion diffuses or migrates into the micro-proportion, making the micro-proportion NCAM composition. Consequently, a cathode active material can be manufactured in which the NCA of the counter-proportion radial secondary particle and the NCAM of the micro-proportion secondary particle are mixed. This is understood to be possible because, within the temperature range of simultaneous calcination, the diffusion rate of the Al component of the counter-proportion is faster than that of the Mn of the micro-proportion, and furthermore, as the counter-proportion precursor takes the form of a radial secondary particle, the Al component is more easily transferred to the micro-proportion. The pre-cathode active material manufactured by this method can exhibit high capacity while realizing high initial charge-discharge efficiency and excellent lifespan characteristics.

[0436] According to the above manufacturing method, the volumetric capacity can be significantly improved compared to the conventional method of manufacturing by individually calcining large and small particles and then mixing them. Furthermore, the initial discharge capacity, volumetric capacity, and energy density can be further improved compared to the case where only the small particles are Al-doped or coated after individual calcination and the large and small particles are mixed. Additionally, according to the method of one embodiment, even when applying a simultaneous calcination method, lifespan characteristics can be improved compared to the case where large and small particles having the same composition are used, and the initial discharge capacity and energy density can be improved compared to the case where Al is separately doped or coated after simultaneous calcination. In the manufacturing method according to one embodiment, while not mixing aluminum raw materials during processes such as the first and second heat treatments, an appropriate amount of aluminum is introduced into the large and small particles to ensure structural stability and improve the problem of capacity reduction caused by the addition of aluminum raw materials.

[0437] The first positive active material precursor can be represented, for example, by the chemical formula 11 below.

[0438] [Chemical Formula 11]

[0439] Ni x11 M 11 y11 M 12 z11 (OH)2

[0440] 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 Each is independently one or more of the elements Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr.

[0441] As a more specific example, the first positive active material precursor may include a nickel-cobalt-aluminum-based complex hydroxide, which can be specifically represented by the following chemical formula 12.

[0442] [Chemical Formula 12]

[0443] Ni x12 Co y12 Al z12 M 13 w12 (OH)2

[0444] In the above chemical formula 12, 0.7 ≤ x 12 < 1, 0 <y12<0.3, 0<z12<0.3, 0≤w12<0.3, 0.9≤x12+y12+z12+w12≤1.1이고, M 13 It is one or more of the elements B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr.

[0445] The first cathode active material precursor may be in the form of secondary particles formed by the aggregation of a plurality of primary particles, wherein at least a portion of the primary particles are arranged radially. The average particle size of the secondary particles may be 10 μm to 25 μm, for example, 11 μm to 20 μm, or 12 μm to 18 μm. Here, the average particle size of the secondary particles is determined by selecting approximately 20 arbitrary particles from an SEM image of the first cathode active material precursor, measuring their particle sizes (diameter, major axis, or length of the major axis), obtaining a particle size distribution, and determining the diameter (D) of the particle whose cumulative volume is 50 volume% in the particle size distribution. 50 It may be that ) was taken as the average particle size.

[0446] The first cathode active material precursor can be prepared by a multi-stage co-precipitation reaction. That is, a complex metal raw material is prepared by mixing metal raw materials such as nickel raw materials, and a complexing agent and a pH adjuster are added to control the pH of the mixture while proceeding with the co-precipitation reaction to produce a nickel-based complex hydroxide of a desired composition. The complexing agent plays a role in controlling the reaction rate of precipitate formation in the co-precipitation reaction and may be, for example, ammonium hydroxide (NH4OH) or citric acid. The pH adjuster may be, for example, sodium hydroxide (NaOH), sodium carbonate (Na2CO3), sodium oxalate (Na2C2O4), etc. The pH of the mixture may be controlled to a range of, for example, 10 to 13.

[0447] The above co-precipitation reaction can proceed in multiple stages, for example, in two, three, or four stages. In each stage, the concentration of the complexing agent, the input rate of the metal raw material, the pH control range, the reaction temperature, the reaction time, or the stirring power can be controlled differently. Through such control, a cathode active material precursor in the form of secondary particles in which at least a portion of the primary particles are arranged radially can be produced, and secondary particles with different internal and external shapes can also be produced.

[0448] For example, a first cathode active material precursor with a radial structure can be manufactured in the following manner. The method for manufacturing the first cathode active material precursor may include a first process, a second process, and a third process for forming a core, an intermediate layer, and a shell in sequence. In the first process, a complexing agent, a pH adjuster, and a metal raw material are introduced into a reactor and reacted. At this time, the concentration of the complexing agent may be 0.1M to 0.7M and the input amount may be 6 mL / min to 12 mL / min. The concentration of the metal raw material may be 0.1M to 3.5M and the input amount may be 50 mL / min to 100 mL / min. Subsequently, in the second process, the complexing agent, the pH adjuster, and the metal raw material are further introduced, at which time the concentration of the complexing agent may be 0.3M to 1.0M and the input amount may be 8 mL / min to 15 mL / min. The concentration of the metal raw material may be 0.1M to 3.5M and the input amount may be 60 mL / min to 120 mL / min. Subsequently, in the third process, the concentration and input amount of the complexing agent and the metal raw material are further increased or maintained at the same level to prevent a decrease in the particle growth rate. At this time, the concentration of the complexing agent may be 0.35M to 1.0M and the input amount may be 12 mL / min to 20 mL / min. The concentration of the metal raw material may be 0.1M to 2.5M and the input amount may be 70 mL / min to 150 mL / min. In the first to third processes, the pH may be adjusted to between 10 and 12.

[0449] The second positive active material precursor may include, for example, a nickel-cobalt-manganese-based complex hydroxide, which can be specifically represented by the following chemical formula 14.

[0450] [Chemical Formula 14]

[0451] Ni x14 Co y14 Mn w14 M 15 v14 (OH)2

[0452] In the above chemical formula 14, 0.7 ≤ x 14 < 1, 0 <y14<0.3, 0<w14<0.3, 0≤v14<0.3, 0.9≤x14+y14+w14+v14≤1.1이고, M 14 It is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr.

[0453] The second cathode active material precursor may be in the form of secondary particles in which a plurality of primary particles are aggregated. The average particle size of the secondary particles may be 2 μm to 8 μm, for example, 2.5 μm to 7 μm, or 3 μm to 6 μm. Here, the average particle size of the secondary particles is determined by selecting approximately 20 arbitrary particles from an SEM image of the second cathode active material precursor, measuring their particle sizes (diameter, major axis, or length of the major axis), obtaining a particle size distribution, and determining the diameter (D) of the particle whose cumulative volume is 50 volume% in the particle size distribution. 50 It may be that ) was taken as the average particle size.

[0454] The second positive active material precursor can be prepared by a general co-precipitation reaction.

[0455] The mixing weight ratio of the first positive active material precursor and the second positive active material precursor may be 60:40 to 95:5, 70:30 to 90:10, or 80:20 to 90:10.

[0456] The above lithium raw material may be, for example, Li2CO3, LiOH, hydrates thereof, or a combination thereof. The lithium content of the above lithium raw material may be mixed in an amount of 0.8 to 1.2 molar parts, 0.8 to 1 molar part, 0.8 to 0.995 molar parts, 0.9 to 0.995 molar parts, or 0.950 to 0.995 molar parts relative to 1 molar part of the total metal in the first positive active material precursor and the second positive active material precursor.

[0457] The first heat treatment can be carried out, for example, at 600°C to 1000°C or 700°C to 900°C. A first positive active material and a second positive active material having optimal compositions can be manufactured, respectively, within the above temperature ranges.

[0458] For example, the first heat treatment includes a heating step and a temperature holding step, and the heating time may be set longer than the temperature holding time. For example, the heating time may be 6 to 16 hours and the temperature holding time may be 1 to 9 hours, and the heating time may be longer than the temperature holding time. In the first heat treatment, the heating time may be, for example, 6 to 15 hours, 6 to 14 hours, 6 to 13 hours, or 7 to 12 hours, and the temperature holding time may be 2 to 9 hours, or 3 to 8 hours. Also, the ratio of (heating time):(temperature holding time) may be 1.1:1 to 10:1, for example, 1.1:1 to 8:1, 1.1:1 to 6:1, 1.1:1 to 5:1, or 1.1:1 to 4:1.

[0459] The preliminary positive electrode active material obtained through the first heat treatment may be a mixture of a preliminary first positive electrode active material in the form of secondary particles, wherein the primary particles are aggregated and at least a portion of the primary particles are arranged radially, and a preliminary second positive electrode active material in the form of secondary particles, wherein the primary particles are aggregated and the primary particles are aggregated, wherein the preliminary second positive electrode active material comprises a lithium nickel-cobalt-aluminum-manganese-based composite oxide represented by the first chemical formula 2.

[0460] In step (ii) above, a zirconium-containing coating layer can be formed on both large and small particles by dry mixing the preliminary cathode active material and the zirconium raw material and performing a second heat treatment, and this Zr coating layer may include ZrO2 and Li6Zr2O7. Since the details regarding step (ii), such as the zirconium raw material and heat treatment, are substantially the same as those described in the method for manufacturing the cathode active material described above, a detailed explanation is omitted.

[0461]

[0462] Example 2-1 (Li6PS5Cl 17 mg / cm² - Li 5.4 PS 4.4 Cl 1.6 17 mg / ㎠ (two-layer anode)

[0463] 1. Preparation of the first nickel-based complex hydroxide

[0464] The first nickel-based complex hydroxide (Ni), which is a precursor of the first positive electrode active material, is obtained through the coprecipitation method described below. 0.945 Co 0.04 Al 0.015 (OH)2) was synthesized. A mixed solution of metal raw materials was prepared by dissolving nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and sodium aluminum sulfate (NaAl(SO4)2·12H2O) in distilled water, the solvent, in a molar ratio of 94.5:4:1.5. In addition, water ammonia (NH4OH) and sodium hydroxide (NaOH) were prepared as a precipitating agent to form a complex.

[0465] [Stage 1: 2.5kW / m³, NH4OH 0.40M, pH 10.5~11.5, Reaction time 6 hours]

[0466] First, ammonia water with a concentration of 0.40 M was added to the reactor. The reaction was started at a stirring power of 2.5 kW / m³ and a reaction temperature of 50°C by adding the metal raw material mixed solution and the complexing agent (NH4OH) at rates of 85 ml / min and 10 ml / min, respectively. The reaction was carried out for 6 hours while adding NaOH to maintain the pH. As a result of the reaction, it was confirmed that the average size of the obtained core particles was in the range of approximately 6.5 µm to 7.5 µm, and the following two steps were performed.

[0467] [Stage 2: 2.0kW / m³, NH4OH 0.45M, pH 10.5~11.5, reaction time 18 hours]

[0468] While maintaining the reaction temperature at 50℃, the metal raw material mixed solution and the complexing agent were added at varying rates of 85 ml / min and 12 ml / min, respectively, so that the concentration of the complexing agent became 0.45 M. The reaction was carried out for 18 hours while adding NaOH to maintain the pH. During this time, the stirring power was lowered to 2.0 kW / m³, which is lower than that of the first step, to proceed with the reaction. After carrying out this reaction, it was confirmed that the average size of the product particles containing the core and intermediate layer was 13.5 μm to 14 μm, and the following three steps were performed.

[0469] [Stage 3: 1.5kW / ㎥, NH4OH 0.45M, pH 10.5~11.5, reaction time 14 hours]

[0470] While maintaining the reaction temperature at 50°C, the input rate and concentration of the metal raw material mixed solution and complexing agent were set identically to those in Step 2 above. The reaction was carried out for 14 hours while adding NaOH to maintain the pH. During this process, the stirring power was lowered to 1.5 kW / m³, lower than that of Step 2, to proceed with the reaction. After washing the obtained product, it was hot-air dried at approximately 150°C for 24 hours to produce a first nickel-based complex hydroxide (Ni) having a structure in which at least some of the primary particles constituting the secondary particles are arranged radially, in the form of secondary particles. 0.945 Co 0.04Al 0.015 (OH)2) obtained.

[0471]

[0472] 2. Preparation of Second Nickel-Based Complex Hydroxide

[0473] The second nickel-based complex hydroxide (Ni), which is a precursor of the second positive active material, is obtained through the coprecipitation method described below. 0.94 Co 0.04 Mn 0.02 (OH)2) was synthesized. A mixed solution of metal raw materials was prepared by dissolving nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) in distilled water, the solvent, in a molar ratio of 94:4:2. To form a complex, water ammonia (NH4OH) and sodium hydroxide (NaOH) were prepared as a precipitating agent.

[0474] First, ammonia solution with a concentration of 0.25 M was introduced into the reactor. The reaction was initiated at a stirring power of 3.0 kW / m³ and a reaction temperature of 50°C, while adding the metal raw material mixed solution and the complexing agent at rates of 142 ml / min and 34 ml / min, respectively. The reaction was carried out for 30 hours while adding NaOH to maintain the pH. As a result of the reaction, the reaction was terminated when the average size of the obtained particles reached approximately 4 µm. After washing the obtained product, it was hot-air dried at approximately 150°C for 24 hours to produce a secondary nickel-based complex hydroxide (Ni) in the form of secondary particles. 0.94 Co 0.04 Mn 0.02 (OH)2) was manufactured.

[0475]

[0476] 3. Preparation of preliminary cathode active material

[0477] First nickel-based complex hydroxide (Ni 0.945 Co 0.04 Al 0.015 80 wt% of (OH)2) and a second nickel-based complex hydroxide (Ni 0.94 Co 0.04 Mn 0.0220 wt% of (OH)2 was mixed, and LiOH was mixed so that the molar ratio of the total metal to Li was 1:1. Then, a first heat treatment was performed in an oxygen atmosphere, raising the temperature to 700°C over 8 hours and maintaining the temperature for 7 hours to prepare a preliminary cathode active material.

[0478] Scanning electron microscope (SEM) analysis of the surface and cross-section of the manufactured preliminary cathode active material confirmed that the first cathode active material is in the form of secondary particles comprising an interior with an irregular porous structure and an exterior with a radial arrangement structure, and the average particle size (D) of the secondary particles 50 ) is confirmed to be approximately 14 μm. The second cathode active material is confirmed to be in the form of secondary particles in which multiple primary particles are aggregated, and the average particle size (D) of the secondary particles. 50 ) is confirmed to be about 4㎛.

[0479] Meanwhile, after separating the first cathode active material (large) and the second cathode active material (small) from the preliminary cathode active material using a turbo classifier, ICP (Inductively Coupled Plasma) emission spectroscopic analysis was performed on the surface of the small particles, and Ni 93.9 mol%, Co 3.9 mol%, Al 0.6 mol%, and Mn 1.6 mol% were measured. Accordingly, it was confirmed that during the first heat treatment process, the small NCM received Al from the large NCA and existed as an Al-doped NCAM at a level of 0.6 mol%.

[0480]

[0481] 4. Formation of Zr coating layer on the positive electrode active material

[0482] The method for forming a Zr coating layer, which acts as a buffer layer on the cathode active material, is a dry coating method as follows. 0.25 molar parts of zirconium oxide (ZrO2) and 0.5 molar parts of anhydrous lithium hydroxide (LiOH) were placed in a mixer and mixed relative to 100 molar parts of the above-mentioned pre-cathode active material and the total metal excluding lithium in the pre-cathode active material, and the coating was carried out. During coating, the mixer was operated at low, medium, and high speeds to ensure even coating without layer separation. Subsequently, a second heat treatment was performed at 500°C for 15 hours in an oxygen atmosphere to form the Zr coating layer on the cathode active material (nickel-based composite oxide; LiNi 0.944 Co 0.04 Al 0.012 Mn 0.004 O2) was manufactured.

[0483] HRTEM and inverse-FFT analyses were performed on the cross-sections of large and small particles of the cathode active material with a Zr coating layer to analyze the crystal structure of the Zr coating layer region. As a result, it was confirmed that there are ZrO2 and Li6Zr2O7 crystal phases, as well as a Zr-containing amorphous region.

[0484]

[0485] 5. Preparation of the first solid electrolyte (Li6PS5Cl, Argyrodite, 0.85㎛)

[0486] An azirodite-type sulfide-based solid electrolyte was synthesized through the process described below. Mixing of raw materials, pre-treatment, and post-treatment of heat treatment were all carried out in a glove box under an argon atmosphere. As raw materials, lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), and lithium chloride (LiCl) were mixed in a molar ratio of 2.5:0.5:1 to prepare a mixed powder. After uniformly mixing the mixed powder with a Henschel mixer, it was first calcined at 250°C for 5 hours in a tubular furnace where argon gas flowed at a constant speed of 8 SLM.

[0487] The powder from the first calcination was homogeneously mixed again using a Henschel mixer and sieved, then subjected to a second calcination at 500°C for 10 hours in a tubular furnace where argon gas flowed at a constant speed of 8 SLM. The powder from the second calcination was ground and sieved to obtain Li6PS5Cl sulfide-based solid electrolyte particles. The size of the first solid electrolyte particles obtained in this way (D 50 ) is confirmed to be approximately 0.85 µm.

[0488]

[0489] 6. Preparation of the second solid electrolyte (Li 5.4 PS 4.4 Cl 1.6 , Argyrodite, 0.8 µm)

[0490] A second sulfide-based solid electrolyte was prepared in substantially the same manner as the first sulfide-based solid electrolyte, except that lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), and lithium chloride (LiCl) were mixed as raw materials in a molar ratio of 1.9:0.5:1.6. The second solid electrolyte thus obtained has a composition of Li 5.4 PS 4.4 Cl 1.6 It is an azyrodite-type solid electrolyte and particle size (D 50 ) is confirmed to be about 0.8 µm.

[0491]

[0492] 7. Preparation of the first positive electrode active material layer

[0493] A first cathode composition was prepared by adding 85 wt% of a cathode active material with a Zr coating layer, 13.44 wt% of an azirodite-type first solid electrolyte of Li6PS5Cl, 1 wt% of a PVdF binder, 0.4 wt% of a carbon nanotube conductive material, and 0.16 wt% of hydrogenated nitrile butadiene rubber (HNBR) as a dispersant to an isobutyryl isobutyrate (IBIB) solvent and mixing. This was applied to a cathode current collector at a loading level of 17 mg / cm² and dried to form a first cathode active material layer.

[0494]

[0495] 8. Preparation of the second positive electrode active material layer

[0496] 85 wt% of cathode active material with a Zr coating layer, Li 5.4 PS 4.4 Cl 1.6 A second cathode composition was prepared by adding 13.44 wt% of an azyrodite-type second solid electrolyte, 1 wt% of a PVdF binder, 0.4 wt% of a carbon nanotube conductive material, and 0.16 wt% of hydrogenated nitrile butadiene rubber (HNBR) as a dispersant to an isobutyryl isobutyrate (IBIB) solvent and mixing. This was applied to the first cathode active material layer at 17 mg / cm² 2 A second positive active material layer was formed by applying it at a loading level and drying it, and a positive was prepared by rolling (hydrostatic press; WIP; 500 Mpa, 85℃, 30 min).

[0497]

[0498] 9. Manufacturing of all-solid-state secondary batteries

[0499] Carbon black and 2-naphthalene thiol powder were mixed in a weight ratio of 10:1 and heat-treated at 90°C. The heat-treated product was added to a water solvent, and AgNO3 and a reducing agent, NaBH4, were added and mixed. At this time, the AgNO3 content was 11 wt% relative to the total content of carbon black and AgNO3 (100 wt%), and the NaBH4 content was 22 wt% relative to 100 wt% of AgNO3. The resulting product was heat-treated at 400°C for 4 hours under a nitrogen atmosphere to produce a compound in which Ag is supported on a carbon material. In the prepared Ag-C supported compound, the carbon material accounted for 94.6 wt% relative to the total amount of carbon material and Ag, the Ag content was 5.4 wt%, and the sulfur content was approximately 1.2 wt% relative to 100 wt% of the Ag-C supported compound. Transmission electron microscopy (TEM) analysis of the prepared Ag-C supported compound confirmed that silver is uniformly dispersed in the carbon material. In addition, X-ray photoelectron spectroscopy (XPS) analysis of the Ag-C supported compound revealed a Sp2 spectrum at approximately 161.8 eV corresponding to the Ag-S binding energy.

[0500] A cathode coating layer composition was prepared by mixing the manufactured Ag-C supported compound, styrene-butadiene rubber, and sodium carboxymethyl cellulose in a water solvent at a weight ratio of 100:6:3.

[0501] A precipitation type cathode was prepared by coating a stainless steel foil current collector with a thickness of 10 μm with the prepared cathode coating layer composition and vacuum drying it at 80°C to form a cathode coating layer with a thickness of 12 μm on the surface of the current collector.

[0502] Azirodite-type solid electrolyte of Li6PS5Cl (D 50A composition for forming a solid electrolyte layer was prepared by adding (=3㎛) to an IBIB solvent containing an acrylic binder and mixing. The composition contains 98.5 wt% of solid electrolyte and 1.5 wt% of binder. The composition was cast onto a release film and dried at room temperature to prepare a solid electrolyte layer.

[0503] A solid electrolyte layer was laminated on the anode, and then a cathode was laminated on top of it. This was sealed in a pouch form and subjected to hydrostatic pressing at a high temperature of 80°C at 500 MPa for 30 minutes to manufacture an all-solid-state secondary battery.

[0504]

[0505] Comparative Example 2-1 (Li6PS5Cl 34 mg / cm² thick film anode)

[0506] A positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 2-1, except that when manufacturing the first positive electrode active material layer, 34 mg / cm² of the first positive electrode composition was applied to the positive electrode current collector and the second positive electrode active material layer was not applied.

[0507]

[0508] Comparative Example 2-2 (Li6PS5Cl 17 mg / cm² - 17 mg / cm² bilayer anode)

[0509] A positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 2-1, except that a first solid electrolyte was used instead of a second solid electrolyte when manufacturing the second positive electrode active material layer.

[0510]

[0511] Comparative Example 2-3 (Li 5.4 PS 4.4 Cl 1.6 34 mg / cm² thick film anode)

[0512] A positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 2-1, except that a second positive electrode composition of 34 mg / cm² was applied without applying a first positive electrode active material layer on the positive electrode current collector.

[0513]

[0514] Comparative Example 2-4 (Li 5.4 PS 4.4 Cl 1.6 17 mg / ㎠ - 17 mg / ㎠ (two-layer anode)

[0515] A positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 2-1, except that a second solid electrolyte was used instead of a first solid electrolyte when manufacturing the first positive electrode active material layer.

[0516]

[0517] To aid understanding, the anode design details of Example 2-1 and Comparative Examples 2-1 to 2-4 are briefly shown in Table 5 below.

[0518] First positive active material layer, second positive active material layer, double layer positive, Example 2 - 1Li6PS5ClLi 5.4 PS 4.4 Cl 1.6 Comparative Example 2-1Li6PS5ClX Comparative Example 2-2Li6PS5ClLi6PS5ClO Comparative Example 2-3Li 5.4 PS 4.4 Cl 1.6 X Comparative Example 2-4Li 5.4 PS 4.4 Cl 1.6 Li 5.4 PS 4.4 Cl 1.6 O

[0519] Evaluation Example 2-1: Evaluation of Initial Charge / Discharge Capacity of All-Solid State Secondary Battery

[0520] The all-solid-state secondary batteries prepared in Example 2-1 and Comparative Examples 2-1 to 2-4 were charged to 4.25V with a constant current of 0.1C at 45℃ and to 0.05C with a constant voltage to measure the initial charge capacity, and discharged to 2.5V with 0.1C to measure the initial discharge capacity. The ratio of discharge capacity to charge capacity was calculated as efficiency, and the results are shown in Table 6.

[0521] Charge Capacity (mAh / g) Discharge Capacity (mAh / g) Efficiency (%) Example 2-1 24 2.4 200 0.9 82.9 Comparative Example 2-1 22 3.4 17 7.2 79.3 Comparative Example 2-2 22 4.3 18 1.7 81.0 Comparative Example 2-3 22 8.1 18 3.8 80.6 Comparative Example 2-4 23 1.0 18 1.7 78.7

[0522] Referring to Table 6, it can be seen that Example 2-1 has improved initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency compared to Comparative Examples 2-1 to 2-4.

[0523] Evaluation Example 2-2: Evaluation of High Rate Characteristics

[0524] For the all-solid-state secondary batteries prepared in Example 2-1 and Comparative Examples 2-1 to 2-4, after performing initial charge and discharge as in Evaluation Example 2-1, the batteries were charged with a constant current of 0.1C to an upper limit voltage of 4.25V and with a constant voltage of 0.05C, and then discharged at 0.33C to a discharge cutoff voltage of 2.5V to measure the discharge capacity at 0.33C. Subsequently, the batteries were charged with a constant current of 0.1C to an upper limit voltage of 4.25V and with a constant voltage of 0.05C, and then discharged at 1.0C to a discharge cutoff voltage of 2.5V to measure the discharge capacity at 1.0C. The high-rate discharge capability was calculated from Equation 1 below, and the discharge capacity and high-rate discharge capability for each cycle are shown in Table 7.

[0525] [Equation 1]

[0526] High-rate discharge characteristic (%) = {(Discharge capacity at 1C) / (Discharge capacity at 0.1C)} x 100

[0527] Discharge Capacity (mAh / g) High Rate Discharge Characteristics (%) 0.1C 1.0C Example 2-1 201 16884 Comparative Example 2-1 1779 151 Comparative Example 2-2 1825 128 Comparative Example 2-3 184 7843 Comparative Example 2-4 1821 0055

[0528] Referring to Table 7 above, it can be confirmed that Example 2-1 has significantly superior high-rate discharge characteristics compared to Comparative Examples 2-1 to 2-4.

[0529] Evaluation Example 2-3: Evaluation of Lifetime Characteristics of All-Solid State Secondary Batteries

[0530] For the all-solid-state secondary batteries prepared in Example 2-1 and Comparative Examples 2-1 to 2-4, after performing initial charge and discharge as in Evaluation Example 2-1, the life characteristics were evaluated by repeating the charging and discharging at 0.33C at 45°C in a voltage range of 2.5V to 4.25V 100 times. Table 8 below shows the initial discharge capacity (1-cycle discharge capacity), 100-cycle discharge capacity, and the capacity retention rate, which is the ratio of the latter to the former.

[0531] Single Discharge Capacity (mAh / g) 100 Discharge Capacity (mAh / g) Capacity Retention Rate (%) Example 2-11 64 14890 Comparative Example 2-11 27 10885 Comparative Example 2-2 125 10584 Comparative Example 2-3 11 99580 Comparative Example 2-4 13 210378

[0532] Referring to Table 8 above, it can be seen that Example 2-1 has a further improved capacity retention rate at 100 cycles compared to Comparative Examples 2-1 to 2-4.

[0533]

[0534] The above second embodiment provides the following technical configuration.

[0535] 1. A positive electrode comprising a positive current collector, and a first positive active material layer and a second positive active material layer located on the positive current collector, and

[0536] The above first positive active material layer

[0537] A positive electrode active material comprising a core particle containing a lithium nickel-based composite oxide and a Zr coating layer located on the core particle, and

[0538] It comprises a first solid electrolyte containing an azirodite-type sulfide containing Li, P, S and halogen elements, and

[0539] The above second positive active material layer

[0540] A positive electrode active material comprising a core particle containing a lithium nickel-based composite oxide and a Zr coating layer located on the core particle, and

[0541] It comprises a second solid electrolyte containing an azirodite-type sulfide containing Li, P, S and halogen elements, and

[0542] The first solid electrolyte and the second solid electrolyte are anodes in which the molar ratio of at least one of Li, P, S and halogen elements is different from each other.

[0543] 2. An anode in which, in paragraph 1, the molar ratio of the halogen element in the second solid electrolyte is higher than the molar ratio of the halogen element in the first solid electrolyte.

[0544] 3. An anode according to paragraph 2, wherein the molar ratio of the halogen element in the second solid electrolyte is 1.1 to 2.5 times the molar ratio of the halogen element in the first solid electrolyte.

[0545] 4. An anode according to claim 1, wherein the content of a halogen element in the first solid electrolyte is 5 mol% to 10 mol% with respect to 100 mol% of the first solid electrolyte, and the content of a halogen element in the second solid electrolyte is 11 mol% to 15 mol% with respect to 100 mol% of the second solid electrolyte.

[0546] 5. In claim 1, the azyrodite-type sulfide of the first solid electrolyte is represented by the following chemical formula 22, and the azyrodite-type sulfide of the second solid electrolyte is represented by the following chemical formula 23, and

[0547] [Chemical Formula 22]

[0548] (Li a2 M 1 b2 M 2 c2 )(Pd2 M 3 e2 )(S f2 M 4 g2 )X h2

[0549] In Chemical Formula 22, 4 ≤ a2 ≤ 8, and M 1 is Mg, Ca, Cu, Ag, or a combination thereof, 0 ≤ b2 < 0.5, and M 2 is Na, K, or a combination thereof, 0 ≤ c2 < 0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, 0 < d2 < 4, 0 ≤ e2 < 1, and M 4 is N, O, SO n , or a combination thereof, 1.5 ≤ n ≤ 5, 3 ≤ f2 ≤ 12, 0 ≤ g2 < 2, X is F, Cl, Br, I, or a combination thereof, 0 < h2 ≤ 2, and

[0550] [Chemical Formula 23]

[0551] (Li a3 M 1 b3 M 2 c3 )(P d3 M 3 e3 )(S f3 M 4 g3 )X h3

[0552] In Chemical Formula 23, 4 ≤ a3 ≤ 8, and M 1 is Mg, Ca, Cu, Ag, or a combination thereof, 0 ≤ b3 < 0.5, and M 2 is Na, K, or a combination thereof, 0 ≤ c3 < 0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, 0 < d3 < 4, 0 ≤ e3 < 1, and M 4 is N, O, SO n, or a combination thereof, 1.5≤n≤5, 3≤f3≤12, 0≤g3<2, and X is F, Cl, Br, I, or a combination thereof, and 0 <h3≤2이며,

[0553] An anode in the above chemical formulas 22 and 23, wherein a2≠a3, d2≠d3, f2≠f3, or h2≠h3.

[0554] 6. An anode according to claim 5, wherein in the above chemical formulas 22 and 23, (a2+b2+c2)≠(a3+b3+c3) or (d2+e2)≠(d3+e3) or (f2+g2)≠(f3+g3) or h2≠h3.

[0555] 7. In paragraph 5, in the above chemical formulas 22 and 23, (a2+b2+c2)>(a3+b3+c3) or (f2+g2)>(f3+g3) or h2 <h3인 양극.

[0556] 8. An anode according to claim 5, wherein in the above chemical formulas 22 and 23, (h2 x 1.1)≤h3≤(h2 x 2.5).

[0557] 9. The anode according to claim 1, wherein the first solid electrolyte is Li6P1S5X1 (where X is a halogen element), and the second solid electrolyte is an anode in which the molar ratio of at least one of Li, P, S and a halogen element is different from that of the first solid electrolyte.

[0558] 10. In paragraph 1, the first solid electrolyte and the second solid electrolyte are each in the form of particles, and their average particle size (D 50 A cathode having ) which are identical or different from each other and each independently have a thickness of 0.1 μm to 5 μm, wherein the content of the first solid electrolyte is 1 wt% to 35 wt% with respect to 100 wt% of the first cathode active material layer, and the content of the second solid electrolyte is 1 wt% to 35 wt% with respect to 100 wt% of the second cathode active material layer.

[0559] 11. An anode according to claim 1, wherein the thickness of each of the first positive active material layer and the second positive active material layer is 15 μm to 100 μm, the ratio of the thickness of the first positive active material layer to the thickness of the second positive active material layer is 20:80 to 80:20, and the first positive active material layer is located on the current collector and the second positive active material layer is located on the first positive active material layer.

[0560] 12. In paragraph 1, the loading level of each of the first positive electrode active material layer and the second positive electrode active material layer is 10 mg / cm² 2 to 80 mg / cm² 2 A positive electrode having a density of 3.0 g / cc to 3.9 g / cc for each of the first positive electrode active material layer and the second positive electrode active material layer.

[0561] 13. An anode according to claim 1, wherein in each of the anode active material of the first anode active material layer and the anode active material of the second anode active material layer, the Zr coating layer comprises ZrO2 and Li6Zr2O7, the Zr content of the Zr coating layer is 0.1 to 0.6 molar parts per 100 molar parts of the total metal excluding lithium in the lithium nickel-based composite oxide of the anode active material, and the thickness of the Zr coating layer is 5 nm to 300 nm.

[0562] 14. In claim 1, the positive active material of the first positive active material layer and the positive active material of the second positive active material layer are identical or different from each other, and each independently comprises: (i) a first positive active material comprising a lithium nickel-based composite oxide, a plurality of primary particles aggregated to form secondary particles in which at least a portion of the primary particles are arranged radially, and a Zr coating layer located on the surface of the secondary particles; and (ii) a lithium nickel-based composite oxide, a plurality of primary particles aggregated to form secondary particles, and a Zr coating layer located on the surface of the secondary particles, wherein the average particle size (D) of the first positive active material 50 Average particle size (D) smaller than ) 50A positive electrode comprising a second positive electrode active material having ).

[0563] 15. In paragraph 14, the average particle size (D of the secondary particles of the first positive electrode active material) 50 ) is 9 μm to 25 μm, and the average particle size (D) of the secondary particles of the second positive active material. 50 ) is 2 μm to 8 μm, and with respect to the total sum of the first and second positive active materials at 100 wt%, the first positive active material is included at 60 wt% to 95 wt% and the second positive active material is included at 5 wt% to 40 wt%.

[0564] 16. A positive electrode according to claim 14, wherein the lithium nickel-based composite oxide of the first positive electrode active material is a lithium nickel-cobalt-aluminum-based composite oxide represented by the following chemical formula 1, and the lithium nickel-based composite oxide of the second positive electrode active material is a lithium nickel-cobalt-aluminum-manganese-based composite oxide represented by the following chemical formula 2:

[0565] [Chemical Formula 1]

[0566] Li a1 Ni x1 Co y1 Al z1 M 1 w1 O 2-b1 X b1

[0567] In the above Chemical Formula 1, 0.9≤a1≤1.2, 0.7≤x1<1, 0 <y1<0.3, 0<z1<0.3, 0≤w1<0.3, 0.9≤x1+y1+z1+w1≤1.1, 및 0≤b1≤0.1이고, M 1 is one or more elements among B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, Y, Zn, and Zr, and X is one or more elements among F, P, and S, and

[0568] [Chemical Formula 2]

[0569] Li a2 Ni x2 Co y2 Alz2 Mn w2 M 2 v2 O 2-b2 X b2

[0570] In the above chemical formula 2, 0.9≤a2≤1.2, 0.7≤x2<1, 0 <y2<0.3, 0<z2<0.3, 0<w2<0.3, 0≤v2<0.3, 0.9≤x2+y2+z2+w2+v2≤1.1, 및 0≤b2≤0.1이고, M 2 is one or more of the elements B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, T, Zn, and Zr, and X is one or more of the elements F, P, and S.

[0571] 17. An all-solid-state secondary battery comprising an anode, a cathode, and a solid electrolyte layer located between the anode and the cathode according to any one of claims 1 to 16.

[0572] 18. An all-solid-state secondary battery according to claim 17, wherein the cathode comprises a cathode current collector and a cathode coating layer located on the cathode current collector and containing a compound in which a lithium-friendly metal is supported on a carbon material, wherein the lithium-friendly metal comprises Al, Ag, Au, Bi, Cu, Ge, In, Mg, Ni, Pd, Pt, Si, Sn, Zn, or a combination thereof, and the carbon material is an amorphous carbon material, wherein the lithium-friendly metal is included in an amount of 3% to 40% by weight and the carbon material is included in an amount of 60% to 97% by weight with respect to a total of 100% by weight of the lithium-friendly metal and the carbon material.

[0573] 19. An all-solid-state secondary battery according to claim 17, wherein the solid electrolyte layer comprises a solid electrolyte, and the average particle size of the solid electrolyte included in the solid electrolyte layer is larger than the average particle size of the first solid electrolyte and the average particle size of the second solid electrolyte.

[0574]

[0575] [Third Implementation Example]

[0576] The third embodiment is substantially identical to the first embodiment above, except that the positive active material Type A is changed to the positive active material Type C. Except for the details regarding the positive active material Type C below, the details described above in the first embodiment can be applied in the same way.

[0577] In one embodiment, a positive electrode is provided comprising a positive current collector, and a first positive active material layer and a second positive active material layer located on the positive current collector. The first positive active material layer comprises a positive active material comprising a core particle containing a lithium nickel-based composite oxide, a first coating layer located on the core particle containing boron, and a second coating layer located on the first coating layer containing zirconium, and a first solid electrolyte containing an azirodite-type sulfide containing Li, P, S, and a halogen element. The second positive active material layer comprises a positive active material comprising a core particle containing a lithium nickel-based composite oxide, a first coating layer located on the core particle containing boron, and a second coating layer located on the first coating layer containing zirconium, and a second solid electrolyte containing an azirodite-type sulfide containing Li, P, S, and a halogen element. Here, the first solid electrolyte and the second solid electrolyte have different compositions from each other, specifically, the molar ratio of at least one of Li, P, S, and a halogen element is different from each other.

[0578]

[0579] Positive electrode active material - Type C

[0580] The positive active material included in the first positive active material layer and the positive active material included in the second positive active material layer may be the same or different from each other, and each independently includes a core particle containing a lithium nickel-based composite oxide, a first coating layer located on the core particle and containing boron, and a second coating layer located on the first coating layer and containing zirconium.

[0581]

[0582] Core particles of the positive electrode active material

[0583] The lithium nickel-based composite oxide of the above core particles can be represented, for example, by the following chemical formula 5.

[0584] [Chemical Formula 5]

[0585] Li a5 Ni x5 M 5 y5 M 6 z5 O 2-b5 X b5

[0586] In the above chemical formula 5, 0.9≤a5≤1.2, 0.3≤x5≤1, 0≤y5≤0.7, 0≤z5≤0.7, 0.9≤x5+y5+z5≤1.1, and 0≤b5≤0.1, and M 5 and M 6 are distinct elements and each independently is one or more of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, T, Zn and Zr, and X is one or more of F, P and S.

[0587] For example, in the above chemical formula 5, 0.6≤x5≤1, 0≤y5≤0.4, 0≤z5≤0.4, or 0.7≤x5≤1, 0≤y5≤0.3, 0≤z5≤0.3, or 0.8≤x5≤1, 0≤y5≤0.2, 0≤z5≤0.2, or 0.9≤x5<1, 0 <y5≤0.1, 0≤z5≤0.1이거나, 0.9≤x5≤1, 0≤y5≤0.1, 0≤z5≤0.1일 수 있다.

[0588] The cathode active material containing the above lithium nickel-based composite oxide as a core particle can achieve high capacity and high energy density.

[0589] The nickel content in the above lithium-nickel composite oxide may be 30 mol% or more with respect to 100 mol% of metal excluding lithium, 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.

[0590] Generally, as the nickel content in the cathode active material increases, Ni 2+ Increased cation mixing, where ions occupy lithium sites, can actually lead to a decrease in capacity, or impurities such as NiO can hinder the diffusion of lithium ions, thereby degrading battery life. Additionally, structural collapse or cracking of the cathode active material during charging and discharging can increase side reactions with the electrolyte, which can reduce battery life and raise safety concerns. According to one embodiment, even when using a high-nickel cathode active material, the problems associated with high nickel concentration are improved by coating an appropriate amount of boron and zirconium onto the cathode active material, selectively coating internal grain boundaries, or forming a boron doping layer. This allows for the realization of high capacity while simultaneously improving lifespan characteristics without a decrease in initial discharge capacity.

[0591]

[0592] Coating layer of positive electrode active material

[0593] A positive electrode active material according to one embodiment comprises a first coating layer containing boron located on the surface of a core particle, and a second coating layer containing zirconium located on the first coating layer. The first coating layer and the second coating layer may be described as a type of buffer layer or buffer layer and can effectively suppress side reactions between a lithium nickel-based composite oxide and a sulfide-based solid electrolyte.

[0594] The first coating layer described above may be said to contain a boron-containing compound, and 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 It may include Li2B4O7, Li3BO3, or a combination thereof.

[0595] The first coating layer may exist on the surface of the core particle in the form of a continuous film or in the form of an island.

[0596] The boron content of the first coating layer may be 0.01 mol% to 0.5 mol% with respect to 100 mol% of the total metal excluding lithium in the positive electrode active material, for example, 0.01 mol% to 0.4 mol%, 0.01 mol% to 0.3 mol%, or 0.1 mol% to 0.3 mol%. Additionally, the boron content may be 0.01 wt% to 0.5 wt% with respect to 100 wt% of the total metal excluding lithium in the positive electrode active material, 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 boron content may be measured, for example, through Inductively Coupled Plasma (ICP) emission spectroscopic analysis. When boron is coated with such a content, it does not act as a resistance and does not degrade battery capacity; furthermore, the diffusion of lithium ions into the positive electrode active material becomes easier, improving initial charge-discharge efficiency and suppressing problems caused by repeated charge-discharge cycles, thereby enhancing the long-life characteristics of the battery.

[0597] Conventionally, when coating boron onto a positive electrode active material, it was common practice to use a method of mixing a boron raw material into a lithium transition metal composite oxide in a wet or dry manner and then heat-treating it. However, in this case, there was a problem in that the boron acted as a resistance on the surface of the positive electrode active material, thereby worsening the capacity and lifespan. According to one embodiment, as described below, a positive electrode active material coated with a boron-containing compound can be obtained by a method such as mixing a first nickel-based composite hydroxide, in which primary particles are radially oriented, with a lithium raw material while simultaneously adding a boron raw material and heat-treating it. In this case, a first lithium nickel-based composite oxide in which primary particles are radially oriented is obtained, and at the same time, an appropriate amount of boron is stably coated on the surface of the first lithium nickel-based composite oxide particles. Consequently, the boron no longer acts as a resistance, the structural stability of the positive electrode active material is secured, and problems arising from contact between the positive electrode active material and the electrolyte are suppressed, thereby improving the capacity characteristics and long-term lifespan characteristics of the battery.

[0598] Nickel-based cathode active materials may experience structural collapse and cation mixing phenomena as NiO and the like form on the surface due to repeated charging and discharging, which may lead to problems such as gas generation or deterioration of lifespan characteristics. Additionally, repeated charging and discharging may cause the cathode active material to break, which increases side reactions between the cathode active material and the electrolyte, resulting in a decrease in battery capacity and deterioration of lifespan characteristics. However, according to one embodiment, an appropriate amount of a boron-containing compound is stably coated on the surface of the cathode active material, and a boron-containing first coating layer and a grain boundary boron coating portion or boron doping layer described later are simultaneously formed on the cathode active material. Consequently, the detachment of oxygen atoms from the surface of the cathode active material is prevented, structural collapse is suppressed, and the breaking phenomenon caused by repeated charging and discharging can be suppressed. Furthermore, the movement of lithium ions within the all-solid-state battery can be made more efficient due to the boron-containing compound present on the surface of the cathode active material, thereby improving rate characteristics.

[0599] The second coating layer may exist as a continuous film on the surface of the first coating layer or as an island.

[0600] The second coating layer described above contains zirconium and, for example, may include a mixed phase of ZrO2 and Li6Zr2O7. The second coating layer may be said to contain ZrO2, which has relatively high crystallinity, and Li6Zr2O7, which has lower crystallinity. The presence or absence of ZrO2 and Li6Zr2O7 can be determined, for example, through the Inverse FFT or FFT rotation pattern of an HRTEM image of the cathode active material. The second coating layer containing ZrO2 and Li6Zr2O7 can facilitate the movement of lithium ions on the surface of the cathode active material and improve the structural stability of the cathode active material, and can improve interfacial resistance by reducing reactivity with the sulfide-based solid electrolyte.

[0601] The second coating layer may further include an amorphous region containing zirconium in addition to the mixed phase of ZrO2 and Li6Zr2O7. For example, the second coating layer may be said to include a ZrO2 crystalline phase, a Li6Zr2O7 crystalline phase, and a Zr-containing amorphous region. Such a zirconium-containing second coating layer can improve lithium ion conductivity and lower the interfacial resistance between the positive electrode active material and the solid electrolyte while having a thin and uniform thickness.

[0602] The zirconium content of the second coating layer may be 0.1 to 0.6 molar parts with respect to 100 molar parts of the total metal excluding lithium in the positive active material, for example, 0.1 to 0.5 molar parts, or 0.1 to 0.4 molar parts. Additionally, the zirconium content of the second coating layer may be 0.1 to 6 weight% with respect to 100 weight% of the positive active material, for example, 0.5 to 6 weight%, or 1 to 5.5 weight%. Alternatively, the zirconium content of the second coating layer may be 0.1 to 10 at% with respect to 100 at% of the total positive active material, for example, 0.1 to 8 at%, 0.1 to 7 at%, 0.5 to 6.5 at%, or 1 to 6 at%. When the zirconium content satisfies the above range, the second coating layer can adequately protect the positive electrode active material without acting as a resistor, and can exist well with a uniform thickness without aggregating or existing locally on the surface of the positive electrode active material particles; accordingly, the lifespan characteristics can be effectively improved without reducing the capacity of the positive electrode active material. For example, if the Zr content is excessive, the second coating layer may become thick and act as a resistor, which may reduce the charge / discharge capacity of the battery; conversely, if the Zr content is too low, it may not adequately perform the buffer function, which may degrade the lifespan characteristics of the positive electrode active material.

[0603] Zirconium in the second coating layer can be introduced by a dry coating method, and nevertheless, it can be formed with a uniform thickness without being locally present or aggregated on the surface of the positive active material.

[0604] The thickness of the first coating layer containing boron may be 10 nm to 1 μm, for example, 10 nm to 500 nm, 10 nm to 300 nm, 10 nm to 100 nm, or 10 nm to 50 nm. By having the first coating layer within the above thickness range, the increase in resistance caused by the coating can be suppressed, and the electrochemical characteristics of the battery can be improved by improving ion conductivity while effectively protecting the positive electrode active material.

[0605] The thickness of the second coating layer may be 5 nm to 300 nm, for example, 5 nm to 200 nm, 5 nm to 100 nm, 5 nm to 80 nm, or 10 nm to 50 nm. By having the second coating layer within the above thickness range, the electrochemical characteristics of the battery can be improved by suppressing the increase in resistance caused by the coating, effectively protecting the positive electrode active material, and improving ion conductivity.

[0606] The second coating layer may be formed with a uniform thickness without being locally present or aggregated on the first coating layer. For example, the deviation in the thickness of the second coating layer may be 20% or less, 10% or less, or 5% or less relative to the diameter of the positive active material, and may be 100 nm or less, 50 nm or less, or 30 nm or less. Here, the deviation in the thickness of the second coating layer refers to the thickness of the coating layer within a single positive active material particle. The deviation in the thickness of the second coating layer may mean, for example, measuring the thickness at about 10 points in an electron microscope image of a cross-section of a single positive active material particle, calculating the arithmetic mean, dividing the absolute value of the difference between one data point and the arithmetic mean value by the arithmetic mean value, and multiplying by 100. The deviation or standard deviation of the second coating layer thickness satisfying the above range means that a coating layer of uniform thickness is formed in a good form on the surface of the positive active material particles, and accordingly, the structural stability of the positive active material is improved, side reactions with the solid electrolyte are effectively suppressed, and the increase in resistance or decrease in capacity caused by the coating can be minimized.

[0607] Meanwhile, the core particle may include a secondary particle formed by the aggregation of a plurality of primary particles. At least some of the primary particles constituting the secondary particle may be arranged radially, and the radial structure is described in detail below in the first positive electrode active material of the bimodal.

[0608] A positive electrode active material according to one embodiment may further include a grain boundary boron coating portion located on the surface of primary particles within the secondary particles, in addition to a boron-containing first coating layer located on the surface of secondary particles. That is, in the positive electrode active material, boron may be coated along the interface of primary particles within the secondary particles. When a boron-containing compound is coated on the surface of the secondary particles and the internal grain boundary surface, the boron does not act as a resistor, and the phenomenon of structural collapse or breakage of the positive electrode active material due to charging and discharging can be effectively suppressed.

[0609] The boron content present on the surface of the secondary particles may be higher than the boron content present at the internal grain boundaries, for example, the weight of boron in the boron-containing first coating layer may be four times or more the weight of boron in the grain boundary boron coating portion. For example, the ratio of the weight of boron in the boron-containing first coating layer to the weight of boron in the grain boundary boron coating portion may be 70:30 to 98:2, for example, 75:25 to 97:3, or 80:20 to 95:5. In this case, boron does not act as a resistor in the positive electrode active material but can play a role in improving performance, and can simultaneously improve the capacity characteristics and lifespan characteristics of the lithium secondary battery.

[0610] For detailed information regarding the grain boundary boron coating portion, refer to the boron-containing first coating layer of the bimodal anode active material below.

[0611] A positive electrode active material according to one embodiment may further include a boron doping layer formed in a layered form along the periphery surface of the secondary particle, located inside the primary particle exposed on the surface of the secondary particle. The boron doping layer may be said to be located inside the secondary particle and within a depth range of about 10 nm from the outer surface of the primary particle exposed on the surface of the secondary particle. Such a boron doping layer can further improve the structural stability of the positive electrode active material and, accordingly, improve the lifespan characteristics of the lithium secondary battery.

[0612] For details regarding the boron doping layer, refer to the boron-containing first coating layer of the bimodal cathode active material below.

[0613]

[0614] Bimodal positive electrode active material

[0615] The positive active material of the first positive active material layer and the positive active material of the second positive active material layer each independently comprise: (i) a first positive active material comprising a lithium nickel-based composite oxide, a plurality of primary particles aggregated to form secondary particles in which at least a portion of the primary particles are arranged radially, a first coating layer located on the surface of the secondary particles and containing boron, and a second coating layer located on the first coating layer and containing zirconium; and (ii) a third coating layer comprising a lithium nickel-based composite oxide, in the form of a single particle, located on the surface of the single particle and containing zirconium, wherein the average particle size (D) of the first positive active material 50 Average particle size (D) smaller than ) 50 It may include a second positive active material having ).

[0616] The first positive active material can be expressed as an opposite or an opposite, and the average particle size of the secondary particle (D 50 ) may be 9 μm to 25 μm, for example, 11 μm to 18 μm, or 12 μm to 16 μm. The second positive active material may be expressed as microparticles or microparticles, and the average particle size (D) of the single particles is 50 ) can be 2 μm to 8 μm, for example 2.5 μm to 7 μm, or 3 μm to 6 μm. Here, the average particle size (D 50 ) may be obtained by selecting approximately 20 random particles from a scanning electron microscope (SEM) image of the positive electrode active material, measuring their particle size (diameter, or major axis, or length of the major axis), obtaining a particle size distribution, and taking the size of the particle with a cumulative volume of 50% of the particle size distribution as the average particle size.

[0617] The first positive active material may be a concept corresponding to the positive active material comprising the aforementioned first coating layer and second coating layer. That is, according to one embodiment, the first positive active material layer and the second positive active material layer may further comprise a second positive active material that is fine and includes a third coating layer in addition to the positive active material comprising the aforementioned first coating layer and second coating layer.

[0618] With respect to the total of 100 wt% of the first positive active material and the second positive active material, the first positive active material may be included in an amount of 60 wt% to 95 wt%, 70 wt% to 90 wt%, or 80 wt% to 90 wt%, and the second positive active material may be included in an amount of 5 wt% to 40 wt%, 10 wt% to 30 wt%, or 10 wt% to 20 wt%. When the first positive active material and the second positive active material are mixed within the above weight ranges, high capacity and lifespan characteristics can be achieved while maximizing the energy density of the positive.

[0619]

[0620] First positive active material of bimodal positive active material

[0621] The first cathode active material may include, for example, a lithium nickel-cobalt-aluminum-based composite oxide, which means an oxide comprising lithium, nickel, cobalt, and aluminum and optionally further comprising other elements, and may be expressed as Ni-Co-Al or NCA.

[0622] The lithium nickel-cobalt-aluminum composite oxide of the first positive electrode active material can be represented by Chemical Formula 1.

[0623] [Chemical Formula 1]

[0624] Li a1 Ni x1 Co y1 Al z1 M 1 w1 O 2-b1 X b1

[0625] In the above Chemical Formula 1, 0.9≤a1≤1.2, 0.7≤x1<1, 0 <y1<0.3, 0<z1<0.3, 0≤w1<0.3, 0.9≤x1+y1+z1+w1≤1.1, 및 0≤b1≤0.1이고, M 1 is one or more of the elements B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more of the elements F, P, and S.

[0626] In the above chemical formula 1, for example, 0.7≤x1≤0.98, 0.01≤y1≤0.29, 0.01≤z1≤0.29, 0≤w1≤0.28, 0.8≤x1≤0.98, 0.01≤y1≤0.19, 0.01≤z1≤0.19, 0≤w1≤0.18, or 0.9≤x1≤0.98, 0.01≤y1≤0.09, 0.01≤z1≤0.09, 0≤w1≤0.08.

[0627] The first positive active material is in the form of secondary particles formed by the aggregation of multiple primary particles, and the secondary particles may be spherical, elliptical, polygonal, amorphous, etc.

[0628] The average particle size of the primary particles constituting the secondary particles of the first cathode active material may be less than 200 nm, for example, 50 nm or more and less than 200 nm, 100 nm or more and less than 200 nm, 50 nm or more and less than 190 nm, or 50 nm or more and less than 180 nm. When the average particle size of the primary particles satisfies the above range, the lithium diffusion path is shortened, thereby reducing resistance and improving charge / discharge efficiency. Here, the average particle size of the primary particles refers to the size of the primary particles observed on the surface of the secondary particles, and can be obtained by selecting approximately 20 random primary particles from an SEM image of the surface of the secondary particles, measuring their particle sizes (diameter or major axis, or length of the major axis), and calculating the arithmetic mean thereof.

[0629] The first positive electrode active material may be characterized in that at least a portion of the primary particles forming the secondary particles are arranged radially. In this case, the diffusivity of lithium is increased, which improves the initial charge-discharge efficiency and enables the securing of a high capacity. Additionally, uniform expansion and contraction are possible during the insertion and extraction of lithium, thereby improving the problem of the positive electrode active material breaking during charge-discharge, which can improve the lifespan characteristics and safety of the battery.

[0630] The above radial structure is substantially the same as that described above, so a detailed explanation is omitted.

[0631]

[0632] Second positive active material of bimodal positive active material

[0633] The second positive electrode active material contains a lithium nickel-based composite oxide and is characterized by being in the form of a single particle. A single particle refers to a particle that exists independently without grain boundaries within the particle and consists of a single particle. Morphologically, it may refer to a single particle, a monolith structure, a monolithic structure, or a non-aggregated particle existing in an independent phase where the particles are not mutually aggregated, and as an example, it may be a single crystal. The single particles may exist independently or may be aggregated together. For example, 2 to 10 single particles may be aggregated and in contact with each other. The positive electrode active material according to one embodiment can achieve high capacity and high energy density while exhibiting improved lifespan characteristics by including the second positive electrode active material in the form of a single particle.

[0634] The shape of the second positive active material is not particularly limited and can have various shapes such as polyhedral, spherical, elliptical, plate-shaped, rod-shaped, and irregular.

[0635] The second cathode active material may include, for example, a lithium nickel-cobalt-aluminum-manganese-based composite oxide, which means an oxide comprising lithium, nickel, cobalt, aluminum, and manganese and optionally further comprising other elements, and can be expressed as Ni-Co-Al-Mn or NCAM.

[0636] The lithium nickel-cobalt-aluminum-manganese-based composite oxide of the second positive electrode active material can be represented by Chemical Formula 2.

[0637] [Chemical Formula 2]

[0638] Li a2 Ni x2 Co y2 Al z2 Mn w2 M 2 v2 O 2-b2 X b2

[0639] In the above chemical formula 2, 0.9≤a2≤1.2, 0.7≤x2<1, 0 <y2<0.3, 0<z2<0.3, 0<w2<0.3, 0≤v2<0.3, 0.9≤x2+y2+z2+w2+v2≤1.1, 및 0≤b2≤0.1이고, M 2 is one or more of the elements B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Z, and X is one or more of the elements F, P, and S.

[0640] In the above chemical formula 2, for example, 0.7≤x2≤0.979, 0.01≤y2≤0.289, 0.001≤z2≤0.289, 0.01≤w2≤0.289, 0≤v2≤0.279, 0.8≤x2≤0.979, 0.01≤y2≤0.189, 0.001≤z2≤0.189, 0.01≤w2≤0.189, 0≤v2≤0.179, and 0.9≤x2≤0.979, 0.01≤y2≤0.089, 0.001≤z2≤0.089, 0.01≤w2≤0.089, 0≤v2≤0.079.

[0641]

[0642] Coating layer of the first positive electrode active material in the bimodal positive electrode active material

[0643] In the above-described bimodal cathode active material, the boron-containing first coating layer may be included only in the first cathode active material. The boron content relative to 100 mol% of the total metal excluding lithium in the first cathode 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%. Additionally, the boron content relative to 100 wt% of the total metal excluding lithium in the first cathode 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 boron content may be measured, for example, through ICP (Inductively Coupled Plasma) emission spectroscopic analysis. When boron is coated on the first positive electrode active material with such content, it does not act as a resistance and the battery capacity does not decrease, and the diffusion of lithium ions into the positive electrode active material becomes easier, thereby improving initial charge-discharge efficiency and suppressing problems caused by repeated charge-discharge cycles, which can improve the long-life characteristics of the battery.

[0644] Meanwhile, the first positive active material, which is in the form of a secondary particle including a radial structure, may further include a grain boundary boron coating portion located on the surface of the primary particles within the secondary particle, in addition to a first coating layer located on the surface of the secondary particle. That is, in the first positive active material, boron may be coated along the interface of the primary particles within the secondary particle. Here, "inside of the secondary particle" refers to the entire interior excluding the surface; for example, it may refer to the entire interior or a part of the interior starting from a depth of approximately 1 μm from the outer surface, or it may be described as the part that is not reached by distilled water when washing the secondary particles of the positive active material with distilled water. In this way, when a boron-containing compound is coated on the surface of the secondary particle and the internal grain boundary surface in the first positive active material, the boron does not act as a resistor, and the structural collapse or breakage of the positive active material due to charging and discharging can be effectively suppressed.

[0645] Here, the boron content present on the surface of the secondary particles may be higher than the boron content present at the internal grain boundaries, for example, it may be four times or more. That is, in the first positive active material, the weight of boron in the first coating layer may be four times or more the weight of boron in the grain boundary boron coating portion. For example, the ratio of the weight of boron in the first coating layer to the weight of boron in the grain boundary boron coating portion may be 70:30 to 98:2, for example, 75:25 to 97:3, or 80:20 to 95:5. In this case, boron does not act as a resistor in the positive active material but can play a role in improving performance, and can simultaneously improve the capacity characteristics and lifespan characteristics of the lithium secondary battery.

[0646] For example, the boron content in the first coating layer may be 0.02 wt% to 0.5 wt% with respect to 100 wt% of the first positive active material, 0.03 wt% to 0.4 wt%, 0.04 wt% to 0.3 wt%, or 0.05 wt% to 0.2 wt%, etc. The boron content in the grain boundary boron coating portion may be 0.001 wt% to 0.05 wt% with respect to 100 wt% of the first positive active material, 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 content in the first coating layer and the grain boundary boron coating portion is such, both the capacity characteristics and lifespan characteristics of the lithium secondary battery can be improved. Here, the boron content may be measured through ICP emission spectroscopic analysis of the anode active material, the boron content in the grain boundary boron coating portion may refer to the boron content remaining in the first anode active material after washing, and the boron content of the first coating layer may refer to the difference between the boron content before washing and the boron content after washing.

[0647] According to one embodiment, the first positive active material, which is in the form of a secondary particle containing a radial structure, may further include a boron doping layer formed in a layer form along the periphery surface of the secondary particle, located inside the primary particle exposed on the surface of the secondary particle. The boron doping layer may be said to be located inside the secondary particle and may be said to be located within a depth range of about 10 nm from the outer surface of the primary particle exposed on the surface of the secondary particle. If the outer surface of the primary particles exposed on the surface of the secondary particle is defined as 0 nm, the doping layer may be said to exist in a depth range of 0 nm to 10 nm starting from the surface. In other words, the boron doping layer may be said to be located within a depth range of 10 nm from the surface of the secondary particle. If the surface of the secondary particle is defined as 0 nm, the doping layer may be said to exist in a depth range of 0 nm to 10 nm starting from the surface. This boron-doped layer can further enhance the structural stability of the cathode active material, thereby improving the lifespan characteristics of the lithium secondary battery.

[0648] The boron doping layer may be located, for example, within a depth range of 9 nm, 8 nm, 7 nm, 6 nm, 5 nm, 4 nm, 3 nm, or 2.5 nm from the outer surface of the primary particles exposed on the surface of the secondary particles. This boron doping layer is distinct from the first coating layer or the grain boundary boron coating portion and is thought to contribute to the structural stability of the cathode active material.

[0649] In one embodiment, the first positive electrode active material may comprise a lithium nickel-based composite oxide, a plurality of primary particles aggregated to form secondary particles in which at least a portion of the primary particles are arranged radially, a first coating layer located on the surface of the secondary particles and containing boron, and a second coating layer located on the first coating layer and containing zirconium, and additionally may comprise a boron grain boundary coating portion located at the internal grain boundary of the secondary particles, and / or a boron doping layer located inside the primary particles exposed on the surface of the secondary particles and formed along the periphery of the surface of the secondary particles.

[0650] The first positive electrode active material comprises a second coating layer containing zirconium. The second coating layer may contain a ZrO2 crystalline phase and a Li6Zr2O7 crystalline phase, and optionally a Zr-containing amorphous region. Since the details regarding the second coating layer containing zirconium are substantially the same as those described for the positive electrode active material, a detailed description is omitted.

[0651]

[0652] Coating layer of the second positive active material in the bimodal

[0653] The second positive electrode active material comprises a third coating layer containing zirconium located on the surface of the core particle. The third coating layer containing zirconium may exist as a uniform film or as an island on the surface of the single-particle core particle of the second positive electrode active material. The zirconium-containing third coating layer may be introduced by a dry coating method, and thus can be formed with a uniform and thin thickness without zirconium aggregating on the surface of the single particle. The third coating layer may contain a ZrO2 crystalline phase and a Li6Zr2O7 crystalline phase, and optionally a Zr-containing amorphous region. Since the details regarding zirconium are substantially the same as those previously described, a detailed explanation is omitted.

[0654]

[0655] Method for manufacturing bimodal positive electrode active material

[0656] A bimodal cathode active material according to one embodiment comprises a first cathode active material precursor containing a first nickel-based composite hydroxide, wherein a plurality of primary particles are aggregated and at least a portion of the primary particles are arranged radially in the form of secondary particles, a lithium raw material, and a boron raw material, mixed and subjected to a first heat treatment at a temperature of 650 ℃ to 850 ℃ to obtain a preliminary first cathode active material containing a first lithium nickel-based composite oxide;

[0657] It contains a second lithium nickel-based composite oxide and is in the form of a single particle, and the average particle size (D) of the first positive electrode active material precursor 50 Average particle size (D) smaller than ) 50 Prepare a preliminary second positive electrode active material having );

[0658] The above-mentioned preliminary first positive active material, the above-mentioned preliminary second positive active material, and zirconium raw material can be manufactured by dry mixing and second heat treatment.

[0659] Through a first heat treatment process, a first nickel-based composite hydroxide and a 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 secondary particles to produce a preliminary first positive active material.

[0660] Conventionally, when coating boron onto a positive electrode active material, a method was generally used in which a lithium nickel-based composite oxide was prepared by mixing a lithium raw material with a nickel-based composite hydroxide and heat-treating it, and then mixing a boron raw material into it in a wet or dry manner and heat-treating it again. However, in this case, the boron attached to the surface of the positive electrode active material acted as a resistor, which actually reduced the capacity and lifespan. On the other hand, the first positive electrode active material prepared according to one embodiment has an appropriate amount of boron coated on the surface of radial secondary particles and selectively on the internal grain boundaries, or a boron doping layer is formed, so that the resistance is low, the pellet density is high, and the initial discharge capacity is high, thereby significantly increasing the capacity per unit volume of the battery, and the initial charge / discharge efficiency is high and the room temperature and high temperature lifespan characteristics can be improved.

[0661] In the above manufacturing method, the first nickel-based composite hydroxide, which is a precursor of the first cathode active material, may be in the form of secondary particles formed by the aggregation of a plurality of primary particles, wherein at least a portion of the primary particles are arranged radially. The average particle size of the secondary particles may be 10 μm to 25 μm, for example, 11 μm to 20 μm, or 12 μm to 18 μm. Here, the average particle size of the secondary particles is determined by selecting approximately 20 arbitrary particles from an SEM image of the first cathode active material precursor, measuring their particle sizes (diameter, or major axis, or length of the major axis), obtaining a particle size distribution, and determining the diameter (D) of the particle whose cumulative volume is 50 volume% in the particle size distribution. 50 It may be that ) was taken as the average particle size.

[0662] The first cathode active material precursor can be prepared by a co-precipitation reaction. That is, a complex metal raw material is prepared by mixing metal raw materials such as nickel raw materials, and a complexing agent and a pH adjuster are added to control the pH of the mixture while carrying out a co-precipitation reaction to produce a nickel-based complex hydroxide of a desired composition. The complexing agent plays a role in controlling the reaction rate of precipitate formation in the co-precipitation reaction and may be, for example, ammonium hydroxide (NH4OH) or citric acid. The pH adjuster may be, for example, sodium hydroxide (NaOH), sodium carbonate (Na2CO3), sodium oxalate (Na2C2O4), etc. The pH of the mixture may be adjusted to a range of, for example, 10 to 13.

[0663] The above co-precipitation reaction can proceed in multiple stages, for example, in two, three, or four stages. In each stage, the concentration of the complexing agent, the input rate of the metal raw material, the pH control range, the reaction temperature, the reaction time, or the stirring power can be controlled differently. Through such control, a cathode active material precursor in the form of secondary particles in which at least a portion of the primary particles are arranged radially can be produced, and secondary particles with different internal and external shapes can also be produced.

[0664] For example, a first cathode active material precursor with a radial structure can be manufactured in the following manner. The method for manufacturing the first cathode active material precursor may include a first process, a second process, and a third process for forming a core, an intermediate layer, and a shell in sequence. In the first process, a complexing agent, a pH adjuster, and a metal raw material are introduced into a reactor and reacted. At this time, the concentration of the complexing agent may be 0.1M to 0.7M and the input amount may be 6 mL / min to 12 mL / min. The concentration of the metal raw material may be 0.1M to 3.5M and the input amount may be 50 mL / min to 100 mL / min. Subsequently, in the second process, the complexing agent, the pH adjuster, and the metal raw material are further introduced, at which time the concentration of the complexing agent may be 0.3M to 1.0M and the input amount may be 8 mL / min to 15 mL / min. The concentration of the metal raw material may be 0.1M to 3.5M and the input amount may be 60 mL / min to 120 mL / min. Subsequently, in the third process, the concentration and input amount of the complexing agent and the metal raw material are further increased or maintained at the same level to prevent a decrease in the particle growth rate. At this time, the concentration of the complexing agent may be 0.35M to 1.0M and the input amount may be 12 mL / min to 20 mL / min. The concentration of the metal raw material may be 0.1M to 2.5M and the input amount may be 70 mL / min to 150 mL / min. In the first to third processes, the pH may be adjusted to between 10 and 12.

[0665] The first nickel-based complex hydroxide can be represented, for example, by the chemical formula 11 below.

[0666] [Chemical Formula 11]

[0667] Ni x11 M 11 y11 M 12 z11 (OH)2

[0668] 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 Each is independently one or more of the elements Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr.

[0669] As a more specific example, the first nickel-based complex hydroxide may be a nickel-cobalt-aluminum-based hydroxide represented by the chemical formula 12 below.

[0670] [Chemical Formula 12]

[0671] Ni x12 Co y12 Al z12 M 13 w12 (OH)2

[0672] In the above chemical formula 12, 0.7 ≤ x 12 < 1, 0 <y12<0.3, 0<z12<0.3, 0≤w12<0.3, 0.9≤x12+y12+z12+w12≤1.1이고, M 13 It is one or more of the elements B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr.

[0673] 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 axis of the plate primary particles is directed toward the surface of the secondary particles.

[0674] The above lithium raw material may be, for example, Li2CO3, LiOH, LiF, their hydrates or anhydrous states, or a combination thereof. Additionally, the lithium raw material may be mixed such that the molar ratio of lithium to the total metal in the above first nickel-based composite hydroxide is 0.8 to 1, 0.8 to 0.995, 0.9 to 0.995, or 0.950 to 0.995. By adjusting the molar ratio of lithium to the above range, a preliminary first positive electrode active material in which a boron-containing first coating layer is effectively formed can be obtained.

[0675] The above boron raw material is a compound containing boron, for example, H3BO3, HBO2, B2O3, C6H5B(OH)2, (C6H5O)3B, [CH3(CH2)3O]3B, (C3H7O)3B, C3H9B3O6, C 13 H 19 It may include BO3, or a combination thereof.

[0676] The content of the boron raw material may be 0.01 to 0.5 molar parts per 100 molar parts of the total amount of metal excluding lithium in the first nickel-based composite hydroxide, for example, 0.01 to 0.3 molar parts, or 0.1 to 0.3 molar parts. When the content of the boron raw material satisfies the above range, boron does not act as a resistor in the cathode active material and can play a role in improving the performance of the lithium secondary battery, thereby increasing capacity and improving lifespan characteristics. If the content of the boron raw material becomes excessive, boron acts as a resistor in the cathode active material, which can reduce the capacity and lifespan of the battery.

[0677] The first heat treatment can be performed at a temperature of, for example, 650°C to 850°C or 690°C to 780°C. Additionally, the first heat treatment can be carried out for 5 to 25 hours, for example, 5 to 20 hours. In this case, a boron-containing compound can be stably coated, and a preliminary first cathode active material that achieves high capacity and high energy density can be manufactured. In conventional coating methods, such as mixing a lithium nickel-based composite oxide with a boron raw material and performing heat treatment, it was common to perform heat treatment at a much lower temperature, for example, 600°C or lower; however, one embodiment is distinguished in that heat treatment is performed at a higher temperature of 650°C to 850°C. By heat treating in this temperature range, a first lithium nickel-based composite oxide in the form of secondary particles with a radial structure can be obtained and simultaneously coated with a boron-containing compound. Accordingly, the cathode active material produced can simultaneously improve initial discharge capacity, initial efficiency, and lifespan characteristics without the resistance increase effect caused by boron, and increase pellet density to improve the capacity per unit volume of the battery.

[0678] In one embodiment, the first heat treatment includes a heating step and a temperature holding step, and the heating time may be set longer than the temperature holding time. For example, the heating time may be 6 to 16 hours and the temperature holding time may be 1 to 9 hours, and the heating time may be longer than the temperature holding time.

[0679] In the first heat treatment, the heating time may be, for example, 6 to 15 hours, 6 to 14 hours, 6 to 13 hours, or 7 to 12 hours, and the temperature holding time may be 2 to 9 hours, or 3 to 8 hours.

[0680] In addition, the ratio of (heating time):(temperature holding time) may be 1.1:1 to 10:1, and for example, 1.1:1 to 8:1, 1.1:1 to 6:1, 1.1:1 to 5:1, or 1.1:1 to 4:1.

[0681] By controlling the first heat treatment profile in this way, a high-efficiency pre-first cathode active material in the form of radial secondary particles can be effectively manufactured, and an appropriate amount of boron-containing compound can be stably coated.

[0682] The second lithium-nickel-based composite oxide in the form of single particles may be manufactured by mixing the second nickel-based composite hydroxide with a lithium raw material, heat treating the mixture, and then optionally undergoing a process such as grinding. Here, the heat treatment may be carried out, for example, in an oxidizing gas atmosphere at 800°C to 1100°C or at 800°C to 1000°C for about 1 to 25 hours or about 5 to 20 hours. The grinding is performed to obtain a single-particle form and is distinct from crushing; it may be carried out using a device such as a jet mill.

[0683] The second nickel-based complex hydroxide is identical or different from the first nickel-based complex hydroxide described above and can be represented by Chemical Formula 11 or Chemical Formula 12. Alternatively, the second nickel-based complex hydroxide can be represented by Chemical Formula 13 below.

[0684] [Chemical Formula 13]

[0685] Ni x13 Co y13 Al z13 Mn w13 M 14 v13 (OH)2

[0686] In the above chemical formula 13, 0.7 ≤ x 13 < 1, 0 <y13<0.3, 0<z13<0.3, 0<w13<0.3, 0≤v13<0.3, 0.9≤x13+y13+z13+w13+v13≤1.1이고, M 14It is one or more of the elements B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, T, Zn, and Zr.

[0687] The second lithium-nickel-based composite oxide of the preliminary second cathode active material may, for example, be represented by the aforementioned Chemical Formula 2. The average particle size (D) of a single particle containing the second lithium-nickel-based composite oxide. 50 ) can be 2 μm to 8 μm, and for example, 2 μm to 5 μm.

[0688] The weight ratio of the mixture of the preliminary first cathode active material and the preliminary second cathode active material may be 60:40 to 95:5, and for example, 70:30 to 90:10. In this case, a cathode active material with high pellet density and energy density, high capacity, and excellent lifespan characteristics can be manufactured.

[0689] By dry mixing a preliminary first positive active material, a preliminary second positive active material, and a zirconium raw material and performing a second heat treatment, a zirconium-containing second coating layer can be formed on the first positive active material and a zirconium-containing third coating layer can be formed on the second positive active material, and these second coating layers and third coating layers may include ZrO2 and Li6Zr2O7.

[0690] The zirconium raw material may be, for example, a zirconium-containing oxide, a zirconium-containing sulfide, a zirconium-containing carbonate, a zirconium-containing hydroxide, etc., and may be, for example, zirconium oxide, zirconium sulfide, zirconium carbonate, zirconium hydroxide, or a combination thereof.

[0691] The zirconium raw material can be mixed in an amount of 0.1 to 0.6 molar parts per 100 molar parts of the total metal excluding lithium in the first lithium-nickel-based composite oxide and the second lithium-nickel-based composite oxide, for example, 0.1 to 0.5 molar parts, or 0.1 to 0.4 molar parts. When the zirconium raw material is introduced within the above range, a coating layer of appropriate content and thickness can be formed, which can sufficiently perform the role of protecting the positive electrode active material and can exist with a uniform thickness without aggregating or existing locally on the surface of the core particles. For example, if the content of the zirconium raw material is excessive, the coating layer becomes thick and may act as a resistive layer, thereby reducing the charge / discharge capacity of the positive electrode active material; conversely, if the content of the zirconium raw material is too low, it may not sufficiently perform the buffer role, which may reduce the lifespan characteristics of the positive electrode active material.

[0692] The zirconium raw material may be in the form of nanoparticles, for example. The zirconium raw material is in the form of particles, and the average particle size (D) of the particles 50 ) may be, for example, 10 nm to 500 nm, 10 nm to 500 nm, or 50 nm to 500 nm. As an example, the zirconium raw material is a particle containing zirconium oxide, and the average particle size (D) of the particle is 50 ) may be 10 nm to 500 nm. In this case, it may be advantageous for synthesizing a coating layer of appropriate thickness.

[0693] The second heat treatment temperature may be 420°C to 580°C, for example, 430°C to 570°C, 440°C to 560°C, 450°C to 550°C, or 460°C to 530°C. By heat treating within the above temperature range, it is possible to synthesize a Zr coating layer having an appropriate crystalline phase, and the Zr coating layer can sufficiently perform the role of a buffer without acting as a resistor, thereby improving the capacity characteristics and lifespan characteristics of the positive electrode active material. For example, if the heat treatment temperature is below 420°C, the Zr coating layer may not form an appropriate crystalline phase and may act only as a resistor, which may degrade the capacity characteristics of the positive electrode active material. If the heat treatment temperature exceeds 580°C, the coating materials may aggregate or be coated only locally, reducing the buffering effect, and the zirconium may be absorbed into the positive electrode active material, failing to perform the buffering role and degrading the capacity characteristics and lifespan characteristics.

[0694] The second heat treatment above may be carried out in an oxygen atmosphere, for example, for 5 to 25 hours, or for 10 to 20 hours. Under these conditions, a good second coating layer and a third coating layer can be formed.

[0695] In one embodiment, when the preliminary first cathode active material, the preliminary second cathode active material, and the zirconium raw material are mixed dry, the lithium raw material may be mixed together. The lithium raw material may be any compound containing lithium that is capable of dry mixing, without limitation. The lithium raw material may be, for example, Li2CO3, LiOH, hydrates thereof, or a combination thereof. In one embodiment, anhydrous lithium hydroxide may be used as the lithium raw material. The lithium raw material may be mixed in an amount of more than 1 mole and less than or equal to 4 moles per 1 mole of the zirconium raw material, for example, more than 1 mole and less than or equal to 3 moles, or more than or equal to 2 moles and less than or equal to 4 moles. When the lithium raw material is mixed together and heat-treated, it is advantageous for the formation of lithium zirconium oxide, for example, a Li6Zr2O7 crystalline phase, in the second and third coating layers, and it is advantageous for increasing lithium ion conductivity and obtaining a coating layer of appropriate thickness in a good form.

[0696]

[0697] Example 3-1 (Li6PS5Cl 17 mg / cm² - Li 5.4 PS 4.4 Cl 1.6 17 mg / ㎠ (two-layer anode)

[0698] 1. Preparation of the first nickel-based complex hydroxide

[0699] The first nickel-based complex hydroxide (Ni), which is a precursor of the first positive electrode active material, is obtained through the coprecipitation method described below. 0.945 Co 0.04 Al 0.015 (OH)2) was synthesized. A mixed solution of metal raw materials was prepared by dissolving nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and sodium aluminum sulfate (NaAl(SO4)2·12H2O) in distilled water, the solvent, in a molar ratio of 94.5:4:1.5. In addition, water ammonia (NH4OH) and sodium hydroxide (NaOH) were prepared as a precipitating agent to form a complex.

[0700] [Stage 1: 2.5kW / m³, NH4OH 0.40M, pH 10.5~11.5, Reaction time 6 hours]

[0701] First, ammonia water with a concentration of 0.40 M was added to the reactor. The reaction was started at a stirring power of 2.5 kW / m³ and a reaction temperature of 50°C by adding the metal raw material mixed solution and the complexing agent (NH4OH) at rates of 85 ml / min and 10 ml / min, respectively. The reaction was carried out for 6 hours while adding NaOH to maintain the pH. As a result of the reaction, it was confirmed that the average size of the obtained core particles was in the range of approximately 6.5 µm to 7.5 µm, and the following two steps were performed.

[0702] [Stage 2: 2.0kW / m³, NH4OH 0.45M, pH 10.5~11.5, reaction time 18 hours]

[0703] While maintaining the reaction temperature at 50℃, the metal raw material mixed solution and the complexing agent were added at varying rates of 85 ml / min and 12 ml / min, respectively, so that the concentration of the complexing agent became 0.45 M. The reaction was carried out for 18 hours while adding NaOH to maintain the pH. During this time, the stirring power was lowered to 2.0 kW / m³, which is lower than that of the first step, to proceed with the reaction. After carrying out this reaction, it was confirmed that the average size of the product particles containing the core and intermediate layer was 13.5 μm to 14 μm, and the following three steps were performed.

[0704] [Stage 3: 1.5kW / ㎥, NH4OH 0.45M, pH 10.5~11.5, reaction time 14 hours]

[0705] While maintaining the reaction temperature at 50°C, the input rate and concentration of the metal raw material mixed solution and complexing agent were set identically to those in Step 2 above. The reaction was carried out for 14 hours while adding NaOH to maintain the pH. During this process, the stirring power was lowered to 1.5 kW / m³, lower than that of Step 2, to proceed with the reaction. After washing the obtained product, it was hot-air dried at approximately 150°C for 24 hours to produce a first nickel-based complex hydroxide (Ni) having a structure in which at least some of the primary particles constituting the secondary particles are arranged radially, in the form of secondary particles. 0.945 Co 0.04 Al 0.015 (OH)2) obtained.

[0706]

[0707] 2. Preparation of the first preliminary cathode active material

[0708] A first nickel-based complex hydroxide and LiOH were mixed to satisfy a molar ratio of Li / (Ni+Co+Al)=0.96, and boric acid was mixed so that boron was 0.25 mol% with respect to all elements excluding Li, O, and H in the mixture, and the mixture was fed into a calcination furnace and subjected to a first heat treatment in an oxygen atmosphere, which was heated to 700°C over 8 hours and maintained at a maximum temperature of 700°C for 7 hours to obtain a first preliminary cathode active material.

[0709] The obtained first preliminary cathode active material is a first lithium nickel-based composite oxide (Li 0.96 Ni 0.945 Co 0.04 Al 0.015 Contains O2) and average particle size (D 50 It was identified as a secondary particle with a diameter of approximately 13.8 μm. SEM analysis of the cross-section of the secondary particle revealed that it was in the form of a secondary particle containing an interior with an irregular porous structure and an exterior with a radial arrangement structure.

[0710] In addition, the first preliminary cathode active material is confirmed by mass spectrometry of ToF-SIMS to have lithium boron oxide, such as LiBO2, evenly coated on the surface of the secondary particles.

[0711] In addition, ICP emission spectroscopic analysis results showed that the boron content of 100 wt% of the first pre-positive active material before washing was 1120 ppm, and the boron content of 100 wt% of the first pre-positive active material after washing was 50 ppm. It was confirmed that the boron detected even after washing was coated on the internal grain boundaries of the secondary particles. The boron removed during the washing process corresponds to the component coated on the surface of the secondary particles and was confirmed to be 1120 - 50 = 1070 ppm. Accordingly, the ratio of the boron weight in the first coating layer to the boron weight in the grain boundary boron coating portion is calculated to be approximately 95:5. Furthermore, as a result of performing TEM-EELS analysis on the cross-section of the secondary particles from the surface inward, it was confirmed that a boron doping layer was formed in the region corresponding to a depth of 2 nm to 5 nm from the outermost surface. In other words, it can be seen that a boron doping layer was formed inside the primary particles exposed on the surface of the secondary particles. The above boron doping layer is located inside the secondary particle and is formed in a layered form along the periphery of the secondary particle, and is distinguished from the concept of being evenly doped inside the secondary particle.

[0712]

[0713] 3. Preparation of the second preliminary cathode active material

[0714] Second nickel-based complex hydroxide (Ni), which is a precursor of the second positive electrode active material, obtained through the co-precipitation method 0.94 Co 0.04 Al 0.01 Mn 0.01 (OH)2) was synthesized. As metal raw materials, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), sodium aluminum sulfate (NaAl(SO4)2·12H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water, a solvent, in a molar ratio of 94:4:1:1 to prepare a mixed solution. Subsequently, the synthesis was carried out in the same manner as the preparation of the first nickel-based complex hydroxide to prepare the second nickel-based complex hydroxide.

[0715] The prepared second nickel-based complex hydroxide and lithium hydroxide were mixed in a 1:1 molar ratio and heat-treated at 850°C in an oxygen atmosphere. The average particle size (D) of the product obtained through an air-flow impingement grinder 50 Grinding was performed so that the ) became approximately 3 μm, thereby producing the second lithium nickel-based composite oxide (LiNi 0.94 Co 0.04 Al 0.1 Mn 0.01 A second preliminary positive active material containing O2 and in the form of a single particle was obtained.

[0716]

[0717] 4. Preparation of mixed cathode active material

[0718] The first pre-positive active material and the second pre-positive active material were mixed in a weight ratio of 7:3, and zirconium oxide (ZrO2) was mixed so that the zirconium content was 0.25 molar parts and lithium hydroxide (LiOH) was mixed so that the lithium content was 0.5 molar parts for every 100 molar parts of the total metal excluding lithium in the first and second pre-positive active materials, and coating was performed in a Henschel mixer. At this time, the mixer was operated at low, medium, and high speeds to ensure even coating without layer separation. Subsequently, a second heat treatment was performed at 500°C for 15 hours in an oxygen atmosphere to produce a mixed positive active material with a zirconium-containing coating layer, namely, a first positive active material with a second coating layer and a second positive active material with a third coating layer. As a result of analyzing the crystal phases of the second and third coating layers formed in this way using STEM-EDS and HRTEM, it was confirmed that they contain ZrO2 crystal phases, Li6Zr2O7 crystal phases, and amorphous phases containing Zr.

[0719] In the obtained mixed cathode active material, the first cathode active material is a first lithium nickel-based composite oxide (Li 0.96 Ni 0.945 Co 0.04 Al 0.015It is in the form of a secondary particle containing O2 and having a radial structure, and the average particle size (D) of the secondary particle. 50 The particle size is confirmed to be approximately 13.8 μm, and it is confirmed that the surface of the secondary particle is primarily coated with a boron-containing compound and secondarily coated with a zirconium compound. The second cathode active material is a second lithium nickel-based composite oxide (LiNi 0.94 Co 0.04 Al 0.1 Mn 0.01 It contains O2) and is in the form of single particles, and the average particle size (D) of the single particles. 50 ) is confirmed to be about 3 μm, and the surface of the single particle is confirmed to be coated with a zirconium compound.

[0720]

[0721] 5. Preparation of the first solid electrolyte (Li6PS5Cl, Argyrodite, 0.85㎛)

[0722] An azirodite-type sulfide-based solid electrolyte was synthesized through the process described below. Mixing of raw materials, pre-treatment, and post-treatment of heat treatment were all carried out in a glove box under an argon atmosphere. As raw materials, lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), and lithium chloride (LiCl) were mixed in a molar ratio of 2.5:0.5:1 to prepare a mixed powder. After uniformly mixing the mixed powder with a Henschel mixer, it was first calcined at 250°C for 5 hours in a tubular furnace where argon gas flowed at a constant speed of 8 SLM.

[0723] The powder from the first calcination was homogeneously mixed again using a Henschel mixer and sieved, then subjected to a second calcination at 500°C for 10 hours in a tubular furnace where argon gas flowed at a constant speed of 8 SLM. The powder from the second calcination was ground and sieved to obtain Li6PS5Cl sulfide-based solid electrolyte particles. The size of the first solid electrolyte particles obtained in this way (D 50 ) is confirmed to be approximately 0.85 µm.

[0724]

[0725] 6. Preparation of the second solid electrolyte (Li 5.4 PS 4.4 Cl 1.6 , Argyrodite, 0.8 µm)

[0726] A second sulfide-based solid electrolyte was prepared in substantially the same manner as the first sulfide-based solid electrolyte, except that lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), and lithium chloride (LiCl) were mixed as raw materials in a molar ratio of 1.9:0.5:1.6. The second solid electrolyte thus obtained has a composition of Li 5.4 PS 4.4 Cl 1.6 It is an azyrodite-type solid electrolyte and particle size (D 50 ) is confirmed to be about 0.8 µm.

[0727]

[0728] 7. Preparation of the first positive electrode active material layer

[0729] A first cathode composition was prepared by adding 85 wt% of a cathode active material with a coating layer formed thereon, 13.44 wt% of a first solid electrolyte of the azirodite type Li6PS5Cl, 1 wt% of a PVdF binder, 0.4 wt% of a carbon nanotube conductive material, and 0.16 wt% of hydrogenated nitrile butadiene rubber (HNBR) as a dispersant to an isobutyryl isobutyrate (IBIB) solvent and mixing. This was applied to a cathode current collector at a loading level of 17 mg / cm² and dried to form a first cathode active material layer.

[0730]

[0731] 8. Preparation of the second positive electrode active material layer

[0732] 85 wt% of cathode active material with a coating layer formed, Li 5.4 PS 4.4 Cl 1.6A second cathode composition was prepared by adding 13.44 wt% of an azyrodite-type second solid electrolyte, 1 wt% of a PVdF binder, 0.4 wt% of a carbon nanotube conductive material, and 0.16 wt% of hydrogenated nitrile butadiene rubber (HNBR) as a dispersant to an isobutyryl isobutyrate (IBIB) solvent and mixing. This was applied to the first cathode active material layer at 17 mg / cm² 2 A second positive active material layer was formed by applying it at a loading level and drying it, and a positive was prepared by rolling (hydrostatic press; WIP; 500 Mpa, 85℃, 30 min).

[0733]

[0734] 9. Manufacturing of all-solid-state secondary batteries

[0735] Carbon black and 2-naphthalene thiol powder were mixed in a weight ratio of 10:1 and heat-treated at 90°C. The heat-treated product was added to a water solvent, and AgNO3 and a reducing agent, NaBH4, were added and mixed. At this time, the AgNO3 content was 11 wt% relative to the total content of carbon black and AgNO3 (100 wt%), and the NaBH4 content was 22 wt% relative to 100 wt% of AgNO3. The resulting product was heat-treated at 400°C for 4 hours under a nitrogen atmosphere to produce a compound in which Ag is supported on a carbon material. In the prepared Ag-C supported compound, the carbon material accounted for 94.6 wt% relative to the total amount of carbon material and Ag, the Ag content was 5.4 wt%, and the sulfur content was approximately 1.2 wt% relative to 100 wt% of the Ag-C supported compound. Transmission electron microscopy (TEM) analysis of the prepared Ag-C supported compound confirmed that silver is uniformly dispersed in the carbon material. In addition, X-ray photoelectron spectroscopy (XPS) analysis of the Ag-C supported compound revealed a Sp2 spectrum at approximately 161.8 eV corresponding to the Ag-S binding energy.

[0736] A cathode coating layer composition was prepared by mixing the manufactured Ag-C supported compound, styrene-butadiene rubber, and sodium carboxymethyl cellulose in a water solvent at a weight ratio of 100:6:3.

[0737] A precipitation type cathode was prepared by coating a stainless steel foil current collector with a thickness of 10 μm with the prepared cathode coating layer composition and vacuum drying it at 80°C to form a cathode coating layer with a thickness of 12 μm on the surface of the current collector.

[0738] Azirodite-type solid electrolyte of Li6PS5Cl (D 50 A composition for forming a solid electrolyte layer was prepared by adding (=3㎛) to an IBIB solvent containing an acrylic binder and mixing. The composition contains 98.5 wt% of solid electrolyte and 1.5 wt% of binder. The composition was cast onto a release film and dried at room temperature to prepare a solid electrolyte layer.

[0739] A solid electrolyte layer was laminated on the anode, and then a cathode was laminated on top of it. This was sealed in a pouch form and subjected to hydrostatic pressing at a high temperature of 80°C at 500 MPa for 30 minutes to manufacture an all-solid-state secondary battery.

[0740]

[0741] Comparative Example 3-1 (Li6PS5Cl 34 mg / cm² thick film anode)

[0742] A positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 3-1, except that when manufacturing the first positive electrode active material layer, 34 mg / cm² of the first positive electrode composition was applied to the positive electrode current collector and the second positive electrode active material layer was not applied.

[0743]

[0744] Comparative Example 3-2 (Li6PS5Cl 17 mg / cm² - 17 mg / cm² bilayer anode)

[0745] A positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 3-1, except that a first solid electrolyte was used instead of a second solid electrolyte when manufacturing the second positive electrode active material layer.

[0746]

[0747] Comparative Example 3-3 (Li 5.4 PS 4.4 Cl 1.6 34 mg / cm² thick film anode)

[0748] A positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 3-1, except that a second positive electrode composition of 34 mg / cm² was applied without applying a first positive electrode active material layer on the positive electrode current collector.

[0749]

[0750] Comparative Examples 3-4 (Li 5.4 PS 4.4 Cl 1.6 17 mg / ㎠ - 17 mg / ㎠ (two-layer anode)

[0751] A positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 3-1, except that a second solid electrolyte was used instead of a first solid electrolyte when manufacturing the first positive electrode active material layer.

[0752]

[0753] To aid understanding, the anode design details of Example 3-1 and Comparative Examples 3-1 to 3-4 are briefly shown in Table 9 below.

[0754] First positive active material layer, second positive active material layer, double layer positive, Example 3 - 1Li6PS5ClLi 5.4 PS 4.4 Cl 1.6 Comparative Example 3 - 1Li6PS5ClX Comparative Example 3 - 2Li6PS5ClLi6PS5ClO Comparative Example 3 - 3Li 5.4 PS 4.4 Cl 1.6 X Comparative Example 3-4Li 5.4 PS 4.4 Cl 1.6 Li5.4 PS 4.4 Cl 1.6 O

[0755] Evaluation Example 3-1: Evaluation of Initial Charge / Discharge Capacity of All-Solid State Secondary Battery

[0756] The all-solid-state secondary batteries prepared in Example 3-1 and Comparative Examples 3-1 to 3-4 were charged to 4.25V with a constant current of 0.1C at 45℃ and to 0.05C with a constant voltage to measure the initial charge capacity, and discharged to 2.5V with 0.1C to measure the initial discharge capacity. The ratio of discharge capacity to charge capacity was calculated as efficiency, and the results are shown in Table 10.

[0757] Charge Capacity (mAh / g) Discharge Capacity (mAh / g) Efficiency (%) Example 3-1 240.6 205.585 Comparative Example 3-1 233.1 181.378 Comparative Example 3-2 231.1 182.679 Comparative Example 3-3 201.3 157.278 Comparative Example 3-4 224.4 178.980

[0758] Referring to Table 10, it can be seen that Example 3-1 has improved initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency compared to Comparative Examples 3-1 to 3-4.

[0759] Evaluation Example 3-2: Evaluation of High Rate Characteristics

[0760] For the all-solid-state secondary batteries prepared in Example 3-1 and Comparative Examples 3-1 to 3-4, after performing initial charge and discharge as in Evaluation Example 3-1, the batteries were charged with a constant current of 0.1C to an upper limit voltage of 4.25V and with a constant voltage of 0.05C, and then discharged at 0.33C to a discharge cutoff voltage of 2.5V to measure the discharge capacity at 0.33C. Subsequently, the batteries were charged with a constant current of 0.1C to an upper limit voltage of 4.25V and with a constant voltage of 0.05C, and then discharged at 1.0C to a discharge cutoff voltage of 2.5V to measure the discharge capacity at 1.0C. The high-rate discharge capability was calculated from Equation 1 below, and the discharge capacity and high-rate discharge capability for each cycle are shown in Table 11.

[0761] [Equation 1]

[0762] High-rate discharge characteristic (%) = {(Discharge capacity at 1C) / (Discharge capacity at 0.1C)} x 100

[0763] Discharge Capacity (mAh / g) High Rate Discharge Characteristics (%) 0.1C 1.0C Example 3-1 206 17083 Comparative Example 3-1 181 13977 Comparative Example 3-2 183 14378 Comparative Example 3-3 157 11473 Comparative Example 3-4 179 12872

[0764] Referring to Table 11 above, it can be confirmed that Example 3-1 has significantly superior high-rate discharge characteristics compared to Comparative Examples 3-1 to 3-4.

[0765] Evaluation Example 3-3: Evaluation of Lifetime Characteristics of All-Solid State Secondary Batteries

[0766] For the all-solid-state secondary batteries prepared in Example 3-1 and Comparative Examples 3-1 to 3-4, after performing initial charge and discharge as in Evaluation Example 3-1, the life characteristics were evaluated by repeating the charging and discharging at 0.33C at 45°C in a voltage range of 2.5V to 4.25V 100 times. Table 12 below shows the initial discharge capacity (1-cycle discharge capacity), 100-cycle discharge capacity, and the capacity retention rate, which is the ratio of the latter to the former.

[0767] Single Discharge Capacity (mAh / g) 100 Discharge Capacity (mAh / g) Capacity Retention Rate (%) Example 3-11 66 147 88 Comparative Example 3-11 43 110 77 Comparative Example 3-2 1 43 119 83 Comparative Example 3-3 1 32 100 76 Comparative Example 3-4 1 22 100 82

[0768] Referring to Table 12 above, it can be seen that Example 3-1 has a further improved capacity retention rate at 100 cycles compared to Comparative Examples 3-1 to 3-4.

[0769]

[0770] The above third embodiment provides the following technical configuration.

[0771] 1. A positive electrode comprising a positive current collector, and a first positive active material layer and a second positive active material layer located on the positive current collector, and

[0772] The above first positive active material layer

[0773] A positive electrode active material comprising a core particle containing a lithium nickel-based composite oxide, a first coating layer located on the core particle and containing boron, and a second coating layer located on the first coating layer and containing zirconium, and

[0774] It comprises a first solid electrolyte containing an azirodite-type sulfide containing Li, P, S and halogen elements, and

[0775] The above second positive active material layer

[0776] A positive electrode active material comprising a core particle containing a lithium nickel-based composite oxide, a first coating layer located on the core particle and containing boron, and a second coating layer located on the first coating layer and containing zirconium, and

[0777] It comprises a second solid electrolyte containing an azirodite-type sulfide containing Li, P, S and halogen elements, and

[0778] The first solid electrolyte and the second solid electrolyte are anodes in which the molar ratio of at least one of Li, P, S and halogen elements is different from each other.

[0779] 2. An anode in which, in paragraph 1, the molar ratio of the halogen element in the second solid electrolyte is higher than the molar ratio of the halogen element in the first solid electrolyte.

[0780] 3. An anode according to paragraph 2, wherein the molar ratio of the halogen element in the second solid electrolyte is 1.1 to 2.5 times the molar ratio of the halogen element in the first solid electrolyte.

[0781] 4. In claim 1, the content of the halogen element in the first solid electrolyte is 5 mol% to 10 mol% based on 100 mol% of the first solid electrolyte, and the content of the halogen element in the second solid electrolyte is 11 mol% to 15 mol% based on 100 mol% of the second solid electrolyte for the positive electrode.

[0782] 5. In claim 1, the aziridite-type sulfide of the first solid electrolyte is represented by the following Chemical Formula 22, and the aziridite-type sulfide of the second solid electrolyte is represented by the following Chemical Formula 23,

[0783] [Chemical Formula 22]

[0784] (Li a2 M 1 b2 M 2 c2 )(P d2 M 3 e2 )(S f2 M 4 g2 )X h2

[0785] In Chemical Formula 22, 4 ≤ a2 ≤ 8, and M 1 is Mg, Ca, Cu, Ag, or a combination thereof, 0 ≤ b2 < 0.5, and M 2 is Na, K, or a combination thereof, 0 ≤ c2 < 0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, 0 < d2 < 4, 0 ≤ e2 < 1, and M 4 is N, O, SO n , or a combination thereof, 1.5 ≤ n ≤ 5, 3 ≤ f2 ≤ 12, 0 ≤ g2 < 2, and X is F, Cl, Br, I, or a combination thereof, 0 < h2 ≤ 2,

[0786] [Chemical Formula 23]

[0787] (Li a3 M 1 b3 M 2 c3 )(P d3 M 3e3 )(S f3 M 4 g3 )X h3

[0788] In the above chemical formula 23, 4≤a3≤8, and M 1 is Mg, Ca, Cu, Ag, or a combination thereof, 0≤b3<0.5, and M 2 is Na, K, or a combination thereof, 0≤c3<0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, and 0 <d3<4, 0≤e3<1 이고, M 4 is N, O, SO n , or a combination thereof, 1.5≤n≤5, 3≤f3≤12, 0≤g3<2, and X is F, Cl, Br, I, or a combination thereof, and 0 <h3≤2이며,

[0789] An anode in the above chemical formulas 22 and 23, wherein a2≠a3, d2≠d3, f2≠f3, or h2≠h3.

[0790] 6. An anode according to claim 5, wherein in the above chemical formulas 22 and 23, (a2+b2+c2)≠(a3+b3+c3) or (d2+e2)≠(d3+e3) or (f2+g2)≠(f3+g3) or h2≠h3.

[0791] 7. In paragraph 5, in the above chemical formulas 22 and 23, (a2+b2+c2)>(a3+b3+c3) or (f2+g2)>(f3+g3) or h2 <h3인 양극.

[0792] 8. An anode according to claim 5, wherein in the above chemical formulas 22 and 23, (h2 x 1.1)≤h3≤(h2 x 2.5).

[0793] 9. The anode according to claim 1, wherein the first solid electrolyte is Li6P1S5X1 (where X is a halogen element), and the second solid electrolyte is an anode in which the molar ratio of at least one of Li, P, S and a halogen element is different from that of the first solid electrolyte.

[0794] 10. In paragraph 1, the first solid electrolyte and the second solid electrolyte are each in the form of particles, and their average particle size (D 50 A cathode having ) which are identical or different from each other and each independently have a thickness of 0.1 μm to 5 μm, wherein the content of the first solid electrolyte is 1 wt% to 35 wt% with respect to 100 wt% of the first cathode active material layer, and the content of the second solid electrolyte is 1 wt% to 35 wt% with respect to 100 wt% of the second cathode active material layer.

[0795] 11. An anode according to claim 1, wherein the thickness of each of the first positive active material layer and the second positive active material layer is 15 μm to 100 μm, the ratio of the thickness of the first positive active material layer to the thickness of the second positive active material layer is 20:80 to 80:20, and the first positive active material layer is located on the current collector and the second positive active material layer is located on the first positive active material layer.

[0796] 12. In paragraph 1, the loading level of each of the first positive electrode active material layer and the second positive electrode active material layer is 10 mg / cm² 2 to 80 mg / cm² 2 A positive electrode having a density of 3.0 g / cc to 3.9 g / cc for each of the first positive electrode active material layer and the second positive electrode active material layer.

[0797] 13. An anode according to claim 1, wherein, in each of the anode active material of the first anode active material layer and the anode active material of the second anode active material layer, the first coating layer comprises boron oxide, lithium boron oxide, or a combination thereof, and the boron content of the first coating layer is 0.01 wt% to 0.5 wt% with respect to 100 wt% of the total metal excluding lithium in the anode active material, and the second coating layer comprises ZrO2 and Li6Zr2O7, and the zirconium content of the second coating layer is 0.1 mol to 0.6 mol with respect to 100 mol of the total metal excluding lithium in the anode active material.

[0798] 14. An anode according to claim 1, wherein in each of the anode active material of the first anode active material layer and the anode active material of the second anode active material layer, the core particle comprises a secondary particle formed by the aggregation of a plurality of primary particles, and the anode active material further comprises a grain boundary boron coating portion located on the surface of the primary particles inside the secondary particle, and the boron content in the boron-containing first coating layer is at least four times the boron content in the grain boundary boron coating portion, or the ratio of the boron content in the boron-containing first coating layer to the boron content in the grain boundary boron coating portion is 70:30 to 98:2.

[0799] 15. In claim 1, in each of the positive active material of the first positive active material layer and the positive active material of the second positive active material layer, the core particle comprises a secondary particle formed by the aggregation of a plurality of primary particles, and the positive active material further comprises a boron doping layer formed in a layer shape along the periphery of the surface of the secondary particle while being located inside the primary particle exposed on the surface of the secondary particle, and the boron doping layer is a positive electrode located within a depth range of 10 nm from the outer surface of the primary particle exposed on the surface of the secondary particle.

[0800] 16. In claim 1, the positive active material of the first positive active material layer and the positive active material of the second positive active material layer are identical or different from each other, and each independently comprises: (i) a first positive active material comprising a lithium nickel-based composite oxide, a plurality of primary particles aggregated to form secondary particles in which at least a portion of the primary particles are arranged radially, a first coating layer located on the surface of the secondary particles and containing boron, and a second coating layer located on the first coating layer and containing zirconium; and (ii) a third coating layer comprising a lithium nickel-based composite oxide, in the form of a single particle, located on the surface of the single particle and containing zirconium, wherein the average particle size (D) of the first positive active material 50 Average particle size (D) smaller than )50 It includes a second positive electrode active material having ), and the average particle size (D) of the secondary particles of the first positive electrode active material. 50 ) is 9 μm to 25 μm, and the average particle size (D) of the single particles of the second positive active material. 50 ) is 2 μm to 8 μm, and with respect to the total sum of the first and second positive active materials at 100 wt%, the first positive active material is included at 60 wt% to 95 wt% and the second positive active material is included at 5 wt% to 40 wt%.

[0801] 17. A positive electrode according to claim 16, wherein the lithium nickel-based composite oxide of the first positive electrode active material is a lithium nickel-cobalt-aluminum-based composite oxide represented by the following chemical formula 1, and the lithium nickel-based composite oxide of the second positive electrode active material is a lithium nickel-cobalt-aluminum-manganese-based composite oxide represented by the following chemical formula 2:

[0802] [Chemical Formula 1]

[0803] Li a1 Ni x1 Co y1 Al z1 M 1 w1 O 2-b1 X b1

[0804] In the above Chemical Formula 1, 0.9≤a1≤1.2, 0.7≤x1<1, 0 <y1<0.3, 0<z1<0.3, 0≤w1<0.3, 0.9≤x1+y1+z1+w1≤1.1, 및 0≤b1≤0.1이고, M 1 is one or more elements among B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, Y, Zn, and Zr, and X is one or more elements among F, P, and S, and

[0805] [Chemical Formula 2]

[0806] Li a2 Ni x2 Co y2 Al z2 Mn w2M 2 v2 O 2-b2 X b2

[0807] In the above chemical formula 2, 0.9≤a2≤1.2, 0.7≤x2<1, 0 <y2<0.3, 0<z2<0.3, 0<w2<0.3, 0≤v2<0.3, 0.9≤x2+y2+z2+w2+v2≤1.1, 및 0≤b2≤0.1이고, M 2 is one or more of the elements B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, T, Zn, and Zr, and X is one or more of the elements F, P, and S.

[0808] 18. An all-solid-state secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode according to any one of claims 1 to 17.

[0809] 19. An all-solid-state secondary battery according to claim 20, wherein the cathode comprises a cathode current collector and a cathode coating layer located on the cathode current collector and containing a compound in which a lithium-friendly metal is supported on a carbon material, wherein the lithium-friendly metal comprises Al, Ag, Au, Bi, Cu, Ge, In, Mg, Ni, Pd, Pt, Si, Sn, Zn, or a combination thereof, and the carbon material is an amorphous carbon material, wherein the lithium-friendly metal is included in an amount of 3% to 40% by weight and the carbon material is included in an amount of 60% to 97% by weight with respect to 100% by weight of the total amount of the lithium-friendly metal and the carbon material.

[0810] 20. An all-solid-state secondary battery according to claim 18, wherein the solid electrolyte layer comprises a solid electrolyte, and the average particle size of the solid electrolyte included in the solid electrolyte layer is larger than the average particle size of the first solid electrolyte and the average particle size of the second solid electrolyte.

[0811]

[0812] [Fourth Implementation Example]

[0813] The fourth embodiment is substantially identical to the first embodiment, except that the anode is designed as follows. Except for the details below, the contents described in the first embodiment above may be applied in the same way.

[0814] anode

[0815] In one embodiment, a positive electrode is provided comprising a positive current collector, and a first positive active material layer and a second positive active material layer located on the positive current collector. The first positive active material layer comprises a positive active material comprising a core particle containing a lithium nickel-based composite oxide and a boron coating layer located on the core particle, and a first solid electrolyte containing a sulfide-based solid electrolyte. The second positive active ma...

Claims

positive current collector, and A positive electrode comprising a first positive active material layer and a second positive active material layer located on the positive current collector, and The above first positive active material layer A positive electrode active material comprising a core particle containing a lithium nickel-based composite oxide and a boron coating layer located on said core particle, and It comprises a first solid electrolyte containing an azirodite-type sulfide containing Li, P, S and halogen elements, and The above second positive active material layer A positive electrode active material comprising a core particle containing a lithium nickel-based composite oxide and a boron coating layer located on said core particle, and It comprises a second solid electrolyte containing an azirodite-type sulfide containing Li, P, S and halogen elements, and The first solid electrolyte and the second solid electrolyte are anodes in which the molar ratio of at least one of Li, P, S and halogen elements is different from each other. In paragraph 1, An anode in which the molar ratio of the halogen element in the second solid electrolyte is higher than the molar ratio of the halogen element in the first solid electrolyte. In paragraph 2, An anode in which the molar ratio of the halogen element in the second solid electrolyte is 1.1 to 2.5 times the molar ratio of the halogen element in the first solid electrolyte. In paragraph 1, The content of the halogen element in the first solid electrolyte is 5 mol% to 10 mol% with respect to 100 mol% of the first solid electrolyte, and An anode in which the content of a halogen element in the second solid electrolyte is 11 mol% to 15 mol% with respect to 100 mol% of the second solid electrolyte. In paragraph 1, The azyrodite-type sulfide of the first solid electrolyte is represented by the following chemical formula 22, and the azyrodite-type sulfide of the second solid electrolyte is represented by the following chemical formula 23, and [Chemical Formula 22] (Li a2 M 1 b2 M 2 c2 (P) d2 M 3 e2 )(S f2 M 4 g2 )X h2 In the above chemical formula 22, 4≤a2≤8, and M 1 is Mg, Ca, Cu, Ag, or a combination thereof, 0≤b2<0.5, and M 2 is Na, K, or a combination thereof, 0≤c2<0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, and 0 <d2<4, 0≤e2<1 이고, M 4 is N, O, SO n , or a combination thereof, 1.5≤n≤5, 3≤f2≤12, 0≤g2<2, and X is F, Cl, Br, I, or a combination thereof, and 0 <h2≤2이며, [Chemical Formula 23] (Li a3 M 1 b3 M 2 c3 (P) d3 M 3 e3 )(S f3 M 4 g3 )X h3 In the above chemical formula 23, 4≤a3≤8, and M 1 is Mg, Ca, Cu, Ag, or a combination thereof, 0≤b3<0.5, and M 2 is Na, K, or a combination thereof, 0≤c3<0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, and 0 <d3<4, 0≤e3<1 이고, M 4 is N, O, SO n , or a combination thereof, 1.5≤n≤5, 3≤f3≤12, 0≤g3<2, and X is F, Cl, Br, I, or a combination thereof, and 0 <h3≤2이며, An anode in the above chemical formulas 22 and 23, wherein a2≠a3, d2≠d3, f2≠f3, or h2≠h3. In paragraph 5, In the above chemical formula 22 and the above chemical formula 23, A positive electrode such that (a2+b2+c2)≠(a3+b3+c3) or (d2+e2)≠(d3+e3) or (f2+g2)≠(f3+g3) or h2≠h3. In paragraph 5, In the above chemical formula 22 and the above chemical formula 23, (a2+b2+c2)>(a3+b3+c3) or (f2+g2)>(f3+g3) or h2 <h3인 양극. In paragraph 5, In the above chemical formula 22 and the above chemical formula 23, Anode such that (h2 x 1.1)≤h3≤(h2 x 2.5). In paragraph 1, The first solid electrolyte is Li6P1S5X1 (where X is a halogen element), and The second solid electrolyte is an anode in which the molar ratio of at least one of Li, P, S and halogen elements is different from that of the first solid electrolyte. In paragraph 1, The first solid electrolyte and the second solid electrolyte are each in the form of particles, and their average particle size (D 50 ) are identical or different from each other and are each independently 0.1 μm to 5 μm, and The content of the first solid electrolyte is 1% to 35% by weight with respect to 100% by weight of the first positive active material layer, and An anode in which the content of the second solid electrolyte is 1% to 35% by weight with respect to 100% by weight of the second anode active material layer. In paragraph 1, The thickness of each of the first positive active material layer and the second positive active material layer is 15 μm to 100 μm, and The ratio of the thickness of the first positive active material layer to the thickness of the second positive active material layer is 20:80 to 80:20, and An anode having a first positive active material layer located on the current collector and a second positive active material layer located on the first positive active material layer. In paragraph 1, The loading level of each of the first positive electrode active material layer and the second positive electrode active material layer is 10 mg / cm² 2 to 80 mg / cm² 2 And, A positive electrode having a density of 3.0 g / cc to 3.9 g / cc for each of the first positive electrode active material layer and the second positive electrode active material layer. In paragraph 1, In each of the positive active material of the first positive active material layer and the positive active material of the second positive active material layer, The above boron coating layer comprises boron oxide, lithium boron oxide, or a combination thereof, and An anode in which the boron content of the boron coating layer is 0.01% to 0.5% by weight based on 100% by weight of the total metal excluding lithium in the anode active material. In paragraph 1, In each of the positive active material of the first positive active material layer and the positive active material of the second positive active material layer, The above core particle includes a secondary particle formed by the aggregation of a plurality of primary particles, and The above positive active material further includes a grain boundary boron coating portion located on the surface of the primary particles inside the secondary particles, and An anode in which the boron content in the boron coating layer is at least four times the boron content in the grain boundary boron coating portion, or the ratio of the boron content in the boron coating layer to the boron content in the grain boundary boron coating portion is 70:30 to 98:

2. In paragraph 1, In each of the positive active material of the first positive active material layer and the positive active material of the second positive active material layer, The above core particle includes a secondary particle formed by the aggregation of a plurality of primary particles, and The above positive active material further includes a boron doping layer formed in a layered form along the surface periphery of the secondary particle, located inside the primary particle exposed to the surface of the secondary particle. The above boron doping layer is an anode located within a depth range of 10 nm from the outer surface of the primary particle exposed to the surface of the secondary particle. In paragraph 1, The positive active material of the first positive active material layer and the positive active material of the second positive active material layer are identical or different from each other, and each independently (i) a first positive electrode active material comprising a lithium nickel-based composite oxide, a plurality of primary particles aggregated to form secondary particles in which at least a portion of the primary particles are arranged radially, and a boron coating layer located on the surface of the secondary particles; and (ii) comprising a lithium nickel-based composite oxide, in the form of a single particle, and a boron coating layer located on the surface of said single particle, and the average particle size (D) of said first positive active material 50 Average particle size (D) smaller than ) 50 It includes a second positive electrode active material having ), Average particle size (D) of the secondary particles of the first positive active material 50 ) is 9 μm to 25 μm, and Average particle size (D of the above single particles of the second positive active material) 50 ) is 2 μm to 8 μm, and A cathode comprising, with respect to a total of 100 weight% of the first cathode active material and the second cathode active material, the first cathode active material is included in an amount of 60 weight% to 95 weight% and the second cathode active material is included in an amount of 5 weight% to 40 weight%. In Paragraph 16, The lithium nickel-based composite oxide of the first positive electrode active material is a lithium nickel-cobalt-aluminum-based composite oxide represented by the following chemical formula 1, and The lithium nickel-based composite oxide of the second positive electrode active material is a positive electrode that is a lithium nickel-cobalt-aluminum-manganese-based composite oxide represented by the following chemical formula 2: [Chemical Formula 1] Li a1 Ni x1 Co y1 Al z1 M 1 w1 O 2-b1 X b1 In the above Chemical Formula 1, 0.9≤a1≤1.2, 0.7≤x1<1, 0 <y1<0.3, 0<z1<0.3, 0≤w1<0.3, 0.9≤x1+y1+z1+w1≤1.1, 및 0≤b1≤0.1이고, M 1 is one or more elements among B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, Y, Zn, and Zr, and X is one or more elements among F, P, and S, and [Chemical Formula 2] Li a2 Ni x2 Co y2 Al z2 Mr w2 M 2 v2 O 2-b2 X b2 In the above chemical formula 2, 0.9≤a2≤1.2, 0.7≤x2<1, 0 <y2<0.3, 0<z2<0.3, 0<w2<0.3, 0≤v2<0.3, 0.9≤x2+y2+z2+w2+v2≤1.1, 및 0≤b2≤0.1이고, M 2 is one or more of the elements B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, T, Zn, and Zr, and X is one or more of the elements F, P, and S. Anode according to any one of paragraphs 1 through 17, cathode, and An all-solid-state secondary battery comprising a solid electrolyte layer located between the anode and the cathode. In Paragraph 18, The above cathode comprises a cathode current collector and a cathode coating layer located on the cathode current collector and containing a compound in which a lithium-friendly metal is supported on a carbon material. The above-mentioned lithium-friendly metal includes Al, Ag, Au, Bi, Cu, Ge, In, Mg, Ni, Pd, Pt, Si, Sn, Zn, or a combination thereof, and The above carbon material is an amorphous carbon material, and A solid-state secondary battery comprising, with respect to a total of 100 weight% of the lithium-friendly metal and the carbon material, the lithium-friendly metal comprising 3 weight% to 40 weight% and the carbon material comprising 60 weight% to 97 weight%. In Paragraph 18, The above solid electrolyte layer comprises a solid electrolyte, and An all-solid-state secondary battery in which the average particle size of the solid electrolyte included in the solid electrolyte layer is larger than the average particle size of the first solid electrolyte and the average particle size of the second solid electrolyte.

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