Positive electrode, method for manufacturing same, and all-solid-state secondary battery

Abstract

The present invention relates to a positive electrode and an all-solid-state secondary battery, the positive electrode comprising a first positive electrode active material, a second positive electrode active material, and a solid electrolyte, wherein the first positive electrode active material comprises: secondary particles including a lithium nickel-based composite oxide and formed by agglomeration of a plurality of primary particles, wherein at least a portion of the primary particles are radially arranged; a first coating layer positioned on the surface of the secondary particles and containing Zr; and a second coating layer positioned on the first coating layer and containing a sulfide-based solid electrolyte, the second positive electrode active material comprises: secondary particles including a lithium nickel-based composite oxide and formed by agglomeration of a plurality of primary particles; a first coating layer containing Zr and positioned on the surface of the secondary particles; and a second coating layer containing a sulfide-based solid electrolyte and positioned on the first coating layer, wherein the second positive electrode active material has a smaller average particle diameter (D50) than the average particle diameter (D50) of the first positive electrode active material, and the solid electrolyte comprises: core particles containing a sulfide-based solid electrolyte; and a third coating layer containing a lithium-metal-phosphate compound and positioned on the surface of the core particles.

Description

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

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

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

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

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

[0005] In one embodiment, a first cathode active material comprising a lithium nickel-based composite oxide, wherein a plurality of primary particles are aggregated and at least a portion of the primary particles are radially arranged secondary particles, a first coating layer positioned on the surface of the secondary particles and containing Zr, and a second coating layer positioned on the first coating layer and containing a sulfide-based solid electrolyte; a lithium nickel-based composite oxide, wherein a plurality of primary particles are aggregated secondary particles, a first coating layer positioned on the surface of the secondary particles and containing Zr, and a second coating layer positioned on the first coating layer and containing a sulfide-based solid electrolyte, wherein the average particle diameter (D) of the first cathode active material 50 ) smaller than the average particle diameter (D 50 ) and a solid electrolyte including a core particle containing a sulfide-based solid electrolyte and a third coating layer located on the surface of the core particle and containing a lithium-metal-phosphate.

[0006] In another embodiment, (i) a first cathode active material precursor comprising a nickel-based composite hydroxide, wherein a plurality of primary particles are aggregated and at least a portion of the primary particles are in the form of secondary particles arranged radially; a nickel-based composite hydroxide, wherein the second particle is in the form of aggregated primary particles and the average particle diameter (D) of the first cathode active material precursor 50 ) smaller than the average particle diameter (D 50) and a lithium raw material, and subjecting them to a first heat treatment to obtain a preliminary positive electrode active material, (ii) dry-mixing the preliminary positive electrode active material and the zirconium raw material and subjecting them to a second heat treatment to prepare a Zr-coated positive electrode active material, (iii) dry-mixing the Zr-coated positive electrode active material and a sulfide-based solid electrolyte and subjecting them to a third heat treatment to obtain a final positive electrode active material, (iv) mixing core particles containing a sulfide-based solid electrolyte and a lithium-metal-phosphate and subjecting them to a fourth heat treatment at 200° C. to 300° C. to prepare a coated solid electrolyte, and (v) mixing the final positive electrode active material and the coated solid electrolyte to produce a positive electrode.

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

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

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

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

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

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

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

[0014] Figure 7 is a graph showing the capacity retention rate according to the number of cycles as a result of the life evaluation of the all-solid-state secondary batteries of Example 1 and Comparative Examples 1 to 5.

[0015] Figure 8 is a graph showing the resistance of the positive electrodes of Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 4, and Comparative Example 5, where R1+R2 represents the resistance of the positive electrode plate.

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

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

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

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

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

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

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

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

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

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

[0026] anode

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

[0028] The above positive electrode may be referred to as a positive electrode for a lithium secondary battery, and more specifically, as a positive electrode for an all-solid-state secondary battery. According to one embodiment, the positive electrode may exhibit reduced resistance and improved initial charge / discharge capacity and efficiency, as well as improved lifespan characteristics.

[0029] The first cathode active material can be expressed as a counter or counter particle, and the average particle diameter of the secondary particles (D 50 ) may be 9 ㎛ to 25 ㎛, for example, 11 ㎛ to 18 ㎛, 12 ㎛ to 16 ㎛. The second positive electrode active material may be expressed as a particle or particles, and the average particle diameter (D of the secondary particles 50 ) may be 2 ㎛ to 8 ㎛, for example 2.5 ㎛ to 7 ㎛, or 3 ㎛ to 6 ㎛. Here, the average particle diameter (D50 ) may be obtained by selecting about 20 random particles from a scanning electron microscope (SEM) image of a positive electrode active material, measuring their particle size (diameter, or major axis, or major axis length), and then obtaining a particle size distribution, and taking the size of particles having a cumulative volume of 50% by volume from the particle size distribution as the average particle size.

[0030] The above sulfide-based solid electrolyte particles contained in the anode have an average particle diameter (D 50 ) may be about 0.1 ㎛ to 2 ㎛, for example, 0.5 ㎛ to 1.9 ㎛, 0.5 ㎛ to 1.5 ㎛, or 0.8 ㎛ to 1 ㎛, and the average particle diameter (D of the second positive electrode active material 50 ) can be smaller.

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

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

[0033] First coating layer of positive electrode active material

[0034] According to one embodiment, a cathode active material includes a first coating layer containing Zr. The first 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, thereby improving the structural stability of the cathode active material.

[0035] According to one embodiment, the first coating layer may be characterized by being formed through a dry coating method. The first coating layer may include ZrO2 and Li6Zr2O7, and may include, for example, a mixed phase of ZrO2 and Li6Zr2O7. That is, the first coating layer may include ZrO2 having a relatively high crystallinity and Li6Zr2O7 having a lower crystallinity. The presence or absence of ZrO2 and Li6Zr2O7 can be determined, for example, through the inverse FFT or FFT rotation pattern of the HRTEM image for the positive electrode active material. The first coating layer containing ZrO2 and Li6Zr2O7 can facilitate the movement of lithium ions on the surfaces of each of the first positive electrode active material and the second positive electrode active material, improve the structural stability of the positive electrode active material, and lower the reactivity with the sulfide-based solid electrolyte, thereby improving the interfacial resistance.

[0036] The first coating layer may further include an amorphous region. For example, the coating layer may include a ZrO2 crystal phase, a Li6Zr2O7 crystal phase, and a Zr-containing amorphous region. Such a first coating layer may have a thin and uniform thickness, while improving lithium ion conductivity and enhancing the lifespan characteristics of the positive electrode active material.

[0037] The first coating layer may be a continuous film or an island. The coating layer may be manufactured using the dry coating method described below, but the coating can be formed with a uniform thickness on the surface of the positive electrode active material without agglomeration or localization. For example, the first coating layer may be formed as a continuous and uniform film on the surface of the secondary particle. In this case, the capacity and cycle life characteristics of the positive electrode active material can be further improved.

[0038] The thickness of the first coating layer in each of the first positive electrode active material and the second positive electrode active material 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. When the first coating layer has the above thickness range, it is possible to suppress an increase in resistance due to the coating, effectively protect the positive electrode active material, and improve ionic conductivity, thereby improving the electrochemical characteristics of the battery.

[0039] According to one embodiment, the first coating layer may be formed with a uniform thickness without being locally present or aggregated on the surface of the positive electrode active material secondary particle. For example, the deviation in the thickness of the first coating layer may be 20% or less, 10% or less, or 5% or less with respect to the diameter of the positive electrode 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 coating layer refers to the thickness of the coating layer within one positive electrode active material particle. The deviation in the thickness of the coating layer may mean, for example, measuring the thickness of about 10 points in an electron microscope image of a cross-section of one positive electrode active material particle, calculating the arithmetic mean, and then dividing the absolute value of the difference between one thickness value and the arithmetic mean by the arithmetic mean and multiplying by 100. The deviation or standard deviation of the coating layer thickness satisfying the above range means that a coating layer of uniform thickness is formed in a good shape on the surface of the positive electrode active material particle, thereby improving the structural stability of the positive electrode active material, effectively suppressing side reactions with the solid electrolyte, and minimizing an increase in resistance or a decrease in capacity due to the coating.

[0040] The total Zr content of the first coating layer of the first positive electrode active material and the first coating layer of the second positive electrode active material may be 0.1 mol part to 0.6 mol part based on 100 mol parts of the total metal excluding lithium in the lithium nickel-based composite oxide of the first positive electrode active material and the lithium nickel-based composite oxide of the second positive electrode active material, for example, 0.1 mol part to 0.5 mol part, or 0.1 mol part to 0.4 mol part.

[0041] Additionally, the total Zr content of the first coating layer of the first positive electrode active material and the first coating layer of the second positive electrode active material may be 0.1 wt% to 6 wt%, for example, 0.5 wt% to 6 wt%, or 1 wt% to 5.5 wt%, with respect to 100 wt% of the positive electrode active material. Alternatively, the total Zr content of the first coating layer of the first positive electrode active material and the first coating layer of the second positive electrode active material may be 0.1 at% to 10 at%, for example, 0.1 at% to 8 at%, 0.1 at% to 7 at%, 0.5 at% to 6.5 at%, or 1 at% to 6 at%, with respect to 100 at% of the positive electrode active material.

[0042] When the total Zr content of the first coating layer satisfies the above range, the first coating layer can sufficiently play a role in protecting the positive electrode active material, without acting as a resistor, and can exist well with a uniform thickness without agglomerating or existing locally on the surface of the secondary particles, thereby effectively improving the life characteristics without reducing the capacity of the positive electrode active material. For example, when the Zr content is excessive, the coating layer may become thicker and act as a resistor layer, thereby reducing the charge / discharge capacity of the battery, and conversely, when the Zr content is too small, the buffer function may not be sufficiently performed, which may reduce the life characteristics of the positive electrode active material.

[0043] Second coating layer of positive electrode active material

[0044] According to one embodiment, a cathode active material is characterized by having a second coating layer formed thereon containing a sulfide-based solid electrolyte. The second coating layer can be described as a sulfide-based solid electrolyte thermally complexed onto the surface of a cathode active material (specifically, a cathode active material having a first coating layer formed thereon). In the second coating layer, the sulfide-based solid electrolyte is not excessively aggregated or exists in the form of grown particles, but is uniformly distributed in a thin thickness, and can be said to maintain high ionic conductivity.

[0045] In the configuration of a positive electrode including a positive electrode active material and a solid electrolyte, when a second coating layer containing a sulfide-based solid electrolyte is formed on the outermost surface of positive electrode active material particles as in one embodiment and then mixed with sulfide-based solid electrolyte particles to form a positive electrode, the resistance of the positive electrode is significantly reduced, and the initial charge / discharge capacity and efficiency of the all-solid-state secondary battery are simultaneously improved, and even the life characteristics can be improved. In addition, by forming a first coating layer containing Zr, which is a type of buffer layer, on the positive electrode active material and then forming a second coating layer and performing heat treatment, a passivation layer is formed at the interface, thereby effectively blocking adverse effects between a lithium nickel-based composite oxide and a sulfide-based solid electrolyte, and furthermore, a good second coating layer having high ionic conductivity and no aggregation can be formed. According to one embodiment, a positive electrode active material can form a passivation layer on the surface of particles, thereby suppressing additional side reactions with solid electrolyte particles in the positive electrode, thereby improving the life characteristics of the battery. In addition, since the buffer layer function on the surface of the positive electrode active material particles is strengthened, the space charge layer can be better controlled, thereby improving the initial charge / discharge capacity and efficiency.

[0046] The thickness of the second coating layer in each of the first positive electrode active material and the second positive electrode active material may be approximately 100 nm to 2 μm, for example, 200 nm to 1 μm, 300 nm to 900 nm, or 400 nm to 800 nm. When the second coating layer has the above thickness range, high ionic conductivity can be achieved without increasing resistance.

[0047] The total amount of the sulfide-based solid electrolyte of the second coating layer of the first positive electrode active material and the sulfide-based solid electrolyte of the second coating layer of the second positive electrode active material may be 0.5 wt% to 3 wt%, for example, 0.5 wt% to 2 wt%, or 1 wt% to 1.5 wt%, based on 100 wt% of the total of the first positive electrode active material and the second positive electrode active material. When the second coating layer satisfies the above content range, the sulfide-based solid electrolyte does not aggregate on the surface of the positive electrode active material and can maintain high ionic conductivity. For example, when the content of the sulfide-based solid electrolyte of the second coating layer is excessive, the sulfide-based solid electrolyte particles may aggregate and grow into large particles with many grain boundaries, thereby increasing the resistance and decreasing the ionic conductivity, and ultimately reducing the capacity of the battery and deteriorating the life characteristics. On the other hand, when the content of the sulfide-based solid electrolyte of the second coating layer is too low, the second coating layer may not be formed effectively, and thus the effect of improving battery performance may not be obtained.

[0048] In addition, in one embodiment, with respect to 100 wt% of the total of the sulfide-based solid electrolyte of the second coating layer of the first positive electrode active material, the sulfide-based solid electrolyte of the second coating layer of the second positive electrode active material, and the solid electrolyte in the positive electrode, the combined amount of the sulfide-based solid electrolyte of the second coating layer of the first positive electrode active material and the sulfide-based solid electrolyte of the second coating layer of the second positive electrode active material may be 1 wt% to 20 wt%, for example, 3 wt% to 15 wt%, 5 wt% to 10 wt%, or 6 wt% to 9 wt%. This can be referred to as the weight ratio of the sulfide-based solid electrolyte thermally complexed on the surface of the positive electrode active material with respect to the total amount of the sulfide-based solid electrolyte present in the positive electrode, and when this ratio is appropriately adjusted within the above range, the resistance of the positive electrode can be significantly reduced while simultaneously improving the capacity, efficiency, and life characteristics of the battery. For example, if the thermal compounding ratio is excessive, sulfide-based solid electrolytes may grow or aggregate on the surface of the positive electrode active material particles, resulting in decreased ionic conductivity and increased resistance. Conversely, if the thermal compounding ratio is too low, it may be difficult to achieve the increased effectiveness of thermal compounding.

[0049] The type or component of the sulfide-based solid electrolyte included in the second coating layer is not specifically suggested. For example, the sulfide-based solid electrolyte is Li2S-P2S5, Li2S-P2S5--LiX (where X is a halogen element, for example, I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m, n are integers, Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MOq (p, q are integers, and M is P, Si, Ge, B, Al, Ga or In), or a combination thereof.

[0050] Such sulfide-based solid electrolytes can be obtained, for example, by mixing Li2S and P2S5 in a molar ratio of 50:50 to 90:10, or 50:50 to 80:20, and optionally heat-treating them. Within the above mixing ratio range, a sulfide-based solid electrolyte having excellent ionic conductivity can be produced. Here, the ionic conductivity can be further improved by further including other components such as SiS2, GeS2, and B2S3.

[0051] Methods for mixing sulfur-containing raw materials for manufacturing sulfide-based solid electrolytes can be either mechanical milling or solution milling. Mechanical milling involves placing starting materials in a ball mill reactor and vigorously stirring them to finely atomize and mix them. Using the solution milling method, the starting materials are mixed in a solvent to obtain a solid electrolyte as a precipitate. Furthermore, heat treatment after mixing can solidify the crystals of the solid electrolyte and improve ionic conductivity. The heat treatment can be performed at a temperature ranging from 400°C to 600°C, for example, from 450°C to 500°C, or from 460°C to 490°C, for 5 to 30 hours, 10 to 24 hours, or 15 to 20 hours. Heat treatment under the above conditions can maximize ionic conductivity. For example, a sulfide-based solid electrolyte can be manufactured by mixing sulfur-containing raw materials and heat-treating them twice or more, in which case a sulfide-based solid electrolyte with high ionic conductivity and strength can be manufactured.

[0052] According to one embodiment, a sulfide-based solid electrolyte can be manufactured through, for example, a first heat treatment in which sulfur-containing raw materials are mixed and calcined at 120°C to 350°C, and a second heat treatment in which the first heat treatment result is mixed and calcined at 350°C to 800°C. The first heat treatment and the second heat treatment can each be performed in an inert gas atmosphere. The first heat treatment can be performed for 1 to 10 hours, and the second heat treatment can be performed for 5 to 20 hours. The first heat treatment can have the effect of milling small raw materials, and the second heat treatment can synthesize the final solid electrolyte. Through two or more such heat treatments, a high-performance sulfide-based solid electrolyte with high ionic conductivity and strength can be obtained, and such a solid electrolyte can be said to be suitable for mass production. The temperature of the first heat treatment may be, for example, 150°C to 330°C, or 200°C to 300°C, and the temperature of the second heat treatment may be, for example, 380°C to 700°C, or 400°C to 600°C.

[0053] For example, the sulfide-based solid electrolyte may include an argyrodite-type sulfide. The argyrodite-type sulfide-based solid electrolyte has an ionic conductivity of 10, which is the ionic conductivity of a typical liquid electrolyte at room temperature. -4 10 inland -2 It has a high ionic conductivity close to the S / cm range and can form a close bond between the positive electrode active material and the solid electrolyte.

[0054] The argyrodite-type sulfide-based solid electrolyte may include, for example, a compound represented by the chemical formula 21 below.

[0055] [Chemical Formula 21]

[0056] (Li a M 1 b M 2 c )(P d M 3 e)(S f M 4 g )X h

[0057] In the above chemical formula 21, 4≤a≤8, and M 1 is Mg, Ca, Cu, Ag, or a combination thereof, and 0≤b<0.5, and M 2 is Na, K, or a combination thereof, 0≤c<0.5, and M 3 is Sn, Zn, Si, Sb, Ge, or a combination thereof, and 0 <d<4, 0≤e<1 이고, M 4 is N,O,SO n , or a combination thereof, and 1.5≤n≤5, 3≤f≤12, 0≤g<2, and X is F, Cl, Br, I, or a combination thereof, and 0≤h≤2.

[0058] For example, in chemical formula 21, a halide element (X) may be included as an essential element, in which case 0 <h≤2로 표시될 수 있다. 일 예로 화학식 21에 M 1 Elements may be required, in which case 0 <b<0.5로 표시될 수 있다. 화학식 21에서 M 3 can be understood as an element substituted in place of P and 0 <e<1일 수 있다. 화학식 21에서 M 4 is substituted in the S position, for example, 0 <g<2일 수 있으며 S의 비율인 f는 예를 들어 3≤f≤7일 수 있다. M 4 Go SO n If SO n It can be, for example, S4O6, S3O6, S2O3, S2O4, S2O5, S2O6, S2O7, S2O8, SO4, or SO5, and can be, for example, SO4.

[0059] For example, in chemical formula 21, a+b+c+h=7, d+e=1, and f+g+h=6.

[0060] As a specific example, argyrodite-type sulfide-based solid electrolyte particles include Li3PS4 and Li7P3S. 11, Li7PS6, Li6PS5Cl, Li6PS5Br, Li 5.8 PS 4.8 Cl 1.2 , Li 6.2 PS 5.2 Br 0.8 , Li 5.75 PS 4.75 Cl 1.25 , (Li 5.69 Cu 0.06 )PS 4.75 Cl 1.25 , (Li 5.72 Cu 0.03 )PS 4.75 Cl 1.25 , (Li 5.69 Cu 0.06 )P(S 4.70 (SO4) 0.05 )Cl 1.25 , (Li 5.69 Cu 0.06 )P(S 4.60 (SO4) 0.15 )Cl 1.25 , (Li 5.72 Cu 0.03 )P(S 4.725 (SO4) 0.025 )Cl 1.25 , (Li 5.72 Na 0.03 )P(S 4.725 (SO4) 0.025 )Cl 1.25 , Li 5.75 P(S 4.725 (SO4) 0.025 )Cl 1.25 , or combinations thereof, but are not limited thereto.

[0061] An argyrodite-type sulfide-based solid electrolyte can be manufactured, for example, by mixing lithium sulfide and phosphorus sulfide, and optionally, lithium halide. After mixing these, a heat treatment may be performed. The heat treatment may include, for example, two or more heat treatment steps. Here, manufacturing an argyrodite-type sulfide-based solid electrolyte may include, for example, a first heat treatment of mixing raw materials and calcining at 120°C to 350°C, and a second heat treatment of mixing the resultant of the first heat treatment again and calcining at 350°C to 800°C.

[0062] In the second coating layer, the sulfide-based solid electrolyte may be in the form of particles, for example, and the average particle diameter (D) of the particles 50 ) may be, for example, 0.1 ㎛ to 1.5 ㎛, 0.3 ㎛ to 1 ㎛, or 0.8 ㎛ to 1 ㎛. The average particle diameter may be measured from an electron microscope image, and for example, a particle size distribution is obtained by measuring the size (diameter or length of the major axis) of about 20 particles in an SEM image, where D 50 It may be calculated. When the particle size of the sulfide-based solid electrolyte satisfies the above range, a second coating layer having a thin and uniform thickness can be formed. The size of the sulfide-based solid electrolyte of the second coating layer may be smaller than or equal to the sulfide-based solid electrolyte particles mixed in the positive electrode.

[0063] First positive electrode active material and second positive electrode active material

[0064] The first and second cathode active materials each contain a lithium-nickel composite oxide. Nickel-based cathode active materials can achieve high capacity and high energy density. The lithium-nickel composite oxide can be represented, for example, by the chemical formula 5 below.

[0065] [Chemical Formula 5]

[0066] Li a5 Ni x5 M 5 y5M 6 z5 O 2-b5 X b5

[0067] In the above chemical formula 5, 0.9≤a5≤1.2, 0.3≤x5<1, 0 <y5≤0.7, 0≤z5≤0.7, 0.9≤x5+y5+z5≤1.1, 및 0≤b5≤0.1이고, M 5 and M 6 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S.

[0068] For example, in the above chemical formula 5, 0.6≤x5<1, 0 <y5≤0.4, 0≤z5≤0.4일 수 있고, 또는 0.7<x5≤1, 0<y5≤0.3, 0≤z5≤0.3이거나, 0.8≤x5<1, 0<y5≤0.2, 0≤z5≤0.2이거나, 또는 0.9≤x5<1, 0<y5≤0.1, 0≤z5≤0.1일 수 있다.

[0069] The lithium nickel-based composite oxide of the first positive electrode active material and the lithium nickel-based composite oxide of the second positive electrode active material may be the same or different. In addition, the nickel content relative to 100 mol% of the metal excluding lithium in the lithium nickel-based composite oxide may be, for example, 60 mol% or more, 70 mol% or more, 80 mol% or more, 90 mol% or more, 91 mol% or more, or 99.9 mol% or less, or 99 mol% or less.

[0070] First positive electrode active material

[0071] The first cathode active material may include, for example, a lithium nickel-cobalt-aluminum composite oxide, which means an oxide containing lithium, nickel, cobalt, and aluminum, and optionally further containing other elements, and may be expressed as Ni-Co-Al, or NCA.

[0072] The lithium nickel-cobalt-aluminum composite oxide of the first positive electrode active material can be represented by chemical formula 1.

[0073] [Chemical Formula 1]

[0074] Li a1 Ni x1 Co y1 Al z1 M 1 w1 O 2-b1 X b1

[0075] In the above chemical formula 1, 0.9≤a1≤1.2, 0.7≤x1<1, 0 <y1<0.3, 0<z1<0.3, 0≤w1<0.3, 0.9≤x1+y1+z1+w1≤1.1, 및 0≤b1≤0.1이고, M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S.

[0076] In the above chemical formula 1, for example, 0.7≤x1≤0.98, 0.01≤y1≤0.29, 0.01≤z1≤0.29, 0≤w1≤0.28 may be present, 0.8≤x1≤0.98, 0.01≤y1≤0.19, 0.01≤z1≤0.19, 0≤w1≤0.18 may be present, or 0.9≤x1≤0.98, 0.01≤y1≤0.09, 0.01≤z1≤0.09, 0≤w1≤0.08 may be present.

[0077] The first positive electrode active material is in the form of a secondary particle in which a plurality of primary particles are aggregated, and the secondary particles may be spherical, ellipsoidal, polygonal, amorphous, etc.

[0078] The average particle diameter of the primary particles forming the secondary particles of the first positive electrode 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 190 nm or less, or 50 nm or more and 180 nm or less. When the average particle diameter of the primary particles satisfies the above range, the lithium diffusion path may be shortened, thereby reducing resistance and improving charge / discharge efficiency. Here, the average particle diameter of the primary particles refers to the size of the primary particles observed on the surface of the secondary particles, and may be obtained by selecting 20 or so primary particles randomly from the SEM image of the surface of the secondary particles, measuring their particle diameters (diameter, major axis, or major axis length), and then calculating the arithmetic mean thereof.

[0079] The first cathode active material is characterized in that at least a portion of the primary particles forming the secondary particles are radially arranged. In this case, the diffusion of lithium increases, thereby improving the initial charge / discharge efficiency and securing a high capacity. In addition, uniform expansion and contraction are possible during the insertion and de-insertion of lithium, thereby improving the problem of the cathode active material breaking during charge / discharge, thereby improving the life characteristics and safety of the battery. In addition, when the first cathode active material is in the form of secondary particles in which at least a portion of the primary particles are radially arranged, in the method for manufacturing a cathode active material according to one embodiment, the Al component in the precursor of the first cathode active material is advantageously diffused into the precursor of the second cathode active material, thereby manufacturing a cathode active material having improved capacity characteristics, initial charge / discharge efficiency, and life characteristics.

[0080] Below, the radial structure is described in detail.

[0081] At least some of the above primary particles may have a plate shape. Fig. 1 is a schematic diagram illustrating the plate shape of the primary particles. Referring to Fig. 1, the primary particles may have a basic plate structure but may also have various detailed shapes, such as (A) a polygonal nanoplate shape such as a hexagon, (B) a nanodisk shape, and (C) a rectangular parallelepiped shape.

[0082] 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 surface of the primary particle. The thickness (t) can be said to be the maximum length of the surface that is approximately perpendicular to the widest surface of the primary particle. The direction containing the length of the major axis (a) and the length of the minor axis (b) is defined as the surface direction, and the direction in which the thickness (t) is defined is defined as the thickness direction.

[0083] The thickness (t) of the above primary particle may be smaller than the length of the major axis (a) and the length of the minor axis (b), which are lengths in the plane direction. Among the lengths in the plane direction, the length of the major axis (a) may be longer than or equal to the length of the minor axis (b).

[0084] The above-mentioned primary particles being arranged radially may mean, for example, that the long axes of the primary particles are arranged in a radial direction. Fig. 2 is a drawing for explaining the definition of radial. In one embodiment, the radial arrangement structure means that the thickness (t) direction of the primary particles is arranged perpendicular to the direction (R) from the center of the secondary particles toward the surface or at an angle of ±5° with the perpendicular direction, as shown in Fig. 2.

[0085] In this way, when at least some of the primary particles are arranged radially, the secondary particles can have relatively many lithium diffusion paths between the primary particles on the surface side, and many crystal planes capable of lithium transport are exposed to the outside, thereby improving lithium diffusion, thereby ensuring high initial efficiency and high capacity. In addition, 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, which can further promote lithium diffusion. In addition, the radially arranged primary particles enable uniform expansion and contraction during lithium insertion and de-insertion, and the pores exist toward the Miller index (001) plane, which is the direction in which the particles expand during lithium de-insertion, and these act as a buffer. Accordingly, the probability of cracks occurring during shrinkage and expansion of the positive electrode active material is lowered, and the internal pores additionally alleviate volume changes, thereby reducing cracks occurring between the primary particles during charge and discharge, ultimately improving the life characteristics of lithium secondary batteries and reducing the increase in resistance.

[0086] 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.

[0087] The above irregular porous structure means a structure having primary particles and pores, but the pore size, shape, location, etc. are not regular. That is, the primary particles arranged inside may be arranged without regularity, unlike the primary particles arranged outside. The above radial arrangement structure may mean a shape in which the primary particles are arranged radially. Here, “outside” may mean, for example, an area from 30% to 50% in length from the outermost surface among the total distance from the center of the secondary particle to the surface, for example, an area from 40% in length from the outermost surface, or may mean an area from the outermost edge of the secondary particle to a depth of approximately 3 ㎛. Additionally, the term "interior" may mean an area from the center of the secondary particle to the surface, from 50% to 70% in length from the center, for example, from 60% in length from the center, or may mean an area excluding an area from the outermost edge of the secondary particle to a depth of approximately 3 μm.

[0088] In addition, the pores present inside the secondary particle may be larger than the pores present outside. For example, the size of the pores present inside may be 150 nm to 1 ㎛, and the size of the pores present outside may be less than 150 nm. In this case, when the pore size inside is larger than that outside, compared to secondary particles having the same pore sizes inside and outside, there is an advantage in that the lithium diffusion distance inside the positive electrode active material is shortened, lithium insertion from the outside is facilitated, and the volume change that occurs during charge and discharge is alleviated. Here, the pore size refers to the diameter when the pore is spherical or circular, and refers to the length of the major axis when the pore is elliptical, etc. The pore size may be a value calculated by randomly measuring the sizes of about 20 pores in an SEM image of a cross-section of the secondary particle and then calculating the arithmetic mean thereof.

[0089] The secondary particle may have open pores on its surface. The size of the open pore may be less than about 150 nm, for example, 10 nm to 148 nm. The open pore is a pore in which a portion of the pore wall is not closed, and is formed by the space between the plate-shaped primary particles arranged radially, and is a pore deeply connected from the surface of the secondary particle toward the center. Such an open pore may be connected to the outside and serve as a passage through which substances can pass. The open pore may be formed to a depth of 150 nm or less on average, for example, 0.001 nm to 100 nm, for example, 1 nm to 50 nm from the surface of the secondary particle. The size and depth of the above open pores may be measured by the BJH (Barrett, Joyner and Halenda) method, which is a method of deriving the content of nitrogen adsorption or desorption.

[0090] Fig. 3 is a schematic diagram showing the cross-sectional structure of a positive electrode active material secondary particle. Referring to Fig. 3, the secondary particle (11) includes an outer portion (14) having a structure in which plate-shaped primary particles (13) are arranged radially, and an inner portion (12) in which the primary particles (13) are irregularly arranged. The inner portion (12) may have more empty spaces between the primary particles than the outer portion. In addition, the pore size and porosity in the inner portion may be larger than those in the outer portion, and the shape, etc. may be irregular. In Fig. 3, the arrow indicates the direction of movement of lithium ions.

[0091] The secondary particles have a porous structure on the inside, which reduces the diffusion distance of lithium ions to the inside, and the primary particles are arranged radially on the outside, which facilitates the insertion of lithium ions into the surface. In addition, the small size of the primary particles facilitates securing a lithium transfer path between the crystal grains. In addition, the small size of the primary particles and the pores between the primary particles alleviate the volume change that occurs during charge and discharge, thereby minimizing the stress due to the volume change during charge and discharge. Such a positive electrode active material can reduce the resistance of a lithium secondary battery and improve the capacity and life characteristics.

[0092] Second positive electrode active material

[0093] The second cathode active material may include, for example, a lithium nickel-cobalt-aluminum-manganese composite oxide, which means an oxide containing lithium, nickel, cobalt, aluminum, and manganese and optionally further containing other elements, and may be expressed as Ni-Co-Al-Mn or NCAM.

[0094] According to one embodiment, a cathode active material can be manufactured by a method of mixing an NCA precursor, which is a precursor of a first cathode active material, and an NCM precursor, which is a precursor of a second cathode active material, with a lithium raw material and then co-firing them. In the co-firing process, the Al component of the first cathode active material precursor, which is in the form of opposing and radial secondary particles, moves or diffuses into the precursor of the second cathode active material, which is in the form of small particles and secondary particles, thereby making the second cathode active material into NCAM, and conversely, the Mn component of the second cathode active material precursor does not diffuse into the first cathode active material precursor, so that the first cathode active material does not become NCAM but can be maintained as NCA.

[0095] In the cathode active material manufactured in this way, the second cathode active material is different in shape and composition distribution from the cathode active material manufactured simply using an NCAM composition precursor, or from the NCAM cathode active material manufactured and then post-treated with an Al raw material to coat or dope with Al, and it is confirmed that the capacity and life characteristics are also superior.

[0096] In addition, the cathode active material manufactured by the conventional method of firing the first cathode active material precursor and the second cathode active material precursor separately and then mixing them instead of firing them simultaneously is different from the cathode active material according to one embodiment in terms of shape and composition distribution, has a low pellet density, which reduces the volumetric capacity of the battery, and has low life characteristics due to different deterioration rates of large and small particles, and has been confirmed to have a problem of capacity decline due to the addition of Al raw material even if the structural stability is improved by separately doping or coating Al on the second cathode active material.

[0097] The lithium nickel-cobalt-aluminum-manganese composite oxide of the second positive electrode active material can be represented by chemical formula 2.

[0098] [Chemical Formula 2]

[0099] Li a2 Ni x2 Co y2 Al z2 Mn w2 M 2 v2 O 2-b2 X b2

[0100] 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 2is one or more elements selected from the group consisting of B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

[0101] In the above chemical formula 2, for example, 0.7≤x2≤0.979, 0.01≤y2≤0.289, 0.001≤z2≤0.289, 0.01≤w2≤0.289, 0≤v2≤0.279 may be present, 0.8≤x2≤0.979, 0.01≤y2≤0.189, 0.001≤z2≤0.189, 0.01≤w2≤0.189, 0≤v2≤0.179 may be present, and 0.9≤x2≤0.979, 0.01≤y2≤0.089, 0.001≤z2≤0.089, 0.01≤w2≤0.089, 0≤v2≤0.079 may be present.

[0102] For example, the second positive electrode active material may have a higher aluminum content in the “surface layer of the secondary particle” than in the “interior of the secondary particle.” This is consistent with the characteristic that the aluminum in the second positive electrode active material is not derived from a precursor, but is a component received from the first positive electrode active material during the simultaneous firing process. Here, the interior of the secondary particle may refer to a region from the center of the secondary particle to about 70 length% of the radius, and the surface layer of the secondary particle may refer to a region surrounding the interior, and may refer to a region from the outermost surface of the secondary particle to a depth corresponding to 30 length% of the radius. The outermost surface refers to the surface of the secondary particle excluding the coating layer, and may be understood as the boundary between the secondary particle and the first coating layer. In other words, the secondary particle of the second positive electrode active material may be said to include an interior, a surface layer surrounding the interior, and a first coating layer and a second coating layer positioned on the surface layer. Both the interior and surface layers of the secondary particles are composed of multiple primary particles.

[0103] 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 of the secondary particle cut by a focused ion beam (FIB), etc. In addition, the Al content can mean the at% content of aluminum with respect to 100 at% of the total metal excluding lithium in a lithium nickel-cobalt-aluminum-manganese composite oxide.

[0104] For example, the Al content in the surface layer of the secondary particle may be 0.2 at% to 2.0 at% with respect to 100 at% of the total metal excluding lithium in the second positive electrode active material, and the Al content in the interior of the secondary particle may be 0 at% to 0.6 at% with respect to 100 at% of the total metal excluding lithium in the second positive electrode active material, and the Al content in the surface layer may be higher than the Al content in the interior.

[0105] In addition, according to one embodiment, the second cathode active material may have a higher aluminum content in the surface layer of the secondary particle at a portion in contact with the first cathode active material during the first heat treatment than at a portion not in contact with the first cathode active material. This is understood to be because the second cathode active material received the Al component from the first cathode active material during the first heat treatment process, and is also a distinguishing feature from cases where an NCAM precursor is used as a small particle or where Al is coated or doped separately.

[0106] For example, in the surface layer of the secondary particles of the second positive electrode active material, the content of aluminum relative to the entire metal excluding lithium in the portion in contact with the first positive electrode 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 entire metal excluding lithium in the portion not in contact with the first positive electrode 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%.

[0107] 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. The content of aluminum in the high-concentration Al region relative to the entire metal excluding lithium may be 0.8 at% to 2.0 at%, for example, 0.8 at% to 1.8 at%, or 0.9 at% to 1.6 at%. The content of aluminum in the low-concentration Al region relative to the entire 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%.

[0108] Additionally, 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%.

[0109] It is well known that after manufacturing a lithium transition metal composite oxide, aluminum raw material is mixed and heat-treated to separately dope or coat Al. However, in this case, unreacted Al raw material, for example, aluminum oxide such as Al2O3, remains in the final positive electrode active material, and furthermore, since Al is unevenly doped on the particle surface, a high-concentration Al doping area exceeding 2 at% is generated on some part of the surface, which causes a problem of reduced capacity. In contrast, the positive electrode active material according to one embodiment does not add a separate Al raw material during the sintering process, and accordingly, in the final positive electrode active material, unreacted Al raw material such as aluminum oxide does not exist on the outermost surface of the secondary particles of each of the first positive electrode active material and the second positive electrode active material. In addition, even in a region with a high Al content in the surface layer of the second positive electrode 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 improvement effects due to Al doping, while problems such as capacity reduction that occur due to the addition of Al raw material during sintering can be effectively suppressed.

[0110] solid electrolyte

[0111] According to one embodiment, a positive electrode includes a solid electrolyte in addition to the first positive electrode active material and the second positive electrode active material described above, and the solid electrolyte is characterized by including core particles containing a sulfide-based solid electrolyte and a third coating layer located on the surface of the core particles and containing a lithium-metal-phosphate.

[0112] The sulfide-based solid electrolyte, which is the core particle of the above solid electrolyte, may include, for example, an argyrodite-type sulfide. Since the general information on the sulfide-based solid electrolyte and its manufacturing method, and the information on the argyrodite-type sulfide-based solid electrolyte and its manufacturing method are as described above, a detailed description thereof will be omitted.

[0113] The lithium metal phosphate of the third coating layer may refer to a phosphate containing lithium and a metal other than lithium. Here, the metal is a concept including general metals, transition metals, and metalloids. In the lithium metal phosphate, the metal may be, for example, one or more elements selected from the group consisting of Al, B, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ta, V, W, and Zr.

[0114] The lithium metal phosphate may be amorphous. According to one embodiment, when an amorphous lithium metal phosphate is coated on the sulfide-based solid electrolyte-containing core particle and heat-treated, the resulting solid electrolyte can exhibit higher ionic conductivity, lower interfacial resistance with other solid particles such as a cathode active material within the battery, prevent agglomeration of solid electrolyte particles, improve ionic conductivity, and enhance capacity characteristics, life characteristics, etc.

[0115] In the third coating layer, the lithium-metal-phosphate may be in the form of particles, and its average particle diameter (D 50) may be, for example, 0.01 ㎛ to 1.0 ㎛, 0.01 ㎛ to 0.9 ㎛, 0.01 ㎛ to 0.8 ㎛, or 0.01 ㎛ to 0.5 ㎛. The average particle diameter of the lithium-metal-phosphate may be smaller than the particle diameter of the sulfide-based solid electrolyte particles. When a lithium-metal-phosphate having such a particle diameter range is used, it can be evenly coated on the surface of the sulfide-based solid electrolyte particles, and the ionic conductivity of the solid electrolyte can be sufficiently increased and the moisture stability can be improved.

[0116] The above lithium-metal-phosphate may exist in the form of a film or island on the surface of the core particle.

[0117] In a solid electrolyte according to one embodiment, the lithium-metal-phosphate may be included in an amount of 0.01 wt% to 3 wt% based on 100 wt% of the solid electrolyte, for example, 0.01 wt% to 2 wt%, 0.01 wt% to 1 wt%, 0.01 wt% to 0.8 wt%, or 0.1 wt% to 1.0 wt%. When the content of the lithium-metal-phosphate is such as this, the solid electrolyte can exhibit an appropriate particle size distribution without particle agglomeration while implementing high ionic conductivity. In particular, when the content of the lithium-metal-phosphate satisfies the range of 0.01 wt% to 0.8 wt% based on 100 wt% of the solid electrolyte, the lithium-metal-phosphate may be evenly coated on the surface of the sulfide-based solid electrolyte particles, and thus the ionic conductivity and moisture stability of the solid electrolyte may be further improved, and the efficiency and life characteristics of the battery may be further improved.

[0118] According to one embodiment, a solid electrolyte is formed in a form in which a lithium-metal-phosphate is coated on the surface of core particles containing a sulfide-based solid electrolyte, and the solid electrolyte has sufficiently high crystallinity to realize excellent ionic conductivity, and at the same time, has an appropriate particle size distribution without particle agglomeration. As the crystallinity of the solid electrolyte increases or the crystal size increases, the half-width of the main peak in X-ray diffraction analysis may decrease, and the solid electrolyte according to one embodiment may have a half-width of the main peak of 0.160 or less. Here, the main peak refers to the peak with the highest diffraction intensity in X-ray diffraction analysis. The half-width of the main peak in the X-ray diffraction analysis of the solid electrolyte according to one embodiment may be, for example, 0.159 or less, or 0.155 or less. It is known that when the half-width decreases, that is, when the crystallinity increases, the ionic conductivity improves. For example, it is understood that when the crystal size increases, the crystal grain boundaries decrease, which improves the ionic conductivity.

[0119] In general, sulfide-based solid electrolytes have particles that are clumped together or have a large particle size immediately after synthesis, and when they are subjected to processes such as pulverization to adjust the particle size to a particle size that can be used in a battery, the crystallinity is reduced and the ionic conductivity decreases. According to one embodiment, the solid electrolyte coats core particles containing the sulfide-based solid electrolyte with lithium-metal-phosphate and heat-treats them at a specific temperature range, thereby increasing the crystallinity and adjusting the half width of the main peak to 0.160 or less, and at the same time, having an even particle size distribution without clumping or growth of the particles, so that the ionic conductivity can be further improved.

[0120] The average particle size (D) of the solid electrolyte contained in the anode 50) may be 0.1 ㎛ to 5 ㎛, for example, 0.1 ㎛ to 3 ㎛, 0.1 ㎛ to 2 ㎛, 0.5 ㎛ to 1.9 ㎛, or 0.8 ㎛ to 1 ㎛. The size of the sulfide-based solid electrolyte particles included in the positive electrode may be larger than or equal to the particles of the sulfide-based solid electrolyte of the second coating layer of the positive electrode active material, and may be smaller than the size of the solid electrolyte included in the solid electrolyte layer described later. By appropriately adjusting the size of the sulfide-based solid electrolyte included in the positive electrode, the capacity and energy density of the positive electrode can be increased and the ionic conductivity can be improved. The average particle diameter of the solid electrolyte may be measured by a microscope image, for example, a particle size distribution is obtained by measuring the sizes of about 20 particles in a scanning electron microscope image, and here D 50 It may have been calculated.

[0121] According to one embodiment, a solid electrolyte is characterized by having a uniform particle size distribution without particle agglomeration. For example, in the particle size distribution for the solid electrolyte, the (D90-D10) / D50 value may be greater than 1 and less than or equal to 5, for example, 1.1 to 4.0, 1.1 to 3.0, or 1.1 to 2.0. The (D90-D10) / D50 value may indicate the degree of peak width in a particle size distribution graph for the solid electrolyte, specifically, in which the horizontal axis represents the particle size (㎛) and the vertical axis represents the cumulative volume % of the particles, and a smaller value may be interpreted as having a uniform particle size because the peak width of the graph is narrower. Here, D10 means the diameter of a particle having a cumulative volume of 10% by volume in the particle size distribution, D50 means the diameter of a particle having a cumulative volume of 50% by volume in the particle size distribution, and D90 means the diameter of a particle having a cumulative volume of 90% by volume in the particle size distribution.

[0122] The D10 of the above solid electrolyte may be, for example, 0.05 ㎛ to 0.7 ㎛, 0.05 ㎛ to 0.6 ㎛, 0.1 ㎛ to 0.5 ㎛, or 0.2 ㎛ to 0.4 ㎛. In addition, the D90 of the above solid electrolyte may be, for example, 0.9 ㎛ to 5.0 ㎛, 1.0 ㎛ to 4.0 ㎛, 1.0 ㎛ to 3.0 ㎛, or 1.2 ㎛ to 2.0 ㎛. When the solid electrolyte has such a particle size distribution, it is possible to improve the performance of the battery by implementing high energy density while implementing excellent ionic conductivity.

[0123] The ionic conductivity of the solid electrolyte at 25°C may be 2.9 mS / cm or more, for example, 2.9 mS / cm to 5.0 mS / cm, 3.0 mS / cm to 4.5 mS / cm, or 3.0 mS / cm to 4.0 mS / cm. The ionic conductivity may be measured through electrochemical impedance spectroscopy (EIS).

[0124] Binders and Challengers

[0125] According to one embodiment, a cathode may include a current collector and a cathode active material layer positioned on the current collector, wherein the cathode active material layer includes the first cathode active material, the second cathode active material, and the solid electrolyte described above, and may further include a binder and / or a conductive material.

[0126] The binder serves to adhere the positive electrode active material particles well to each other and also to adhere the positive electrode active material well to the current collector, and representative examples thereof include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0127] The content of the binder may be approximately 0.1 wt% to 5 wt%, or 0.1 wt% to 3 wt%, based on 100 wt% of the entire positive electrode active material layer.

[0128] The conductive material is used to provide conductivity to the electrode, and any material that does not cause a chemical change and is electronically conductive can be used in the battery to be constructed. Examples of conductive materials that can be used include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof.

[0129] The content of the conductive agent may be 0.1 wt% to 5 wt%, or 0.1 wt% to 3 wt%, based on 100 wt% of the total positive electrode active material layer.

[0130] Aluminum foil or stainless steel (SUS) can be used as the current collector of the positive electrode, but is not limited thereto.

[0131] Method for manufacturing anode

[0132] In one embodiment, (i) a first cathode active material precursor comprising a nickel-based composite hydroxide, wherein a plurality of primary particles are aggregated and at least a portion of the primary particles are in the form of secondary particles arranged radially; a nickel-based composite hydroxide, wherein the second particle is in the form of aggregated primary particles and the average particle diameter (D) of the first cathode active material precursor 50 ) smaller than the average particle diameter (D 50 ) and a lithium raw material, and subjecting them to a first heat treatment to obtain a preliminary positive electrode active material, (ii) dry-mixing the preliminary positive electrode active material and the zirconium raw material and subjecting them to a second heat treatment to prepare a Zr-coated positive electrode active material, (iii) dry-mixing the Zr-coated positive electrode active material and a sulfide-based solid electrolyte and subjecting them to a third heat treatment to obtain a final positive electrode active material, (iv) mixing core particles containing a sulfide-based solid electrolyte and a lithium-metal-phosphate and subjecting them to a fourth heat treatment at 200° C. to 300° C. to prepare a coated solid electrolyte, and (iv) mixing the final positive electrode active material and the coated solid electrolyte to produce a positive electrode.

[0133] In step (i), the first cathode active material precursor may include, for example, a nickel-cobalt-aluminum composite hydroxide, and the second cathode active material precursor may include, for example, a nickel-cobalt-manganese composite hydroxide.

[0134] Steps (i) and (ii) can be defined as a method of mixing a precursor of a large NCA radial secondary particle and a precursor of a small NCM secondary particle with a lithium raw material, co-firing them, and then dry-coating zirconium. During the co-firing process, the Al component of the large particle can diffuse or migrate to the small particle to form an NCAM composition in the small particle, and thus a cathode active material mixed with the NCA of the large radial secondary particle and the NCAM of the small particle secondary particle can be manufactured. This is understood to be possible because the diffusion rate of the Al component of the large particle is faster than that of the Mn component of the small particle in the temperature range of co-firing, and also because the Al component is more easily transferred to the small particle as the precursor of the large particle takes the form of a radial secondary particle. The preliminary cathode active material manufactured by this method can exhibit high capacity while realizing high initial charge / discharge efficiency and excellent cycle characteristics.

[0135] According to the above manufacturing method, compared to the existing method of manufacturing by separately firing large and small particles and then mixing them, the volumetric capacity can be significantly improved, and compared to the case where only the small particles are doped or coated with Al after the individual firing and then the large and small particles are mixed, the initial discharge capacity, volumetric capacity, energy density, etc. can be further improved. In addition, according to the method according to one embodiment, even if the simultaneous firing method is applied, the life characteristics can be improved compared to the case where large and small particles having the same components are used, and the initial discharge capacity and energy density can be improved compared to the case where Al is doped or coated separately after the simultaneous firing. In the manufacturing method according to one embodiment, structural stability can be secured by introducing an appropriate amount of aluminum into the large and small particles without mixing the aluminum raw material in the processes such as the first heat treatment and the second heat treatment, and the problem of capacity reduction due to the addition of the aluminum raw material can be improved.

[0136] The first cathode active material precursor may be, for example, a nickel-cobalt-aluminum composite hydroxide, which may be specifically represented by the following chemical formula 11.

[0137] [Chemical Formula 11]

[0138] Ni x11 Co y11 Al z11 M 11 w11 (OH)2

[0139] In the above chemical formula 11, 0.7≤x11<1, 0 <y11<0.3, 0<z11<0.3, 0≤w11<0.3, 0.9≤x11+y11+z11+w11≤1.1이고, M 11 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Z.

[0140] The first positive electrode active material precursor may be formed by agglomerating a plurality of primary particles, and at least some of the primary particles may be in the form of secondary particles arranged radially. The average particle diameter of the secondary particles may be 10 ㎛ to 25 ㎛, for example, 11 ㎛ to 20 ㎛, or 12 ㎛ to 18 ㎛. Here, the average particle diameter of the secondary particles is obtained by selecting arbitrarily 20 or so particles from an SEM image of the first positive electrode active material precursor, measuring the particle diameter (diameter, or major axis, or major axis length) thereof, and then obtaining a particle size distribution, and in the particle size distribution, the diameter (D) of the particles having a cumulative volume of 50% by volume 50 ) may be taken as the average particle diameter.

[0141] The first cathode active material precursor can be prepared by a coprecipitation reaction. That is, a composite metal raw material is prepared by mixing metal raw materials such as nickel raw materials, and a complexing agent and a pH adjusting agent are added thereto to control the pH of the mixture while performing a coprecipitation reaction, thereby producing a nickel-based composite hydroxide of a desired composition. The complexing agent serves to control the reaction rate of precipitate formation in the coprecipitation reaction, and may be, for example, ammonium hydroxide (NH4OH) or citric acid. The pH adjusting agent may be, for example, sodium hydroxide (NaOH), sodium carbonate (Na2CO3), sodium oxalate (Na2C2O4), or the like. The pH of the mixture may be adjusted to, for example, a range of 10 to 13.

[0142] The above-described coprecipitation reaction can proceed in multiple stages, for example, in two, three, or four stages. In each stage, the concentration of the complexing agent, the rate of introduction of the metal raw material, the pH control range, the reaction temperature, the reaction time, or the stirring power can be adjusted differently. Through such adjustment, it is possible to manufacture a positive electrode active material precursor in the form of secondary particles in which at least a portion of the primary particles are radially arranged, and also to manufacture secondary particles with different internal and external shapes.

[0143] For example, a first positive electrode active material precursor having a radial structure can be manufactured, for example, by the following method. The method for manufacturing the first positive electrode active material precursor can include a first process, a second process, and a third process for forming a core, an intermediate layer, and a shell in that order. In the first process, a complexing agent, a pH adjusting agent, and a metal raw material are introduced into a reactor and reacted. At this time, the concentration of the complexing agent may be 0.1 M to 0.7 M, and the input amount may be 6 mL / min to 12 mL / min. The concentration of the metal raw material may be 0.1 M to 3.5 M, and the input amount may be 50 mL / min to 100 mL / min. Subsequently, in the second process, a complexing agent, a pH adjusting agent, and a metal raw material are further introduced, and at this time, the concentration of the complexing agent may be 0.3 M to 1.0 M, and the input amount may be 8 mL / min to 15 mL / min. The concentration of the metal raw material may be 0.1 M to 3.5 M and the input amount may be 60 mL / min to 120 mL / min. In the third process, the concentration and input amount of the complexing agent and the metal raw material may be further increased or maintained the same so as not to decrease the particle growth rate. At this time, the concentration of the complexing agent may be 0.35 M to 1.0 M and the input amount may be 12 mL / min to 20 mL / min. The concentration of the metal raw material may be 0.1 M to 2.5 M and the input amount may be 70 mL / min to 150 mL / min. In the first to third processes, the pH may be controlled between 10 and 12.

[0144] The second cathode active material precursor may be, for example, a nickel-cobalt-manganese composite hydroxide, which may be specifically represented by the following chemical formula 12.

[0145] [Chemical Formula 12]

[0146] Ni x12 Co y12 Mn w12 M 12 v12 (OH)2

[0147] In the above chemical formula 12, 0.7≤x12<1, 0 <y12<0.3, 0<w12<0.3, 0≤v12<0.3, 0.9≤x12+y12+w12+v12≤1.1이고, M 12 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.

[0148] The second positive electrode active material precursor may be in the form of secondary particles in which a plurality of primary particles are aggregated. The average particle diameter of the secondary particles may be 2 ㎛ to 8 ㎛, for example, 2.5 ㎛ to 7 ㎛, or 3 ㎛ to 6 ㎛. Here, the average particle diameter of the secondary particles is obtained by selecting 20 or so random particles from an SEM image of the second positive electrode active material precursor, measuring their particle diameters (diameter, or major axis, or major axis length), and then obtaining a particle size distribution, and in the particle size distribution, the diameter (D) of particles having a cumulative volume of 50% by volume 50 ) may be taken as the average particle diameter.

[0149] The second cathode active material precursor can be prepared by a general co-precipitation reaction.

[0150] The mixing weight ratio of the first positive electrode active material precursor and the second positive electrode active material precursor may be 60:40 to 95:5, 70:30 to 90:10, or 80:20 to 90:10.

[0151] The lithium source may be, for example, Li2CO3, LiOH, a hydrate thereof, or a combination thereof. The lithium source 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 cathode active material precursor and the second cathode active material precursor.

[0152] The first heat treatment may be performed at, for example, 600°C to 1000°C, or 700°C to 900°C. Within the above temperature range, a first positive electrode active material and a second positive electrode active material having an optimal composition can be manufactured.

[0153] For example, the first heat treatment includes a temperature raising step and a temperature holding step, and the temperature raising time may be set to be longer than the temperature holding time. For example, the temperature raising time may be 6 hours to 16 hours and the temperature holding time may be 1 hour to 9 hours, and the temperature raising time may be longer than the temperature holding time. In the first heat treatment, the temperature raising time may be, for example, 6 hours to 15 hours, 6 hours to 14 hours, 6 hours to 13 hours, or 7 hours to 12 hours, and the temperature holding time may be 2 hours to 9 hours, or 3 hours to 8 hours. In addition, the ratio of (temperature raising 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.

[0154] The preliminary positive electrode active material obtained through the first heat treatment may be a mixture of a first preliminary positive electrode active material in the form of secondary particles, which include a lithium nickel-cobalt-aluminum composite oxide represented by the chemical formula 1 and are formed by agglomeration of a plurality of primary particles, and at least a portion of the primary particles are arranged radially, and a second preliminary positive electrode active material in the form of secondary particles, which include a lithium nickel-cobalt-aluminum-manganese composite oxide represented by the chemical formula 2 and are formed by agglomeration of a plurality of primary particles.

[0155] In one embodiment, a method is provided for forming a zirconium-containing coating layer on both large and small particles by dry-mixing a preliminary positive electrode active material and a zirconium raw material in step (ii) and performing a second heat treatment. The method applies a dry coating method, and is economical and environmentally friendly because it does not use an organic solvent and expensive coating raw materials and can use existing equipment, and enables practical mass production. According to the method, a positive electrode active material having a coating layer containing ZrO2 and Li6Zr2O7 formed on both large and small particles can be synthesized, and a coating layer having an appropriate content and thickness can be synthesized in a good form, thereby manufacturing a positive electrode active material having both improved capacity characteristics and cycle life characteristics. For example, such a positive electrode active material has low reactivity with sulfide-based solid electrolyte particles and low interfacial resistance, and thus can be applied to all-solid-state secondary batteries, etc., to improve capacity characteristics, rate characteristics, cycle life characteristics, etc.

[0156] Zirconium raw materials are compounds containing the element zirconium, and any compound capable of dry mixing can be applied without limitation. Zirconium raw materials may be, for example, zirconium-containing oxides, zirconium-containing sulfides, zirconium-containing carbonates, zirconium-containing hydroxides, etc., and may be, for example, zirconium oxide, zirconium sulfide, zirconium carbonate, zirconium hydroxide, or combinations thereof.

[0157] The zirconium raw material can be mixed in an amount of 0.1 to 0.6 mol parts based on 100 mol parts of the total metal excluding lithium in the preliminary positive electrode active material, for example, 0.1 to 0.5 mol parts, or 0.1 to 0.4 mol parts. When the zirconium raw material is added in the above range, a coating layer having an appropriate amount and thickness can be formed, so that the coating layer can sufficiently perform its role of protecting the positive electrode active material, and can exist in a uniform thickness without being aggregated or locally present on the surface of the secondary particles. For example, when the amount of the zirconium raw material is excessive, the coating layer may become thicker and act as a resistive layer, thereby reducing the charge / discharge capacity of the positive electrode active material. On the other hand, when the amount of the zirconium raw material is too small, the buffer function cannot be sufficiently performed, so that the life characteristics of the positive electrode active material may be reduced.

[0158] 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 diameter (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 diameter (D of the particles 50 ) may be from 10 nm to 500 nm. In this case, it may be advantageous for synthesizing a coating layer of an appropriate thickness.

[0159] In one embodiment, dry mixing means mixing without a solvent and can be understood as a solid coating method. This is distinguished from wet coating or liquid coating.

[0160] (ii) In step (ii), by performing a second heat treatment after dry mixing, a coating layer containing a mixed phase of ZrO2 and Li6Zr2O7 and having a uniform thickness can be formed. 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 performing the second heat treatment within the above temperature range, it is possible to synthesize a first coating layer having an appropriate crystal phase, and the first coating layer does not act as a resistor but sufficiently performs a buffer function, thereby improving the capacity characteristics and life characteristics of the positive electrode active material. For example, when the second heat treatment temperature is less than 420°C, the first coating layer may not form an appropriate crystal phase and may act only as a resistor, thereby deteriorating the capacity characteristics of the positive electrode active material. If the second heat treatment temperature exceeds 580℃, the coating materials may coagulate or be coated only locally, reducing the buffer effect. In addition, zirconium may be absorbed into the positive electrode active material, failing to function as a buffer and causing deterioration in capacity characteristics and life characteristics.

[0161] The second heat treatment can be performed in an oxygen atmosphere, for example, for 5 to 25 hours, or 10 to 20 hours. Under these conditions, a good coating layer can be formed.

[0162] In one embodiment, when dry-mixing the preliminary positive electrode active material and the zirconium raw material in step (ii), a lithium raw material may be mixed together. The lithium raw material is a lithium-containing compound that can be dry-mixed, and can be applied without limitation. The lithium raw material may be, for example, Li2CO3, LiOH, a hydrate 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 mol part to less than 4 mol parts with respect to 1 mol part of the zirconium raw material, for example, more than 1 mol part to less than 3 mol parts, or more than 2 mol parts to less than 4 mol parts. When the lithium raw materials are mixed together and heat-treated, it is advantageous for forming a lithium zirconium oxide, for example, a Li6Zr2O7 crystal phase, in the coating layer, and it is advantageous for increasing lithium ion conductivity and obtaining a coating layer of an appropriate thickness in a good shape.

[0163] (iii) In step (iii), the Zr-coated positive electrode active material can be expressed as a positive electrode active material having a first coating layer formed thereon, and by dry mixing this with a sulfide-based solid electrolyte and then performing a third heat treatment, the positive electrode active material and the sulfide-based solid electrolyte can be thermally complexed, and a second coating layer containing a sulfide-based solid electrolyte can be formed on the surface of the first coating layer.

[0164] (iii) The sulfide-based solid electrolyte mixed in step (iii) has an average particle diameter (D 50 ) may be 0.1 ㎛ to 1.5 ㎛, for example, 0.3 ㎛ to 1 ㎛, or 0.8 ㎛ to 1 ㎛. When the particle size of the sulfide-based solid electrolyte satisfies the above range, a second coating layer having a thin and uniform thickness may be formed. The size of the sulfide-based solid electrolyte of the second coating layer may be smaller than or equal to the size of the sulfide-based solid electrolyte particles mixed in the positive electrode.

[0165] (iii) The content of the sulfide-based solid electrolyte mixed in step (iii) may be 0.5 parts by weight to 3 parts by weight with respect to 100 parts by weight of the Zr-coated positive electrode active material, for example, 0.5 parts by weight to 2 parts by weight, or 1 part by weight to 1.5 parts by weight.

[0166] In addition, with respect to the total of 100 wt% of the sulfide-based solid electrolyte mixed in step (iii) and the sulfide-based solid electrolyte particles of step (iv), the content of the sulfide-based solid electrolyte mixed in step (iii) may be 1 wt% to 20 wt%, for example, 3 wt% to 15 wt%, 5 wt% to 10 wt%, or 6 wt% to 9 wt%.

[0167] In this way, by appropriately adjusting the content of the sulfide-based solid electrolyte that is thermally complexed in step (iii), the resistance of the positive electrode can be significantly reduced while simultaneously improving the capacity, efficiency, and life characteristics of the battery.

[0168] (iii) The sulfide-based solid electrolyte mixed in step may be, for example, an argyrodite-type sulfide-based solid electrolyte. Since the overall details of the sulfide-based solid electrolyte and the argyrodite-type are the same as those described in the anode section, a detailed description thereof will be omitted.

[0169] The third heat treatment can be performed at, for example, 200°C to 300°C, and can be performed at, for example, 210°C to 290°C, 220°C to 280°C, 230°C to 270°C, or 240°C to 260°C. When the third heat treatment is performed in the above temperature range, a second coating layer having a solid and good shape can be formed, and the sulfide-based solid electrolyte in the second coating layer can be prevented from agglomerating and high ionic conductivity can be realized.

[0170] (iv) In step (iv), coating of the solid electrolyte to be injected into the anode is performed.

[0171] In general, solid electrolytes must exhibit excellent ion conductivity and high energy density within a battery, possessing an appropriate particle size distribution. Furthermore, they must exhibit excellent particle flowability, i.e., high-density electrode plates and electrolyte membranes. Simultaneously, the solid electrolyte must maintain high crystallinity to exhibit enhanced ionic conductivity. Sulfide-based solid electrolytes are among the most promising solid electrolytes for high ionic conductivity. However, immediately after synthesis at high temperatures, the particles are highly agglomerated or have large particle sizes, requiring pulverization. However, pulverization reduces ionic conductivity, and heat treatment to increase ionic conductivity causes the particles to re-agglomerate and grow. In one embodiment, to address these issues, pulverized sulfide-based solid electrolyte particles are coated with lithium-metal-phosphate and heat-treated at a temperature ranging from 200°C to 300°C. This method enhances the crystallinity of the solid electrolyte, thereby enhancing ionic conductivity. At the same time, particle agglomeration and growth are suppressed, resulting in an appropriate particle size distribution. These solid electrolytes also have high moisture stability and can improve the capacity characteristics, initial charge / discharge efficiency, and life characteristics of batteries.

[0172] For example, if the fourth heat treatment is performed at a temperature lower than 200℃, the crystallinity may not be sufficiently increased, and thus high ionic conductivity may not be achieved. If the heat treatment is performed at a temperature higher than 300℃, the particles may agglomerate and grow, resulting in an inappropriate particle size distribution and thus reduced crystallinity. In addition, the higher the heat treatment temperature, the more coating agent is required, which may lead to a problem in which the ionic conductivity actually decreases.

[0173] The fourth heat treatment can be performed in an inert gas atmosphere, such as He, Ar, or N2. Furthermore, the heat treatment can be performed with the highest temperature retention time set to 1 to 10 hours, for example, 1 to 8 hours, or 2 to 7 hours. When heat-treated under these conditions, the solid electrolyte produced can exhibit excellent ionic conductivity while achieving an appropriate particle size distribution.

[0174] The lithium-metal-phosphate may be mixed in an amount of 0.01 to 3 parts by weight based on 100 parts by weight of the sulfide-based solid electrolyte-containing core particles, for example, 0.01 to 2 parts by weight, 0.01 to 1 part by weight, 0.01 to 0.8 parts by weight, or 0.1 to 0.75 parts by weight. When mixed in this content range, the solid electrolyte produced may exhibit high ionic conductivity and have an appropriate particle size distribution without particle agglomeration. In particular, when 0.01 to 0.8 parts by weight of the lithium-metal-phosphate is mixed based on 100 parts by weight of the core particles, the ionic conductivity of the solid electrolyte may be further improved as an appropriate amount of lithium-metal-phosphate is evenly coated on the surface of the core particles.

[0175] Since the core particles containing a sulfide-based solid electrolyte and the lithium-metal-phosphate are as described above, a detailed description thereof will be omitted.

[0176] As a specific example, the step (iv) above may be to mix sulfur-containing raw materials and perform heat treatment to synthesize a sulfide-based solid electrolyte, pulverize the synthesized sulfide-based solid electrolyte to prepare core particles, mix the core particles and lithium-metal-phosphate, and perform a fourth heat treatment at 200°C to 300°C to obtain a solid electrolyte in which a third coating layer containing lithium-metal-phosphate is formed on the surface of the core particles.

[0177] Step (iv) above is a more specific example, in which sulfur-containing raw materials are mixed and first fired at 120°C to 350°C, and second fired at 350°C to 800°C to manufacture a sulfide-based solid electrolyte, and the manufactured sulfide-based solid electrolyte is pulverized to obtain an average particle size (D 50 ) may be obtained by obtaining core particles having a diameter of 0.1 ㎛ to 2.0 ㎛, mixing the obtained core particles and lithium-metal-phosphate, and performing a fourth heat treatment at 200°C to 300°C, thereby obtaining a solid electrolyte in which a third coating layer containing lithium-metal-phosphate is formed on the surface of the core particles. Through this method, a solid electrolyte having very high ionic conductivity, a uniform particle size distribution, and little side reaction can be provided.

[0178] In one embodiment, mixing core particles and lithium-metal-phosphate and performing a fourth heat treatment can be considered a type of dry coating method. Unlike other oxide-based inorganic solid electrolytes or positive electrode active materials, sulfide-based solid electrolytes are difficult to wet coat and are vulnerable to high-temperature heat treatment, and are materials that require design of demanding coating conditions. In addition, wet coating methods generally use alcohol-based solvents or alkoxide-based raw materials, which may cause local carbon components to remain after coating, which may adversely affect conductivity, etc. In the method for manufacturing a positive electrode according to one embodiment, step (iv) has different conditions from those for coating other types of solid electrolyte particles, and is also distinguished from general wet coating.

[0179] Step (v) may be defined as a process for manufacturing a positive electrode by mixing the final positive electrode active material manufactured in step (iii) and the coated solid electrolyte manufactured in step (iv). In this step, the coated solid electrolyte may be mixed in an amount of 1 wt% to 35 wt% based on a total of 100 wt% of the final positive electrode active material and the coated solid electrolyte, and may be included in an amount of, for example, 5 wt% to 30 wt%, 10 wt% to 25 wt%, 10 wt% to 20 wt%, or 11 wt% to 15 wt%. When the solid electrolyte in the positive electrode satisfies the above range, the ionic conductivity can be improved while minimizing the capacity degradation of the positive electrode, thereby improving the overall performance of the all-solid-state secondary battery.

[0180] Step (v) may be to prepare a positive electrode composition by mixing the final positive electrode active material and the prepared solid electrolyte, apply the positive electrode composition onto a positive electrode current collector, and then dry and press to prepare a positive electrode. At this time, a binder and / or a conductive material may be further added to the positive electrode composition.

[0181] All-solid-state secondary battery

[0182] In one example, an all-solid-state secondary battery is provided that includes the aforementioned positive electrode. The all-solid-state secondary battery includes the aforementioned positive electrode, the negative electrode, and a solid electrolyte layer positioned between the positive electrode and the negative electrode.

[0183] FIG. 4 is a cross-sectional view of an all-solid-state secondary battery according to an embodiment. Referring to FIG. 4, the all-solid-state secondary battery (100') may have a structure in which an electrode assembly in which a negative electrode (400) including a negative electrode 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 collector (201) are laminated is housed in a battery case. The all-solid-state secondary battery (100') may further include an elastic layer (500) on the outer side of at least one of the positive electrode (200) and the negative electrode (400). Although FIG. 4 illustrates one electrode assembly including the negative electrode (400), the solid electrolyte layer (300), and the positive electrode (200), an all-solid-state secondary battery may be manufactured by laminating two or more electrode assemblies.

[0184] cathode

[0185] The negative electrode (400) may include a current collector (401) and a negative electrode active material layer (403) positioned on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder and / or a conductive material.

[0186] 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.

[0187] The material capable of reversibly intercalating / deintercalating the lithium ions may include a carbon-based negative electrode active material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as natural graphite or artificial graphite in an amorphous, plate-like, flake-like, spherical, or fibrous form, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0188] As the above lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0189] As the material capable of doping and dedoping the lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material is silicon, a silicon-carbon composite, SiOx(0 <x<2), Si-Q 합금(상기 Q는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소(Si를 제외함), 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합에서 선택됨), 또는 이들의 조합일 수 있다. 상기 Sn계 음극 활물질로는 Sn, SnO2, Sn계 합금 또는 이들의 조합일 수 있다.

[0190] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the composite may include secondary particles (cores) in which silicon primary particles are assembled and an amorphous carbon coating layer (shell) positioned on the surface of the secondary particles. The amorphous carbon may also be positioned between the silicon primary particles, such that, for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0191] The silicon-carbon composite may further comprise crystalline carbon. For example, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles and an amorphous carbon coating layer positioned on the surface of the core.

[0192] The above Si-based negative electrode active material or Sn-based negative electrode active material can be used in a mixture with a carbon-based negative electrode active material.

[0193] The content of the negative active material in the above negative active material layer may be 95 wt% to 99 wt% with respect to the total weight of the negative active material layer.

[0194] In one embodiment, the negative electrode active material layer further includes a binder and may optionally further include a conductive material. The content of the binder in the negative electrode active material layer may be 1 wt% to 5 wt% based on the total weight of the negative electrode active material layer. In addition, when the negative electrode active material layer further includes a conductive material, the negative electrode active material layer may include 90 wt% to 98 wt% of the negative electrode active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material.

[0195] The above binder serves to adhere the negative electrode active material particles well to each other and also to adhere the negative electrode active material well to the current collector. The binder may be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0196] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0197] The above-mentioned aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoroelastomer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0198] When using an aqueous binder as the above-mentioned negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li.

[0199] The above dry binder is a polymeric material capable of being fiberized, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0200] The conductive material is used to provide conductivity to the electrode, and any material that does not cause chemical changes and is electronically conductive can be used in the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metal-based materials in the form of metal powder or metal fibers, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0201] The negative electrode current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and a combination thereof.

[0202] precipitation cathode

[0203] As an example, the negative electrode for an all-solid-state secondary battery may be a precipitation-type negative electrode, unlike the above-mentioned one. The precipitation-type negative electrode may refer to a negative electrode that does not include a negative electrode active material when the battery is assembled, but in which lithium metal or the like is precipitated or deposited on the negative electrode when the battery is charged, and this acts as a negative electrode active material.

[0204] Fig. 5 is a schematic cross-sectional view of an all-solid-state secondary battery including a precipitation-type negative electrode. Referring to Fig. 5, the precipitation-type negative electrode (400') may include a current collector (401) and a negative electrode coating layer (405) positioned on the current collector. An all-solid-state secondary battery including such a precipitation-type negative electrode (400') starts initial charging in a state in which no negative electrode active material is present, and during charging, high-density lithium metal is precipitated or deposited between the current collector (401) and the negative electrode coating layer (405) or on the negative electrode coating layer (405) to form a lithium metal layer (404), which may function as a negative electrode active material. Accordingly, in an all-solid-state secondary battery that has been charged more than once, the precipitation-type negative electrode (400') may include, for example, a current collector (401), a lithium metal layer (404) positioned on the current collector, and a negative electrode coating layer (405) positioned on the metal layer. The lithium metal layer (404) refers to a layer in which lithium metal or the like is precipitated during the charging process of the battery, and may be referred to as a metal layer, a lithium layer, a lithium deposition layer, or a negative electrode active material layer.

[0205] The cathode coating layer (405) may be referred to as a lithium electrodeposition induction layer or a cathode catalyst layer, and may include a lithium-philic metal, a carbon material, or a combination thereof.

[0206] The above-mentioned lithium-philic metal may include, for example, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, zinc, or a combination thereof, and may be composed of one type of these or may be composed of several types of alloys. When the lithium-philic metal is present in the form of particles, its average particle diameter (D 50 ) may be about 4 ㎛ or less, for example, 10 nm to 4 ㎛, 10 nm to 1 ㎛, 10 nm to 600 nm. As an example, the lithium-philic metal may be in the form of nanoparticles having an average particle size of several to several hundred nanometers.

[0207] The carbon material may be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The crystalline carbon may be, for example, natural graphite, artificial graphite, mesophase carbon microbeads, or a combination thereof. The amorphous carbon may be, for example, carbon black, activated carbon, acetylene black, Denka black, Ketjen black, or a combination thereof.

[0208] When the negative electrode coating layer (405) includes both a lithium-philic metal and a carbon material, the mixing ratio of the metal and the carbon material may be, for example, a weight ratio of 1:10 to 2:1. In this case, the precipitation of lithium metal can be effectively promoted and the characteristics of the all-solid-state secondary battery can be improved. The negative electrode coating layer (405) may include, for example, a carbon material loaded with a lithium-philic metal, or may include a mixture of lithium-philic metal particles and carbon material particles.

[0209] The cathode coating layer (405) may include, for example, a lithium-philic metal and amorphous carbon, in which case the precipitation of lithium metal can be effectively promoted.

[0210] Supported compounds

[0211] In one embodiment, the negative electrode coating layer may include a compound in which a lithium-philic metal is supported on a carbon material. The supported compound is distinguished from a simple mixture of a lithium-philic metal and a carbon material. When the negative electrode coating layer includes a supported compound, the lithium metal layer described below can be formed more uniformly, and the reversibility of lithium precipitation and dissociation can be improved, thereby improving the life characteristics of the all-solid-state secondary battery. Here, the lithium-philic metal is the same as described above, and the carbon material can be, for example, amorphous carbon.

[0212] The amorphous carbon material may be, for example, a single particle, or an assembly having the form of secondary particles assembled from primary particles. When the amorphous carbon material is a single particle, the average particle size may be 100 nm or less, for example, a nano-size of 10 nm to 100 nm. When the amorphous carbon material is an assembly, the particle size of the primary particles may be 20 nm to 100 nm, and the particle size of the secondary particles may be 1 μm to 20 μm.

[0213] In one embodiment, the particle size of the primary particles of the amorphous carbon material in the assembly shape may be 20 nm or more, 30 nm or more, 40 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, or 90 nm or more, and may be 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 40 nm or less, or 30 nm or less. The shape of the primary particles may be spherical, elliptical, plate-like, and a combination thereof, and in one embodiment, the shape of the primary particles may be spherical, elliptical, and a combination thereof.

[0214] In one embodiment, the particle size of the secondary particles of the amorphous carbon material in the assembly shape may be 1 µm or more, 3 µm or more, 5 µm or more, 7 µm or more, 10 µm or more, or 15 µm or more, and may be 20 µm or less, 15 µm or less, 10 µm or less, 7 µm or less, 5 µm or less, or 3 µm or less.

[0215] The lithium-philic metal may be included in an amount of 3 wt% to 40 wt% based on 100 wt% of the compound in which the lithium-philic metal is supported on the carbon material, for example, 3 wt% to 30 wt%, 4 wt% to 25 wt%, 5 wt% to 20 wt%, or 5 wt% to 15 wt%. The carbon material may be included in an amount of 60 wt% to 97 wt% based on 100 wt% of the compound in which the lithium-philic metal is supported on the carbon material, for example, 70 wt% to 97 wt%, 75 wt% to 96 wt%, 80 wt% to 95 wt%, or 85 wt% to 95 wt%. When the contents of the lithium-philic metal and the carbon material satisfy the above ranges, a uniform lithium metal layer can be effectively formed during charging.

[0216] In one embodiment, the carbon material and the lithium-philic metal may be chemically bonded via sulfur. That is, the carbon material and the lithium-philic metal may not be simply physically mixed, but may be chemically bonded to each other. In this case, the bonding strength between the carbon material and the lithium-philic metal is excellent, and the problem of the carbon material and the lithium-philic metal separating from each other during the mixing process can be effectively prevented. In addition, the phenomenon of the lithium-philic metal agglomerating is prevented, so that it can be uniformly dispersed within the negative electrode coating layer, thereby uniformly distributing the current within the negative electrode and inducing uniform deposition of the lithium metal.

[0217] When carbon materials and a lithiophilic metal are chemically bonded via sulfur, peaks related to the bonding of the lithiophilic metal and sulfur can be identified in the X-ray photoelectron spectroscopy (XPS) spectrum. For example, when the lithiophilic metal contains Ag, a peak can be identified in the S2p spectrum obtained by XPS analysis in the range of 160 eV to 162 eV, which is the Ag-S bond energy.

[0218] A composite in which carbon material and a lithium-philic metal are chemically bonded via sulfur can be manufactured by mixing carbon material and sulfur-containing raw materials in a dry or wet manner, optionally heat-treating them, then supporting the lithium-philic metal and heat-treating the mixture.

[0219] A method for supporting a lithiophilic metal may be, for example, a method of mixing a mixture of a carbon material and a sulfur-containing raw material, a lithiophilic metal compound, and a reducing agent in a solvent. The solvent may include, for example, water, ethanol, glycerol, benzene, xylene, or a combination thereof, and the reducing agent may include NaBH4, ascorbic acid, trisodium citrate, ethylene glycol, or a combination thereof. The lithiophilic metal compound may be a nitrate, sulfate, perchlorate, or the like containing a lithiophilic metal, and may include, for example, AgNO3, Ag2SO4, AgClO4, or a combination thereof.

[0220] The heat treatment after supporting the lithium-philic metal can usually be carried out at a temperature at which the sulfur-containing raw material can be decomposed and removed, for example, at 100°C to 500°C, 150°C to 500°C, 200°C to 450°C, or 200°C to 400°C. Specifically, when a thiol compound is used as the sulfur-containing raw material, the heat treatment can be carried out at 100°C to 400°C. The heat treatment can be carried out in an atmosphere of nitrogen, argon, or a combination thereof for about 2 to 20 hours.

[0221] 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.

[0222] The cathode coating layer may further include a binder, for example, a conductive binder. The cathode coating layer may also further include additives such as fillers, dispersants, and ionic conductive agents.

[0223] The binder of the cathode coating layer may include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0224] Non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0225] The aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluoroelastomer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0226] When using an aqueous binder as the cathode binder, a cellulose-based compound capable of imparting viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li.

[0227] The dry binder is a polymeric material capable of being fiberized, such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0228] The binder may be included in an amount of 0.1 to 5 wt%, 0.1 to 3 wt%, or 0.5 to 2 wt%, based on 100 wt% of the cathode coating layer.

[0229] lithium metal layer

[0230] According to one embodiment, the negative electrode is a type of precipitation-type negative electrode, and an all-solid-state secondary battery including the same starts initial charging in a state in which no negative electrode active material is present, and during charging, a high-density lithium metal is precipitated or deposited between the negative electrode current collector and the negative electrode coating layer, or on the negative electrode coating layer, to form a lithium metal layer, which can function as the negative electrode active material. Therefore, an all-solid-state secondary battery that has been charged at least once may include, for example, a negative electrode current collector, a lithium metal layer positioned on the negative electrode current collector, and a negative electrode coating layer positioned on the lithium metal layer. The lithium metal layer means a layer in which lithium ions are precipitated as lithium metal during the charging process of the battery, and may be expressed as a metal layer, a lithium layer, a lithium deposition layer, or a negative electrode active material layer.

[0231] 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.

[0232] The thickness of the lithium metal layer may be, for example, 1 μm to 500 μm, 5 μm to 500 μm, 5 μm to 400 μm, 5 μm to 300 μm, or 10 μm to 200 μm. If the thickness of the lithium metal layer is too thin, it may be difficult to perform the role of a lithium storage tank, and if it is too thick, the battery volume may increase and the performance may deteriorate.

[0233] In one embodiment, a lithium metal layer having a uniform thickness and flatness can be formed by applying a compound in which the aforementioned lithium-philic metal is supported on a carbon material to the negative electrode coating layer. Therefore, according to one embodiment, the lithium metal layer formed during charging may have a very uniform thickness and a small thickness deviation. For example, the deviation in the thickness of the lithium metal layer may be 40% or less, 30% or less, 20% or less, 15% or less, 10% or less, or 5% or less. Here, the deviation in the thickness of the lithium metal layer may mean that the thickness of the lithium metal layer is measured at about 10 points in an electron microscope image of the negative electrode cross-section, the arithmetic mean is calculated, and then the absolute value of the difference between one data and the arithmetic mean is divided by the arithmetic mean and multiplied by 100. Also, for example, the thickness of the lithium metal layer may be 5 ㎛ to 80 ㎛, and the standard deviation of the thickness may be 0.1 ㎛ to 20 ㎛, 0.1 ㎛ to 15 ㎛, 0.1 ㎛ to 10 ㎛, 0.1 ㎛ to 5 ㎛, and 0.1 ㎛ to 3 ㎛. Similarly, the standard deviation of the thickness of the lithium metal layer may be calculated by measuring the thickness at about 10 points in an electron microscope photograph. The fact that the deviation or standard deviation of the thickness of the lithium metal layer satisfies the above range means that the lithium metal is well deposited in the form of a film with a uniform thickness, and accordingly, the electrochemical characteristics of the all-solid-state secondary battery may be improved.

[0234] etc

[0235] Meanwhile, the negative electrode according to one embodiment may further include a thin film on the surface of the negative electrode current collector, that is, between the negative electrode current collector and the negative electrode coating layer, or between the negative electrode current collector and the lithium metal layer. The thin film may include an element capable of forming an alloy with lithium. The element capable of forming an alloy with lithium may include, for example, Al, Ag, Au, Bi, Cu, Ge, In, Mg, Ni, Pd, Pt, Si, Sn, Zn, or a combination thereof. The thin film may further flatten the deposition morphology of the lithium metal layer and assist in forming a lithium metal layer with a uniform thickness. The thin film may be formed by, for example, a vacuum deposition method, a sputtering method, a plating method, or the like. The thickness of the thin film may be, for example, 1 nm to 500 nm.

[0236] negative current collector

[0237] The negative electrode current collector may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li) or an alloy thereof, and may be in the form of a foil or a sheet. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0238] solid electrolyte layer

[0239] The solid electrolyte layer (300) may include an inorganic solid electrolyte, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halide-based solid electrolyte, etc. The sulfide-based solid electrolyte is substantially the same as that described in the positive electrode section, so a detailed description thereof is omitted.

[0240] Oxide-based solid electrolytes include, for example, Li 1+x Ti 2-x Al(PO4)3(LTAP)(0≤x≤4), Li 1+x+y Al x Ti2-x Si y P 3-y O 12 (0 <x<2, 0≤y<3), BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT)(0≤x<1, 0≤y<1), PB(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 <x<2, 0<y<3), Li 1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0≤x≤1, 0≤y≤1), lithium lanthanum titanate (Li x La y TiO3, 0 <x<2, 0<y<3), Li2O, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2계 세라믹스, 가넷(Garnet)계 세라믹스 Li 3+x La3M2O 12 (M= Te, Nb, or Zr; x is an integer from 1 to 10), or mixtures thereof.

[0241] A halide-based solid electrolyte contains a halogen element as a main component, and may mean that the ratio of the halide element to all elements constituting the solid electrolyte is 50 mol% or more, 70 mol% or more, 90 mol% or more, or 100 mol%. For example, the halide-based solid electrolyte may not contain a sulfur element.

[0242] The halide-based solid electrolyte may contain lithium element, a metal element other than lithium, and a halogen element. The metal element other than lithium may be Al, As, B, Bi, Ca, Cd, Co, Cr, Fe, Ga, Hf, In, Mg, Mn, Ni, Sb, Sc, Sn, Ta, Ti, Y, Zn, Zr, or a combination thereof. The halogen element may be F, Cl, Br, I, or a combination thereof, and may be Cl, Br, or a combination thereof. The halide-based solid electrolyte may contain, for example, Li a M1X6 (M is Al, As, B, Bi, Ca, Cd, Co, Cr, Fe, Ga, Hf, In, Mg, Mn, Ni, Sb, Sc, Sn, Ta, Ti, Y, Zn, Zr, or a combination thereof, X is F, Cl, Br, I, or a combination thereof, and 2≤a≤3) can be represented. The halide-based solid electrolyte is, for example, Li2ZrCl6, Li 2.7 Y 0.7 Zr 0.3 Cl6, Li 2.5 Y 0.5 Zr 0.5 Cl6, Li 2.5 In 0.5 Zr 0.5 Cl6, Li2In 0.5 Zr 0.5 Cl6, Li3YBr6, Li3YCl6, Li3YBr2Cl4, Li3YbCl6, Li 2.6 Hf 0.4 Yb 0.6 Cl6, or combinations thereof, but is not limited thereto.

[0243] Meanwhile, the average particle diameter (D) of the solid electrolyte included in the solid electrolyte layer (300) 50 ) is the average particle diameter (D) of the solid electrolyte contained in the positive electrode (200). 50) may be larger than that. In this case, the overall performance can be improved by increasing the mobility of lithium ions while maximizing the energy density of the all-solid-state secondary battery. For example, the average particle diameter (D) of the sulfide-based solid electrolyte particles included in the positive electrode (200) 50 ) may be 0.1 ㎛ to 1.9 ㎛, or 0.1 ㎛ to 1.0 ㎛, and the average particle diameter (D) of the solid electrolyte included in the solid electrolyte layer (300) 50 ) may be 2.0 ㎛ to 5.0 ㎛, or 2.0 ㎛ to 4.0 ㎛, or 2.5 ㎛ to 3.5 ㎛. When this particle size range is satisfied, the energy density of the all-solid-state secondary battery can be maximized while the transfer of lithium ions is facilitated, thereby suppressing the resistance and improving the overall performance of the all-solid-state secondary battery. Here, the average particle diameter (D of the solid electrolyte 50 ) may be measured using a particle size analyzer using laser diffraction.

[0244] The solid electrolyte layer (300) may further include a binder in addition to the solid electrolyte. At this time, the binder may be styrene butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, an acrylate polymer, or a combination thereof, but is not limited thereto, and any binder used in the relevant technical field may be used. The acrylate polymer may be, for example, butyl acrylate, polyacrylate, polymethacrylate, or a combination thereof.

[0245] The solid electrolyte layer (300) can be formed by adding a solid electrolyte to a binder solution, coating the same on a substrate film, and drying the same. The solvent of the binder solution may be isobutyryl isobutyrate, xylene, toluene, benzene, hexane, or a combination thereof. Since the solid electrolyte layer formation process is widely known in the art, a detailed description thereof will be omitted.

[0246] The thickness of the solid electrolyte layer (300) may be, for example, 10 μm to 800 μm.

[0247] The solid electrolyte layer (300) may further include an alkali metal salt, and / or an ionic liquid, and / or a conductive polymer.

[0248] The above alkali metal salt may be, for example, a lithium salt. The content of the lithium salt in the solid electrolyte layer may be 1 M or more, for example, 1 M to 4 M. In this case, the lithium salt may improve ion conductivity by enhancing the lithium ion mobility of the solid electrolyte layer.

[0249] The lithium salt may be applied without limitation on type, and may include, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiSCN, LiN(CN)2, lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, or a combination thereof.

[0250] For example, the lithium salt may be an imide-based lithium salt such as LiTFSI, LiFSI, LiBETI, or a combination thereof. The imide-based lithium salt can maintain or improve ionic conductivity by appropriately maintaining chemical reactivity with the ionic liquid.

[0251] Ionic liquids are salts or molten salts that are composed only of ions and are liquid at room temperature, with a melting point below room temperature.

[0252] 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.

[0253] The ionic liquid may be, for example, one or more selected from the group consisting of N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(3-trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide.

[0254] In the solid electrolyte layer, the weight ratio of the solid electrolyte to the ionic liquid may be 0.1:99.9 to 90:10, for example, 10:90 to 90:10, 20:80 to 90:10, 30:70 to 90:10, 40:60 to 90:10, or 50:50 to 90:10. A solid electrolyte layer satisfying the above range can maintain or improve ionic conductivity by improving the electrochemical contact area with the electrode. Accordingly, the energy density, discharge capacity, rate characteristics, etc. of the all-solid-state secondary battery can be improved.

[0255] The all-solid-state secondary battery may be a unit cell having a structure of positive electrode / solid electrolyte layer / negative electrode, a bi-cell having a structure of negative electrode / solid electrolyte layer / positive electrode / solid electrolyte layer / negative electrode, or a laminated battery in which the structure of the unit cell is repeated.

[0256] The shape of the above-mentioned all-solid-state secondary battery is not particularly limited, and may be, for example, coin-shaped, button-shaped, sheet-shaped, stacked, cylindrical, flat, etc. In addition, the above-mentioned all-solid-state secondary battery can be applied to large-scale batteries used in electric vehicles, etc. For example, the above-mentioned all-solid-state secondary battery can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). In addition, it can be used in fields requiring a large amount of power storage, and for example, it can be used in electric bicycles or power tools, etc. In addition, the above-mentioned all-solid-state secondary battery can be used in various fields such as portable electronic devices.

[0257] Hereinafter, examples and comparative examples of the present invention are described. The following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0258] Example 1

[0259] 1. Manufacturing of the first nickel-based composite hydroxide

[0260] Through the coprecipitation method described below, the first nickel-based composite hydroxide (Ni), which is a precursor of the first positive electrode active material, 0.945 Co 0.04 Al 0.015 (OH)2) was synthesized. Nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and sodium aluminum sulfate (NaAl(SO4)2·12H2O) were dissolved in distilled water as a solvent at a molar ratio of 94.5:4:1.5 to prepare a mixed solution of metal raw materials. In addition, ammonia water (NH4OH) and sodium hydroxide (NaOH) were prepared as a precipitant to form a complex compound.

[0261] [Step 1: 2.5 kW / ㎥, NH4OH 0.40 M, pH 10.5~11.5, reaction time 6 hours]

[0262] First, ammonia water with a concentration of 0.40 M was added to the reactor. The reaction was initiated by adding a mixed solution of metal raw materials and a complexing agent (NH4OH) at a rate of 85 ml / min and 10 ml / min, respectively, at a stirring power of 2.5 kW / ㎥ and a reaction temperature of 50°C. The reaction was carried out for 6 hours while adding NaOH to maintain the pH. As a result of the reaction, it was confirmed that the average size of the obtained core particles was in the range of approximately 6.5 μm to 7.5 μm, and the second step was carried out as follows.

[0263] [Step 2: 2.0 kW / ㎥, NH4OH 0.45 M, pH 10.5~11.5, reaction time 18 hours]

[0264] While maintaining the reaction temperature at 50℃, the metal raw material mixture solution and complexing agent were introduced at a rate of 85 ml / min and 12 ml / min, respectively, so that the concentration of the complexing agent became 0.45 M. The reaction was continued for 18 hours while adding NaOH to maintain the pH. At this time, the stirring power was lowered to 2.0 kW / ㎥, which was lower than in step 1, and the reaction was conducted. By conducting this reaction, it was confirmed that the average size of the product particles containing the core and the intermediate layer was 13.5 ㎛ to 14 ㎛, and the following 3 steps were performed.

[0265] [Step 3: 1.5 kW / ㎥, NH4OH 0.45 M, pH 10.5~11.5, reaction time 14 hours]

[0266] While maintaining the reaction temperature at 50℃, the injection speed of the metal raw material mixture solution and the complexing agent and the concentration of the complexing agent were the same as in the second step. The reaction was conducted for 14 hours while adding NaOH to maintain the pH. At this time, the stirring power was lowered to 1.5 kW / ㎥, which was lower than in the second step, to proceed with the reaction. After washing the obtained result, it was dried with hot air at about 150℃ for 24 hours to obtain the first nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH)2) was obtained.

[0267] 2. Manufacturing of secondary nickel-based composite hydroxides

[0268] Through the coprecipitation method described below, a second nickel-based composite hydroxide (Ni), which is a precursor of the second positive electrode active material, is prepared. 0.94 Co 0.04 Mn 0.02 (OH)2) was synthesized. Nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were dissolved in distilled water as a solvent in a molar ratio of 94:4:2 to prepare a mixed solution of metal raw materials. Ammonia water (NH4OH) and sodium hydroxide (NaOH) were prepared as a precipitant to form a complex compound.

[0269] First, ammonia water with a concentration of 0.25 M was put into the reactor. The reaction was started by adding a mixed solution of metal raw materials and a complexing agent at a rate of 142 ml / min and 34 ml / min, respectively, at a stirring power of 3.0 kW / ㎥ and a reaction temperature of 50℃. The reaction was carried out for 30 hours while adding NaOH to maintain the pH. The reaction was terminated when the average size of the obtained particles reached about 4 ㎛. After washing the obtained result, it was dried with hot air at about 150℃ for 24 hours to obtain a second nickel-based composite hydroxide (Ni0.94 Co 0.04 Mn 0.02 (OH)2) was prepared.

[0270] 3. Preparation of preliminary cathode active material

[0271] First nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH)2) 80 wt% and second nickel-based composite hydroxide (Ni 0.94 Co 0.04 Mn 0.02 (OH)2) 20 wt% was mixed, and LiOH was mixed so that the molar ratio of the entire metal and Li was 1:1. Afterwards, a first heat treatment was performed in an oxygen atmosphere, in which the temperature was raised to 700°C for 8 hours and the temperature was maintained for 7 hours, to manufacture a preliminary positive electrode active material.

[0272] Scanning electron microscope (SEM) analysis of the surface and cross-section of the manufactured preliminary positive electrode active material revealed that the first positive electrode active material was in the form of secondary particles, including an interior with an irregular porous structure and an exterior with a radial array structure, and the average particle diameter (D) of the secondary particles was 50 ) is confirmed to be about 14 ㎛. The second positive electrode active material is confirmed to be in the form of secondary particles in which multiple primary particles are aggregated, and the average particle diameter (D) of the secondary particles 50 ) is confirmed to be approximately 4㎛.

[0273] Meanwhile, after separating the first cathode active material (large particles) and the second cathode active material (small particles) from the preliminary cathode active material through a turbo classifier, ICP (Inductively Coupled Plasma) emission spectroscopic analysis was performed on the surface of the small particles, and as a result, 93.9 mol% of Ni, 3.9 mol% of Co, 0.6 mol% of Al, and 1.6 mol% of Mn were measured. Accordingly, it is confirmed that the small-grain NCM receives Al from the large-grain NCA during the first heat treatment process and exists as NCAM doped with Al at a level of 0.6 mol%.

[0274] 4. Formation of the first coating layer

[0275] The method for forming the first coating layer, which is a kind of buffer layer, on the positive electrode active material is a dry coating method as follows. For 100 mol parts of the total metal excluding lithium in the preliminary positive electrode active material, 0.25 mol parts of zirconium oxide (ZrO2) and 0.5 mol parts of anhydrous lithium hydroxide (LiOH) were mixed in a mixer and coating was performed. During coating, the mixer was operated at low, medium, and high speeds to ensure even coating without layer separation. Afterwards, a second heat treatment was performed at 500°C for 15 hours in an oxygen atmosphere, and the nickel-based composite oxide (LiNi) on which the first coating layer was formed 0.944 Co 0.04 Al 0.012 Mn 0.004 O2) was manufactured.

[0276] HRTEM and inverse-FFT analyses were performed on the cross-sections of large and small particles in the positive electrode active material on which the first coating layer was formed, and the crystal structure of the first coating layer region was analyzed. As a result, it was confirmed that there was a ZrO2 crystal phase, a Li6Zr2O7 crystal phase, and an amorphous portion containing Zr.

[0277] 5. Preparation of solid electrolyte (Li6PS5Cl, Argyrodite)

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

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

[0280] 6. Thermal complexation of positive electrode active materials

[0281] Through the method described below, the manufactured argyrodite-type sulfide-based solid electrolyte was thermally complexed with the positive electrode active material on which the first coating layer was formed.

[0282] 85 parts by weight of the positive electrode active material having the first coating layer formed and 1 part by weight of the manufactured argyrodite-type sulfide-based solid electrolyte were mixed using a Hansel mixer. The mixed powder was subjected to a third heat treatment at 250°C for 5 hours in a tube furnace through which argon gas flowed at a constant rate of 8 SLM. Through this, the sulfide-based solid electrolyte particles were evenly thermally complexed on the surface of the positive electrode active material, thereby manufacturing the final positive electrode active material having the second coating layer formed thereon.

[0283] 7. Coating of solid electrolyte

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

[0285] As a result of performing X-ray diffraction analysis on the manufactured solid electrolyte, it was confirmed that the lithium-zirconium-phosphate located on the surface of the core particle is in an amorphous state, as no peak corresponding to LZP was observed. In addition, the half width of the main peak was 0.152, indicating that the crystal size increased and the crystallinity was enhanced. The change in particle size distribution and the effect of increasing ionic conductivity due to the coating are described later in Evaluation Examples 4 and 5.

[0286] 8. Manufacturing of the anode

[0287] A cathode composition was prepared by mixing 86 wt% of the final cathode active material, 12.44 wt% of the coated solid electrolyte, 1 wt% of the PVdF binder, 0.45 wt% of the carbon nanotube conductive agent, and 0.11 wt% of hydrogenated nitrile butadiene rubber (HNBR) as a dispersant in an isobutyryl isobutyrate (IBIB) solvent. This was applied to the cathode current collector, dried, and then rolled (hydrostatic pressing (WIP), 500 Mpa, 85°C, 30 min) to prepare the cathode.

[0288] 9. Manufacturing of precipitation-type cathode

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

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

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

[0292] 10. Manufacturing of all-solid-state secondary batteries

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

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

[0295] Comparative Example 1

[0296] An all-solid-state secondary battery was manufactured in substantially the same manner as in Example 1, except that the sulfide-based solid electrolyte manufactured in Step 5 was used as a solid electrolyte in the manufacture of the positive electrode in Step 8, instead of forming a third coating layer on the solid electrolyte as in Step 7 of Example 1.

[0297] Comparative Example 2

[0298] In the process of manufacturing a positive electrode active material, a positive electrode active material having only a first coating layer formed without forming a second coating layer was used, and an all-solid-state secondary battery was manufactured in substantially the same manner as in Comparative Example 1, except that in the manufacturing of the positive electrode, the positive electrode active material was mixed at 85 wt% and the solid electrolyte at 13.44 wt%.

[0299] Comparative Example 3

[0300] In the thermal complexation process of the positive electrode active material, i.e., the second coating layer formation process, 85 parts by weight of the positive electrode active material on which the first coating layer was formed and 3 parts by weight of the manufactured argyrodite-type sulfide-based solid electrolyte were mixed, and an all-solid-state secondary battery was manufactured in substantially the same manner as in Comparative Example 1, except that 88% by weight of the final thermally complexed positive electrode active material and 10.44% by weight of the solid electrolyte were mixed during the positive electrode manufacturing process.

[0301] Comparative Example 4

[0302] In the thermal composite process of the positive electrode active material, 85 parts by weight of the positive electrode active material on which the first coating layer was formed and 5 parts by weight of the manufactured argyrodite-type sulfide-based solid electrolyte were mixed, and an all-solid-state secondary battery was manufactured in substantially the same manner as in Comparative Example 1, except that 90% by weight of the final thermal composite positive electrode active material and 8.44% by weight of the solid electrolyte were mixed during the manufacture of the positive electrode.

[0303] Comparative Example 5

[0304] An all-solid-state secondary battery was manufactured in substantially the same manner as in Comparative Example 4, except that the third heat treatment was not performed in the thermal complexation process of the positive electrode active material.

[0305] To aid understanding, the positive electrode active materials and positive electrode designs of Example 1 and Comparative Examples 1 to 5 are briefly presented in Table 1 below.

[0306] Cathode active material thermal composite Amount of electrolyte added during manufacture of anode (wt%) Type of electrolyte added to anode Whether heat treated Electrolyte (weight part) Example 101.0012.44Li6PS5Cl / LZP Comparative example 101.0012.44Li6PS5Cl Comparative example 2X013.44 Comparative example 303.0010.44 Comparative example 405.008.44 Comparative example 5X5.008.44

[0307] Reference example (electrolyte only heat treatment at 250℃)

[0308] The solid electrolyte manufactured in step 5 of Example 1 was heat-treated at 250°C for 5 hours in a tube furnace through which argon gas flowed at a constant rate of 8 SLM, thereby preparing a solid electrolyte according to a reference example.

[0309] Evaluation Example 1: Evaluation of the initial charge / discharge capacity of an all-solid-state secondary battery.

[0310] The all-solid-state secondary batteries manufactured in Example 1 and Comparative Examples 1 to 5 were charged at 45°C with a constant current of 0.1 C to an upper limit voltage of 4.25 V, and then discharged at 0.1 C to an end-of-discharge voltage of 2.5 V to measure the initial discharge capacity. The ratio of the initial discharge capacity to the initial charge capacity was calculated as efficiency, and the results are shown in Fig. 6 and Table 2.

[0311] Charge capacity (mAh / g)Discharge capacity (mAh / g)Efficiency (%)Example 1239.8216.890.4%Comparative example 1242.3207.285.5%Comparative example 2239.4205.285.7%Comparative example 3235.7201.385.4%Comparative example 4235.5200.084.9%Comparative example 5239.4204.285.3%

[0312] Referring to FIG. 6 and Table 2, it can be seen that in Example 1, the initial discharge capacity increases and the initial charge / discharge efficiency is greatly improved compared to Comparative Example 1, which did not use a solid electrolyte coated on the positive electrode. In addition, it can be seen that the initial charge / discharge capacity and the initial charge / discharge efficiency are greatly improved compared to Comparative Example 2, which did not thermally complex a sulfide-based solid electrolyte on the outermost surface of the positive electrode active material.

[0313] Specifically, Comparative Example 1 is a case where the surface of the positive electrode active material in Comparative Example 2 was thermally composited with a sulfide-based solid electrolyte, and it was shown that the initial charge / discharge capacity was improved through this, and Example 1 is a case where the ionic conductivity was further improved by applying a solid electrolyte coated with lithium-zirconium-phosphate as the solid electrolyte in the positive electrode in Comparative Example 1, and it was shown that the discharge capacity and charge / discharge efficiency of the all-solid-state secondary battery were greatly improved through this.

[0314] It can be seen that the charge and discharge capacities are somewhat lower in Comparative Examples 3 and 4, which have a larger amount of thermal complexing compared to Example 1. This is because, as described later in Evaluation Examples 4 and 5 below, if the amount of solid electrolyte used for coating the positive electrode active material is too large, the particles may aggregate and grow during the heat treatment process, which deteriorates the contact between the solid electrolyte and the positive electrode active material and reduces the connectivity of the solid electrolyte particles, resulting in a lower capacity.

[0315] Evaluation Example 2: Evaluation of the Lifetime Characteristics of All-Solid-State Secondary Batteries

[0316] For the all-solid-state secondary batteries of Example 1 and Comparative Examples 1 to 5, initial charging and discharging were performed as in Evaluation Example 1, and then charging at 0.33 C and discharging at 0.33 C in a voltage range of 2.5 V to 4.25 V at 45°C was repeated 100 times, and the ratio of the discharge capacity after 100 cycles to the initial discharge capacity was evaluated and shown as the capacity retention rate in Table 3 below, and the change in the capacity retention rate according to the number of cycles is shown in Fig. 7.

[0317] Initial discharge capacity (mAh / g) 100 cycles capacity retention rate (%) Example 1216.888.2% Comparative example 1207.287.8% Comparative example 2205.286.2% Comparative example 3201.383.3% Comparative example 4200.080.0% Comparative example 5204.286.7%

[0318] Comparative Example 5, which simply coated the surface of the positive electrode active material with a solid electrolyte without heat treatment, showed a somewhat lower discharge capacity than Comparative Example 2, but similar life characteristics. On the other hand, Comparative Example 4, which was heat treated, showed a sharp decrease in capacity and lifespan. This is understood to be due to poor contact with the positive electrode active material due to solid electrolyte agglomeration when an excessive amount of solid electrolyte was thermally complexed.

[0319] However, when thermal compounding is performed in an appropriate amount such that aggregation does not occur, as in Example 1 and Comparative Example 1, it can be seen that the capacity and life characteristics are improved compared to Comparative Example 2. In Comparative Example 1, where thermal compounding is performed in an appropriate amount for the positive electrode active material to improve performance, Example 1, where a solid electrolyte coated with lithium-zirconium-oxide is applied to the positive electrode, improves the ionic conductivity within the positive electrode, greatly improving the initial discharge capacity and efficiency of the battery. It can also be seen that the lithium-zirconium-phosphate coated on the solid electrolyte suppresses side reactions during the charge and discharge process, thereby improving the life characteristics.

[0320] Evaluation Example 3: Bipolar Plate Resistance Evaluation

[0321] An electrolyte film was attached to the top and bottom of the positive electrode plates manufactured in Example 1 and Comparative Examples 1, 2, 4, and 5, and a pressure of 40 kgf / cm 2 After pressurizing with a pressure of , a torque cell is manufactured. Electrochemical impedance spectroscopy (EIS) was performed on the manufactured cells to calculate the ionic conductivity. EIS was performed with an amplitude of approximately 10 mV and a frequency of 0.1 Hz to 10 6 The experiment was conducted at Hz, air atmosphere, and 45℃. The results of obtaining the resistance value from the arc of the Nyquist plot through EIS are shown in Table 4 and Fig. 8 below. Here, R1+R2 are the resistances of the positive electrode plates, and Rs is the resistance of the electrolyte membrane.

[0322] RsR1R2R1+R2Example 1154662108Comparative Example 1154689135Comparative Example 21160118178Comparative Example 49374299673Comparative Example 51473135208

[0323] According to Table 4 and Fig. 8, the resistances (RS) of the electrolyte membranes are all similar, while the resistances (R1+R2) of the positive electrode plates are very different. Comparative Example 5, which was simply coated with electrolyte, has a resistance similar to that of Comparative Example 2, whereas the resistance of Comparative Example 4, which was heat-treated, is significantly increased.

[0324] In addition, it can be confirmed that the resistance of the positive electrode is significantly reduced in the case of Example 1 and Comparative Example 1, in which an appropriate amount of solid electrolyte is thermally complexed. From this, it can be seen that when the positive electrode plate is manufactured by thermally complexing the electrolyte without agglomeration on the surface of the positive electrode active material, the resistance is significantly reduced, thereby greatly improving the performance of the all-solid-state secondary battery.

[0325] In addition, unlike Comparative Example 1, in Example 1, where a solid electrolyte with improved ionic conductivity was applied to the anode by coating and heat-treating lithium-zirconium-phosphate, it can be seen that the resistance of the anode plate was further reduced as the resistance of R2 was lowered.

[0326] Evaluation Example 4: Evaluation of particle size distribution of solid electrolyte

[0327] The particle size distributions for the sulfide-based solid electrolyte prepared in step 5 of Example 1 (before coating, i.e., the solid electrolyte of Comparative Example 1), the solid electrolyte coated with lithium-zirconium-phosphate in step 7 of Example 1 (after coating), and the solid electrolyte of the reference example (heat-treated without coating) were analyzed and shown in Fig. 9. The particle size distributions were measured using a particle size analysis device that uses xylene from which moisture has been removed as a solvent and utilizes laser diffraction.

[0328] Also, the cumulative size of 10% by volume is D 10 , 50% of the cumulative size of D 50 , and 90% of the cumulative size is D 90 , and are shown in Table 5 below, and to compare the wideness of the particle size distribution (D 90 -D 10 ) / D 50was calculated and shown as Span in Table 5.

[0329] MV (㎛)D 10 D 50 D 90 Span Example 1 Before coating 0.92 0.26 0.85 1.64 1.63 Example 1 After coating 0.88 0.26 0.87 1.46 1.37 Reference example 4 0.07 0.37 1.14 12.89 10.94

[0330] Referring to Figure 9 and Table 5, as in the reference example, when only the solid electrolyte is heat-treated at 250℃ for 5 hours under the thermal complexing condition, rapid aggregation occurs and D 90 It can be confirmed that the Span increases significantly. Through this, it can be understood that when the amount of solid electrolyte used for coating the positive electrode active material is excessive, as in Comparative Examples 3 and 4, the solid electrolyte particles may leave the surface of the positive electrode active material and aggregate with each other during the heat treatment process, resulting in a decrease in performance.

[0331] On the other hand, the solid electrolyte coated with lithium-zirconium-phosphate and heat-treated does not have a wide particle size distribution or an increase in D90 due to aggregation, but rather, the fine particles grow and the D10 increases, so that the particle sizes of the solid electrolyte particles become more uniform, as shown in Fig. 9. In summary, when combined with the results of improved ionic conductivity in Evaluation Example 5 below, it is understood that the coated electrolyte of Example 1 has a decrease in grain boundaries contained in the particles due to the growth of fine particles without aggregation of the particles, thereby lowering the resistance.

[0332] Evaluation Example 5: Evaluation of the ionic conductivity of a solid electrolyte

[0333] 0.15 g of each was charged into the sulfide-based solid electrolyte prepared in step 5 of Example 1 (before coating, i.e., the solid electrolyte of Comparative Example 1), the solid electrolyte coated with lithium-zirconium-phosphate in step 7 of Example 1 (after coating and heat treatment), and the solid electrolyte of the reference example (heat treatment without coating) and 40 kgf / cm 2After pressurizing with a pressure of , a torque cell is manufactured. Electromagnetic interference (EIS) analysis was performed on the manufactured cells to calculate the ionic conductivity. EIS has an amplitude of approximately 10 mV and a frequency of 0.1 Hz to 10 6 The experiments were conducted at Hz, air atmosphere, and 25℃. The resistance value was obtained from the arc of the Nyquist plot through EIS, and the ionic conductivity was calculated by considering the thickness and area of ​​the cell, etc., and the results are shown in Table 6 below.

[0334] Ionic Conductivity (mS / cm) Comparative Example 1 (Uncoated) 2.73 Example 1 (Coated and Heat Treated) 3.59 Reference Example (Heat Treated Without Coating) 1.95

[0335] Referring to Table 6, it can be seen that the ionic conductivity is greatly improved when the solid electrolyte is coated with lithium-zirconium-phosphate and then heat-treated as in Example 1. When the sulfide-based solid electrolyte is coated with lithium-metal-phosphate and then heat-treated, Ostwald ripening, in which small particles are integrated into large particles, is induced, which reduces the number of small particles and, accordingly, reduces the grain boundaries provided by the small particles, and increases the crystallinity of the solid electrolyte particles themselves. Since the ionic conductivity at grain boundaries is usually much lower than that of the bulk, it is understood that the solid electrolyte of Example 1 has greatly improved ionic conductivity as the number of grain boundaries is reduced.

[0336] However, as in the reference example, it can be seen that the ionic conductivity is greatly reduced when only heat treatment is performed without coating. In the case of the reference example where heat treatment was performed without coating, the solid electrolyte particles coagulate with each other and coagulate into large particles, so particles containing many particle boundaries are generated, which is understood to be the cause of the low ionic conductivity. In addition, it is thought that the increase in crystallinity is minimal because the thermal energy is consumed in particle coagulation, and therefore the effect of improving ionic conductivity due to the increase in crystallinity is not observed.

[0337] In addition, in the case of Example 1, it is understood that the ionic conductivity of the solid electrolyte in the positive electrode is further improved compared to Comparative Example 1, the aggregation phenomenon between particles is reduced, and the particle size distribution is uniform, thereby reducing the resistance and improving the initial discharge capacity, initial charge / discharge efficiency, and life characteristics.

[0338] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the following claims also fall within the scope of the present invention.

[0339] [Explanation of symbols]

[0340] 11: Secondary particle 12: Inside the secondary particle

[0341] 13: Primary particle 14: External of secondary particle

[0342] 100': All-solid-state battery 200: Anode

[0343] 201: Cathode current collector 203: Cathode active material layer

[0344] 300: Solid electrolyte layer 400: Cathode

[0345] 401: Negative current collector 403: Negative active material layer

[0346] 400': Precipitation type cathode 404: Lithium metal layer

[0347] 405: Cathode coating layer 500: Elastic layer

Claims

1. A first cathode active material comprising a lithium nickel-based composite oxide, a plurality of primary particles agglomerated, and secondary particles in which at least a portion of the primary particles are radially arranged, a first coating layer located on the surface of the secondary particles and containing Zr, and a second coating layer located on the first coating layer and containing a sulfide-based solid electrolyte; A lithium nickel-based composite oxide is included, and a secondary particle is formed by agglomerating a plurality of primary particles, a first coating layer located on the surface of the secondary particle and containing Zr, and a second coating layer located on the first coating layer and containing a sulfide-based solid electrolyte, and the average particle diameter (D) of the first positive electrode active material is 50 ) smaller than the average particle diameter (D 50 ) having a second positive electrode active material; and A positive electrode comprising a solid electrolyte comprising a core particle containing a sulfide-based solid electrolyte and a third coating layer located on the surface of the core particle and containing a lithium-metal-phosphate.

2. In paragraph 1, The average particle diameter (D) of the secondary particles of the first positive electrode active material 50 ) is 9 ㎛ to 25 ㎛, The average particle diameter (D) of the secondary particles of the second positive electrode active material 50 ) is 2 ㎛ to 8 ㎛, The thickness of each of the first coating layer of the first positive electrode active material and the first coating layer of the second positive electrode active material is 5 nm to 300 nm, A positive electrode, wherein the thickness of each of the second coating layer of the first positive electrode active material and the second coating layer of the second positive electrode active material is 100 nm to 2 ㎛.

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

4. In paragraph 1, The first coating layer of the first positive electrode active material and the first coating layer of the second positive electrode active material each include ZrO2 and Li6Zr2O7, A positive electrode in which the total content of Zr in the first coating layer of the first positive electrode active material and the first coating layer of the second positive electrode active material is 0.1 mol part to 0.6 mol part based on 100 mol parts of the total metal excluding lithium in the lithium nickel-based composite oxide of the first positive electrode active material and the lithium nickel-based composite oxide of the second positive electrode active material.

5. In paragraph 1, The second coating layer of the first positive electrode active material and the second coating layer of the second positive electrode active material each contain an argyrodite-type sulfide-based solid electrolyte, A positive electrode in which the total amount of the sulfide-based solid electrolyte of the second coating layer of the first positive electrode active material and the sulfide-based solid electrolyte of the second coating layer of the second positive electrode active material is 0.5 wt% to 3 wt% based on 100 wt% of the total of the first positive electrode active material and the second positive electrode active material.

6. In paragraph 1, A positive electrode, wherein the combined amount of the sulfide-based solid electrolyte of the second coating layer of the first positive electrode active material and the sulfide-based solid electrolyte of the second coating layer of the second positive electrode active material is 1 to 20 wt%, based on 100 wt% of the total of the sulfide-based solid electrolyte of the second coating layer of the first positive electrode active material, the sulfide-based solid electrolyte of the second coating layer of the second positive electrode active material, and the solid electrolyte in the positive electrode.

7. In paragraph 1, The nickel-based composite oxide of the first positive electrode active material is a lithium nickel-cobalt-aluminum composite oxide represented by the following chemical formula 1: [Chemical Formula 1] Li a1 Ni x1 Co y1 Al z1 M 1 w1 O 2-b1 X b1 In the above chemical formula 1, 0.9≤a1≤1.2, 0.7≤x1<1, 0 <y1<0.3, 0<z1<0.3, 0≤w1<0.3, 0.9≤x1+y1+z1+w1≤1.1, 및 0≤b1≤0.1이고, M 1 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S. A positive electrode comprising the secondary particles of the first positive electrode active material having an interior having an irregular porous structure and an exterior having a radial array structure as a region surrounding the interior.

8. In paragraph 1, The nickel-based composite oxide of the second positive electrode active material is a lithium nickel-cobalt-aluminum-manganese composite oxide represented by the following chemical formula 2: [Chemical Formula 2] Li a2 Ni x2 Co y2 Al z2 Mr w2 M 2 v2 O 2-b2 X b2 In the above chemical formula 2, 0.9≤a2≤1.2, 0.7≤x2<1, 0 <y2<0.3, 0<z2<0.3, 0<w2<0.3, 0≤v2<0.3, 0.9≤x2+y2+z2+w2+v2≤1.1, 및 0≤b2≤0.1이고, M 2 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S. The second cathode active material has a higher aluminum content in the surface layer of the secondary particle than in the interior of the secondary particle. The above interior refers to an area from the center of the secondary particle to about 70% of the radius in length, and the above surface layer refers to an area surrounding the interior from the outermost surface of the secondary particle to a depth corresponding to 30% of the radius in length. The Al content in the surface layer of the secondary particles of the second cathode active material is 0.2 at% to 2.0 at% with respect to 100 at% of the total metal excluding lithium in the lithium nickel-cobalt-aluminum-manganese composite oxide, A cathode having an Al content inside the secondary particles of the second cathode active material of 0 at% to 0.6 at% with respect to 100 at% of the total metal excluding lithium in the lithium nickel-cobalt-aluminum-manganese composite oxide.

9. In paragraph 1, The sulfide-based solid electrolyte contained in the core particles of the above solid electrolyte includes argyrodite-type sulfide, The average particle diameter (D) of the above solid electrolyte 50 ) is 0.1 ㎛ to 2 ㎛, The above solid electrolyte has a (D90-D10) / D50 value in the particle size distribution of greater than 1 and less than or equal to 5, An anode having a half-width of the main peak of 0.160 or less in X-ray diffraction analysis of the above solid electrolyte.

10. In paragraph 1, In the lithium-metal-phosphate of the third coating layer included in the solid electrolyte, the metal is at least one element selected from the group consisting of Al, B, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ta, V, W, and Zr, The lithium-metal-phosphate of the third coating layer included in the above solid electrolyte is amorphous, The content of lithium-metal-phosphate in the third coating layer is 0.01 wt% to 3 wt% with respect to 100 wt% of the solid electrolyte, 11.(i) A first positive electrode active material precursor comprising a 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; It contains a nickel-based composite hydroxide, and is in the form of secondary particles in which a plurality of primary particles are aggregated, and the average particle diameter (D) of the first cathode active material precursor 50 ) smaller than the average particle diameter (D 50 ) a second positive electrode active material precursor; and A preliminary cathode active material is obtained by mixing lithium raw materials and performing a first heat treatment, (ii) Dry mixing the above-mentioned preliminary positive electrode active material and zirconium raw material and performing a second heat treatment to prepare a Zr-coated positive electrode active material, (iii) Dry mixing of the Zr-coated positive electrode active material and the sulfide-based solid electrolyte and performing a third heat treatment to obtain the final positive electrode active material, (iv) Prepare a coated solid electrolyte by mixing core particles containing a sulfide-based solid electrolyte and lithium-metal-phosphate and performing a fourth heat treatment at 200°C to 300°C, (v) A method for manufacturing a positive electrode, comprising manufacturing a positive electrode by mixing the final positive electrode active material and coated solid electrolyte particles.

12. In paragraph 11, The nickel-based composite hydroxide of the first cathode active material precursor is a nickel-cobalt-aluminum-based composite hydroxide represented by the following chemical formula 11, The nickel-based composite hydroxide of the second cathode active material precursor is a nickel-cobalt-manganese composite hydroxide represented by the following chemical formula 12: [Chemical Formula 11] Ni x11 Co y11 Al z11 M 11 w11 (OH)2 In the above chemical formula 11, 0.7≤x11<1, 0 <y11<0.3, 0<z11<0.3, 0≤w11<0.3, 0.9≤x11+y11+z11+w11≤1.1이고, M 11 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, and Zr, [Chemical Formula 12] Ni x12 What y12 Mn w12 M 12 v12 (OH)2 In the above chemical formula 12, 0.7≤x12<1, 0 <y12<0.3, 0<w12<0.3, 0≤v12<0.3, 0.9≤x12+y12+w12+v12≤1.1이고, M 12 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Sn, Ti, V, W, and Zr, The average particle diameter of the secondary particles of the first positive electrode active material precursor is 9 ㎛ to 25 ㎛, and the average particle diameter of the secondary particles of the second positive electrode active material precursor is 2 ㎛ to 8 ㎛. The mixing weight ratio of the first positive electrode active material precursor and the second positive electrode active material precursor is 60:40 to 95:5, A method for manufacturing an anode, wherein the first heat treatment is performed at a temperature range of 600°C to 1000°C.

13. In paragraph 11, The above zirconium raw material is mixed in an amount of 0.1 to 0.6 molar parts per 100 molar parts of the total metal excluding lithium in the above preliminary active material, The above zirconium raw material is a particle containing zirconium oxide, and the average particle diameter (D) of the particles 50 ) is 10 nm to 500 nm, The second heat treatment is carried out in an oxygen atmosphere at a temperature range of 420°C to 580°C for 5 to 25 hours. When mixing the above preliminary positive electrode active material and zirconium raw material in a dry manner, the lithium raw material is mixed together, A method for producing a positive electrode active material, wherein the content of the lithium raw material is more than 1 mol part and less than 4 mol parts with respect to 1 mol part of the zirconium raw material.

14. In paragraph 11, The content of the sulfide-based solid electrolyte mixed in the above step (iii) is 0.5 to 3 parts by weight based on 100 parts by weight of the Zr-coated positive electrode active material. With respect to the total of 100 wt% of the sulfide-based solid electrolyte mixed in step (iii) and the core particles containing the sulfide-based solid electrolyte of step (iv), the content of the sulfide-based solid electrolyte mixed in step (iii) is 1 wt% to 20 wt%, A method for manufacturing an anode in which the third heat treatment is performed at 200°C to 300°C.

15. In paragraph 11, In the step (iv) above, 0.01 to 3 parts by weight of the lithium-metal-phosphate is mixed with 100 parts by weight of core particles containing a sulfide-based solid electrolyte, In the above step (iv), the sulfide-based solid electrolyte of the core particle contains an argyrodite-type sulfide, The average particle diameter (D) of the above core particles 50 ) is 0.1 ㎛ to 2 ㎛, In the lithium-metal-phosphate, the metal is one or more elements selected from the group consisting of Al, B, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ta, V, W, and Zr, The above lithium-metal-phosphate is in particle form and has an average particle diameter (D 50 ) is 0.01 ㎛ to 1.0 ㎛, A method for manufacturing an anode, wherein the fourth heat treatment is performed in an inert gas atmosphere with the highest temperature maintenance time set to 1 to 10 hours.

16. In paragraph 11, Step (iv) above A sulfide-based solid electrolyte is manufactured by mixing sulfur-containing raw materials and calcining them for the first time at 120°C to 350°C and then calcining them for the second time at 350°C to 800°C. The manufactured sulfide solid electrolyte was pulverized to obtain an average particle size (D 50 ) to obtain core particles having a size of 0.1 ㎛ to 2.0 ㎛, The obtained core particles and lithium-metal-phosphate are mixed and subjected to a fourth heat treatment at 200°C to 300°C, A method for manufacturing a positive electrode, wherein the coated solid electrolyte is mixed in an amount of 1 to 35 wt% with respect to a total of 100 wt% of the final positive electrode active material and the coated solid electrolyte in step (v).

17. The anode according to any one of paragraphs 1 to 10; cathode, and An all-solid-state secondary battery comprising a solid electrolyte layer positioned between the positive electrode and the negative electrode.

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

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

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

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