Positive electrode active materials, methods of preparing same, and all-solid-state rechargeable batteries

Abstract

The present invention relates to a positive electrode active material, a method for preparing same and all-solid-state rechargeable batteries, the positive electrode active material comprising: a first positive electrode active material comprising a secondary particle that contains a first lithium nickel-based composite oxide and is formed by aggregation of a plurality of primary particles, a first coating layer that is positioned on the surface of the secondary particle and contains boron, and a second coating layer that is positioned on the first coating layer and contains lithium aluminate; and a second positive electrode active material which comprises a particle that contains a second lithium nickel-based composite oxide and is in the form of a single particle, a first coating layer that is positioned on the surface of the single particle and contains boron, and a second coating layer that is positioned on the first coating layer and contains lithium aluminate, and which has an average particle diameter smaller than the average particle diameter of the first positive electrode active material.

Description

Positive electrode active material, method for producing the same, and all-solid-state secondary battery

[0001] It relates to a cathode active material, a method for producing the same, 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, active research is underway to utilize high-energy-density lithium secondary batteries as power sources for hybrid and electric vehicles, or as power storage devices.

[0003] Among lithium secondary batteries, all-solid-state batteries are composed entirely of solid materials, specifically those that utilize solid electrolytes. These all-solid-state batteries are safe, eliminating the risk of electrolyte leakage and explosion, and offer the advantage of being easy to manufacture in thinner sizes.

[0004] Recently, various cathode active materials for use in these all-solid-state batteries are being investigated. Conventional materials such as lithium nickel oxide, lithium nickel manganese cobalt composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium cobalt oxide are primarily being considered. However, these materials have limitations in achieving satisfactory performance for all-solid-state batteries. Therefore, the development of new cathode active materials and new cathode compositions is required to realize all-solid-state batteries with high capacity, high energy density, and long-life characteristics.

[0005] Provided are a high-capacity, high-efficiency, long-life cathode active material, which realizes high charge / discharge capacity in an all-solid-state secondary battery while simultaneously improving life characteristics, and also has high plate density and initial discharge capacity, thereby improving capacity per volume of the cathode, a method for producing the same, and an all-solid-state secondary battery including the same.

[0006] In one embodiment, a cathode active material is provided, comprising: a first cathode active material comprising a first lithium nickel-based composite oxide, a secondary particle formed by agglomeration of a plurality of primary particles; a first coating layer positioned on the surface of the secondary particle and containing boron; and a second coating layer positioned on the first coating layer and containing lithium aluminate; and a second cathode active material comprising a second lithium nickel-based composite oxide, a first coating layer in the form of a single particle and containing boron, and a second coating layer positioned on the first coating layer and containing lithium aluminate, wherein the second cathode active material has an average particle diameter smaller than an average particle diameter of the first cathode active material.

[0007] In one embodiment, a method for manufacturing a positive electrode active material is provided, comprising: (i) mixing and heat-treating a first positive electrode active material precursor containing a first nickel-based composite hydroxide and having a secondary particle form formed by agglomeration of a plurality of primary particles, a second positive electrode active material primary sintered product containing a second lithium nickel-based composite oxide and having a single particle form and a smaller average particle diameter than the first positive electrode active material precursor, a lithium raw material, and a boron raw material to obtain a preliminary positive electrode active material having a boron-containing first coating layer formed thereon, and (ii) dry-mixing the preliminary positive electrode active material and lithium aluminate particles to obtain a final positive electrode active material having a lithium aluminate-containing second coating layer formed on the surface of the preliminary positive electrode active material.

[0008] In one embodiment, an all-solid-state secondary battery is provided, comprising a positive electrode including the aforementioned positive electrode active material and a solid electrolyte, a negative electrode, and a solid electrolyte layer positioned between the positive electrode and the negative electrode.

[0009] According to one embodiment, a cathode active material and an all-solid-state secondary battery including the same have high charge / discharge capacity while simultaneously improving life characteristics, and have high plate density and initial discharge capacity, thereby improving the capacity per volume of the cathode.

[0010] Figure 1 is a schematic diagram showing the shape of a plate-shaped primary particle according to one implementation example.

[0011] Figure 2 is a drawing for explaining the definition of radiality in secondary particles according to one implementation example.

[0012] Figure 3 is a schematic diagram showing the cross-sectional structure of a secondary particle according to one implementation example.

[0013] Figures 4 and 5 are cross-sectional views schematically illustrating an all-solid-state secondary battery according to one embodiment.

[0014] Figure 6 shows the results of comparing voltages according to charge / discharge capacities of Example 1 and Comparative Example 1.

[0015] Figure 7 shows the results of evaluating the life characteristics of all-solid-state secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 and 2.

[0016] Figure 8 shows the results of quantitative analysis of each element on the surface of the cathode active material manufactured in Example 1 using TEM-EDS.

[0017] Figure 9 shows the results of quantitative analysis of each element on the surface of small particles using TEM-EDS among the positive electrode active materials manufactured in Example 1.

[0018] Figure 10 is a TEM photograph of a primary particle exposed on the surface of a secondary particle in the first positive electrode active material of Example 1.

[0019] Figure 11 is a TEM-EELS analysis graph for a total of 10 points from point 1 to point 10 shown in Figure 10.

[0020] Figure 12 is an SEM photograph of the cross-section of the first positive electrode active material of Example 1.

[0021] Figure 13 is an SEM photograph of the surface of the first positive electrode active material of Example 1.

[0022] Figure 14 shows the results of TEM-EELS analysis on the positive electrode active material manufactured in Example 1.

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

[0024] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

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

[0026] It should be understood that the terms "include," "comprising," or "having" herein are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0027] To clearly illustrate various layers and regions in the drawings, their thicknesses are enlarged, and similar parts are designated by the same drawing reference numerals throughout the specification. When an element such as a layer, film, region, or plate is said to be "over" or "on" another element, this includes not only the case where it is "directly over" the other element, but also the case where there is another element in between. Conversely, when an element is said to be "directly over" another element, it means that there is no other element in between.

[0028] Also, here, “layer” includes not only the shape formed on the entire surface when observed in a plan view, but also the shape formed on a portion of the surface.

[0029] The average particle size can also 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 a transmission electron microscope photograph or a scanning electron microscope photograph. Alternatively, the average particle size can be obtained by measuring using dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and calculating from the counted number. The average particle size can be measured with a microscope image or by measuring with a particle size analyzer, and is the diameter (D) of particles having a cumulative volume of 50% by volume in the particle size distribution. 50 ) can mean.

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

[0031] Here, the length and thickness, etc. may be measured by a scanning electron microscope or an optical microscope, and the average length may mean the arithmetic mean value of any 5 to 30 (for example, 5, 10, 20, or 30) length data, and the average thickness may mean the arithmetic mean value of any 5 to 30 (for example, 5, 10, 20, or 30) thickness data.

[0032] positive electrode active material

[0033] In one embodiment, a cathode active material is provided, which includes a first cathode active material and a second cathode active material.

[0034] The first cathode active material includes a first lithium nickel-based composite oxide and a secondary particle formed by agglomerating a plurality of primary particles, a first coating layer located on the surface of the secondary particle and containing boron, and a second coating layer located on the first coating layer and containing lithium aluminate.

[0035] The second positive electrode active material comprises a second lithium nickel-based composite oxide, is in the form of a single particle, and comprises a first coating layer located on the surface of the single particle and containing boron, and a second coating layer located on the first coating layer and containing lithium aluminate, and the average particle diameter (D) of the first positive electrode active material 50 ) smaller than the average particle diameter (D 50 ) has.

[0036] When used for all-solid-state secondary batteries, these positive electrode active materials have high initial charge / discharge capacity and initial charge / discharge efficiency, excellent life characteristics, and high density in the positive electrode plate, enabling very high volumetric capacity to be realized.

[0037] According to one embodiment, a cathode active material can improve capacity and charge / discharge efficiency by including a first cathode active material in the form of secondary particles designed to be advantageous for charging and discharging an all-solid-state secondary battery. At the same time, the density of the cathode plate can be increased by including a second cathode active material in the form of single particles.

[0038] All-solid-state secondary batteries are manufactured by applying pressure after the electrode assembly is manufactured. When a second cathode active material, which is in the form of a single particle and close to a spherical shape, is mixed with the first cathode active material, pressure transmission is very easy, so that the empty space between the particle components existing in the cathode can be minimized, and the solid electrolyte can effectively penetrate between the cathode active materials. Accordingly, the connectivity between the solid electrolytes can be improved, and the contact between the solid electrolyte and the cathode active material can be enhanced. An all-solid-state secondary battery using such a cathode can realize high energy density, high capacity, high efficiency, and excellent life characteristics. On the other hand, if the second positive electrode active material is not mixed, or if the second positive electrode active material is mixed in the form of secondary particles rather than single particles and has a smaller particle size than the first positive electrode active material, not only is the effect of improving the pellet density and energy density small, but due to its shape, pressure transmission is not easy during the manufacturing process of the all-solid-state battery, and accordingly, the permeability of the solid electrolyte is reduced, and the connectivity between the solid electrolyte and the contact between the solid electrolyte and the positive electrode active material may be reduced.

[0039] Conventionally, when coating boron on positive electrode active materials, it has been common to mix boron raw materials with lithium metal composite oxides, either wet or dry, and then heat-treat them. However, this method has the problem that boron acts as a resistor on the surface of the positive electrode active material, which actually worsens capacity and lifespan. In particular, when mixing two types of positive electrode active materials, coating each with boron before mixing them significantly reduces the density and initial discharge capacity of the positive electrode plates, significantly reducing the volumetric capacity and deteriorating lifespan characteristics.

[0040] On the other hand, according to one embodiment, a preliminary positive electrode active material having a first coating layer containing boron is obtained by adding a primary sintered product of a second positive electrode active material in the form of a single particle and a lithium raw material to a first positive electrode active material precursor in the form of a secondary particle, while simultaneously adding a boron raw material and performing heat treatment. Then, a positive electrode active material having a second coating layer containing lithium aluminate particles formed on the surface of the preliminary positive electrode active material is obtained by dry mixing lithium aluminate particles into the preliminary positive electrode active material. Through this, a first positive electrode active material having primary particles radially oriented is obtained, and at the same time, an appropriate amount of a first coating layer containing boron is stably formed on the surfaces of the first positive electrode active material and the second positive electrode active material, so that boron no longer acts as a resistor, the structural stability of the positive electrode active material is secured, and problems due to contact between the positive electrode active material and the electrolyte are suppressed, so that the capacity characteristics and long-term life characteristics of the battery can be improved. In addition, by forming a second coating layer containing lithium aluminate on the surface of the first coating layer, a thin and uniform coating layer can be formed on the outermost surface of the positive electrode active material, whereby the second coating layer containing lithium aluminate does not act as a resistor, and capacity characteristics and rate characteristics can be improved. In addition, a thin and uniform coating layer can be formed on the outermost surface of the positive electrode active material without additional heat treatment after the dry mixing, so that an additional process can be omitted, and thus the cost can be drastically reduced, and a positive electrode active material with good performance can be manufactured economically.

[0041] In addition, nickel-based cathode active materials can have a structural collapse due to the formation of NiO and other substances on the surface with repeated charge and discharge, which can cause cation mixing and gas generation or deterioration of life characteristics. In addition, repeated charge and discharge can cause the cathode active material to break, which can cause the connection between the cathode active material and the solid electrolyte to be broken, resulting in a decrease in battery capacity and deterioration of life characteristics. In addition, when the solid cathode active material and the solid electrolyte come into direct contact, the solid electrolyte can decompose and a space charge layer that hinders lithium movement can be formed, which can cause problems such as deterioration of capacity and life characteristics.

[0042] Accordingly, in one embodiment, by sequentially forming a first coating layer containing boron and a second coating layer containing lithium aluminate on the surfaces of a first positive electrode active material and a second positive electrode active material, an appropriate amount of a coating layer is uniformly formed on the surface of the positive electrode active material, thereby preventing the desorption of oxygen atoms from the surface of the positive electrode active material and suppressing structural collapse, thereby suppressing the cracking phenomenon due to repeated charge and discharge. In addition, the first coating layer and the second coating layer on the surface of the positive electrode active material can serve as a buffer layer (insulator, or protective layer) to suppress the decomposition phenomenon of the solid electrolyte and the formation of a space charge layer due to the contact between the positive electrode active material and the solid electrolyte, thereby improving the capacity characteristics and life characteristics of the battery.

[0043] In addition, by using a single particle type second cathode active material, the volume change of the cathode plate according to charge and discharge can be reduced, thereby minimizing short circuit of the cathode active material, solid electrolyte, and conductive material, thereby improving the life characteristics.

[0044] In addition, it is common to coat a buffer layer containing a non-conductive material such as LiNbO3 on the positive electrode active material for an all-solid-state secondary battery, but in one embodiment, the first coating layer containing boron and the second coating layer containing lithium aluminate on the surface of the positive electrode active material sufficiently function as a buffer layer, so there is no need to coat a separate buffer layer, which is advantageous in terms of process, economical, and practical.

[0045] First positive electrode active material

[0046] The first cathode active material includes a first lithium nickel-based composite oxide and a secondary particle formed by agglomerating a plurality of primary particles, a first coating layer located on the surface of the secondary particle and containing boron, and a second coating layer located on the first coating layer and containing lithium aluminate.

[0047] The first coating layer may contain boron, for example, a boron-containing compound. For example, the first coating layer may contain boron oxide, lithium borate, or a combination thereof, for example, B2O2, B2O3, B4O3, B4O5, LiBO2, Li3B7O 12 , Li6B4O9, Li3B 11 O 18 , Li2B4O7, Li3BO3, or a combination thereof.

[0048] The content of boron relative to the total content of elements excluding lithium and oxygen in the entire positive electrode active material may be 0.01 mol% to 0.5 mol%, for example, 0.01 mol% to 0.4 mol%, 0.01 mol% to 0.3 mol%, or 0.1 mol% to 0.3 mol%. In addition, the content of boron relative to the total content of elements excluding lithium and oxygen in the entire positive electrode active material may be 0.01 wt% to 0.5 wt%, for example, 0.01 wt% to 0.3 wt%, 0.01 wt% to 0.2 wt%, or 0.01 wt% to 0.1 wt%. The content of boron may be measured, for example, through ICP (Inductively Coupled Plasma) emission spectroscopy. When boron is coated with such a content, it does not act as a resistor and the battery capacity does not decrease, the diffusion of lithium ions into the positive electrode active material becomes easier, improving the initial charge / discharge efficiency, etc., and problems caused by repeated charge / discharge can be suppressed, thereby improving the long-life characteristics of the battery.

[0049] In one embodiment, the first coating layer containing boron may be present in the form of a continuous film on the surface of the first positive electrode active material and the surface of the second positive electrode active material, or may be present in the form of an island.

[0050] For example, in the first positive electrode active material, the average thickness of the first coating layer may be 1 nm to 500 nm, for example, 10 nm to 300 nm, 10 nm to 200 nm, 10 nm to 150 nm, or 10 nm to 100 nm. In this range, structural stability can be secured without the boron included in the first coating layer acting as a resistor, and excellent capacity characteristics and long-term life characteristics can be effectively secured.

[0051] In one embodiment, the first positive electrode active material may further include a boron-containing first coating layer located on the surface of the secondary particle, as well as a boron-doped layer located inside the primary particle exposed to the surface of the secondary particle. The boron-doped layer may be said to be located inside the secondary particle, and may be said to be located within a depth range of about 10 nm from the outer surface of the primary particle exposed to the surface of the secondary particle. If the outer surface of the primary particles exposed to the surface of the secondary particle is 0 nm, the doped layer may be said to exist in a depth range of 0 nm to 10 nm starting from the surface. In other words, the boron-doped layer may be said to be located within a depth range of 10 nm from the surface of the secondary particle. If the surface of the secondary particle is 0 nm, the doped layer may be said to exist in a depth range of 0 nm to 10 nm starting from the surface. This boron-doped layer can further improve the structural stability of the positive electrode active material, and thus can improve the life characteristics of the all-solid-state secondary battery. The boron-doped layer may be located, for example, within a depth range of 9 nm, within a depth range of 8 nm, within a depth range of 7 nm, within a depth range of 6 nm, within a depth range of 5 nm, within a depth range of 4 nm, within a depth range of 3 nm, or within a depth range of 2.5 nm from the outer surface of the primary particles exposed to the surface of the secondary particles. This boron-doped layer is distinct from the boron-containing first coating layer and also from the grain boundary boron coating portion described below, and is thought to contribute to the structural stability of the positive electrode active material.

[0052] In one embodiment, the boron-containing compound in the first positive electrode active material may exist not only on the surface of the secondary particle but also on the surface of the primary particles inside the secondary particle. That is, the boron-containing compound may be coated along the interface of the primary particles inside the secondary particle. Here, the inside of the secondary particle means the entire inside excluding the surface, for example, it may mean the entire inside from a depth of about 2 ㎛ from the outer surface, and it may also be expressed as a part that is not touched by distilled water when the positive electrode active material secondary particle is washed with distilled water. In this way, when the boron-containing compound is coated on the surface of the secondary particle and the internal grain boundary surface in the first positive electrode active material, boron does not act as a resistor and can effectively suppress the phenomenon of structural collapse or breakage of the positive electrode active material due to charge and discharge.

[0053] Here, the boron content present on the surface of the secondary particle may be higher than the boron content present at the internal grain boundary, and thus the boron content in the first coating layer of the first positive electrode active material may be greater than the boron content in the grain boundary boron coating portion. For example, the boron content in the first coating layer of the first positive electrode active material may be four times or more the boron content in the grain boundary boron coating portion, and for example, the ratio of the boron content in the first coating layer on the surface to the boron content in the grain boundary boron coating portion may be, by weight, 70:30 to 98:2, for example, 75:25 to 97:3, or 80:20 to 95:5. In this case, boron may play a role in improving performance without acting as a resistor in the positive electrode active material, and may simultaneously improve the capacity characteristics and life characteristics of the all-solid-state secondary battery.

[0054] The boron content in the first coating layer located on the surface of the secondary particle may be 0.02 wt% to 0.5 wt%, 0.03 wt% to 0.4 wt%, 0.04 wt% to 0.3 wt%, or 0.05 wt% to 0.2 wt%, etc., with respect to 100 wt% of the first positive electrode active material. The boron content in the grain boundary boron coating portion may be, for example, 0.001 wt% to 0.05 wt%, 0.001 wt% to 0.04 wt%, 0.002 wt% to 0.03 wt%, or 0.003 wt% to 0.02 wt%, but is not limited thereto. When the boron contents in the first coating layer and the grain boundary boron coating portion are as described above, both the capacity characteristics and the life characteristics of the all-solid-state secondary battery can be improved. Here, the boron content in the first coating layer may be measured through ICP emission spectroscopy analysis of the positive electrode active material, and the boron content in the grain boundary boron coating portion may be measured through ICP emission spectroscopy analysis, and may mean the difference between the boron content of the positive electrode active material before washing and the boron content after washing.

[0055] Additionally, in the first positive electrode active material, the second coating layer positioned on the first coating layer contains lithium aluminate. For example, the lithium aluminate may include LiAlO2, LiAl2O3, or a combination thereof.

[0056] For example, the first positive electrode active material may contain 0.5 at% to 10 at% of aluminum, for example, 1 at% to 9.5 at%, 3 at% to 9 at%, or 5 at% to 8 at%, relative to the total of 100 at% of nickel and aluminum.

[0057] For example, the first positive electrode active material may comprise 90 at% to 99.5 at% of the total 100 at% of nickel and aluminum, for example, 90.5 at% to 99 at%, 91 at% to 97 at%, or 92 at% to 95 at%.

[0058] In one embodiment, the second coating layer may be present in the form of a continuous film or in the form of an island on the surface of the first coating layer of the first positive electrode active material.

[0059] For example, in the first positive electrode active material, the average thickness of the second coating layer may be 1 nm to 500 nm, for example, 10 nm to 400 nm, 10 nm to 300 nm, 30 nm to 300 nm, 10 nm to 100 nm, or 50 nm to 100 nm. In this range, the second coating layer can be formed thinly and uniformly, and excellent capacity characteristics and rate characteristics can be effectively secured without lithium aluminate acting as a resistor.

[0060] In one embodiment, lithium aluminate may be present in the form of particles in the second coating layer of the first positive electrode active material, thereby reducing process costs and economically obtaining the positive electrode active material, while being advantageous in securing high capacity characteristics and long-term life characteristics.

[0061] For example, in the first positive electrode active material, the second coating layer may include lithium aluminate particles, and the average particle diameter (D) of the lithium aluminate particles 50 ) can be from 1 nm to 200 nm, for example, from 10 nm to 200 nm, from 30 nm to 150 nm, or from 50 nm to 100 nm. In this range, formation of a thin and uniform second coating layer becomes possible, thereby securing a high-performance positive electrode active material without the second coating layer acting as a resistor.

[0062] The first positive electrode active material may be included in an amount of 50 wt% to 90 wt% based on 100 wt% of the positive electrode active material, for example, 55 wt% or more, 60 wt% or more, or 65 wt% or more, and for example, 85 wt% or less, 80 wt% or less, or 75 wt% or less. In this range, the effects of improving capacity and charge / discharge efficiency by adding the first positive electrode active material together with the second positive electrode active material can be harmoniously achieved.

[0063] In one embodiment, the first positive electrode active material may include secondary particles in which at least two or more primary particles are aggregated, and the first positive electrode active material may be in the form of secondary particles in which at least a portion of the primary particles have a radial arrangement structure.

[0064] At least some of the above primary particles may have a plate shape. Fig. 1 is a schematic diagram showing the plate shape of the primary particles of the first positive electrode active material. Referring to Fig. 1, the primary particles according to one embodiment may have a basic plate structure but may also have various detailed shapes, such as (A) a polygonal nanoplate shape such as a hexagon, (B) a nanodisk shape, and (C) a rectangular parallelepiped shape. In Fig. 1, “a” refers to the length of the major axis of the primary particle, “b” refers to the length of the minor axis, and “t” refers to the thickness. Here, the major axis length (a) refers to the maximum length based on the widest surface of the primary particle. The thickness (t) may be said to be the maximum length of a surface that is approximately perpendicular to the widest surface of the primary particle. The direction in which the major axis length (a) and the minor axis length (b) are contained is defined as the surface direction, and the direction in which the thickness (t) is defined is defined as the thickness direction.

[0065] 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).

[0066] In the above positive electrode active material, at least some of the primary particles may have a radial array structure, for example, the long axes of the primary particles may be arranged in a radial direction. Fig. 2 is a drawing for explaining the definition of radial in secondary particles according to one embodiment. In one embodiment, the radial array structure means that the thickness (t) direction of the primary particles is arranged perpendicular to the direction (R) from the center of the secondary particles toward the surface, or forms an angle of ±5° with the perpendicular direction, as shown in Fig. 2.

[0067] The average length of the primary particles constituting the secondary particles may be 0.01 ㎛ to 5 ㎛, for example, 0.01 ㎛ to 2 ㎛, 0.01 ㎛ to 1 ㎛, 0.02 ㎛ to 1 ㎛, 0.05 ㎛ to 0.5 ㎛, or 150 nm to 500 nm. Here, the average length refers to the average length of the major axis length (a) in the plane direction when the primary particles are plate-shaped, and refers to the average particle diameter when the primary particles are spherical.

[0068] When the primary particles are plate-shaped, the average thickness of the primary particles may be, for example, 50 nm or more, 100 nm or more, 200 nm or more, 300 nm or more, 400 nm or more, 500 nm or more, 600 nm or more, 700 nm, 800 nm or more, or 900 nm or more, and may be, for example, 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, 1 μm or less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, or 500 nm or less, and may be, for example, 100 nm to 200 nm. For example, in the primary particles, the ratio of the average thickness to the average length may be 1:1 to 1:10, for example, 1:1 to 1:8, 1:1 to 1:6, or 1:2 to 1:5.

[0069] Here, the length and thickness, etc. may be measured by a scanning electron microscope or an optical microscope, and the average length may mean the arithmetic mean value of any 5 to 30 (for example, 5, 10, 20, or 30) length data, and the average thickness may mean the arithmetic mean value of any 5 to 30 (for example, 5, 10, 20, or 30) thickness data.

[0070] In this way, when the average length, average thickness, and the ratio of the average thickness to the average length of the primary particles satisfy the above-described ranges, and the primary particles are arranged radially, a relatively large number of lithium diffusion paths between grain boundaries can be provided on the surface, and a large number of crystal faces capable of lithium transfer are exposed to the outside, thereby improving lithium diffusion, thereby securing high initial efficiency and capacity. In addition, when the primary particles are arranged radially, the pores exposed on the surface can be oriented toward the center of the secondary particles, thereby promoting lithium diffusion. In addition, uniform shrinkage and expansion are possible during lithium desorption and / or insertion by the radially arranged primary particles, and the pores exist in the (001) direction, which is the direction in which the particles expand during lithium desorption, so that a buffering effect can be provided. In addition, the size and arrangement of the primary particles can reduce the probability of cracks occurring during shrinkage and expansion of the active material, and the internal pores can further alleviate volume changes, thereby reducing cracks occurring between the primary particles during charge and discharge, thereby improving the life characteristics of the all-solid-state secondary battery and reducing the phenomenon of resistance increase.

[0071] The first positive electrode active material may have an irregular porous structure in at least one of the inside and the outside of the secondary particle. The irregular porous structure refers to a structure having primary particles and pores, but the pore size, shape, location, etc. are not regular. For example, the secondary particle may have an inside including an irregular porous structure and an outside including a radially arranged structure as a region surrounding the inside. That is, the primary particles arranged inside may be arranged without regularity, unlike the primary particles arranged outside. The radially arranged structure refers to at least some of the primary particles being arranged radially.

[0072] Here, the term "outside" may mean a region of 30% to 50% in length from the outermost surface, for example, 40% in length from the outermost surface, among the total distance from the center of the secondary particle to the surface, or may mean a region from the outermost edge of the secondary particle to a depth of about 3 ㎛. In addition, the term "inside" may mean a region of 50% to 70% in length from the center, for example, 60% in length from the center, among the total distance from the center of the secondary particle to the surface, or may mean a remaining region excluding a region from the outermost edge of the secondary particle to a depth of about 3 ㎛.

[0073] The secondary particles of the first positive electrode active material may include an exterior oriented in a radial structure and an interior having an irregular porous structure, wherein the interior of the secondary particles may include pores larger in size than the pores present on the exterior. For example, the size of the pores present on the interior of the first positive electrode active material may be 150 nm to 1 μm, and the size of the pores present on the exterior may be less than 150 nm. In this case, when the interior pore size is larger than the exterior pore size, compared to secondary particles having the same interior and exterior pore sizes, there is an advantage in that the lithium diffusion distance within the active material is shortened, lithium insertion from the exterior is facilitated, and volume changes occurring during charge and discharge are alleviated. Here, the pore size may refer to the diameter when the pore is spherical or circular, and may refer to the length of the major axis when the pore is elliptical, etc., and may be measured using a microscope such as a scanning electron microscope.

[0074] The secondary particles of the first positive electrode active material may have open pores on their surfaces. The size of the open pores may be less than about 150 nm, for example, 10 nm to 148 nm. The open pores are pores in which a portion of the pore walls is not closed, and are formed by spaces between radially arranged plate-shaped primary particles, and refer to pores that are deeply connected from the surface of the secondary particles toward the center. These open pores may be connected to the outside and serve as passages through which substances can pass. The open pores may be formed to a depth of, on average, 150 nm or less, for example, 0.001 nm to 100 nm, for example, 1 nm to 50 nm from the surface of the secondary particles. 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.

[0075] The secondary particles described above may have closed pores within them, and closed and / or open pores outside them. While the closed pores are unlikely to contain electrolytes, the open pores can contain electrolytes within them. The closed pores are formed with a structure in which all of their walls are closed, and thus can be considered independent pores that are not connected to other pores.

[0076] Fig. 3 is a schematic diagram showing the cross-sectional structure of the secondary particles of the first positive electrode active material. Referring to Fig. 3, the secondary particles (11) of the first positive electrode active material according to one embodiment may contain an outer portion (14) having a structure in which primary particles (13) having a plate shape are arranged in a radial direction, and an inner portion (12) in which the primary particles (13) are arranged irregularly. In the inner portion (12), more empty spaces may exist between the primary particles than in the outer portion. In addition, the pore size and porosity in the inner portion may be larger and irregular than those in the outer portion. In Fig. 3, arrows indicate the direction of movement of lithium ions.

[0077] 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, so that the stress due to the volume change during charge and discharge can be minimized. Such a positive electrode active material can reduce the resistance of an all-solid-state secondary battery and improve the capacity and life characteristics.

[0078] Meanwhile, in the secondary particle, a plurality of primary particles may be arranged toward one (1) center to form surface contact along the thickness direction of the primary particle, thereby forming a radial array structure. Alternatively, the secondary particle may have a multi-center radial array structure having multiple centers. In this way, when the secondary particle has a single-center or multi-center radial array structure, lithium is easily inserted / de-inserted to the center of the secondary particle.

[0079] The above secondary particles may include radial primary particles and non-radial primary particles. The content of the non-radial primary particles may be 40 wt% or less, for example, 0.01 wt% to 30 wt%, specifically 0.1 wt% to 20 wt%, based on 100 wt% of the total weight of the radial primary particles and the non-radial primary particles. When the secondary particles include non-radial primary particles in the above-described content range in addition to the radial primary particles, an all-solid-state secondary battery with improved lifespan characteristics can be manufactured because lithium diffusion is facilitated.

[0080] The average particle diameter of the first positive electrode active material (D 50 ) may be 5 ㎛ to 25 ㎛, for example, 8 ㎛ to 20 ㎛, or 10 ㎛ to 18 ㎛, etc. When this is satisfied, the positive electrode active material can increase the capacity of the all-solid-state secondary battery and further increase the pellet density and energy density. The average particle diameter of the first positive electrode active material is obtained by measuring the particle size in a scanning electron microscope image to obtain a particle size distribution, for example, where D 50 It may be calculated. In the positive electrode of an all-solid-state battery, the size, size ratio, shape, etc. of each particle of the second positive electrode active material, solid electrolyte, etc., including the first positive electrode active material, act as important factors, and the performance of the all-solid-state battery can be maximized by appropriately controlling the average particle diameter, etc.

[0081] Second positive electrode active material

[0082] The second positive electrode active material includes a second lithium nickel-based composite oxide and is in the form of a single particle. Here, the single particle form means a monolithic structure, which exists alone without grain boundaries within the particle and is composed of a single particle, and a structure in which particles exist as independent phases without being mutually aggregated in terms of morphology, and may mean a single particle (single grian), a single-body structure, or a non-aggregated particle. The positive electrode active material according to one embodiment can exhibit improved life characteristics while implementing high capacity and high energy density by including the second positive electrode active material.

[0083] The shape of the second positive electrode active material is not particularly limited, and may have various shapes such as polyhedral, spherical, oval, plate-shaped, rod-shaped, and irregular.

[0084] The second cathode active material has an average particle diameter (D) of the first cathode active material. 50 ) smaller than the average particle diameter (D 50 ) has. During the manufacturing process of an all-solid-state secondary battery, when applying pressure to an electrode assembly, by using a second positive electrode active material having an average particle diameter smaller than that of the first positive electrode active material, pressure transmission is facilitated, thereby minimizing empty space between components existing in the positive electrode, and the solid electrolyte can effectively penetrate between the positive electrode active materials. Accordingly, the connectivity between the solid electrolytes can be improved, and the contact between the solid electrolyte and the positive electrode active material can be improved, thereby improving the energy density, and thereby securing high-capacity and high-efficiency characteristics, and excellent life characteristics.

[0085] For example, the average particle diameter (D) of the second positive electrode active material 50) may be 0.05 μm to 8 μm, for example, 0.1 μm to 7 μm, 0.1 μm to 6 μm, 0.1 μm to 5 μm, or 1 μm to 4 μm. In this case, the pellet density and energy density of the positive electrode active material can be further increased. The average particle diameter of the second positive electrode active material is obtained by measuring the particle size in a scanning electron microscope image to obtain a particle size distribution, and here, D 50 It may have been calculated.

[0086] The second positive electrode active material includes a first coating layer containing boron on the surface of the single particle. For example, the first coating layer may include a boron-containing compound, and the boron-containing compound may include, for example, boron oxide, lithium borate, or a combination thereof, and may include, for example, B2O2, B2O3, B4O3, B4O5, LiBO2, Li2B4O7, Li3BO3, or a combination thereof. In the single particle form, lithium is difficult to diffuse into the particle, but by forming the first coating layer containing boron on the surface, the formation of a space charge layer is suppressed, thereby facilitating lithium diffusion, and reaction with a solid electrolyte is suppressed, thereby improving life characteristics.

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

[0088] For example, in the second positive electrode active material, the average thickness of the first coating layer may be 1 nm to 500 nm, for example, 10 nm to 300 nm, 10 nm to 200 nm, 10 nm to 150 nm, or 10 nm to 100 nm. In this range, structural stability can be secured without the boron included in the first coating layer acting as a resistor, and excellent capacity characteristics and long-term life characteristics can be effectively secured.

[0089] For example, the average thickness of the first coating layer in the second positive electrode active material may be less than the average thickness of the first coating layer in the first positive electrode active material.

[0090] The content of boron relative to the total content of elements excluding lithium and oxygen in the entire positive electrode active material including the first positive electrode active material and the second positive electrode active material may be 0.01 mol% to 0.5 mol%, for example, 0.01 mol% to 0.4 mol%, 0.01 mol% to 0.3 mol%, or 0.1 mol% to 0.3 mol%, or 0.01 wt% to 0.5 wt%, 0.01 wt% to 0.3 wt%, 0.01 wt% to 0.2 wt%, or 0.01 wt% to 0.1 wt%. In this range, the first coating layer can maximize the effect of improving the life characteristics by facilitating the diffusion of lithium and suppressing the reaction with the solid electrolyte. On the other hand, if the boron content becomes excessive, friction between particles may increase, which may deteriorate the density of the positive electrode plate.

[0091] Additionally, the second positive electrode active material comprises a second coating layer positioned on the first coating layer and containing lithium aluminate. For example, the lithium aluminate may include LiAlO2, LiAl2O3, or a combination thereof.

[0092] For example, the second positive electrode active material may contain 0.5 at% to 10 at% of aluminum, for example, 1 at% to 9.5 at%, 3 at% to 9 at%, or 5 at% to 8 at%, relative to the total of 100 at% of nickel and aluminum.

[0093] For example, the second positive electrode active material may comprise 90 at% to 99.5 at% of the total 100 at% of nickel and aluminum, for example, 90.5 at% to 99 at%, 91 at% to 97 at%, or 92 at% to 95 at%.

[0094] In one embodiment, the second coating layer may be present in the form of a continuous film or in the form of an island on the surface of the first coating layer of the second positive electrode active material.

[0095] For example, in the second positive electrode active material, the average thickness of the second coating layer may be 1 nm to 500 nm, for example, 10 nm to 400 nm, 10 nm to 300 nm, 30 nm to 300 nm, 10 nm to 100 nm, or 50 nm to 100 nm. In this range, the second coating layer can be formed thinly and uniformly, and excellent capacity characteristics and rate characteristics can be effectively secured without lithium aluminate acting as a resistor.

[0096] For example, the average thickness of the second coating layer in the second positive electrode active material may be equal to or less than the average thickness of the second coating layer in the first positive electrode active material.

[0097] In one embodiment, lithium aluminate in the second coating layer of the second positive electrode active material may be present in the form of particles, thereby reducing process costs and economically obtaining the positive electrode active material, while being advantageous in securing high capacity characteristics and long-life characteristics.

[0098] For example, in the second positive electrode active material, the second coating layer may include lithium aluminate particles, and the average particle diameter (D) of the lithium aluminate particles 50 ) can be from 1 nm to 200 nm, for example, from 10 nm to 200 nm, from 30 nm to 150 nm, or from 50 nm to 100 nm. In this range, formation of a thin and uniform second coating layer becomes possible, thereby securing a high-performance positive electrode active material without the second coating layer acting as a resistor.

[0099] The second positive electrode active material may be included in an amount of 10 wt% to 50 wt% based on 100 wt% of the positive electrode active material, for example, 15 wt% or more, 20 wt% or more, or 25 wt% or more, and for example, 45 wt% or less, 40 wt% or less, or 35 wt% or less. In this range, the effects of securing high capacity and high energy density by adding the second positive electrode active material together with the first positive electrode active material can be harmoniously achieved.

[0100] In one embodiment, the lithium aluminate may be included in an amount of 0.01 wt% to 3 wt%, based on 100 wt% of the total weight of the positive electrode active material, for example, 0.01 wt% to 1.0 wt%, 0.05 wt% to 0.5 wt%, 0.1 wt% to 0.5 wt%, or 0.25 wt% to 0.5 wt%.

[0101] The first lithium nickel-based composite oxide and the second lithium nickel-based composite oxide may be the same or different.

[0102] In the lithium nickel-based composite oxide, the content of nickel may be 30 mol% or more, for example, 40 mol% or more, 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more, or 90 mol% or more, and 99.9 mol% or less, or 99 mol% or less, based on the total amount of elements excluding lithium and oxygen. For example, the content of nickel in the lithium nickel-based composite oxide may be higher than the content of each of other metals such as cobalt, manganese, and aluminum. When the content of nickel satisfies the above range, the positive electrode active material may exhibit excellent battery performance while implementing a high capacity.

[0103] The first lithium nickel-based composite oxide and the second lithium nickel-based composite oxide can each be independently represented by the following chemical formula 1.

[0104] [Chemical Formula 1]

[0105] Li a1 Ni x1 M 1 y1 M 2 1-x1-y1 O 2-z X z

[0106] In the above chemical formula 1, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7 and 0≤z≤0.1, and M 1 and M 2 are each independently Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, Zn, Zr or a combination thereof, and X is F, P, S or a combination thereof.

[0107] In the above chemical formula 1, 0.4≤x1≤1 and 0≤y1≤0.6 may be, 0.5≤x1≤1 and 0≤y1≤0.5, 0.6≤x1≤1 and 0≤y1≤0.4, 0.7≤x1≤1 and 0≤y1≤0.3, 0.8≤x1≤1 and 0≤y1≤0.2, or 0.9≤x1≤1 and 0≤y1≤0.1.

[0108] The first lithium nickel-based composite oxide and the second lithium nickel-based composite oxide may each be independently represented, for example, by the following chemical formula 2.

[0109] [Chemical Formula 2]

[0110] Li a2 Ni x2 Co y2 M 3 1-x2-y2 O 2-z X z

[0111] In the above chemical formula 2, 0.9≤a2≤1.8, 0.3≤x2<1, 0 <y2≤0.7 및 0≤z≤0.1이고 M 3is Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, Zn, Zr or a combination thereof, and X is F, P, S or a combination thereof.

[0112] In the above chemical formula 2, 0.3≤x2≤0.99 and 0.01≤y2≤0.7 may be satisfied, 0.4≤x2≤0.99 and 0.01≤y2≤0.6 may be satisfied, 0.5≤x2≤0.99 and 0.01≤y2≤0.5 may be satisfied, 0.6≤x2≤0.99 and 0.01≤y2≤0.4 may be satisfied, 0.7≤x2≤0.99 and 0.01≤y2≤0.3 may be satisfied, 0.8≤x2≤0.99 and 0.01≤y2≤0.2 may be satisfied, or 0.9≤x2≤0.99 and 0.01≤y2≤0.1 may be satisfied.

[0113] The first lithium nickel-based composite oxide and the second lithium nickel-based composite oxide may each be independently represented, for example, by the following chemical formula 3.

[0114] [Chemical Formula 3]

[0115] Li a3 Ni x3 Co y3 M 4 z3 M 5 1-x3-y3-z3O 2-z X z

[0116] In the above chemical formula 3, 0.9≤a3≤1.8, 0.3≤x3≤0.98, 0.01≤y3≤0.69, 0.01≤z3≤0.69, and 0≤z≤0.1, and M 4 is Al, Mn or a combination thereof, and M 5 is B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sr, Ti, V, W, Zn, Zr or a combination thereof, and X is F, P, S or a combination thereof.

[0117] In the above chemical formula 3, 0.4≤x3≤0.98, 0.01≤y3≤0.59, and 0.01≤z3≤0.59, or 0.5≤x3≤0.98, 0.01≤y3≤0.49, and 0.01≤z3≤0.49, or 0.6≤x3≤0.98, 0.01≤y3≤0.39, and 0.01≤z3≤0.39, or 0.7≤x3≤0.98, 0.01≤y3≤0.29, and 0.01≤z3≤0.29, or 0.8≤x3≤0.98, 0.01≤y3≤0.19, and 0.01≤z3≤0.19, or 0.9≤x3≤0.98, 0.01≤y3≤0.09, and 0.01≤z3≤0.09.

[0118] In general, as the nickel content in the positive electrode active material increases, the Ni 2+ The mixing of cations occupying the lithium site may increase, which may actually reduce the capacity, or the diffusion of lithium ions may be hindered by impurities such as NiO, which may reduce the battery life. In addition, structural collapse or cracks in the positive electrode active material due to charge and discharge may increase side reactions with the electrolyte, which may reduce the battery life. In addition, the use of solid electrolytes may form a depletion layer due to the bonding of solids and the reaction of the sulfide-based solid electrolyte and the positive electrode active material, which may decompose the solid electrolyte, which may cause problems with the life characteristics and safety of the all-solid-state battery. To solve these problems, in the past, various additional elements were doped into the positive electrode active material, or zirconium (Zr), niobium (Nb), etc. were made into an ion in a separate organic solvent to suppress the reaction with the solid electrolyte and the formation of the depletion layer, and this was coated as a buffer layer on the surface of the positive electrode active material. However, this method is difficult to control the coating thickness and mass production, and there may be cost and environmental issues.

[0119] On the other hand, according to an embodiment of the present invention, even if a high-nickel type cathode active material is used, the first cathode active material and the second cathode active material are simultaneously coated with appropriate amounts of boron and lithium aluminate, thereby improving problems occurring between the cathode active material and the solid electrolyte without a separate buffer layer coating, and simultaneously implementing high capacity without deteriorating the initial discharge capacity, and improving the life characteristics.

[0120] According to one embodiment, a cathode active material for an all-solid-state secondary battery can realize high plate density and specific capacity, thereby increasing the energy density of the battery. The plate density of the cathode active material for the all-solid-state secondary battery may be, for example, 3.5 g / cc or more, or 3.6 g / cc to 3.7 g / cc. In addition, the specific capacity of the cathode active material for the all-solid-state secondary battery may be 190 mAh / g or more. An all-solid-state secondary battery using such a cathode active material can exhibit high energy density.

[0121] Method for manufacturing positive electrode active material

[0122] In one embodiment, (i) a first cathode active material precursor in the form of secondary particles comprising a first nickel-based composite hydroxide and formed by agglomeration of a plurality of primary particles, and a second lithium nickel-based composite oxide in the form of single particles and having an average particle diameter (D) smaller than that of the first cathode active material precursor. 50 ) and heat-treating a first sintered product of a second positive electrode active material, a lithium raw material, and a boron raw material to obtain a preliminary positive electrode active material having a first coating layer containing boron formed thereon, and (ii) dry-mixing the preliminary positive electrode active material and lithium aluminate particles to obtain a final positive electrode active material having a second coating layer containing lithium aluminate formed on the surface of the preliminary positive electrode active material.

[0123] The above-described positive electrode active material can be manufactured in the same manner. Through the heat treatment process, the first positive electrode active material precursor and the lithium raw material react to manufacture a first lithium nickel-based composite oxide, and at the same time, a first coating layer containing boron is formed on the surface thereof. In addition, a first coating layer containing boron is formed on the surface of a first sintered product of the second positive electrode active material in the form of a single particle. Subsequently, through a subsequent dry mixing process with lithium aluminate particles, a final positive electrode active material is obtained in which an aluminate-containing second coating layer is formed on the outermost surfaces of both the first positive electrode active material and the second positive electrode active material.

[0124] According to an embodiment, a method for manufacturing a positive electrode active material is not a method of manufacturing a first lithium nickel-based composite oxide and a second lithium nickel-based composite oxide separately, performing a boron coating on them separately, and then mixing them to perform a lithium aluminate coating, but a method of mixing, for example, a precursor of a first positive electrode active material, a first sintered product of a second positive electrode active material, a lithium raw material, and a boron raw material, sintering them simultaneously, and then performing a lithium aluminate coating. In this method, not only is the manufacturing method simple and efficient, but the density and initial discharge capacity of the final positive electrode plate are improved, so that the capacity per volume of the battery is significantly improved, and both the initial charge / discharge capacity and the life characteristics of the battery can be improved.

[0125] Previously, when coating a positive electrode active material with boron, a common method was to mix a lithium source material with a nickel-based composite hydroxide, heat-treat it, and then produce a lithium-nickel-based composite oxide. Then, the boron source material was mixed into the resulting composite oxide, either wet or dry, and heat-treated again. However, this method presented problems: the boron attached to the surface of the positive electrode active material acted as resistance, increasing friction between components in the positive electrode of an all-solid-state battery, reducing the positive electrode plate density and hindering the connection for ion and electron transfer.

[0126] In addition, when only one of the first positive electrode active material and the second positive electrode active material is mixed after being subjected to boron coating, or when the first positive electrode active material and the second positive electrode active material are each subjected to boron coating separately and then mixed to manufacture the positive electrode active material, there are problems in that the density and energy density of the electrode plate are lower, the initial discharge capacity is lower, and the initial charge / discharge efficiency and life characteristics are inferior compared to the positive electrode active material manufactured according to one embodiment. On the other hand, the positive electrode active material manufactured according to one embodiment has a high initial charge / discharge capacity, excellent life characteristics, and a high density of the electrode plate, so that the capacity per volume is significantly increased.

[0127] In the above manufacturing method, the first positive electrode active material precursor may be in the form of a secondary particle formed by agglomeration of a plurality of primary particles, and for example, may be in the form of a secondary particle in which at least a portion of the primary particles are radially arranged, and may be manufactured by a co-precipitation method or the like.

[0128] In one embodiment, a composite metal raw material is prepared by mixing a nickel raw material and optionally a metal raw material other than nickel, 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 first nickel-based composite hydroxide having a desired composition. The coprecipitation reaction may be performed in several stages, for example, in two, three, or four stages. In each stage, the concentration of the complexing agent, the rate at which the composite metal raw material is added, the pH adjustment range, the reaction temperature, the reaction time, the stirring power, etc. may be adjusted differently. Through such adjustment, a first nickel-based composite hydroxide in the form of secondary particles in which at least a portion of the primary particles are radially arranged can be produced, and further, secondary particles having different internal and external shapes can be produced.

[0129] The first nickel-based composite hydroxide can be represented, for example, by the following chemical formula 11.

[0130] [Chemical Formula 11]

[0131] Ni x11 M 11 y11 M 12 1-x11-y11 (OH)2

[0132] In the above chemical formula 11, 0.3≤x11≤1, 0≤y11≤0.7, and M 11 and M 12 are each independently Al, B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zn, Zr or a combination thereof.

[0133] As a specific example, the first nickel-based composite hydroxide may be represented by the following chemical formula 12 or chemical formula 13.

[0134] [Chemical Formula 12]

[0135] Ni x12 Co y12 M 13 1-x12-y12 (OH)2

[0136] In the above chemical formula 12, 0.3≤x12<1, 0 <y12≤0.7이고 M 13 is Al, B, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zn, Zr or a combination thereof.

[0137] [Chemical Formula 13]

[0138] Ni x13 Co y13 M 14 z13 M 15 1-x13-y13-z13(OH)2

[0139] In the above chemical formula 13, 0.3≤x13≤0.98, 0.01≤y13≤0.69, 0.01≤z13≤0.69, and M 14 is Al, Mn or a combination thereof, and M 15is B, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zn, Zr or a combination thereof.

[0140] The average particle diameter (D) of the first nickel-based composite hydroxide 50 ) may be, for example, 5 μm to 25 μm, or 10 μm to 20 μm. This may be measured by a particle size analyzer using laser diffraction.

[0141] The description of the radial array structure in the first nickel-based composite hydroxide is the same as described above. For example, the secondary particles of the first nickel-based composite hydroxide may include an interior having an irregular porous structure and an exterior having a radial array structure as a region surrounding the interior. The interior of the secondary particles has a porous structure, which has the effect of reducing the diffusion distance of lithium ions to the interior, and the exterior has the advantage of being able to produce a first nickel-based composite oxide in which lithium ions can be easily inserted and deintercalated because the primary particles are arranged radially.

[0142] In the first nickel-based composite hydroxide, at least some of the primary particles may have a plate shape. In this case, the secondary particles may have a radial arrangement structure in which the long axes of the plate-shaped primary particles are directed toward the surfaces of the secondary particles.

[0143] The second lithium nickel-based composite oxide in the form of single particles may be manufactured by mixing the second nickel-based composite hydroxide and a lithium raw material, heat-treating the mixture, and then optionally performing a process such as pulverization. Here, the heat treatment may be performed, for example, at 800°C to 1100°C, or 800°C to 1000°C, for about 1 to 25 hours or about 5 to 20 hours in an oxidizing gas atmosphere. The pulverization is performed to obtain a single particle form, is distinct from crushing, and may be performed using a device such as a jet mill. The second nickel-based composite hydroxide is the same as or different from the first nickel-based composite hydroxide described above, and may be represented by Chemical Formula 11, Chemical Formula 12, or Chemical Formula 13.

[0144] The second lithium nickel-based composite oxide may be represented by the aforementioned chemical formula 1, chemical formula 2, or chemical formula 3. The average particle diameter of the second lithium nickel-based composite oxide may be from 0.05 μm to 8 μm, for example, from 0.5 μm to 5 μm.

[0145] For example, the mixing ratio of the first nickel-based composite hydroxide and the second lithium nickel-based composite oxide may be 5:5 to 9:1 by weight, for example, 6:4 to 9:1, 6:4 to 8:2, or 7:3 to 9:1. In this case, a cathode active material having high pellet density and energy density, high capacity, and excellent life characteristics can be manufactured.

[0146] The lithium source may include, for example, Li2CO3, LiOH, LiF, a hydrate thereof, or a combination thereof. For example, the lithium source may be mixed in an amount of 0.9 molar parts to 1.1 molar parts, or 0.9 molar parts to 1.05 molar parts, or 0.95 molar parts to 1.05 molar parts, based on 1 mol of the total content of elements excluding oxygen and hydrogen in the first nickel-based composite hydroxide.

[0147] The above boron raw material is a compound containing boron, for example, H3BO3, HBO2, B2O3, C6H5B(OH)2, (C6H5O)3B, [CH3(CH2)3O]3B, (C3H7O)3B, C3H9B3O6, C 13 H 19 BO3, or a combination thereof.

[0148] The above boron raw material can be mixed in an amount of 0.01 to 0.5 mol parts based on 100 mol parts of the total amount of elements excluding lithium, oxygen, and hydrogen in the first nickel-based composite hydroxide and the second lithium nickel-based composite oxide, for example, 0.01 to 3 mol parts, or 0.1 to 0.3 mol parts. When the content of the boron raw material satisfies the above range, a preliminary positive electrode active material in which a first coating layer is formed so that boron does not act as a resistor can be obtained, and can play a role in improving the performance of an all-solid-state secondary battery, thereby improving the capacity and life characteristics. When the content of the boron raw material becomes excessive, boron can act as a resistor in the positive electrode active material, thereby reducing the capacity and life characteristics of the battery.

[0149] In the above manufacturing method, the heat treatment can be performed at a temperature of, for example, 650°C to 850°C, or 690°C to 780°C. In addition, the heat treatment can be performed for 5 to 25 hours, for example, 5 to 20 hours. Within this range, a preliminary positive electrode active material in which a first coating layer containing boron is formed safely can be effectively obtained, thereby producing a positive electrode active material with high capacity and high energy density.

[0150] In the conventional coating method of boron coating, which involves mixing a lithium nickel-based composite oxide and a boron raw material and heat-treating them, heat treatment was generally performed at a much lower temperature, for example, below 500°C. However, one embodiment is distinguished by heat treatment at a higher temperature, such as 650°C to 850°C. By heat-treating in this temperature range, a first lithium nickel-based composite oxide in the form of secondary particles with a radial structure can be obtained, while a first coating layer containing boron can be stably formed. In addition, at the same time, a first coating layer containing boron can be formed on the surface of the second lithium nickel-based composite oxide in the form of a single particle, thereby effectively obtaining a preliminary positive electrode active material. Accordingly, the final positive electrode active material can simultaneously improve initial discharge capacity, initial efficiency, and life characteristics without the resistance-increasing effect caused by boron, and the density of the positive electrode plate using the same can be increased, thereby improving the capacity per volume of the battery.

[0151] In one embodiment, the heat treatment includes a temperature raising step and a temperature holding step, and the temperature raising time may be set longer than the temperature holding time. For example, the temperature raising time may be 6 to 16 hours and the temperature holding time may be 1 to 9 hours, and the temperature raising time may be longer than the temperature holding time.

[0152] In the above heat treatment, the temperature elevation time may be, for example, 6 hours to 16 hours, 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 1 hour to 9 hours, 2 hours to 9 hours, or 3 hours to 8 hours.

[0153] For example, the ratio of the heating time to the temperature holding time (heating time: temperature holding time) may be from 1.1:1 to 10:1, for example from 1.1:1 to 8:1, from 1.1:1 to 6:1, from 1.1:1 to 5:1, or from 1.1:1 to 4:1.

[0154] By controlling the heat treatment profile in this way, a first positive electrode active material in the form of a high-efficiency radial secondary particle can be effectively manufactured, and a preliminary positive electrode active material in which a first coating layer containing an appropriate amount of boron is stably formed on the first positive electrode active material and the second positive electrode active material can be obtained.

[0155] Next, the preliminary positive electrode active material and lithium aluminate particles are dry mixed. Through this process, a final positive electrode active material is obtained in which a second coating layer containing lithium aluminate is formed on the surface of the preliminary positive electrode active material. In this case, the manufacturing method according to one embodiment may not perform additional heat treatment after the dry mixing.

[0156] In the past, an additional heat treatment process was essential when forming a coating layer containing aluminum. However, in a manufacturing method according to one embodiment, a first coating layer is formed on each surface of a secondary particle and a single particle through the unique boron coating process described above, and then a second coating layer containing lithium aluminate is formed, thereby enabling a thin and uniform lithium aluminate coating to be performed even without an additional heat treatment process. As a result, compared to the conventional technology in which a heat treatment process was essential, a cost can be reduced, and a high-performance positive electrode active material can be manufactured economically.

[0157] For example, the average particle diameter (D) of the lithium aluminate particles 50) can be 1 nm to 200 nm, for example, 10 nm to 200 nm, 30 nm to 150 nm, or 50 nm to 100 nm. In this range, a second coating layer can be formed stably, thinly, and uniformly, and a high-performance positive electrode active material can be manufactured so that the second coating layer does not act as a resistor.

[0158] In one embodiment, the lithium aluminate particles may be added in an amount of 0.01 wt% to 3 wt% relative to 100 wt% of the total positive electrode active material, for example, 0.01 wt% to 1.0 wt%, 0.05 wt% to 0.5 wt%, 0.1 wt% to 0.5 wt%, or 0.25 wt% to 0.5 wt%.

[0159] Cathode for all-solid-state batteries

[0160] A positive electrode for an all-solid-state secondary battery may include a positive electrode current collector and a positive electrode active material layer positioned on the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material and a solid electrolyte, and may further include a binder and / or a conductive material.

[0161] solid electrolyte

[0162] The above solid electrolyte may be an inorganic solid electrolyte such as a sulfide-based solid electrolyte or an oxide-based solid electrolyte, or a solid polymer electrolyte.

[0163] In one embodiment, the solid electrolyte may be a sulfide-based solid electrolyte having excellent ion conductivity. The sulfide-based solid electrolyte may be, for example, Li3PS4, Li7P3S. 11, Li7PS6, Li2S-P2S5, Li2S-P2S5-LiX (X is a halogen element, for example, I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m and n are integers, respectively, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are each integers, and M is P, Si, Ge, B, Al, Ga, or In).

[0164] The above sulfide-based solid electrolyte may be obtained, for example, by mixing Li2S and P2S5 in a molar ratio of 50:50 to 90:10, or a molar ratio of 50:50 to 80:20. 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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] The above argyrodite-type sulfide may include, for example, a compound represented by the chemical formula 21 below.

[0169] [Chemical Formula 21]

[0170] (Li a M 1 b M 2 c )(P d M 3 e )(Sf M 4 g )X h

[0171] 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≤2이다.

[0172] For example, in chemical formula 21, 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.

[0173] For example, in chemical formula 21, a+b+c+h=7, d+e=1, and f+g+h=6.

[0174] As a specific example, argyrodite-type sulfides include Li6PS5Cl, Li6PS5Br, Li 5.8 PS 4.8 Cl 1.2 , Li 6.2 PS 5.2 Br0.8 , 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.

[0175] Argyrodite-type sulfides can be produced, for example, by mixing lithium sulfide and phosphorus sulfide, optionally with a lithium halide. These can be mixed and then heat-treated. The heat-treatment can include, for example, two or more heat-treatment steps. Here, producing an argyrodite-type sulfide-based solid electrolyte can include, for example, a first heat-treatment step of mixing raw materials and calcining at 120°C to 350°C, and a second heat-treatment step of mixing the resultant of the first heat-treatment step again and calcining at 350°C to 800°C.

[0176] The above sulfide-based solid electrolyte may be amorphous or crystalline, or may be a mixture of the two.

[0177] The above solid electrolyte may include, in addition to a sulfide-based material, an oxide-based inorganic solid electrolyte, a halide-based solid electrolyte, etc. The above oxide-based inorganic solid electrolyte may include, for example, Li 1+x Ti 2-x Al(PO4)3(LTAP)(0≤x≤4), Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 <x<2, 0≤y<3), BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT)(0≤x<1, 0≤y<1), Pb(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 <x<2, 0<y<3), Li 1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0≤x≤1, 0≤y≤1), lithium lanthanum titanate (Li x La y TiO3, 0 <x<2, 0<y<3), Li2O, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2계 세라믹스, 가넷(Garnet)계 세라믹스 Li 3+x La3M2O 12 (M= Te, Nb, or Zr, x is an integer from 1 to 10), or a mixture thereof.

[0178] 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.

[0179] 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.

[0180] The above solid electrolyte may be in the form of solid electrolyte particles, and the average particle diameter (D) of the particles 50 ) may be 5.0 ㎛ or less, for example, 0.5 ㎛ to 5.0 ㎛. Such a solid electrolyte can effectively penetrate between positive electrode active materials, and has excellent contact with the positive electrode active material and connectivity between solid electrolyte particles. The average particle diameter of the solid electrolyte may be measured from a microscope image, for example, a particle size distribution is obtained by measuring the size of particles in a scanning electron microscope image, where D 50 It may have been calculated.

[0181] For example, the solid electrolyte (e.g., the first solid electrolyte) included in the above anode may have the same composition as the solid electrolyte (e.g., the second solid electrolyte) included in the solid electrolyte layer described below.

[0182] For example, both the solid electrolyte included in the anode (e.g., the first solid electrolyte) and the solid electrolyte included in the solid electrolyte layer described below (e.g., the second solid electrolyte) may include an argyrodite-type sulfide, or both may be argyrodite-type sulfides.

[0183] For example, the average particle diameter (D) of the solid electrolyte (e.g., the first solid electrolyte) included in the above anode 50 ), and the average particle diameter (D) of the solid electrolyte (e.g., the second solid electrolyte) included in the solid electrolyte layer described below 50 ) may be the same or different from each other, and may each independently be 0.5 μm to 5.0 μm.

[0184] For example, the average particle diameter (D) of the solid electrolyte (e.g., the first solid electrolyte) included in the above anode 50 ) is the average particle diameter (D) of the solid electrolyte (e.g., the second solid electrolyte) included in the solid electrolyte layer described below. 50) may be smaller than. By reducing the average particle size of the solid electrolyte included in the positive electrode, the space between the positive electrode active material particles included in the positive electrode active material layer can be densely filled with the fine particles of the first solid electrolyte, thereby increasing the interfacial contact area and reducing the interfacial resistance, thereby facilitating ion transfer. By greatly adjusting the average particle size of the solid electrolyte included in the solid electrolyte layer, the large solid electrolyte particles can serve as a skeleton within the solid electrolyte layer to support the particles, thereby enhancing mechanical strength and structural stability.

[0185] For example, the average particle diameter (D) of the solid electrolyte (e.g., the first solid electrolyte) included in the above anode 50 ) may be 0.5 ㎛ to 2.0 ㎛, and the average particle diameter (D) of the solid electrolyte (e.g., the second solid electrolyte) included in the solid electrolyte layer described below 50 ) may be 2.1 ㎛ to 5.0 ㎛. By reducing the average particle diameter of the solid electrolyte included in the positive electrode, the first solid electrolyte fine particles can densely fill the space between the positive electrode active material particles included in the positive electrode active material layer, thereby increasing the interfacial contact area and reducing the interfacial resistance, thereby facilitating ion transfer. By greatly adjusting the average particle diameter of the solid electrolyte included in the solid electrolyte layer, the large solid electrolyte particles can serve as a skeleton within the solid electrolyte layer to support the particles, thereby enhancing mechanical strength and structural stability.

[0186] The content of the solid electrolyte in the positive electrode for the all-solid-state battery may be 0.1 wt% to 35 wt%, for example, 1 wt% to 35 wt%, 5 wt% to 30 wt%, 8 wt% to 25 wt%, or 10 wt% to 20 wt%. This is the content relative to the total weight of the components in the positive electrode, and specifically, it can be said to be the content relative to the total weight of the positive electrode active material layer.

[0187] In addition, in the positive electrode for the all-solid-state battery, the positive electrode active material may be comprised in an amount of 65 wt% to 99 wt% and the solid electrolyte in an amount of 1 wt% to 35 wt%, based on the total weight of the positive electrode active material and the solid electrolyte, for example, the positive electrode active material may be comprised in an amount of 80 wt% to 90 wt% and the solid electrolyte in an amount of 10 wt% to 20 wt%. When the solid electrolyte is comprised in the positive electrode in such an amount, the efficiency and life characteristics of the all-solid-state battery can be improved without reducing the capacity.

[0188] bookbinder

[0189] The above binder serves to adhere the positive electrode active material particles and the solid electrolyte particles well to each other, and also to adhere the particles well to the positive electrode current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0190] The above binder may be included in an amount of 0.1 wt% to 5 wt%, or 0.1 wt% to 3 wt%, based on the total weight of each component of the positive electrode for the all-solid-state battery, or based on the total weight of the positive electrode active material layer. Within the above content range, the binder can sufficiently exhibit adhesive ability without deteriorating battery performance.

[0191] Challenge

[0192] 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 in the battery to be constructed can be used. Examples thereof include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and carbon nanotube; 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 including mixtures thereof.

[0193] The conductive material may be included in an amount of 0.1 wt% to 5 wt%, or 0.1 wt% to 3 wt%, based on the total weight of each component of the positive electrode for the all-solid-state battery, or based on the total weight of the positive electrode active material layer. Within the above content range, the conductive material can improve electrical conductivity without degrading battery performance.

[0194] All-solid-state secondary battery

[0195] In one embodiment, an all-solid-state secondary battery is provided, comprising the aforementioned positive electrode, negative electrode, and a solid electrolyte layer positioned between the positive electrode and negative electrode. The all-solid-state secondary battery may also be referred to as an all-solid-state battery or an all-solid-state lithium secondary battery.

[0196] FIG. 4 is a cross-sectional view of an all-solid-state battery according to an embodiment. Referring to FIG. 4, the all-solid-state battery (100) may have a structure in which an electrode assembly in which a negative electrode (400) including a negative electrode current collector (401) and a negative electrode active material layer (403), a solid electrolyte layer (300), and a positive electrode (200) including a positive electrode active material layer (203) and a positive electrode current collector (201) are laminated is housed in a case such as a pouch. The all-solid-state 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 a negative electrode (400), a solid electrolyte layer (300), and a positive electrode (200), an all-solid-state battery may be manufactured by laminating two or more electrode assemblies.

[0197] cathode

[0198] An anode for an all-solid-state battery may include, for example, an anode current collector and an anode active material layer positioned on the anode current collector. The anode active material layer includes an anode active material and may further include a binder, a conductive material, and / or a solid electrolyte.

[0199] The above negative active material may include 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.

[0200] 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.

[0201] As the above lithium metal alloy, an alloy of lithium and one or more metals selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0202] 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, and the Si-based negative electrode active material may be silicon, a silicon-carbon composite, or SiO. x (0 <x≤2), Si-Q 합금(상기 Q는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합에서 선택되는 하나 이상의 원소이며, Si은 아님), 상기 Sn계 음극 활물질로는 Sn, SnO2, Sn-R 합금(상기 R은 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합에서 선택되는 하나 이상의 원소이며, Sn은 아님) 등을 들 수 있고, 또한 이들 중 적어도 하나와 SiO2를 혼합하여 사용할 수도 있다. 상기 원소 Q 및 R로는 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, 및 이들의 조합에서 선택되는 하나 이상의 것을 사용할 수 있다.

[0203] The silicon-carbon composite may be, for example, a silicon-carbon composite including a core including crystalline carbon and silicon particles and an amorphous carbon coating layer positioned on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. As the amorphous carbon precursor, coal pitch, mesophase pitch, petroleum pitch, coal oil, petroleum heavy oil, or a polymer resin such as a phenol resin, a furan resin, or a polyimide resin may be used. At this time, the content of silicon may be 10 wt% to 50 wt% with respect to the total weight of the silicon-carbon composite. In addition, the content of the crystalline carbon may be 10 wt% to 70 wt% with respect to the total weight of the silicon-carbon composite, and the content of the amorphous carbon may be 20 wt% to 40 wt% with respect to the total weight of the silicon-carbon composite. In addition, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm.

[0204] The average particle diameter (D) of the above silicon particles 50 ) may be 10 nm to 20 μm, for example, 10 nm to 200 nm. The silicon particles may exist in an oxidized form, and atomic content ratio of Si:O in the silicon particles, which indicates the degree of oxidation, may be 99:1 to 33:67. The silicon particles may be SiO x It can be a particle, in which case SiO x The range of x in can be greater than 0 and less than 2.

[0205] Here, the average particle diameter (D 50 ) is measured by a particle size analyzer using laser diffraction and means the diameter of particles with a cumulative volume of 50% in the particle size distribution.

[0206] The above Si-based negative electrode active material or Sn-based negative electrode active material can be used in combination with a carbon-based negative electrode active material. The mixing ratio of the Si-based negative electrode active material or Sn-based negative electrode active material and the carbon-based negative electrode active material can be 1:99 to 90:10 by weight.

[0207] 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.

[0208] 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.

[0209] 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 negative electrode current collector. The binder may be an insoluble binder, a water-soluble binder, or a combination thereof.

[0210] The above-mentioned non-water-soluble binder may be selected from polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, an ethylene propylene copolymer, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0211] The water-soluble binder may be a rubber-based binder or a polymer resin binder. The rubber-based binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymer resin binder may be selected from polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0212] When a water-soluble binder is used as the 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. The amount of such thickener may be 0.1 to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

[0213] The conductive material is used to impart conductivity to the electrode, and any material that does not cause chemical changes and has electronic conductivity can be used. The conductive material may include, for example, carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, 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.

[0214] 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.

[0215] Meanwhile, as an example, the above-mentioned all-solid-state battery negative electrode may be a precipitation-type negative electrode. The precipitation-type negative electrode refers to a negative electrode that does not have a negative electrode active material when the battery is assembled, but in which lithium metal or the like is precipitated when the battery is charged, and this acts as a negative electrode active material.

[0216] 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 negative electrode current collector (401) and a negative electrode coating layer (405) positioned on the negative electrode 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, a high-density lithium metal may be precipitated or deposited between the negative electrode 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.

[0217] 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.

[0218] 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 less than about 4 μm, for example, 10 nm to 4 μm, 10 nm to 1 μm, 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.

[0219] 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.

[0220] 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.

[0221] 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.

[0222] Supported compounds

[0223] 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.

[0224] The amorphous carbon material may be, for example, a single particle, or may be 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.

[0225] 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.

[0226] 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.

[0227] 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.

[0228] 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.

[0229] 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.

[0230] 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.

[0231] 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.

[0232] 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.

[0233] The thickness of the cathode coating layer may be, for example, 100 nm to 40 μm, or 500 nm to 30 μm, or 1 μm to 20 μm. When the cathode coating layer satisfies the above thickness range, a lithium metal layer of uniform thickness can be effectively formed during charging.

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

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

[0236] 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.

[0237] 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.

[0238] 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.

[0239] 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.

[0240] 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.

[0241] lithium metal layer

[0242] 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.

[0243] 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.

[0244] 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.

[0245] 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.

[0246] etc

[0247] 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.

[0248] negative current collector

[0249] 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.

[0250] solid electrolyte layer

[0251] The solid electrolyte layer (300) includes a solid electrolyte, and the solid electrolyte may be an inorganic solid electrolyte such as a sulfide-based solid electrolyte or an oxide-based solid electrolyte, or a solid polymer electrolyte. A description of the types of solid electrolytes is omitted as they are as described above.

[0252] For example, the solid electrolyte included in the positive electrode (200) and the solid electrolyte included in the solid electrolyte layer (300) may include the same compound, for example, they may be the same sulfide-based solid electrolyte, for example, they may be the same argyrodite-type sulfide-based solid electrolyte. In this case, the overall performance of the all-solid-state battery may be improved and stable operation may be possible.

[0253] Also, the average particle diameter (D) of the solid electrolyte included in the positive electrode (200) 50 ) is the average particle diameter (D) of the solid electrolyte included in the solid electrolyte layer (300). 50 ) may be smaller than the average particle size of the solid electrolyte (200). In this case, the overall performance can be improved by increasing the mobility of lithium ions while maximizing the energy density of the all-solid-state battery. For example, the average particle size (D) of the solid electrolyte included in the positive electrode (200) 50 ) may be 0.5 ㎛ to 2.0 ㎛, or 0.5 ㎛ to 1.5 ㎛, and the average particle diameter (D) of the solid electrolyte included in the solid electrolyte layer (300) 50 ) may be 2.1 ㎛ to 5.0 ㎛, or 2.1 ㎛ to 4.0 ㎛, or 2.5 ㎛ to 3.5 ㎛. When this particle size range is satisfied, the energy density of the all-solid-state battery can be maximized while the transfer of lithium ions is facilitated, thereby suppressing the resistance, and thus improving the overall performance of the all-solid-state battery. Here, the average particle diameter (D of the solid electrolyte 50 ) may be measured by a particle size analyzer using laser diffraction. Alternatively, the particle size is measured by selecting about 30 random particles from a microscope image such as a scanning electron microscope and obtaining a particle size distribution, where D 50 You can also calculate the value.

[0254] The above solid electrolyte layer 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.

[0255] The above solid electrolyte layer can be formed by adding a solid electrolyte to a binder solution, coating the same on a base 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.

[0256] The thickness of the solid electrolyte layer may be, for example, 10 μm to 150 μm.

[0257] The solid electrolyte layer may further include an alkali metal salt, and / or an ionic liquid, and / or a conductive polymer.

[0258] 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.

[0259] The above lithium salts include, for example, LiSCN, LiN(CN)2, Li(CF3SO2)3C, LiC4F9SO3, LiN(SO2CF2CF3)2, LiCl, LiF, LiBr, LiI, LiB(C2O4)2, LiBF4, LiBF3(C2F5), lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LIODFB), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(trifluoro methanesulfonyl)imide (LiTFSI, LiN(SO2CF3)2), lithium bis(fluorosulfonyl)imide (LiFSI, It may include LiN(SO2F)2), LiCF3SO3, LiAsF6, LiSbF6, LiClO4 or mixtures thereof.

[0260] In addition, the lithium salt may be an imide-based one, and for example, the imide-based lithium salt may include lithium bis(trifluoro methanesulfonyl)imide (LiTFSI, LiN(SO2CF3)2), lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO2F)2). The lithium salt may maintain or improve ionic conductivity by appropriately maintaining chemical reactivity with an ionic liquid.

[0261] The above ionic liquid has a melting point below room temperature and is a salt or room-temperature molten salt that is liquid at room temperature and consists only of ions.

[0262] The above ionic liquid comprises a) one or more cations selected from ammonium, pyrrolidinium, pyridinium, pyrimidinium, imidazolium, piperidinium, pyrazolium, oxazolium, pyridazinium, phosphonium, sulfonium, triazolium, and mixtures thereof, and b) BF4. - , PF6 - , AsF6 - , SbF6 - , AlCl4 - , HSO4 - , ClO4 - , CH3SO3 - , CF3CO2 - , Cl - , Br - , I - , BF4 - , SO4 - , CF3SO3 - , (FSO2)2N - , (C2F5SO2)2N - , (C2F5SO2)(CF3SO2)N - , and (CF3SO2)2N - It may be a compound containing one or more anions selected from among.

[0263] The ionic liquid may be at least one selected from the group consisting of, for example, 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.

[0264] In the above solid electrolyte layer, the weight ratio of the solid electrolyte and 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 battery can be improved.

[0265] The above-mentioned all-solid-state battery may be a unit battery 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 battery is repeated.

[0266] The shape of the above-mentioned all-solid-state 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 battery can be applied to large-scale batteries used in electric vehicles, etc. For example, the above-mentioned all-solid-state battery can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). In addition, it can be used in fields requiring large amounts of power storage, and for example, it can be used in electric bicycles or power tools.

[0267] 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 examples described below.

[0268] Example 1

[0269] 1. Manufacturing of positive electrode active material

[0270] (1) Manufacturing of the first nickel-based composite hydroxide

[0271] 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. In the manufacturing process below, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and sodium aluminum sulfate (NaAl(SO4)2·12H2O) are 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) are prepared as a precipitant to form a complex compound.

[0272] [Step 1: 2.5 kW / ㎥, NH4OH 0.40 M, pH 10.5~11.5, reaction time 6 hours]

[0273] 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.

[0274] [Step 2: 2.0 kW / ㎥, NH4OH 0.45 M, pH 10.5~11.5, reaction time 18 hours]

[0275] 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 performing this reaction, it was confirmed that the average size of the product particles containing the core and intermediate layer was 13.5 ㎛ to 14.5 ㎛, and the following 3 steps were performed.

[0276] [Step 3: 1.5 kW / ㎥, NH4OH 0.45 M, pH 10.5~11.5, reaction time 14 hours]

[0277] While maintaining the reaction temperature at 50°C, the addition rate and concentration of the metal raw material mixture solution and complexing agent were the same as in Step 2. The reaction was continued for 14 hours, with NaOH added to maintain the pH. At this time, the stirring power was reduced to 1.5 kW / ㎥, which was lower than in Step 2, to allow the reaction to proceed.

[0278] [Post-processing]

[0279] After washing the above result, it was dried with hot air at about 150℃ for 24 hours to obtain the first nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH)2) was obtained.

[0280] (2) Manufacturing of a second lithium nickel-based composite oxide

[0281] Nickel-based composite hydroxide (Ni), a precursor of the second cathode active material, was prepared through a co-precipitation method. 0.94 Co 0.04 Al 0.01 Mn 0.01(OH)2) is synthesized. As metal raw materials, nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), sodium aluminum sulfate (NaAl(SO4)2·12H2O), and manganese sulfate (MnSO4·H2O) are dissolved in distilled water as a solvent at a molar ratio of 94:4:1:1 to prepare a mixed solution. The subsequent synthesis is the same as the production of the first nickel-based composite hydroxide.

[0282] Nickel-based composite hydroxide and lithium hydroxide prepared by the above method were mixed in a molar ratio of 1:1 and heat-treated at 850°C in an oxygen atmosphere. The average particle size (D) of the obtained product was measured through an air impingement crusher. 50 ) is crushed to about 3 ㎛ to obtain a single-crystal lithium nickel composite oxide (LiNi 0.94 Co 0.04 Al 0.1 Mn 0.01 A second positive electrode active material (O2) was obtained.

[0283] (3) Manufacturing of preliminary positive electrode active material

[0284] A first nickel-based composite hydroxide and a second lithium nickel-based composite oxide are mixed in a weight ratio of 7:3, LiOH is mixed so as to satisfy a molar ratio of Li / (Ni+Co+Al)=0.98 in the relationship between the first nickel-based composite hydroxide and LiOH, and 0.125 mol% of boric acid is mixed with respect to all elements except Li, O, and H in the mixture, and the mixture is put into a kiln, and the temperature is increased to 700°C for 8 hours in an oxygen atmosphere and heat-treated for 7 hours to obtain a preliminary cathode active material having a first coating layer of LiBO2 formed on the surface.

[0285] (4) Manufacturing of final positive electrode active material

[0286] D in 99.5 wt% of the above preliminary positive electrode active material 50 The final positive electrode active material is obtained by adding 0.5 wt% of 0.07 ㎛ LiAlO2 and dry mixing with a Henschel mixer at 2,000 rpm for 3 minutes at 25 to 30 °C.

[0287] In the obtained final positive electrode active material, the first positive electrode active material is a first lithium nickel-based composite oxide (Li 0.96 Ni 0.945 Co 0.04 Al 0.015 O2) and has a radial structure, and a first coating layer containing LiBO2 is formed on the surface thereof, and a second coating layer containing LiAlO2 particles is formed on the surface of the first coating layer, and the average particle diameter is confirmed to be approximately 14.3 ㎛. At this time, in the first positive electrode active material, the average thickness of the first coating layer is confirmed to be 10 nm, and the average thickness of the second coating layer is confirmed to be 80 nm.

[0288] The second cathode active material is a second lithium nickel composite oxide (LiNi 0.94 Co 0.04 Al 0.1 Mn 0.01 O2) and is in the form of a single particle, and a first coating layer containing LiBO2 is formed on the surface thereof, and a second coating layer containing LiAlO2 particles is formed on the surface of the first coating layer, and the average particle diameter is confirmed to be about 3.5 ㎛. At this time, in the first positive electrode active material, the average thickness of the second coating layer is confirmed to be 10 nm, and the average thickness of the second coating layer is confirmed to be 80 nm.

[0289] Here, the measurement of the above average thickness was performed by obtaining the arithmetic mean value of 30 arbitrary thickness data, in the same manner as described above in the specification.

[0290] 2. Manufacturing of the anode

[0291] 87.5 wt% of cathode active material, argyrodite type solid electrolyte (Li6PS5Cl, D 50=1 ㎛) 9.44 wt%, PVdF binder 1 wt%, carbon nanotube conductive material 0.45 wt%, and hydrogenated nitrile butadiene rubber (HNBR) 0.11 wt% as a dispersant were mixed in an isobutyryl isobutyrate (IBIB) solvent to prepare a positive electrode composition. This was applied to a positive electrode current collector, dried, and then rolled (hydrostatic pressing (WIP), 500 Mpa, 85°C, 30 min) to prepare a positive electrode.

[0292] 3. Manufacturing of all-solid-state secondary batteries

[0293] Carbon black with a primary particle size of about 30 nm and an average particle size (D 50 ) was prepared by mixing silver (Ag) having a thickness of approximately 60 nm in a weight ratio of 3:1, and 0.25 g of the above complex was added to 2 g of an NMP solution containing 7 wt% of polyvinylidene fluoride binder, and mixed to prepare a negative electrode coating layer composition. This was applied onto a negative electrode current collector and then dried, thereby preparing a deposition-type negative electrode in which a negative electrode coating layer was formed on the current collector.

[0294] Argyrodite-type solid electrolyte (Li6PS5Cl, D 50 =3 ㎛) was added to an IBIB solvent containing an acrylic binder and mixed to prepare a composition for forming a solid electrolyte layer. The composition was cast on a release film and dried at room temperature to prepare a solid electrolyte layer.

[0295] The prepared positive electrode, negative electrode, and solid electrolyte layers were cut, a solid electrolyte layer was laminated on the positive electrode, and then the 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.

[0296] Comparative Example 1

[0297] Except that the lithium aluminate coating was not performed during the manufacture of the final positive electrode active material, a positive electrode active material was manufactured and a positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1.

[0298] Example 2

[0299] In the manufacture of the above final positive electrode active material, 99.75 wt% of the preliminary positive electrode active material is D 50 Except that the final positive electrode active material was manufactured by adding 0.25 wt% of 0.07 ㎛ LiAlO2, a positive electrode active material was manufactured and a positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1.

[0300] Example 3

[0301] In the manufacture of the above final positive electrode active material, 99 wt% of the preliminary positive electrode active material is added to D 50 Except that the final positive electrode active material was manufactured by adding 1 wt% of 0.07 ㎛ of LiAlO2, a positive electrode active material was manufactured and a positive electrode and an all-solid-state secondary battery were manufactured in substantially the same manner as in Example 1.

[0302] Comparative Example 2

[0303] In the manufacture of the above final positive electrode active material, D 50 Instead of this 0.07 ㎛ LiAlO2, D 50 This 0.07 ㎛ Li4Ti5O 12 Except for the change, a positive electrode active material was manufactured in substantially the same manner as in Example 1, and a positive electrode and an all-solid-state secondary battery were manufactured.

[0304] Table 1 below is a table briefly showing the design contents of the positive electrode active materials of the examples and comparative examples.

[0305] First positive electrode active materialSecond positive electrode active materialTotal positive electrode active materialCore structureBoron loading (mol%)Core structureBoron loading (mol%)Lithium aluminate (LAO) or lithium titanate (LTO) loading (weight%)Example 1Radial secondary particle0.125Single particle0.1250.5Comparative example 1Radial secondary particle0.125Single particle0.125-Example 2Radial secondary particle0.125Single particle0.1250.25Example 3Radial secondary particle0.125Single particle0.1251Comparative example 2Radial secondary particle0.125Single particle0.1250.5

[0306] Evaluation Example 1: Evaluation of the initial charge / discharge capacity of an all-solid-state secondary battery.

[0307] The solid-state secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 and 2 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 a constant voltage of 0.05 C to an end-of-discharge voltage of 2.5 V at 0.1 C to measure the initial discharge capacity, and the results are shown in Table 2. In addition, the voltages according to the charge / discharge capacities of Example 1 and Comparative Example 1 were compared and shown in Fig. 6.

[0308] Charging capacity (mAh / g)Discharging capacity (mAh / g)Efficiency (%)Example 1240.7201.783.8Comparative example 1242.2202.783.7Example 2240.6201.583.8Example 3236.9198.883.9Comparative example 2240.7201.283.6

[0309] Referring to the results of Table 2 and Fig. 6, it can be seen that Comparative Example 1, which formed only the first coating layer containing boron and did not form the second coating layer containing lithium aluminate, exhibited charge / discharge characteristics at a level similar to those of the examples, but the charge / discharge efficiency was somewhat lower.

[0310] Also, Li4Ti5O2, not lithium aluminate 12 In the case of Comparative Example 2, which formed the second coating layer of the content, it can be confirmed that the charge / discharge efficiency is the lowest.

[0311] In contrast, in the case of Examples 1 to 3, it can be confirmed that the charge / discharge efficiency is excellent by forming the first coating layer containing boron and the second coating layer containing lithium aluminate.

[0312] In particular, among these, in the case of Examples 1 and 2 in which the amount of lithium aluminate added is in the range of 0.25 wt% to 0.5 wt%, it is possible to implement excellent charge / discharge capacity without a large capacity decrease, so it can be seen that the case in which the amount of lithium aluminate added by the second coating layer is 0.25 wt% to 0.5 wt% is more effective.

[0313] Evaluation Example 2: Evaluation of the Lifetime Characteristics of All-Solid-State Secondary Batteries

[0314] For the all-solid-state secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 and 2, the initial discharge capacity was evaluated by performing the initial charge and discharge as in Evaluation Example 1, and when charging at 0.33C and discharging at 0.33C in a voltage range of 2.5 V to 4.25 V at 45°C were repeated 100 times, the retention of the discharge capacity after 100 cycles compared to the first cycle was evaluated, and the results are shown in Table 3 and Fig. 7 below.

[0315] Discharge capacity per cycle (mAh / g) 100 cycle lifespan maintenance rate (%) Example 1159.08 6.8 Comparative example 1159.88 4.7 Example 2158.68 6 Example 3155.98 8.9 Comparative example 2158.68 5.3

[0316] Referring to the results in Table 3 and Figure 7 above, it can be confirmed that the lifespan maintenance rate is the lowest in Comparative Example 1, in which only the first coating layer is formed and the second coating layer is not formed.

[0317] On the other hand, in the case of Examples 1 to 3, the life maintenance rate is higher compared to Comparative Example 1, so it can be confirmed that it is more advantageous to secure long-life characteristics when not only the first coating layer but also the second coating layer is applied.

[0318] Meanwhile, among these, in the case of Examples 1 and 2 in which the amount of lithium aluminate added is in the range of 0.25 wt% to 0.5 wt%, the initial charge / discharge capacity characteristics are better than in Example 3, and it can be confirmed that it is advantageous to secure better initial charge / discharge capacity characteristics when lithium aluminate coating is performed with an appropriate coating amount.

[0319] Evaluation Example 3: Analysis of component content on the surface of the positive electrode active material

[0320] The results of quantitative analysis of each element on the surface of the positive electrode active material manufactured in Example 1 using TEM-EDS are shown in Fig. 8, and the results of quantitative analysis of each element on the surface of the small particles manufactured in Example 1 using TEM-EDS are shown in Fig. 9.

[0321] Referring to Fig. 8, it can be confirmed that among the positive electrode active materials manufactured in Example 1, Al exists as a second coating layer at 7.3 at% on the outermost surface of the first positive electrode active material, based on 100 at% of the first positive electrode active material.

[0322] Referring to Fig. 9, it can be confirmed that among the positive electrode active materials manufactured in Example 1, Al exists as 5.6 at% as a second coating layer on the outermost surface of the second positive electrode material, which is a small particle, based on 100 at% of the second positive electrode active material.

[0323] Evaluation Example 4: Confirmation of the boron-doped layer of the first cathode active material

[0324] Fig. 10 is a TEM photograph of the primary particles exposed on the surface of the secondary particles, i.e., the primary particles at the outermost edge of the secondary particles, in the first positive electrode active material among the final positive electrode active materials of Example 1. Electron energy loss spectroscopy (EELS) was performed on a total of 10 points at equal intervals from point 1 to point 10 indicated in Fig. 10, and the results are shown in Fig. 11. For example, ① in Fig. 11 means the analysis graph at point 1 of Fig. 11. Referring to the graph below in Fig. 11, since cobalt was detected from point 4, the starting point of the surface of the positive electrode active material can be said to be approximately point 4. Referring to the upper graph of Fig. 11, boron was detected at points 3 to 8, where the point 3 position is understood to be a boron-containing first coating layer existing on the surface of the positive electrode active material, and the boron detected at points 4 to 8 is understood to be a very thin boron doping layer existing inside the positive electrode active material.

[0325] Evaluation Example 5: Confirmation of boron coating on the surface and internal grain boundaries of the first cathode active material.

[0326] The first positive electrode active material and the second positive electrode active material were prepared by separating them from the final positive electrode active material manufactured in Example 1. The separation of the active materials was performed using a turbo classifier (Nisshin Engineering Inc.) and nitrogen as a transport gas.

[0327] In addition, 0.125 mol% of boric acid was dry-mixed into the first positive electrode active material (first lithium nickel-based composite oxide) manufactured in substantially the same manner as Comparative Example 1 except that boric acid was not mixed, and heat-treated at 350°C for 8 hours to prepare the positive electrode active material of Reference Example 1. Reference Example 1 is a case where boron was coated on a secondary particle active material in the form of an oxide using a conventional coating method.

[0328] The boron content is measured by performing ICP (Inductively Coupled Plasma) emission spectrometry on the three types of positive electrode active materials mentioned above. After that, 10g of each positive electrode active material is added to 100g of distilled water, stirred for 30 minutes, and filtered. Through this washing process, all boron existing on the surface or near the surface of the positive electrode active material is removed. After drying the recovered positive electrode active material at 130℃ for 24 hours, ICP emission spectrometry is performed again to measure the amount of boron remaining in the positive electrode active material, which is expressed as the amount of boron existing inside the positive electrode active material, i.e., at the grain boundary. In addition, the amount of boron removed through the washing process is expressed as the amount of boron existing on the surface of the positive electrode active material, which is the value obtained by subtracting the amount of boron after washing from the amount of boron before washing. In Table 4 below, the unit is ppm, which is 10 -4 It means weight% and refers to the ratio of the weight of boron to the total weight of the positive electrode active material.

[0329] Boron before washing (ppm) Internal grain boundary boron (ppm) Surface boron (ppm) Example 1 1st positive electrode active material 54030510 Example 1 2nd positive electrode active material 3500350 Reference example 15400540

[0330] Referring to Table 4 above, it can be seen that the first positive electrode active material of Example 1 was coated with boron not only on the surface but also on the internal grain boundaries, and the boron coating content on the surface was about 0.0510 wt% with respect to 100 wt% of the positive electrode active material, and the boron coating content on the internal grain boundaries was about 0.003 wt% with respect to 100 wt% of the positive electrode active material, and these weight ratios were about 94:6. On the other hand, the second positive electrode active material in the form of a single particle of Example 1 was not coated with boron on the inside of the particles. In addition, it is understood that in the case of Reference Example 1, in which boron coating was performed on a secondary particle active material in the form of an oxide using a conventional method, boron was not coated on the internal grain boundaries.

[0331] Evaluation Example 6: SEM Photo Confirmation

[0332] Figure 12 is an SEM photograph of a cross-section of the first nickel-based composite hydroxide of Example 1. It can be confirmed that there is a region in the center where pores are formed, and the surface portion surrounding this is radially oriented with primary particles in the direction of the surface of the secondary particles.

[0333] Fig. 13 is a SEM photograph of the surface of the first nickel-based composite hydroxide of Example 1, showing that the surface is porous. The pores on the surface shown in Fig. 13 are a type of open pore, formed by the spaces between the plate-shaped primary particles arranged radially, and represent pores that are deeply connected from the surface of the secondary particles toward the center.

[0334] Evaluation Example 7: Analysis of components on the surface of the positive electrode active material

[0335] To analyze the components of the surface of the positive electrode active material, transmission electron microscopy-cell energy loss spectroscopy (TEM-EELS) analysis was performed on the positive electrode active material manufactured in Example 1, and the analysis results are shown in Fig. 14.

[0336] Referring to Figure 14, it was confirmed that boron elements were distributed on the surface of the core secondary particles or single particles, and aluminum elements were distributed on the outermost surface, which is closer to the surface than the boron elements.

[0337] Through this, it can be seen that the positive electrode active material manufactured in Example 1 contains lithium aluminate, which is a coating material including boron as a first coating layer positioned on the surface of a secondary particle or single particle, which is a core of a lithium nickel-based composite oxide, and aluminum as a second coating layer positioned on the first coating layer.

[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: Cathode

[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 catalyst layer 500: Elastic layer

Claims

A first positive electrode active material comprising a secondary particle containing a first lithium nickel-based composite oxide and formed by agglomeration of a plurality of primary particles, a first coating layer located on the surface of the secondary particle and containing boron, and a second coating layer located on the first coating layer and containing lithium aluminate, and A cathode active material comprising a second lithium nickel-based composite oxide, a first coating layer in the form of single particles and containing boron located on the surface of the single particles, and a second coating layer located on the first coating layer and containing lithium aluminate, and a second cathode active material having an average particle diameter smaller than the average particle diameter of the first cathode active material. In the first paragraph, The first coating layer is a positive electrode active material including boron oxide, lithium borate, or a combination thereof. In the first paragraph, The first coating layer is B2O2, B2O3, B4O3, B4O5, LiBO2, Li3B7O 12 , Li6B4O9, Li3B 11 O 18 , a cathode active material comprising Li2B4O7, Li3BO3 or a combination thereof. In the first paragraph, A cathode active material having a boron content of 0.01 wt% to 0.5 wt% based on the total content of elements excluding lithium and oxygen in the cathode active material. In the first paragraph, The second coating layer is a positive electrode active material comprising LiAlO2, LiAl2O3, or a combination thereof. In the first paragraph, A cathode active material comprising the lithium aluminate in an amount of 0.01 wt% to 3 wt% based on 100 wt% of the total cathode active material. In the first paragraph, The first cathode active material is a cathode active material further comprising a boron-doped layer located inside the primary particle exposed on the surface of the secondary particle. In paragraph 7, A positive electrode active material, wherein the boron doping layer in the first positive electrode active material is located within a depth range of 10 nm from the outer surface of the primary particle exposed to the surface of the secondary particle. In the first paragraph, A first cathode active material further comprising a grain boundary boron coating portion located on the surface of the primary particles inside the secondary particles. In paragraph 9, A positive electrode active material having a boron content in the first coating layer of the first positive electrode active material greater than the boron content in the grain boundary boron coating portion. In paragraph 9, A positive electrode active material in which the boron content in the first coating layer of the first positive electrode active material is at least four times the boron content in the grain boundary boron coating portion. In paragraph 9, A cathode active material having a ratio of the boron content in the first coating layer of the first cathode active material and the boron content in the grain boundary boron coating portion of the first cathode active material of 70:30 to 98:

2. In paragraph 9, A cathode active material in which the boron content in the boron coating layer on the surface of the secondary particle is 0.02 wt% to 0.5 wt%, and the boron content in the grain boundary boron coating portion is 0.001 wt% to 0.05 wt%, relative to 100 wt% of the first cathode active material. In paragraph 1, The first lithium nickel-based composite oxide and the second lithium nickel-based composite oxide are the same or different from each other, and are each independently represented by the following chemical formula 1, wherein the positive electrode active material: [Chemical Formula 1] Li a1 Ni x1 M 1 y1 M 2 1-x1-y1 O 2-z X z In the above chemical formula 1, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7 and 0≤z≤0.1, and M 1 and M 2 are each independently Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, Zn, Zr or a combination thereof, and X is F, P, S or a combination thereof. In the first paragraph, The average particle diameter of the first positive electrode active material is 5 ㎛ to 25 ㎛, A cathode active material having an average particle diameter of 0.05 ㎛ to 8 ㎛. In the first paragraph, For 100 wt% of the above positive electrode active material, 50 wt% to 90 wt% of a first positive electrode active material, and A positive electrode active material comprising 10 to 50 wt% of a second positive electrode active material. In the first paragraph, The average thickness of the first coating layer is 1 nm to 500 nm, A cathode active material having an average thickness of the second coating layer of 1 nm to 500 nm. In the first paragraph, The above first positive electrode active material is a positive electrode active material in the form of secondary particles in which at least a portion of the primary particles have a radial arrangement structure. (i) a first cathode active material precursor in the form of a secondary particle containing a first nickel-based composite hydroxide and formed by agglomeration of a plurality of primary particles; A first sintered product of a second cathode active material containing a second lithium nickel-based composite oxide, having a single particle form and an average particle diameter smaller than that of the first cathode active material precursor, Lithium raw materials, and A preliminary positive electrode active material is obtained by mixing boron raw materials and heat-treating them to form a first coating layer containing boron, (ii) A method for producing a positive electrode active material, comprising dry mixing the above-mentioned preliminary positive electrode active material and lithium aluminate particles to obtain a final positive electrode active material having a second coating layer containing lithium aluminate formed on the surface of the above-mentioned preliminary positive electrode active material. A positive electrode comprising a positive electrode active material according to any one of claims 1 to 18, and a solid electrolyte; cathode, and An all-solid-state secondary battery comprising a solid electrolyte layer positioned between the positive electrode and the negative electrode.

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