Positive electrode active material for all solid state battery, method of preparing the same, and all solid state battery

Abstract

The present invention relates to a positive active material for an all-solid-state battery, a method for manufacturing the same, and an all-solid-state battery comprising the same, wherein the positive active material comprises a plurality of primary particles aggregated and a secondary particle having at least a portion of the primary particles having a radial arrangement structure, wherein the positive active material comprises a first boron coating portion present on the surface of the secondary particle and a second boron coating portion present on the surface of the primary particles inside the secondary particle.

Description

Technology Field

[0001] The invention relates to a positive electrode active material for an all-solid-state battery, a method for manufacturing the same, and an all-solid-state battery including the same. Background Technology

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

[0003] Among lithium-ion batteries, all-solid-state batteries are batteries composed entirely of solid materials, specifically referring to batteries that use a solid electrolyte. These all-solid-state batteries are safe as they eliminate the risk of explosions caused by electrolyte leakage, and they have the advantage of being easy to manufacture in a thin form factor.

[0004] Recently, various cathode active materials applicable to such all-solid-state batteries are being reviewed. While 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 examined, they currently face limitations in achieving satisfactory performance for all-solid-state batteries. Therefore, there is a need to develop new cathode active materials to realize all-solid-state batteries that ensure long lifespan characteristics while achieving high capacity and high energy density. The problem to be solved

[0005] The present invention provides a positive electrode active material for an all-solid-state battery with improved lifespan characteristics while achieving high capacity, a method for manufacturing the same, and an all-solid-state battery including the same. means of solving the problem

[0006] In one embodiment, a positive electrode active material for an all-solid-state battery comprising a lithium nickel-based composite oxide is provided, the positive electrode active material for an all-solid-state battery comprising a plurality of primary particles aggregated to form secondary particles in which at least a portion of the primary particles have a radial arrangement structure, a first boron coating portion present on the surface of the secondary particles, and a second boron coating portion present on the surface of the primary particles inside the secondary particles.

[0007] The first boron coating part and the second boron coating part may each include boron oxide, lithium boron oxide, or a combination thereof.

[0008] The weight of the first boron coating part may be greater than the weight of the second boron coating part.

[0009] With respect to the total amount of the first boron coating part and the second boron coating part, the first boron coating part may be included in an amount of 70% to 98% by weight, and the second boron coating part may be included in an amount of 2% to 30% by weight.

[0010] The content of the first boron coating portion may be 0.02 weight% to 0.3 weight% with respect to the positive active material.

[0011] The content of the second boron coating portion may be 0.001 weight% to 0.05 weight% with respect to the positive active material.

[0012] The total amount of the first boron coating part and the second boron coating part may be 0.1 mol% to 3 mol% with respect to the positive active material, and may be 0.1 mol% to 1.5 mol%.

[0013] The above primary particles have a plate shape, and at least some of the plate-shaped primary particles may have their major axes arranged in a radial direction.

[0014] The average length of the primary particles of the above plate shape is 150 nm to 500 nm, the average thickness is 100 nm to 200 nm, and the ratio of the average thickness to the average length may be 1:2 to 1:5.

[0015] The above secondary particle may contain an interior having an irregular porous structure and an exterior having a radial arrangement structure.

[0016] The interior of the secondary particle has a larger pore size than the exterior, the pore size inside the secondary particle is 150 nm to 1 µm, and the pore size outside the secondary particle may be less than 150 nm.

[0017] The above secondary particles may include open pores of less than 150 nm in size toward the center of the interior.

[0018] The above positive active material may be represented by the following chemical formula 1.

[0019] [Chemical Formula 1]

[0020] Li a1 Ni x1 M 1 y1 M 2 1-x1-y1 O2

[0021] In the above Chemical Formula 1, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, and M 1 and M 2 Each is independently selected from Al, B, Ce, Co, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof.

[0022] In another embodiment, a method for manufacturing a positive electrode active material for an all-solid-state battery is provided, comprising mixing a lithium raw material, a nickel-based hydroxide, and a boron raw material and heat-treating them.

[0023] The content of the above boron raw material may be 0.1 mol% to 3 mol% with respect to 100 mol% of the above nickel-based hydroxide.

[0024] The above heat treatment may be performed at a temperature of 650 ℃ to 850 ℃ for 5 to 20 hours.

[0025] In another embodiment, an all-solid-state battery is provided comprising a positive electrode including the positive active material, a negative electrode, and a solid electrolyte located between the positive electrode and the negative electrode. Effects of the invention

[0026] A positive electrode active material for an all-solid-state battery according to one embodiment and an all-solid-state battery containing the same can exhibit excellent lifespan characteristics while realizing high capacity and high energy density. Brief explanation of the drawing

[0027] FIG. 1 is a schematic diagram showing the shape of a plate-shaped primary particle according to one embodiment. FIG. 2 is a diagram illustrating the definition of radial in secondary particles according to one embodiment. FIG. 3 is a schematic diagram showing the cross-sectional structure of a secondary particle according to one embodiment. FIG. 4a is a cross-sectional view schematically illustrating an all-solid-state battery according to one embodiment. FIG. 4b is a cross-sectional view schematically illustrating an all-solid-state battery according to one embodiment. Figure 5 is a scanning electron microscope image of the fracture surface of the precursor of the positive electrode active material of Example 1. Figure 6 is a scanning electron microscope image of a cross-section of the positive electrode active material of Example 1. Figure 7 is a scanning electron microscope image of a cross-section of the positive electrode active material of Example 2. Figure 8 is a scanning electron microscope image of a cross-section of the positive electrode active material of Comparative Example 2. Figure 9 is a ToF-SIMS analysis image of the positive electrode active material of Example 1. Figure 10 is the mass spectrum result of ToF-SIMS analysis for the positive electrode active material of Example 1. Figure 11 shows the X-ray spectroscopic analysis (XPS) results for the positive electrode active material of Example 1. Figure 12 shows the lifespan evaluation results for the all-solid-state batteries of the example and comparative example. Specific details for implementing the invention

[0028] Specific embodiments are described below in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0029] The terms used herein are for describing exemplary embodiments only and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0030] Here, "combinations of these" refers to mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, etc.

[0031] The terms "include," "equip," or "have" used herein are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0032] In the drawings, thicknesses have been enlarged to clearly represent various layers and regions, and the same reference numerals have been used for similar parts throughout the specification. When a part such as a layer, film, region, or plate is described as being "on" or "on" another part, this includes not only cases where it is "immediately on" another part, but also cases where there is another part in between. Conversely, when a part is described as being "immediately on" another part, it means that there is no other part in between.

[0033] In addition, the term “layer” here includes not only shapes formed on the entire surface when viewed in a plan view, but also shapes formed on some surfaces.

[0034] In addition, the average particle size can be measured by methods widely known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with transmission electron microscope images or scanning electron microscope images. Alternatively, the average particle size value can be obtained by measuring using dynamic light scattering and performing data analysis to count the number of particles for each particle size range and then calculating from thereon. Unless otherwise defined, the average particle size may refer to the diameter (D50) of a particle whose cumulative volume in the particle size distribution is 50% by volume.

[0035] positive electrode active material

[0036] In one embodiment, a positive electrode active material for an all-solid-state battery comprising a lithium nickel-based composite oxide is provided, the positive electrode active material for an all-solid-state battery comprising a plurality of primary particles aggregated to form secondary particles in which at least a portion of the primary particles have a radial arrangement structure, a first boron coating portion present on the surface of the secondary particles, and a second boron coating portion present on the surface of the primary particles inside the secondary particles.

[0037] All-solid-state batteries face a problem where their capacity is not fully realized due to high resistance occurring at the interface between the positive electrode active material and the solid electrolyte. This is understood to be because an impurity layer is formed by the chemical reaction between the positive electrode active material and the solid electrolyte, and a space charge layer is formed upon contact between the solid active material and the solid electrolyte. To address this issue, technologies have been developed to form a buffer layer with lithium ion conductivity at the interface between the positive electrode active material and the solid electrolyte. However, forming this buffer layer requires the use of methods such as the sol-gel method using organic solvents, spray drying, or atomic layer deposition. Since these methods result in excessive process costs, there are limitations to their application in actual mass production.

[0038] According to one embodiment, the positive electrode active material has a lithium boron composite or the like coated on the surface and internal grain boundaries of secondary particles without a process of forming a separate buffer layer, thereby suppressing the interfacial resistance between the positive electrode active material and the solid electrolyte and enabling high capacity. In addition, since the lithium boron composite or the like is coated not only on the surface of the secondary particles but also on the internal grain boundaries, the buffer layer is maintained even with volume changes of the positive electrode active material due to charging and discharging, thereby enabling long-term lifespan characteristics.

[0039] The above-described positive active material comprises a first boron coating portion present on the surface of the secondary particles and a second boron coating portion present on the surface of the primary particles inside the secondary particles. The first boron coating portion and the second boron coating portion comprise a boron compound. The boron compound may include, for example, boron oxide, lithium boron oxide, or a combination thereof, and may include, for example, B2O2, B2O3, B4O3, B4O5, LiBO2, Li2B4O7, Li3BO3, or a combination thereof.

[0040] The second boron coating portion described above exists inside rather than on the surface of the secondary particle, and can be described as being coated along the interface of the primary particles inside the secondary particle, and accordingly, can be expressed as being coated on the grain boundary. Here, the term "inside of the secondary particle" refers to the entire interior excluding the surface, and for example, it can refer to the entire interior starting from a depth of approximately 2 μm from the outer surface, and can also be described as the part that does not come into contact with distilled water when washing the cathode active material secondary particle with distilled water.

[0041] Conventionally, when coating boron onto a positive electrode active material, it was common practice to use a method of mixing boron raw materials into a lithium metal composite oxide in a wet or dry manner and then heat-treating it. However, in this case, there was a problem in that boron acted as a resistance on the surface of the positive electrode active material, thereby worsening the capacity and lifespan. On the other hand, according to one embodiment, a positive electrode active material coated with boron not only on the surface but also on the internal grain boundaries can be obtained by introducing a boron raw material together with a lithium source when introducing a precursor in which primary particles are oriented radially, and then heat-treating it. By simultaneously coating an appropriate amount of boron on the internal grain boundaries and the surface of the positive electrode active material, the boron no longer acts as a resistance, the structural stability of the positive electrode active material is ensured, and the interfacial resistance between the positive electrode active material and the solid electrolyte is suppressed, thereby improving the capacity characteristics and long-term lifespan characteristics of the battery.

[0042] According to one embodiment, the weight of the first boron coating part may be greater than the weight of the second boron coating part. For example, with respect to the total amount of the first boron coating part and the second boron coating part, the second boron coating part may be included in an amount of 2% to 30% by weight, specifically 3% to 25% by weight, or 5% to 20% by weight, and the first boron coating part may be included in an amount of 70% to 98% by weight, 75% to 97% by weight, or 80% to 95% by weight, etc. For example, the weight ratio of the first boron coating part and the second boron coating part may be 70:30 to 98:2, for example 70:30 to 97:3, or 75:25 to 95:5. When the content ratio of the first boron coating part and the second boron coating part is such, boron does not act as a resistor in the cathode active material but can play a role in improving performance, and the cathode active material containing such boron coating parts can achieve high capacity while exhibiting improved lifespan characteristics.

[0043] The content of the first boron coating portion may, for example, be 0.02 wt% to 0.3 wt% with respect to the total weight of the second positive active material, 0.03 wt% to 0.3 wt%, 0.04 wt% to 0.2 wt%, or 0.05 wt% to 0.1 wt%, etc. The content of the second boron coating portion may, for example, be 0.001 wt% to 0.05 wt% with respect to the positive active material, 0.001 wt% to 0.04 wt%, 0.002 wt% to 0.03 wt%, or 0.003 wt% to 0.02 wt%, but is not limited thereto. When the content of the first boron coating portion and the second boron coating portion with respect to the positive active material is such, boron may not act as a resistor in the second positive active material, and the positive active material containing it may exhibit high capacity and excellent lifespan characteristics.

[0044] The total amount of the first boron coating part and the second boron coating part may be 0.1 mol% to 3 mol% with respect to 100 mol% of the second positive active material, for example, 0.1 mol% to 2.5 mol%, 0.1 mol% to 2 mol%, 0.1 mol% to 1.5 mol%, 0.1 mol% to 1.3 mol%, or 0.5 mol% to 1.3 mol%. If the total amount of the first boron coating part and the second boron coating part deviates from a certain content, the initial discharge capacity may decrease and the lifespan characteristics may deteriorate. In particular, if the content of the first boron coating part present on the surface of the secondary particle becomes excessive, the boron acts as a resistor, and the initial discharge capacity of the all-solid-state battery may decrease significantly.

[0045] Meanwhile, the positive electrode active material comprises secondary particles formed by the aggregation of at least two primary particles, and at least a portion of the primary particles have a radial arrangement structure. At least some of the primary particles may have a plate shape. The primary particles may be formed such that their thickness is smaller than their major axis length. Here, the major axis length refers to the maximum length based on the widest surface of the primary particles. That is, the primary particles may have a structure in which the length (t) in one axial direction (i.e., thickness direction) is smaller than the major axis length (a) in the other direction (i.e., surface direction).

[0046] FIG. 1 is a schematic diagram showing the plate shape of a primary particle of a positive electrode active material. Referring to FIG. 1, a primary particle according to one embodiment may have various detailed shapes while basically having a plate structure, such as (A) a polygonal nanoplate shape like a hexagon, (B) a nanodisk shape, and (C) a rectangular prism shape. In FIG. 1, “a” represents the length of the major axis of the primary particle, “b” represents the length of the minor axis, and “t” represents the thickness. The thickness t of the primary particle may be smaller than the lengths a and b in the plane direction. Among the lengths in the plane direction, a may be longer than or equal to b. In the primary particle, the direction in which the thickness t is defined is defined as the thickness direction, and the direction containing lengths a and b is defined as the plane direction.

[0047] In the above-described positive active material, at least some of the primary particles may have a radial arrangement structure, for example, the major axis of the primary particles may be arranged in a radial direction. FIG. 2 is a diagram illustrating the definition of radial in secondary particles according to one embodiment. In one embodiment, a radial arrangement structure means that, as shown in FIG. 2, the thickness (t) direction of the primary particles is arranged to be perpendicular to the direction (R) toward the center of the secondary particles or to form an angle of ±5° with the perpendicular direction.

[0048] The average length of the primary particles constituting the secondary particles above 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 150nm to 500nm. 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.

[0049] When the above primary particle is in the form of a plate, the average thickness of the above primary particle 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, 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 for example, 100 nm to 200 nm. In addition, in the above primary particles, the ratio of the average thickness to the average length may be 1:1 to 1:10, and for example, 1:1 to 1:8, 1:1 to 1:6, or 1:2 to 1:5.

[0050] In this way, when the average length, average thickness, and ratio of average thickness to average length of the primary particles satisfy the ranges described above and the primary particles are arranged radially, there can be relatively many lithium diffusion pathways between grain boundaries on the surface side, and many crystal planes capable of lithium transfer are exposed to the outside, thereby improving lithium diffusivity and enabling the securing of high initial efficiency and capacity. In addition, when the primary particles are arranged radially, the pores exposed on the surface are oriented toward the center of the secondary particles, thereby promoting the diffusion of lithium. Furthermore, uniform shrinkage and expansion are possible during the extraction and / or insertion of lithium by the radially arranged primary particles, and pores exist in the direction of (001), which is the direction in which the particles expand during lithium extraction, thereby providing a buffering effect. In addition, due to the size and arrangement of primary particles, the probability of cracking occurring during the shrinkage and expansion of the active material is reduced, and the internal pores further mitigate volume changes, thereby reducing cracks occurring between primary particles during charging and discharging, which can improve the lifespan characteristics of the all-solid-state battery and reduce the phenomenon of resistance increase.

[0051] The above-described positive active material may have an irregular porous structure in at least one of the interior and exterior of the secondary particle. The irregular porous structure refers to a structure having pores that are not regular and lack uniformity in pore size and shape. For example, the secondary particle may contain an interior containing an irregular porous structure and an exterior containing a radial arrangement structure. That is, the primary particle placed inside may be arranged without regularity, unlike the primary particle placed outside. The interior containing the irregular porous structure contains primary particles, just like the exterior.

[0052] Here, "outer" may mean an area of ​​30% to 50%, for example 40%, from the outermost surface of the total distance from the center of the secondary particle to the surface, or an area within approximately 2 μm from the outermost edge of the secondary particle. Also, "inner" may mean an area of ​​50% to 70%, for example 60%, from the center of the total distance from the center of the secondary particle to the surface, or the remaining area excluding the area within approximately 2 μm from the outermost edge of the secondary particle.

[0053] The secondary particles of the above-described positive electrode active material may contain an outer layer oriented in a radial structure and an inner layer containing an irregular porous structure, wherein the inner layer of the secondary particles may have a larger pore size compared to the outer layer. For example, in the above-described positive electrode active material, the inner pore size may be 150 nm to 1 μm, and the outer pore size may be less than 150 nm. When the inner pore size is larger than the outer pore size in this manner, compared to secondary particles in which the inner and outer pore sizes are the same, there is an advantage of a shorter lithium diffusion distance within the active material, easier insertion of lithium from the outside, and an effect of mitigating volume changes occurring during charging and discharging. Here, the pore size may refer to the average diameter when the pore is spherical or circular, and the length of the major axis when the pore is elliptical, etc.

[0054] The secondary particles of the above-described positive active material may have open pores of less than 150 nm in size, for example, 10 nm to 148 nm, from the surface toward the center of the interior. The open pores are exposed pores through which a material 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.

[0055] Closed pores exist inside the secondary particle, and closed pores and / or open pores may exist outside. While it is difficult for the closed pores to contain electrolytes, the open pores may contain electrolytes. The closed pores are independent pores formed with a structure in which all pore walls are closed and are not connected to other pores, whereas the open pores are continuous pores formed with at least a portion of the pore walls in which they are open and connected to the outside of the particle.

[0056] FIG. 3 is a schematic diagram showing the cross-sectional structure of the secondary particles of the positive active material. Referring to FIG. 3, the secondary particles (11) of the positive active material according to one embodiment contain an outer layer (14) having a structure in which primary particles (13) having a plate shape are arranged in a radial direction, and an inner layer (12) in which the primary particles (13) are arranged irregularly. In the inner layer (12), there may be more empty spaces between the primary particles compared to the outer layer. Also, the pore size and porosity in the inner layer are larger and irregular compared to the pore size and porosity in the outer layer. In FIG. 3, the arrows indicate the direction of movement of lithium ions.

[0057] The interior of the above secondary particles has a porous structure, which has the effect of reducing the diffusion distance of lithium ions to the interior, and the exterior is arranged radially toward the surface, making it easier for lithium ions to be inserted into the surface. In addition, the small size of the primary particles makes it easier to secure lithium transport pathways between the crystal grains. Furthermore, the small size of the primary particles and the pores between them mitigate volume changes that occur during charging and discharging, thereby minimizing stress caused by volume changes during charging and discharging. Such a cathode active material can reduce the resistance of an all-solid-state battery and improve capacity and lifespan characteristics.

[0058] Meanwhile, in the above secondary particle, a plurality of primary particles may be arranged toward a center (1) to form surface contact along the thickness direction of the primary particle, thereby having a radial arrangement structure. Alternatively, the above secondary particle may have a multicenter radial arrangement structure having a plurality of centers. In this way, when the secondary particle has a single center or a multicenter radial arrangement structure, it becomes easier for lithium to be removed or inserted up to the center of the secondary particle.

[0059] The above secondary particles may include radial primary particles and non-radial primary particles. The content of non-radial primary particles may be 20% by weight or less, for example, from 0.01% to 10% by weight, specifically from 0.1% to 5% by weight, based on 100 parts by weight of the total weight of the radial primary particles and non-radial primary particles. When non-radial primary particles are included in the above secondary particles in addition to the radial primary particles within the aforementioned content range, lithium diffusion is facilitated, thereby enabling the manufacture of an all-solid-state battery with improved lifespan characteristics.

[0060] The above-mentioned cathode active material comprises a nickel composite oxide, and may also be said to comprise a lithium nickel composite oxide. The nickel content in the lithium nickel composite oxide may be 30 mol% or more based on the total amount of transition metals excluding lithium, for example, 40 mol% or more, 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more, or 90 mol% or more, and 99.9 mol% or less, or 99 mol% or less. As an example, the nickel content in the lithium nickel composite oxide may be higher than the respective content of other transition metals such as cobalt, manganese, and aluminum. When the nickel content satisfies the above range, the cathode active material can exhibit excellent battery performance while achieving high capacity.

[0061] The above lithium nickel-based composite oxide can be specifically represented by the following chemical formula 1.

[0062] [Chemical Formula 1]

[0063] Li a1 Ni x1 M 1 y1 M 2 1-x1-y1 O2

[0064] In the above Chemical Formula 1, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, and M 1 and M 2Each is independently selected from Al, B, Ce, Co, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof.

[0065] 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.

[0066] The above lithium nickel-based composite oxide may also be represented, for example, by Chemical Formula 2 below.

[0067] [Chemical Formula 2]

[0068] Li a2 Ni x2 Co y2 M 3 1-x2-y2 O2

[0069] In the above chemical formula 2, 0.9≤a2≤1.8, 0.3≤x2<1, 0 <y2≤0.7이고 M 3 It is selected from Al, B, Ce, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof.

[0070] In the above chemical formula 2, 0.3≤x2≤0.99 and 0.01≤y2≤0.7 may be 0.4≤x2≤0.99 and 0.01≤y2≤0.6, or 0.5≤x2≤0.99 and 0.01≤y2≤0.5, or 0.6≤x2≤0.99 and 0.01≤y2≤0.4, or 0.7≤x2≤0.99 and 0.01≤y2≤0.3, or 0.8≤x2≤0.99 and 0.01≤y2≤0.2, or 0.9≤x2≤0.99 and 0.01≤y2≤0.1.

[0071] The above lithium nickel-based composite oxide may also be represented, for example, by the following chemical formula 3.

[0072] [Chemical Formula 3]

[0073] Li a3 Ni x3 Co y3 M 4 z3 M 5 1-x3-y3-z3 O2

[0074] 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 M 4 is selected from Al, Mn, and combinations thereof, and M 5 is selected from B, Ce, Cr, F, Mg, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof.

[0075] In the above chemical formula 3, 0.4≤x3≤0.98, 0.01≤y3≤0.59, and 0.01≤z3≤0.59 may be 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 may be possible.

[0076] Generally, as the nickel content in the cathode active material increases, Ni 2+In the case of an increase in cation mixing where ions occupy lithium sites, the capacity may decrease, or the diffusion of lithium ions may be hindered by impurities such as NiO, which may reduce battery life. Additionally, structural collapse or cracking of the positive electrode active material during charging and discharging may increase side reactions with the electrolyte, thereby reducing battery life and raising safety concerns. In order to solve this, if boron is coated only on the surface of the active material using conventional methods, the boron acts as a resistor, which actually reduces capacity and lifespan. On the other hand, in the positive electrode active material according to one embodiment, even if a high-nickel system is used, the problem caused by high nickel concentration is improved by coating an appropriate amount of boron on the surface of the secondary particles of the active material and even on the grain boundaries inside them, thereby enabling high capacity to be achieved while simultaneously improving lifespan characteristics without reducing the initial discharge capacity.

[0077] Method for manufacturing positive electrode active material

[0078] In one embodiment, a method for manufacturing a positive electrode active material for an all-solid-state battery is provided, comprising mixing a lithium raw material, a nickel-based hydroxide, and a boron raw material and heat-treating them.

[0079] Conventionally, when coating boron onto a positive electrode active material, it was common practice to prepare a lithium nickel-based composite oxide by mixing a lithium raw material with a nickel transition metal composite hydroxide and performing heat treatment, and then mixing a boron source into the mixture in a wet or dry manner and performing heat treatment again. In this case, boron is coated only on the surface of the positive electrode active material, and consequently, the boron acts as a resistor, which actually reduces capacity and lifespan. On the other hand, according to the manufacturing method of one embodiment, a positive electrode active material can be obtained in which boron is coated not only on the surface of the positive electrode active material but also on the grain boundaries inside the positive electrode active material.

[0080] According to this, the boron coating portion of the positive electrode active material within the all-solid-state battery functions as a buffer layer, thereby suppressing the interfacial resistance between the positive electrode active material and the solid electrolyte and improving the capacity characteristics of the all-solid-state battery. Furthermore, since the positive electrode active material is coated with boron even at internal grain boundaries, compared to conventional cases where a coating layer or buffer layer is formed only on the surface of the active material, the performance of the buffer layer can be maintained even with volume changes of the positive electrode active material due to charging and discharging, thereby improving the long-term lifespan characteristics of the all-solid-state battery.

[0081] In the above manufacturing method, the nickel-based hydroxide may be a nickel transition metal complex hydroxide as a precursor of the positive electrode active material and may be manufactured by a co-precipitation method, etc. The nickel-based hydroxide may have at least a portion of its primary particles having a radial arrangement structure. Details regarding such a radial arrangement structure are as described above.

[0082] The above nickel-based hydroxide can be represented, for example, by the following chemical formula 11.

[0083] [Chemical Formula 11]

[0084] Ni x11 M 11 y11 M 12 1-x11-y11 (OH)2

[0085] In the above chemical formula 11, 0.3≤x11≤1, 0≤y11≤0.7, and M 11 and M 12 Each is independently selected from Al, B, Ce, Co, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof.

[0086] As a specific example, the above nickel-based hydroxide can be represented by the following chemical formula 12 or chemical formula 13.

[0087] [Chemical Formula 12]

[0088] Ni x12Co y12 M 13 1-x12-y12 (OH)2

[0089] In the above chemical formula 12, 0.3≤x12<1, 0 <y12≤0.7이고 M 13 It is selected from Al, B, Ce, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof.

[0090] [Chemical Formula 13]

[0091] Ni x13 Co y13 M 14 z13 M 15 1-x13-y13-z13 (OH)2

[0092] 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 selected from Al, Mn, and combinations thereof, and M 15 is selected from B, Ce, Cr, F, Mg, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof.

[0093] The above lithium raw material may be, for example, lithium hydroxide, and may be mixed in a ratio of 0.8 to 1.8 moles or 0.8 to 1.2 moles per 1 mole of the above nickel-based hydroxide.

[0094] The above boron raw material is a compound containing boron, for example, H3BO3, HBO2, B2O3, C6H5B(OH)2, (C6H5O)3B, [CH3(CH2)3O]3B, (C3H7O)3B, C3H9B3O6, C 13 H 19 It may include BO3, or a combination thereof.

[0095] The content of the boron raw material may be 0.1 mol% to 5 mol% with respect to 100 mol% of the nickel transition metal complex hydroxide, for example, 0.1 mol% to 4 mol%, 0.1 mol% to 3 mol%, 0.1 mol% to 2.9 mol%, 0.1 mol% to 2.5 mol%, 0.1 mol% to 2 mol%, 0.1 mol% to 1.5 mol%, or 0.5 mol% to 1.3 mol%. When the content of the boron raw material satisfies the above range, boron does not act as a resistor in the cathode active material and can play a role in improving the performance of the all-solid-state battery, thereby improving capacity and lifespan characteristics. If the content of the boron raw material becomes excessive, the content of the first boron coating part increases excessively, causing boron to act as a resistor in the cathode active material, which can reduce the capacity and lifespan of the battery.

[0096] The above heat treatment can be performed at a temperature of, for example, 650 ℃ to 850 ℃ or 690 ℃ to 780 ℃, and in this case, a positive electrode active material for an all-solid-state battery with a stable structure including both a first boron coating part and a second boron coating part can be manufactured.

[0097] In addition, the heat treatment may be carried out for 5 to 15 hours, for example, 8 to 12 hours, and in this case, a positive electrode active material for an all-solid-state battery with a stable structure including both the first boron coating part and the second boron coating part can be manufactured.

[0098] All-solid-state battery

[0099] In one embodiment, an all-solid-state battery is provided, comprising a positive electrode including the aforementioned positive active material, a negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode. The all-solid-state battery may also be described as an all-solid-state secondary battery.

[0100] FIG. 4a is a cross-sectional view of an all-solid-state battery according to one embodiment. Referring to FIG. 4a, the all-solid-state battery (100) may have a structure in which an electrode assembly is stacked, comprising 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), and the assembly 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). FIG. 4a shows a single electrode assembly including a negative electrode (400), a solid electrolyte layer (300), and a positive electrode (200), but an all-solid-state battery may be manufactured by stacking two or more electrode assemblies.

[0101] anode

[0102] A positive electrode for an all-solid-state battery may include a current collector and a positive electrode active material layer located on the current collector. The positive electrode active material layer includes the aforementioned positive electrode active material and may further include a binder, a conductive material, a dispersant, and / or a solid electrolyte.

[0103] The above binder serves to adhere the positive active material particles well to each other and also to adhere the positive active material well to the current collector. Representative examples include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0104] The content of the binder in the above positive active material layer may be approximately 0.1% to 5% by weight, or 0.5% to 3% by weight, based on the total weight of the positive active material layer.

[0105] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fiber, 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 comprising a mixture thereof. The content of the conductive material in the positive electrode active material layer may be 0.1% to 5% by weight, or 0.3% to 3% by weight, based on the total weight of the positive electrode active material layer.

[0106] The content of the solid electrolyte in the above positive active material layer may be 0% to 35% by weight, for example, 0.1% to 35% by weight, 1% to 35% by weight, 5% to 30% by weight, 8% to 25% by weight, or 10% to 20% by weight. A specific description of the type of solid electrolyte will be provided later in the all-solid-state battery section below.

[0107] Aluminum foil may be used as the anode current collector, but is not limited thereto.

[0108] cathode

[0109] A negative electrode for an all-solid-state battery may, for example, include a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer may include a negative electrode active material and may further include a binder, a conductive material, and / or a solid electrolyte.

[0110] The above-mentioned negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0111] A 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 amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0112] As the above lithium metal alloy, an alloy of a metal selected from the group consisting of lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0113] As a material capable of doping and undoping the above lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material may be used, and the Si-based negative electrode active material may include silicon, a silicon-carbon composite, or SiO₂. xExamples of the above Sn-based negative electrode active materials include (0 < x < 2), Si-Q alloy (where Q is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO2, Sn-R alloy (where R is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), and at least one of these may be mixed with SiO2. The above elements Q and R may be selected from the group consisting of 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, and combinations thereof.

[0114] The silicon-carbon composite may be, for example, a silicon-carbon composite comprising a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. As the amorphous carbon precursor, coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, or polymer resins such as phenolic resin, furan resin, or polyimide resin may be used. In this case, the silicon content may be 10% to 50% by weight of the total weight of the silicon-carbon composite. Additionally, the content of the crystalline carbon may be 10% to 70% by weight of the total weight of the silicon-carbon composite, and the content of the amorphous carbon may be 20% to 40% by weight of the total weight of the silicon-carbon composite. Furthermore, the thickness of the amorphous carbon coating layer may be 5nm to 100nm. The average particle size (D50) of the silicon particles may be 10 nm to 20 μm. The average particle size (D50) of the silicon particles may preferably be 10 nm to 200 nm. The silicon particles may exist in an oxidized form, wherein the atomic content ratio of Si:O within the silicon particles indicating the degree of oxidation may be a weight ratio of 99:1 to 33:66. The silicon particles are SiO x It can be a particle, and in this case, SiO x In this specification, the range of x may be greater than 0 and less than 2. Unless otherwise defined, the average particle size (D50) refers to the diameter of a particle in which the cumulative volume in the particle size distribution is 50 volume%.

[0115] The above Si-based negative electrode active material or Sn-based negative electrode active material may be used in combination with a carbon-based negative electrode active material. When the Si-based negative electrode active material or Sn-based negative electrode active material and the carbon-based negative electrode active material are mixed and used, the mixing ratio may be 1:99 to 90:10 by weight.

[0116] The content of the negative electrode active material in the above negative electrode active material layer may be 95% to 99% by weight with respect to the total weight of the negative electrode active material layer.

[0117] In one embodiment, the negative active material layer further comprises a binder and optionally further comprises a conductive material. The content of the binder in the negative active material layer may be 1% to 5% by weight with respect to the total weight of the negative active material layer. Additionally, when further comprising a conductive material, the negative active material layer may comprise 90% to 98% by weight of the negative active material, 1% to 5% by weight of the binder, and 1% to 5% by weight of the conductive material.

[0118] The above binder serves to effectively bond the negative electrode active material particles to each other and also to effectively bond the negative electrode active material to the current collector. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

[0119] Examples of the above-mentioned water-insoluble binders include 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.

[0120] Examples of the above water-soluble binders include rubber-based binders or polymer resin binders. 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, ethylenepropylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0121] When a water-soluble binder is used as the above-mentioned cathode binder, a cellulose-based compound capable of imparting viscosity may be further included. As this cellulose-based compound, one or more types such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K, or Li may be used as the alkali metal. The content of such a thickener may be 0.1 to 3 parts by weight per 100 parts by weight of the cathode active material.

[0122] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube; metal-based materials in the form of metal powder or metal fibers including copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or conductive materials including mixtures thereof.

[0123] The above-mentioned cathode current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0124] Meanwhile, as an example, the negative electrode for an all-solid-state battery may be a precipitation type negative electrode. The precipitation type negative electrode may refer to a negative electrode that does not have a negative electrode active material when assembling the electrochemical battery, but where lithium metal, etc., is precipitated during charging of the electrochemical battery and acts as the negative electrode active material. FIG. 4b is a schematic cross-sectional view of an all-solid-state battery including a precipitation type negative electrode. Referring to FIG. 4b, the precipitation type negative electrode (400') may include a current collector (401) and a negative electrode catalyst layer (405) located on the current collector. A lithium secondary battery having such a precipitation type negative electrode (400') may start initial charging in a state where no negative electrode active material is present, and during charging, a high-density lithium metal, etc., is precipitated between the current collector (401) and the negative electrode catalyst layer (405) to form a lithium metal layer (404), which may act as the negative electrode active material. Accordingly, in a solid-state battery that has undergone one or more charges, the precipitation type negative electrode (400') may include a current collector (401), a lithium metal layer (404) located on the current collector, and a negative electrode catalyst layer (405) located on the metal layer. The lithium metal layer (404) refers to a layer in which lithium metal, etc. is precipitated during the charging process of an electrochemical battery, and may be referred to as a metal layer or a negative electrode active material layer, and may serve as a negative electrode active material.

[0125] The above cathode catalyst layer (405) may include a metal or carbon material that acts as a catalyst.

[0126] The above metal may include gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, zinc, or a combination thereof, and may be composed of one of these or may be composed of several types of alloys. The average particle size (D50) of the metal included in the cathode catalyst layer may be about 4 μm or less, and may be, for example, 10 nm to 4 μm.

[0127] The carbon material may be, for example, crystalline carbon, non-graphite carbon, or a combination thereof. The crystalline carbon may be at least one selected from, for example, natural graphite, artificial graphite, mesophase carbon micro beads, and combinations thereof. The non-graphite carbon may be at least one selected from carbon black, activated carbon, acetylene black, Denka black, Ketjen black, and combinations thereof.

[0128] When the above-mentioned cathode catalyst layer (405) includes both the metal and the 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 battery can be improved. The above-mentioned cathode catalyst layer may include, for example, a carbon material supported with a catalyst metal, or may include a mixture of metal particles and carbon material particles.

[0129] The above cathode catalyst layer (405) may further include a binder, and the binder may be a conductive binder. Additionally, the cathode catalyst layer may further include common additives such as fillers, dispersants, ion conductive agents, etc. In one embodiment, the cathode catalyst layer may not include a cathode active material.

[0130] The thickness of the above cathode catalyst layer (405) may be, for example, 1 μm to 20 μm.

[0131] The above-described precipitation type cathode (400') may, for example, further include a thin film on the surface of the current collector, that is, between the current collector and the cathode catalyst 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 be, for example, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., and may be composed of one of these or composed of several types of alloys. The thin film can further flatten the precipitation shape of the metal layer and further improve the characteristics of the all-solid-state battery. The thin film may be formed by, for example, vacuum deposition, sputtering, plating, etc. The thickness of the thin film may be, for example, 1 nm to 500 nm.

[0132] solid electrolyte layer

[0133] The above 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.

[0134] In one embodiment, the solid electrolyte may be a sulfide-based solid electrolyte having excellent ion conductivity. The sulfide-based solid electrolyte is, for example, Li2S-P2S5, Li2S-P2S5-LiX (where X is a halogen element, for example, I or Cl), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO qExamples include (p, q are integers, and M is P, Si, Ge, B, Al, Ga, or In).

[0135] The above-mentioned 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 manufactured. The ionic conductivity may be further improved by including other components such as SiS2, GeS2, and B2S3. Mechanical milling or a solution method may be applied as the mixing method. Mechanical milling is a method in which starting materials are placed in a reactor and vigorously stirred with a ball mill or similar device to finely atomize and mix the starting materials. When using the solution method, the starting materials are mixed in a solvent to obtain a solid electrolyte as a precipitate. Additionally, calcination may be performed after mixing. If additional calcination is performed, the crystals of the solid electrolyte can become more robust.

[0136] For example, the solid electrolyte may be an argyrodite-type sulfide-based solid electrolyte. The sulfide-based solid electrolyte is, for example, Li a M b P c S d A e (a, b, c, d, and e are all between 0 and 12 inclusive, M is Ge, Sn, Si, or a combination thereof, and A is one of F, Cl, Br, or I), and specifically Li3PS4, Li7P3S 11 It may be Li6PS5Cl, etc. These sulfide-based solid electrolytes have an ionic conductivity of 10 at room temperature, which is the same as that of typical liquid electrolytes. -4 to 10 -2It has high ionic conductivity close to the S / cm range, allowing for the formation of a tight interface between the electrode layer and the solid electrolyte layer without causing a decrease in ionic conductivity. An all-solid-state secondary battery containing this can improve battery performance, such as rate characteristics, Coulomb efficiency, and lifespan characteristics.

[0137] The above sulfide-based solid electrolyte may be amorphous or crystalline, or may be in a mixed state.

[0138] The above solid electrolyte may be an oxide-based inorganic solid electrolyte in addition to sulfide-based materials, 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 yTiO3, 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), or a mixture thereof may be included.

[0139] The solid electrolyte included in the solid electrolyte layer is in the form of particles, and the average particle size (D50) may be 5.0 μm or less, for example, 0.5 μm to 5.0 μm. Such a solid electrolyte can form a tight interface between the anode layer and the solid electrolyte layer without causing a short circuit.

[0140] The above solid electrolyte layer may further include a binder. In this case, styrene butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, acrylate-based polymers, or combinations thereof may be used as the binder, but are not limited thereto, and any material used as a binder in the relevant technical field may be used. The above acrylate-based polymer may be, for example, butyl acrylate, polyacrylate, polymethacrylate, or a combination thereof.

[0141] The above solid electrolyte layer can be formed by adding a solid electrolyte to a binder solution, coating it onto a substrate film, and drying it. The solvent of the binder solution may be isobutyryl isobutylate, xylene, toluene, benzene, hexane, or a combination thereof. Since the process for forming the above solid electrolyte layer is widely known in the field, a detailed description will be omitted.

[0142] The thickness of the solid electrolyte layer may be, for example, 10 μm to 150 μm.

[0143] The solid electrolyte layer may further comprise an alkali metal salt and / or an ionic liquid and / or a conductive polymer. For example, the solid electrolyte layer may further comprise a lithium salt and / or an ionic liquid and / or a conductive polymer.

[0144] The content of the lithium salt in the solid electrolyte layer may be 1M or more, for example, 1M to 4M. In this case, the lithium salt can improve ion conductivity by improving the lithium ion mobility of the solid electrolyte layer.

[0145] The above lithium salts are, 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(trifluoromethanesulfonyl)imide (LiTFSI, LiN(SO2CF3)2), lithium bis(fluorosulfonyl)imide (LiFSI), It may include LiN(SO2F)2), LiCF3SO3, LiAsF6, LiSbF6, LiClO4, or a mixture thereof. Additionally, the lithium salt may be imide-based, for example, the imide-based lithium salt may include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, LiN(SO2CF3)2) and lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO2F)2). The lithium salt may maintain or improve ionic conductivity by appropriately maintaining chemical reactivity with the ionic liquid.

[0146] The above ionic liquid may include, for example, Li2S-P2S5-LiX (where X is a halogen element), etc.

[0147] The weight ratio of the solid electrolyte to the ionic liquid in the above solid electrolyte layer may be 0.1:99.9 to 90:10, and for example, 10:90 to 90:10, 20:80 to 90:10, 30:70 to 90:10, 40:60 to 90:10, or 50:50 to 90:10. A solid electrolyte layer satisfying the above range can maintain or improve ionic conductivity by increasing the electrochemical contact area with the electrode. Accordingly, the energy density, discharge capacity, rate characteristics, etc. of the all-solid-state battery can be improved.

[0148] The above-mentioned all-solid-state secondary battery may be a unit cell having a structure of a positive electrode / solid electrolyte layer / negative electrode, a bicell having a structure of a positive electrode / solid electrolyte layer / negative electrode / solid electrolyte layer / positive electrode, or a stacked battery in which the structure of the unit cell is repeated.

[0149] The shape of the above-described solid-state battery is not particularly limited and may be, for example, coin-type, button-type, sheet-type, stacked-type, cylindrical-type, flat-type, etc. In addition, the above-described solid-state battery can be applied to large batteries used in electric vehicles, etc. For example, the above-described 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 a large amount of power storage, for example, electric bicycles or power tools.

[0150] Examples and comparative examples of the present invention are described below. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0151] Example 1

[0152] 1. Preparation of positive electrode active material precursor

[0153] Through the coprecipitation method described below, nickel-based hydroxide Ni 0.91 Co 0.09(OH)2 is synthesized. Nickel sulfate and cobalt sulfate are used as metal raw materials. The reaction system uses a batch reactor with an effective reaction volume of 85.5 L, and a concentration system capable of continuously removing the solution other than the co-precipitate is used.

[0154] [Stage 1: 4.5kW / ㎥, NH 4 OH 0.25M, pH 11.8 to 12.0, reaction time 6 hours]

[0155] First, ammonia solution with a concentration of 0.25 M is added to the reactor. The reaction is started at a stirring power of 4.5 kW / m³ and a reaction temperature of 50℃ while adding the metal raw material and the complexing agent at rates of 107 ml / min and 25 ml / min, respectively. The reaction is carried out for 6 hours while adding NaOH to maintain the pH. After confirming that the size of the particles obtained as a result of the reaction continues to decrease for up to 6 hours to form a core, Step 2 is carried out as follows.

[0156] [Stage 2: 3.5kW / ㎥, NH 4 OH 0.30M, pH 11.8 to 12.0, reaction time 15 hours]

[0157] While maintaining the reaction temperature at 50°C, the metal raw material and the complexing agent are added at varying rates of 142 ml / min and 33 ml / min, respectively, so that the concentration of the complexing agent is maintained at 0.20 M. The reaction is carried out for 16 hours while adding NaOH to maintain the pH. During this time, the stirring power is lowered to 3.5 kW / m³, which is lower than that of the first stage, to proceed with the reaction. The reaction is terminated after confirming that the average size of the product particles containing the core and surface layer obtained from this reaction is 3.5 μm to 3.8 μm.

[0158] [Post-processing]

[0159] After washing the obtained product, it is hot-air dried at approximately 150°C for 24 hours to obtain nickel-based hydroxide Ni 0.91 Co 0.09 (OH)2 is obtained.

[0160] 2. Preparation of positive electrode active material

[0161] A positive electrode active material (LiNi) in which a boron compound is coated on the internal grain boundaries and surface is obtained by mixing the obtained nickel-based hydroxide with LiOH in a 1:1 molar ratio, mixing 1.0 mol% of boric acid with respect to the nickel-based hydroxide, and heat-treating at 725°C in an oxygen atmosphere for 10 hours. 0.91 Co 0.09 Obtain O2.

[0162] 3. Manufacture of the anode

[0163] 85 wt% of the obtained positive active material, 13.5 wt% of the lithium azyrodite-type solid electrolyte Li6PS5Cl, 1.0 wt% of the binder, 0.4 wt% of the carbon nanotube conductive material, and 0.1 wt% of the dispersant are placed in an isobutylyl isobutylate (IBIB) solvent, 2 mm zirconia balls are added, and the mixture is stirred with a sinker mixer to prepare a slurry. The prepared slurry is applied to a positive current collector and dried to prepare a positive electrode.

[0164] 4. Preparation of Solid Electrolyte Layer

[0165] Isobutylyl isobutylate (IBIB) is added as a binder solution to an azirodite-type solid electrolyte Li6PS5Cl and mixed. At this time, the mixture is stirred with a Thinky mixer to adjust the viscosity to an appropriate level. After adjusting the viscosity, 2 mm zirconia balls are added and stirred again with a Thinky mixer to prepare a slurry. The slurry is cast onto a release PET film and dried at room temperature to produce a solid electrolyte layer.

[0166] 5. Preparation of the cathode

[0167] The cathode is a cathode-free system, and the cathode is prepared by applying carbon supported with Ag, which is a catalyst, as a slurry onto the cathode current collector and drying it.

[0168] 6. Manufacturing of All-Solid State Batteries

[0169] The prepared positive electrode, negative electrode, and solid electrolyte layer were cut, and the solid electrolyte layer was laminated onto the positive electrode, and then the negative electrode was laminated on top of it. This was sealed in a pouch form and subjected to WIP (Warm Isostatic Press) at a high temperature of 500 MPa for 30 minutes to manufacture an all-solid-state battery.

[0170] Example 2

[0171] In the preparation of the anode active material precursor of Example 1 above, aluminum nitrate is further used as a metal raw material to Ni 0.945 Co 0.04 Al 0.015 (OH)2 is obtained and used as a precursor for the positive active material. In the preparation of the positive active material of Example 1, 0.5 mol% of boric acid is added and heat-treated at 700°C, except that the positive active material and the all-solid-state battery are prepared in the same manner as in Example 1.

[0172] Comparative Example 1

[0173] A positive electrode active material is prepared in the same manner as in Example 1, except that boric acid is not added during the preparation of the positive electrode active material of Example 1. The positive electrode active material, lithium ethoxide, and zirconium propoxide are mixed in ethanol, and a buffer layer in the form of Li2O·ZrO2 is formed on the surface of the active material through spray drying, which allows for the recovery of the organic solvent without contact with the outside air. Subsequently, a positive electrode and an all-solid-state battery are prepared in the same manner as in Example 1.

[0174] Comparative Example 2

[0175] A positive electrode active material precursor is prepared by the following method, and a positive electrode active material and an all-solid-state battery are prepared in the same manner as in Example 1, except that boric acid is not added in the preparation of the positive electrode active material.

[0176] Nickel-based hydroxides, Ni 0.91 Co0.09 A continuous reactor (CSTR), commonly used in the industry, is used for the synthesis of (OH)2. The effective reaction volume is 83 L. Nickel sulfate and cobalt sulfate are used as metal feedstocks.

[0177] First, ammonia water with a concentration of 0.35 M is added to the reactor. The reaction is started at a stirring power of 3.0 kW / m³ and a reaction temperature of 50℃ while adding the metal raw material and the complexing agent at rates of 71 ml / min and 25 ml / min, respectively. After reacting for 30 hours while adding NaOH to maintain the pH, the precursor is obtained.

[0178] Comparative Example 3

[0179] In the preparation of the anode active material of Example 1 above, LiNi without boron compound coating and without adding boric acid 0.91 Co 0.09 After manufacturing the O2 active material, a boron compound is coated onto the cathode active material using a conventional method. That is, LiNi 0.91 Co 0.09 A positive electrode active material coated with a boron compound on its surface is obtained by mixing 1.0 mol% of O2 and boric acid and performing a secondary heat treatment at 350°C for 8 hours in an oxygen atmosphere. A positive electrode and an all-solid-state battery are manufactured in the same manner as in Example 1, except that this is used as the positive electrode active material.

[0180] Evaluation Example 1: Confirmation of SEM image

[0181] FIG. 5 is a photograph of the fracture surface of the positive electrode active material precursor of Example 1, characterized by having a porous layer in the center and a surface portion that is radially oriented in which primary particles are oriented toward the surface direction of secondary particles. In addition, it was confirmed that the surface is porous and easy to shrink, so after manufacturing the active material as shown in FIG. 6 and 7, the structure in which small primary particles are radially oriented is maintained.

[0182] Figure 8 is a cross-sectional photograph of the active material synthesized by Comparative Example 2, confirming that when a general precursor is synthesized and boron is not added, the primary particles are large and do not form an oriented structure.

[0183] Evaluation Example 2: Examination of the composition of the active material surface

[0184] Figure 9 is a Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) analysis image, Figure 10 is the mass spectrum result of the ToF-SIMS analysis, and Figure 11 is the X-ray Photoelectron Spectroscopy (XPS) result.

[0185] As shown in Figure 11, the presence of Li-BO bonds was confirmed by analyzing the bond energy, and it was confirmed through literature that it is lithium borate.

[0186] In Figure 9, by mapping lithium, boron, and lithium and boron simultaneously, it was confirmed that these lithium borates are evenly distributed on the surface of the cathode active material. In addition, through the mass spectrometry results in Figure 10, it was confirmed that there is a large amount of the BO2 form.

[0187] When combining the results of Figures 9 to 11, it is understood that a lithium boron compound is evenly coated on the surface of the secondary particles of the positive active material, and that LiBO2 is the main component.

[0188] Evaluation Example 3: Evaluation of Boron Content at Surface and Internal Grain Boundaries of Anode Active Material

[0189] The boron content is measured by performing ICP (Inductively Coupled Plasma) emission spectroscopic analysis on the cathode active material prepared in Example 1. 10 g of this cathode active material is placed in 100 g of distilled water and stirred for 30 minutes, after which the cathode active material is filtered. Through this washing process, all boron present on the surface of the cathode active material is removed. After drying the recovered cathode active material at 130°C for 24 hours, ICP emission spectroscopic analysis is performed again to measure the amount of boron remaining in the cathode active material, and this is expressed as the amount of boron present inside the cathode active material, i.e., at the grain boundaries. Additionally, the value obtained by subtracting the amount of boron after washing from the amount of boron before washing—that is, the amount of boron removed through the washing process—is expressed as the amount of boron present on the surface of the cathode active material. In Table 1 below, the unit ppm is 10 -4 It can mean weight %, and can mean the ratio of the weight of boron to the total weight of the cathode active material.

[0190] Amount of boron before washing (ppm) Amount of boron (ppm) present at internal grain boundaries Amount of boron present on the surface (ppm) Example 1 940 185 755 Example 2 540 30 510 Comparative Example 3 1,020 0 1,020

[0191] In Table 1, the amount of boron present on the surface represents the content of the first boron coating portion, and the amount of boron present at the internal grain boundaries represents the content of the second boron coating portion. Referring to Table 1, it can be seen that in Example 1, the content of the first boron coating portion is 0.0755 wt% relative to the total positive electrode active material, and the content of the second boron coating portion is 0.0185 wt% relative to the total positive electrode active material. Additionally, the weight ratio of the first boron coating portion to the second boron coating portion is calculated to be approximately 80:20. Furthermore, in Example 2, which contains 50% of the boron from Example 1, the weight ratio of the first boron coating portion to the second boron coating portion is calculated to be approximately 94:6. Additionally, it was confirmed that boron is not coated inside the secondary particles of the positive electrode active material with a conventional boron coating, as in Comparative Example 3.

[0192] Evaluation Example 4: Evaluation of Initial Discharge Capacity

[0193] The all-solid-state batteries prepared in the examples and comparative examples were charged at 45°C with a constant current of 0.1C to an upper limit voltage of 4.25V, and then discharged at 0.1C to a discharge cutoff voltage of 2.5V to measure the initial discharge capacity, and the results are shown in Table 2. Referring to Table 2, it can be confirmed that Comparative Example 2, which does not use the positive active material according to one embodiment and does not form a buffer layer, shows a significantly lower initial discharge capacity, while Example 1 achieves a higher initial capacity even compared to Comparative Example 1, which has a buffer layer formed. Furthermore, Comparative Example 3, which simply coats boron only on the surface of the secondary particles, can be understood as having a simultaneous decrease in charge and discharge capacity because the boron acts as a resistor.

[0194] Charging capacity (mAh / g) Discharge capacity (mAh / g) ICE (%) Example 1 233 213 91 Example 2 235 215 91 Comparative Example 1 230 188 82 Comparative Example 2 226 176 78 Comparative Example 3 223 182 81

[0195] Evaluation Example 5: Life Characteristics Evaluation

[0196] For the all-solid-state batteries of the example and comparative example that underwent initial charging and discharging in Evaluation Example 4 above, the lifespan characteristics were evaluated by repeating charging at 0.33C and discharging at 0.33C 150 times in a voltage range of 2.5V to 4.25V at 45℃, and the results are shown in FIG. 12. Referring to FIG. 12, in the case of Comparative Examples 2 and 3, a rapid decrease in lifespan was observed, while in the case of Examples 1 and 2, the capacity was maintained at a superior level compared to Comparative Example 1, in which a buffer layer was formed by the conventional method. Therefore, it can be confirmed that the lifespan characteristics of Examples 1 and 2 are excellent.

[0197] Although preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concepts defined in the following claims are also included within the scope of the present invention. Explanation of the symbols

[0198] 11: Secondary particle 12: Interior of the secondary particle 13: Primary particle 14: External part of the secondary particle 100: All-solid-state battery 200: Cathode 201: Positive current collector 203: Positive active material layer 300: Solid electrolyte layer 400: Cathode 401: Cathode current collector 403: Cathode active material layer 400': Precipitation type cathode 404: Lithium metal layer 405: Cathode catalyst layer 500: Elastic layer

Claims

Claim 1 A positive electrode active material for an all-solid-state battery comprising a lithium nickel-based composite oxide, wherein the positive electrode active material comprises a plurality of primary particles aggregated to form a secondary particle having at least a portion of the primary particles having a radial arrangement structure, a first boron coating portion present on the surface of the secondary particle, and a second boron coating portion present on the surface of the primary particles inside the secondary particle, wherein the interior of the secondary particle of the second boron coating portion is a portion excluding the surface of the secondary particle, and the second boron coating portion is coated along the interface of the primary particles located inside the secondary particle. Claim 2 In claim 1, the first boron coating portion and the second boron coating portion each comprise a positive electrode active material for an all-solid-state battery comprising boron oxide, lithium boron oxide, or a combination thereof. Claim 3 A positive electrode active material for an all-solid-state battery, wherein, in claim 1, the weight of the first boron coating part is greater than the weight of the second boron coating part. Claim 4 A positive electrode active material for an all-solid-state battery according to claim 1, wherein, with respect to the total amount of the first boron coating part and the second boron coating part, the first boron coating part is included in an amount of 70% to 98% by weight and the second boron coating part is included in an amount of 2% to 30% by weight. Claim 5 A positive electrode active material for an all-solid-state battery according to claim 1, wherein the content of the first boron coating portion is 0.02 weight% to 0.3 weight% with respect to the positive electrode active material. Claim 6 A positive electrode active material for an all-solid-state battery according to claim 1, wherein the content of the second boron coating portion is 0.001 weight% to 0.05 weight% with respect to the positive electrode active material. Claim 7 A positive electrode active material for an all-solid-state battery according to claim 1, wherein the total amount of the first boron coating part and the second boron coating part is 0.1 mol% to 3 mol% with respect to the positive electrode active material. Claim 8 A positive electrode active material for an all-solid-state battery according to claim 7, wherein the total amount of the first boron coating part and the second boron coating part is 0.1 mol% to 1.5 mol% with respect to the positive electrode active material. Claim 9 A positive electrode active material for an all-solid-state battery according to claim 1, wherein the primary particles have a plate shape, and at least some of the primary particles of the plate shape have their long axes arranged in a radial direction. Claim 10 A positive electrode active material for an all-solid-state battery according to claim 9, wherein the average length of the plate-shaped primary particles is 150 nm to 500 nm, the average thickness is 100 nm to 200 nm, and the ratio of the average thickness to the average length is 1:2 to 1:

5. Claim 11 A positive electrode active material for an all-solid-state battery according to claim 1, wherein the secondary particle comprises an interior having an irregular porous structure and an exterior having a radial arrangement structure. Claim 12 A positive electrode active material for an all-solid-state battery according to claim 1, wherein the interior of the secondary particle has a larger pore size than the exterior, the pore size inside the secondary particle is 150 nm to 1 μm, and the pore size outside the secondary particle is less than 150 nm. Claim 13 A positive electrode active material for an all-solid-state battery according to claim 1, wherein the secondary particles comprise open pores having a size of less than 150 nm and a depth of 150 nm or less from the surface, extending from the surface toward the center of the interior. Claim 14 A positive electrode active material for an all-solid-state battery according to claim 1, wherein the lithium nickel-based composite oxide is represented by the following chemical formula 1: [Chemical Formula 1]Li a1 Ni x1 M 1 y1 M 2 1-x1-y1 In the above chemical formula 1, O2, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, and M 1 and M 2 Each is independently selected from Al, B, Ce, Co, Cr, F, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof. Claim 15 A method for manufacturing a positive electrode active material for an all-solid-state battery, comprising mixing a lithium raw material, a nickel-based hydroxide, and a boron raw material and heat-treating them to obtain a positive electrode active material according to any one of claims 1 to 14. Claim 16 A method for manufacturing a positive electrode active material for an all-solid-state battery according to claim 15, wherein the content of the boron raw material is 0.1 mol% to 3 mol% with respect to 100 mol% of the nickel-based hydroxide. Claim 17 A method for manufacturing a positive electrode active material for an all-solid-state battery, wherein, in claim 15, the heat treatment is performed at a temperature of 650 ℃ to 850 ℃ for 5 to 20 hours. Claim 18 An all-solid-state battery comprising a positive electrode containing a positive active material according to any one of claims 1 to 14, a negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode. Claim 19 In claim 18, the positive electrode comprises a current collector and a positive electrode active material layer located on the current collector, the positive electrode active material layer comprises the positive electrode active material and a solid electrolyte, and the solid electrolyte comprises 0.1% to 35% by weight with respect to the total weight of the positive electrode active material layer, in an all-solid-state battery. Claim 20 In claim 18, the all-solid-state battery comprises a current collector and a negative active material layer or a negative catalyst layer located on the current collector. Claim 21 In claim 18, the all-solid-state battery comprises a current collector and a negative electrode catalyst layer located on the current collector, and a lithium metal layer formed during initial charging between the current collector and the negative electrode catalyst layer.

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