Positive electrode active material for rechargeable lithium battery, method of preparing the same, and rechargeable lithium battery

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery comprising a lithium nickel-based composite oxide, wherein the positive electrode active material comprises a plurality of primary particles aggregated to form secondary particles, at least a portion of said primary particles arranged radially, a boron coating layer containing lithium borate located on the surface of said secondary particles, and a boron doping layer located inside the primary particles exposed on the surface of said secondary particles, a method for manufacturing the same, and a lithium secondary battery comprising the same.

Description

Technology Field

[0001] The invention relates to a positive electrode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery containing 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] Various cathode active materials are being investigated to realize lithium secondary batteries suitable for these applications. Among them, lithium nickel-based oxides, lithium nickel manganese cobalt composite oxides, lithium nickel cobalt aluminum composite oxides, and lithium cobalt oxides are primarily used as cathode active materials. However, these cathode active materials face problems such as structural collapse or cracking due to repeated charge-discharge cycles, which degrades the long-term lifespan of the lithium secondary battery and increases resistance, resulting in unsatisfactory capacity characteristics. Therefore, there is a need to develop new cathode active materials that can secure long-term lifespan characteristics while achieving high capacity and high energy density. The problem to be solved

[0004] The present invention provides a positive electrode active material for a lithium secondary battery with improved lifespan characteristics while achieving high capacity, a method for manufacturing the same, and a lithium secondary battery including the same. means of solving the problem

[0005] In one embodiment, a positive electrode active material for a lithium secondary battery comprising a lithium nickel-based composite oxide is provided, the positive electrode active material for a lithium secondary battery comprising a plurality of primary particles aggregated to form secondary particles in which at least a portion of the primary particles are arranged radially, a boron coating layer containing lithium borate located on the surface of the secondary particles, and a boron doping layer located inside the primary particles exposed on the surface of the secondary particles.

[0006] In another embodiment, a method for manufacturing a positive electrode active material for a lithium secondary battery is provided, comprising mixing a nickel-based hydroxide, a lithium raw material, and a boron raw material and heat-treating them.

[0007] In another embodiment, a lithium secondary battery is provided comprising a positive electrode including the aforementioned positive active material, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte. Effects of the invention

[0008] A positive electrode active material for a lithium secondary battery according to one embodiment and a lithium secondary battery containing the same can exhibit excellent lifespan characteristics while realizing high capacity and high energy density. Brief explanation of the drawing

[0009] Figure 1 is a schematic diagram showing the shape of a plate-shaped primary particle. Figure 2 is a diagram illustrating the definition of radial in secondary particles. FIG. 3 is a schematic diagram showing the cross-sectional structure of a secondary particle according to one embodiment. FIG. 4 is a cross-sectional view schematically illustrating a lithium secondary battery according to one embodiment. Figure 5 is a scanning electron microscope (SEM) image of a cross-section of the positive electrode active material precursor prepared in Example 1. Figure 6 is an SEM image of a cross-section of the positive electrode active material prepared in Example 1. Figure 7 is a transmission electron microscope (TEM) image of primary particles exposed on the surface of secondary particles in the positive electrode active material of Example 1. Figure 8 is a TEM-EELS (Transmission Electron Microscope - Electron Energy Loss Spectroscopy) analysis graph for a total of 10 points from point 1 to point 10 shown in Figure 7. Figure 9 is a ToF-SIMS analysis image of the surface of the positive electrode active material of Example 1. Figure 10 is the mass spectrum result of the ToF-SIMS analysis of Figure 9. Figure 11 is a graph showing the boron content of the boron coating layer (external) and the grain boundary boron coating part (internal) according to the amount of boron input, measured through ICP emission spectroscopic analysis. FIG. 12 is a graph showing the initial charge / discharge capacity and the 50-cycle capacity retention rate at high temperature for the batteries of Example 1 and Comparative Examples 1 to 3. FIG. 13 is a graph of life characteristics showing the 50-cycle capacity retention rate at high temperature for the batteries of Example 1 and Comparative Examples 1 to 3. Specific details for implementing the invention

[0010] 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.

[0011] 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.

[0012] Here, "combinations of these" refers to mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, etc.

[0013] 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.

[0014] 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.

[0015] In addition, the term “layer” here includes not only the shape formed on the entire surface when viewed in a plan view, but also the shape formed on some surfaces.

[0016] 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.

[0017] positive electrode active material

[0018] In one embodiment, a positive electrode active material for a lithium secondary battery comprising a lithium nickel-based composite oxide is provided, the positive electrode active material for a lithium secondary battery comprising a plurality of primary particles aggregated to form secondary particles in which at least a portion of the primary particles are arranged radially, a boron coating layer containing lithium borate located on the surface of the secondary particles, and a boron doping layer located inside the primary particles exposed on the surface of the secondary particles.

[0019] Conventionally, when coating boron onto a positive electrode active material, it is common practice to manufacture a lithium metal composite oxide and then mix it with a boron raw material in a wet or dry manner and heat treat 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, by introducing a lithium raw material and a boron raw material together into a specific positive electrode active material precursor, such as a nickel-based hydroxide, and heat treating it under specific conditions, a positive electrode active material in the form of secondary particles in which at least a portion of the primary particles are arranged radially can be manufactured, and a positive electrode active material in which a boron coating layer and a boron doping layer are simultaneously formed can be obtained. By simultaneously forming an appropriate amount of a boron coating layer and a boron doping layer, boron no longer acts as a resistance, thereby improving the structural stability of the positive electrode active material and simultaneously improving the capacity characteristics and high-temperature lifespan characteristics of the lithium secondary battery.

[0020] The boron coating layer is located on the surface of the secondary particle and may be evenly coated on the surface of the secondary particle. The lithium borate in the boron coating layer can be expressed as lithium boron oxide or lithium borate, for example, LiBO2, Li3B7O 12 , Li6B4O9, Li3B 11 O 18 , Li2B4O7, Li3BO3, Li8B6O 13 , Li5B3O7, Li4B2O5, Li10 B4O 11 It may include , Li8B2O7, or a combination thereof.

[0021] The content of lithium borate in the boron coating layer may be 0.02 wt% to 0.5 wt% with respect to the total weight of the positive electrode active material, for example, 0.03 wt% to 0.4 wt%, 0.04 wt% to 0.3 wt%, or 0.05 wt% to 0.2 wt%, etc. When such a content range is satisfied, the boron coating layer does not act as a resistor and can improve the structural stability of the positive electrode active material and improve lifespan characteristics.

[0022] The boron doping layer can be said to be located inside the secondary particle, specifically, inside the primary particles exposed on the surface of the secondary particle. The primary particles exposed on the surface of the secondary particle may refer to the primary particles located at the outermost edge of the secondary particle. For example, the boron doping layer may be located within a depth range of 10 nm from the outer surface of the primary particles exposed on the surface of the secondary particle. If the outer surface of the primary particles exposed on the surface of the secondary particle is defined as 0 nm, the doping layer can be said to exist within a depth range of 0 nm to 10 nm starting from the surface. In other words, the boron doping layer may be said to be located within a depth range of 10 nm from the surface of the secondary particle. If the surface of the secondary particle is defined as 0 nm, the doping layer can be said to exist within a depth range of 0 nm to 10 nm starting from the surface.

[0023] The boron doping layer may be located, for example, within a depth range of 9 nm, 8 nm, 7 nm, 6 nm, 5 nm, 4 nm, 3 nm, or 2.5 nm from the outer surface of the primary particles exposed on the surface of the secondary particles. This boron doping layer is distinct from the boron coating layer and is also distinct from the grain boundary boron coating portion described later, and is thought to contribute to the structural stability of the cathode active material.

[0024] Meanwhile, the above-mentioned positive active material may further include a grain boundary boron coating portion containing lithium borate located on the surface of the primary particles inside the secondary particles. This grain boundary boron coating portion exists inside rather than on the surface of the secondary particles, and can be described as being coated along the interface of the primary particles located inside the secondary particles. Here, the term "inside" of the secondary particles refers to the entire interior excluding the surface, and for example, it may refer to the entire interior starting from a depth of approximately 2 μm from the outer surface, or it may be described as the part that does not come into contact with distilled water when washing the positive active material secondary particles with distilled water.

[0025] According to one embodiment, the weight of the boron coating layer may be greater than the weight of the grain boundary boron coating portion. For example, with respect to the total amount of the boron coating layer and the grain boundary boron coating portion, the grain boundary boron coating portion 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 boron coating layer 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 boron coating layer and the grain boundary boron coating portion may be 70:30 to 98:2, for example 75:25 to 97:3, or 80:20 to 95:5. When the content ratio of the boron coating layer and the grain boundary boron coating part is as described above, boron does not act as a resistor in the cathode active material but can play a role in improving performance, and can simultaneously improve the capacity and lifespan characteristics of the lithium secondary battery.

[0026] The content of the boron coating layer, that is, the content of lithium borate in the boron coating layer, may be, for example, 0.02 wt% to 0.5 wt% with respect to the total weight of the positive electrode active material, 0.03 wt% to 0.4 wt%, 0.04 wt% to 0.3 wt%, or 0.05 wt% to 0.2 wt%, etc. The content of the grain boundary boron coating portion, that is, the content of lithium borate in the grain boundary boron coating portion, may be, for example, 0.001 wt% to 0.05 wt% with respect to the positive electrode 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 boron coating layer and the grain boundary boron coating portion of the above-mentioned positive electrode active material is such, both the capacity characteristics and lifespan characteristics of the lithium secondary battery can be improved.

[0027] The total amount of the boron coating layer and the grain boundary boron coating portion may be 0.1 mol% to 5 mol% with respect to the entire positive electrode active material, for example, 0.1 mol% to 3 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%. If the total amount of the boron coating layer and the grain boundary boron coating portion deviates from a certain content, the initial discharge capacity may decrease and lifespan characteristics may deteriorate. In particular, if the content of the boron coating layer present on the surface of the secondary particles becomes excessive, the boron acts as a resistor, and the initial discharge capacity of the lithium secondary battery may decrease significantly.

[0028] 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 plate-shaped primary particles may be formed with a thickness smaller than the major axis length. Here, the major axis length refers to the maximum length based on the widest surface of the primary particle. That is, the primary particle 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).

[0029] FIG. 1 is a schematic diagram showing the plate shape of a primary particle of a first positive 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 such as 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 of the primary particle, and “t” represents the thickness of the primary particle. 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.

[0030] In the above-described positive active material, at least some of the primary particles are arranged radially, 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 radiality 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) from the center of the secondary particles toward the surface, or to form an angle of ±5° with the perpendicular direction.

[0031] 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.

[0032] 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.

[0033] 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 at least a portion of 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, if 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 improves the lifespan characteristics of the lithium secondary battery and reduces the phenomenon of resistance increase.

[0034] 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 have 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.

[0035] The ratio of the inner radius to the radius of the secondary particle (distance from the center of the particle to the surface) may be 40% to 60%, and such a region may be defined as the interior. The outer region may refer to the area from the outermost surface to 40% to 60% of the radius of the secondary particle. Additionally, the ratio of the outer volume to the volume of the secondary particle may be 90% or less, 87% or less, or 85% or less.

[0036] The secondary particles of the above-described positive electrode active material may contain an outer layer radially oriented 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.

[0037] The secondary particles of the above-described positive active material may have open pores located on the surface and facing toward the center inside, and the size of the open pores may be less than about 150 nm, for example, 10 nm to 148 nm. 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.

[0038] 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.

[0039] 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 having a plate shape are arranged in a radial direction, and an inner layer (12) in which primary particles (13) are arranged irregularly. In the inner layer (12), there may be more empty spaces between the primary particles 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.

[0040] 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 has a radial structure, which facilitates the insertion of lithium ions into the surface. In addition, the small size of the primary particles makes it easy to secure lithium transport pathways between the crystal grains. Furthermore, the small size of the primary particles and the pores between them mitigate volume changes that occur during charging and discharging, thereby minimizing stress caused by volume changes during charging and discharging. Such a cathode active material can reduce the resistance of a lithium secondary battery and improve capacity and lifespan characteristics.

[0041] Meanwhile, in the 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, or the 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.

[0042] The above secondary particles may include radial primary particles and non-radial primary particles. The content of non-radial primary particles may be 30 weight% or less, for example, from 0.01 weight% to 30 weight%, specifically from 0.1 weight% to 20 weight%, based on the total weight of the radial primary particles and non-radial primary particles.

[0043] The above-mentioned cathode active material comprises a lithium nickel-based composite oxide. The nickel content in the lithium nickel-based composite oxide may be 30 mol% or more based on the total amount of 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-based composite oxide may be higher than the respective content of other 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.

[0044] The above lithium nickel-based composite oxide can specifically be represented by the following chemical formula 1.

[0045] [Chemical Formula 1]

[0046] Li a1 Ni x1 M 1 y1 M 2 1-x1-y1 O2

[0047] 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, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof.

[0048] 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.

[0049] The above lithium nickel-based composite oxide may also be represented, for example, by Chemical Formula 2 below.

[0050] [Chemical Formula 2]

[0051] Li a2 Ni x2 Co y2 M 3 1-x2-y2 O2

[0052] 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, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof.

[0053] 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.

[0054] The above lithium nickel-based composite oxide may also be represented, for example, by the following chemical formula 3.

[0055] [Chemical Formula 3]

[0056] Li a3 Ni x3 Co y3 M 4z3 M 5 1-x3-y3-z3 O2

[0057] 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, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof.

[0058] 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.

[0059] Generally, as the nickel content in the cathode active material increases, Ni 2+Increased cation mixing, where ions occupy lithium sites, can actually lead to a decrease in capacity, or impurities such as NiO can hinder the diffusion of lithium ions, thereby degrading battery life. Additionally, structural collapse or cracking of the cathode active material during charging and discharging can increase side reactions with the electrolyte, resulting in reduced battery life and safety issues. To address this, conventional methods of coating boron only on the surface of the active material have been used, but the boron acts as a resistor, causing a decrease in capacity and lifespan. In contrast, according to one embodiment, even when using a high-nickel system, the problems associated with high nickel concentration are improved by appropriately forming a boron coating layer and a boron doping layer. This allows for the realization of high capacity while simultaneously improving lifespan characteristics without a decrease in initial discharge capacity.

[0060] Method for manufacturing positive electrode active material

[0061] In one embodiment, a method for manufacturing a positive electrode active material for a lithium secondary battery is provided, comprising mixing a nickel-based hydroxide, a lithium raw material, and a boron raw material and heat-treating them.

[0062] 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 heat-treating it, and then mixing a boron source into it in a wet or dry manner and heat-treating it again. In this case, boron is coated only on the surface of the positive electrode active material, and consequently, there was a problem in that the boron acts as a resistor, thereby reducing capacity and lifespan. On the other hand, according to the manufacturing method of one embodiment, a secondary particle shape in which at least a portion of the primary particles are arranged radially is produced, and at the same time, a boron coating layer and a boron doping layer are appropriately formed, so that boron does not act as a resistor, thereby allowing for the acquisition of a positive electrode active material that is structurally stable and has excellent lifespan characteristics.

[0063] In the above manufacturing method, the nickel-based hydroxide can be expressed as a nickel metal complex hydroxide or a nickel transition metal complex hydroxide, etc., as a precursor of the positive electrode active material, and can be manufactured by a co-precipitation method, etc.

[0064] The above nickel-based hydroxide can be represented, for example, by the following chemical formula 11.

[0065] [Chemical Formula 11]

[0066] Ni x11 M 11 y11 M 12 1-x11-y11 (OH)2

[0067] 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, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof.

[0068] As a specific example, the above nickel-based hydroxide can be represented by the following chemical formula 12 or chemical formula 13.

[0069] [Chemical Formula 12]

[0070] Ni x12 Co y12 M 13 1-x12-y12 (OH)2

[0071] In the above chemical formula 12, 0.3≤x12<1, 0 <y12≤0.7이고 M 13 It is selected from Al, B, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof.

[0072] [Chemical Formula 13]

[0073] Ni x13 Co y13 M 14 z13 M15 1-x13-y13-z13 (OH)2

[0074] 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, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof.

[0075] 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.

[0076] 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.

[0077] The content of the boron raw material may be 0.1 mol to 5 mol per 100 mol of the nickel-based 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 lithium secondary battery, thereby increasing capacity and improving lifespan characteristics. If the content of the boron raw material becomes excessive, the content of the boron coating layer increases excessively, causing boron to act as a resistor in the cathode active material, which can reduce the capacity and lifespan of the battery.

[0078] 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 a lithium secondary battery with a stable structure including both a boron coating layer and a boron doping layer can be manufactured.

[0079] In addition, the heat treatment can be carried out for 5 to 15 hours, for example, 8 to 12 hours, and in this case, a positive electrode active material for a lithium secondary battery with a stable structure including both a boron coating layer and a boron doping layer can be manufactured.

[0080] lithium secondary battery

[0081] Another embodiment provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator located between the positive electrode and the positive electrode, and an electrolyte.

[0082] FIG. 4 is a schematic diagram illustrating a lithium secondary battery according to one embodiment. Referring to FIG. 4, a lithium secondary battery (100) according to one embodiment of the present invention comprises a battery cell including a positive electrode (114), a negative electrode (112) positioned opposite to the positive electrode (114), a separator (113) disposed between the positive electrode (114) and the negative electrode (112), and an electrolyte for a lithium secondary battery impregnating the positive electrode (114), the negative electrode (112), and the separator (113); a battery container (120) containing the battery cell; and a sealing member (140) sealing the battery container (120).

[0083] anode

[0084] A positive electrode for a lithium secondary battery may include a current collector and a positive electrode active material layer located on the current collector. The positive electrode active material layer may include a positive electrode active material and may further include a binder and / or a conductive material.

[0085] 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.

[0086] The content of the binder in the above positive active material layer may be approximately 1% to 5% by weight with respect to the total weight of the positive active material layer.

[0087] 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 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.

[0088] The content of the conductive material in the above positive active material layer may be 1% to 5% by weight relative to the total weight of the positive active material layer.

[0089] Aluminum foil may be used as the above-mentioned house, but is not limited thereto.

[0090] cathode

[0091] A negative electrode for a lithium secondary battery comprises a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer comprises a negative electrode active material and may further comprise a binder and / or a conductive material.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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%.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] The above 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.

[0106] electrolytes

[0107] The above electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0108] The above-mentioned non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents may be used as non-aqueous organic solvents. As for the above-mentioned carbonate-based solvents, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. may be used. The above ester-based solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, etc. The above ether-based solvents may include dibutyl ether, tetraglyme, deglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc., and the above ketone-based solvents may include cyclohexanone, etc. In addition, the above alcohol-based solvent may include ethyl alcohol, isopropyl alcohol, etc., and the above aprotic solvent may include nitriles such as R-CN (where R is a C2 to C20 straight-chain, branched, or cyclic hydrocarbon group and may include a double bond, directional ring, or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes.

[0109] The above-mentioned non-aqueous organic solvents may be used alone or in a mixture of one or more. When used in a mixture of one or more, the mixing ratio can be appropriately adjusted according to the desired battery performance, which is widely understood by those engaged in the relevant field.

[0110] In addition, the above carbonate-based solvent may be used by mixing cyclic carbonates and chain carbonates. In this case, when the cyclic carbonates and chain carbonates are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent.

[0111] The above-mentioned non-aqueous organic solvent may further include an aromatic hydrocarbon organic solvent in addition to the carbonate-based solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon organic solvent may be mixed in a volume ratio of about 1:1 to about 30:1.

[0112] As the above aromatic hydrocarbon solvent, an aromatic hydrocarbon compound of the following chemical formula I may be used.

[0113] [Chemical Formula I]

[0114]

[0115] In the above chemical formula I, R 4 to R 9 The groups are identical or different and are selected from the group consisting of hydrogen, halogen, alkyl groups having 1 to 10 carbon atoms, haloalkyl groups, and combinations thereof.

[0116] Specific examples of the above aromatic hydrocarbon solvents include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene. It is selected from the group consisting of 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

[0117] The above electrolyte may further include vinylene carbonate or an ethylene-based carbonate compound of the following chemical formula II as a life-enhancing additive to improve battery life.

[0118] [Chemical Formula II]

[0119]

[0120] In the above chemical formula II, R 10 and R 11 The groups are identical or different from each other and are selected from the group consisting of hydrogen, halogen groups, cyano groups, nitro groups, and fluorinated C1 to C5 alkyl groups, and the R 10 and R 11 At least one of the groups is selected from the group consisting of halogen groups, cyano groups, nitro groups, and fluorinated C1 to C5 alkyl groups, provided that R 10and R 11 Not all of them are hydrogen.

[0121] Representative examples of the above-mentioned ethylene-based carbonate compounds include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. When using more of these lifespan-enhancing additives, the amount used can be appropriately controlled.

[0122] The above lithium salt is a material that is dissolved in a non-aqueous organic solvent and acts as a source of lithium ions within the battery, enabling the operation of a basic lithium secondary battery and facilitating the movement of lithium ions between the positive and negative electrodes.

[0123] Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide): LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, and LiN(C x F 2x+1 SO2)(C y F 2y+1 One or more selected from the group consisting of SO2)(where x and y are natural numbers, for example, integers from 1 to 20), lithium difluoro(bisoxolato) phosphate, LiCl, LiI, LiB(C2O4)2 (lithium bis(oxalato) borate: LiBOB), and lithium difluoro(oxalato) borate (LiDFOB).

[0124] It is preferable to use a lithium salt concentration within the range of 0.1M to 2.0M. When the lithium salt concentration falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0125] separator

[0126] The separator (113), also referred to as a separator membrane, separates the positive electrode (114) and the negative electrode (112) and provides a pathway for the movement of lithium ions; any material commonly used in lithium-ion batteries can be used. That is, a material having low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity can be used. For example, it may be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, and may be in the form of a non-woven fabric or a woven fabric. For example, polyolefin-based polymer separators such as polyethylene and polypropylene are mainly used in lithium-ion batteries, and coated separators containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0127] Lithium secondary batteries can be classified into lithium-ion batteries, lithium-ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used, and can be classified into cylindrical, prismatic, coin, and pouch types depending on their shape, and into bulk and thin-film types depending on their size. Since the structure and manufacturing methods of these batteries are widely known in this field, a detailed description is omitted.

[0128] A lithium secondary battery according to one embodiment can be used in electric vehicles (EVs) and hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs) because it has high capacity, excellent storage stability, lifespan characteristics, and high rate characteristics at high temperatures.

[0129] 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.

[0130] Example 1

[0131] 1. Preparation of positive electrode active material precursor

[0132] A cathode active material precursor is prepared through the following coprecipitation method. Nickel sulfate, cobalt sulfate, and aluminum nitrate are used as metal raw materials.

[0133] [Stage 1: 1.5kW / m³, NH4OH 0.35M, pH 11.5 to 11.7, reaction time 6 hours]

[0134] First, ammonia solution with a concentration of 0.35 M is added to the reactor. The reaction is started at a stirring power of 1.5 kW / m³ and a reaction temperature of 50℃ while adding the metal raw material and the complexing agent at rates of 85 ml / min and 9 ml / min, respectively. The reaction is carried out for 6 hours while adding NaOH to maintain the pH. After confirming that the average size of the core particles obtained as a result of the reaction is in the range of approximately 6.5 µm to 7.5 µm, the following two steps are performed.

[0135] [Stage 2: 1.0 kW / m³, NH4OH 0.40 M, pH 11.5 to 11.7, reaction time 16 hours]

[0136] While maintaining the reaction temperature at 50℃, the metal raw material and complexing agent are added at varying rates of 107 ml / min and 13 ml / min, respectively, while maintaining the concentration of the complexing agent at 0.40 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 1.0 kW / m³, which is lower than that of Step 1, to proceed with the reaction. After confirming that the average size of the product particles containing the core and intermediate layer obtained from this reaction is 10.5 μm to 11.5 μm, Step 3 is carried out as follows.

[0137] [Stage 3: 0.5kW / m³, NH4OH 0.40M, pH 11.5 to 11.7, reaction time 5 hours]

[0138] While maintaining the reaction temperature at 50℃, the metal raw material and the complexing agent are added at varying rates of 142 ml / min and 17 ml / min, respectively, while ensuring that the concentration of the complexing agent is maintained at the same level as in Step 2 above. NaOH is added to maintain the pH, and the reaction is carried out for 5 hours until the average particle size reaches 14㎛. During this time, the stirring power is lowered to 0.5 kW / ㎥, which is lower than in Step 2, to proceed with the reaction.

[0139] [Post-process]

[0140] After washing the above product, the washed product is hot-air dried at approximately 150°C for 24 hours to obtain nickel-based hydroxide (Ni), which is a precursor of the cathode active material. 0.945 Co 0.04 Al 0.015 (OH)2) is obtained. Fig. 5 is an SEM image of a cross- section of the cathode active material precursor prepared in Example 1.

[0141] 2. Preparation of cathode active material

[0142] A obtained nickel-based hydroxide and LiOH are mixed in a molar ratio of 1:1, and 1.0 molar part of boric acid is mixed with the nickel-based hydroxide, and the mixture is heat-treated at 725°C in an oxygen atmosphere for 10 hours to obtain a positive electrode active material. Fig. 6 is an SEM image of a cross- section of the positive electrode active material prepared in Example 1. Referring to Fig. 6, it can be confirmed that the positive electrode active material has a structure of secondary particles formed by the aggregation of multiple primary particles, has a porous center inside, and has a structure in which primary particles are arranged radially on the outside.

[0143] 3. Manufacture of the anode

[0144] A slurry for forming an anode active material layer is prepared by mixing 96 wt% of the obtained anode active material, 2 wt% of polyvinylidene fluoride, 2 wt% of carbon nanotubes, and N-methylpyrrolidone, a solvent, in a mixer. The slurry for forming an anode active material layer is coated onto an aluminum foil to form an electrode plate, and then dried at 135°C for at least 3 hours, followed by rolling and vacuum drying processes to produce an anode.

[0145] 4. Battery Manufacturing

[0146] A coin half-cell is manufactured using the above-mentioned positive electrode and a lithium metal counter electrode as the counter electrode. A separator (thickness: about 16 μm) made of a porous polyethylene film is interposed between the above-mentioned positive electrode and the lithium metal counter electrode, and an electrolyte is injected. The electrolyte used is a solution containing 1.1 M LiPF6 dissolved in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 3:5.

[0147] Comparative Example 1

[0148] LiNi composed of typical secondary particles with a particle size of approximately 14 µm 0.945 Co 0.04 Al 0.015 O2 is used as the positive active material of Comparative Example 2, and the positive and battery are manufactured in the same manner as in Example 1 otherwise.

[0149] Comparative Example 2

[0150] The positive active material (LiNi) of Comparative Example 1 0.945 Co 0.04 Al 0.015 A positive electrode active material coated with a boron compound is prepared by mixing 1.0 mol% of boric acid with O2 and heat-treating it at 350°C in an oxygen atmosphere for 8 hours. This is used as the positive electrode active material of Comparative Example 2, and the positive electrode and battery are prepared in the same manner as in Example 1.

[0151] Comparative Example 3

[0152] The positive active material (LiNi) of Comparative Example 1 0.945 Co 0.04 Al 0.015 A positive electrode active material is prepared by heat-treating at 350°C for 8 hours in an oxygen atmosphere without adding boric acid to O2. This is used as the positive electrode active material of Comparative Example 3, and otherwise, a positive electrode and a battery are prepared in the same manner as in Example 1.

[0153] Evaluation Example 1: Confirmation of Boron Doping Layer via TEM-EELS Analysis

[0154] Figure 7 is a TEM image of the primary particles exposed on the surface of the secondary particles in the cathode active material prepared in Example 1, specifically the primary particles located at the outermost edge of the secondary particles. Electron energy loss spectroscopy (EELS) was performed on a total of 10 locations, from point 1 to point 10, indicated in Figure 7, and the results are shown in Figure 8. In Figure 8, for example, ① represents the analysis graph at point 1. Referring to the lower graph in Figure 8, cobalt was detected starting from point 4, that is, from point 4 to point 10. According to this, the starting point of the surface of the active material can be said to be approximately point 4. Referring to the upper graph in Figure 8, it can be seen that boron is detected from point 3 to point 8. Here, the boron detected at point 3 can be described as a boron coating layer existing on the surface of the active material, and the boron detected at points 4 to 8 can be described as a boron doping layer of very thin thickness existing inside the active material.

[0155] Evaluation Example 2: Confirmation of coating layer

[0156] Figure 9 is a Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) analysis image of the surface of the positive electrode active material prepared in Example 1, and Figure 10 is the mass spectrum result of the ToF-SIMS analysis. In Figure 9, it can be confirmed that boron elements are evenly distributed on the surface of the positive electrode active material, and in Figure 10, it can be confirmed that there are many BO2 forms. Through this, it is understood that lithium boron compounds are evenly coated on the surface of the positive electrode active material of Example 1, and that lithium borate such as LiBO2 is the main component.

[0157] Evaluation Example 3: Evaluation of boron content in the boron coating layer and the grain boundary boron coating portion

[0158] The boron content is measured by performing ICP (Inductively Coupled Plasma) emission spectroscopic analysis on the cathode active material prepared in Example 1. Subsequently, 10g of the cathode active material is placed in 100g 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 indicated as the 'internal' boron content. This refers to the content of the grain boundary boron coating. 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 indicated as the 'external' boron content. This refers to the content of the boron coating layer.

[0159] For examples in which the cathode active material was prepared in the same manner as in Example 1, but the amount of boric acid added was changed to 0 molar part, 0.5 molar part, 1.5 molar part, 3.0 molar part, and 5.0 molar part (in Example 1, 1.0 molar part was added), the internal and external boron content was analyzed in the same manner as above, and the results are shown in FIG. 11. In FIG. 11, the unit ppm is 10 -4 It can mean weight %, and can mean the weight ratio of boron to the total weight of the cathode active material.

[0160] Referring to Fig. 11, in Example 1 where the boron input amount is 1.0 molar part, it can be seen that the boron content of the outer layer (boron coating layer) is approximately 1000 ppm, or 0.1 wt%, relative to the total anode active material, and the boron content of the inner layer (grain boundary boron coating part) is approximately 50 ppm, or 0.005 wt%, relative to the total anode active material. Here, the boron weight ratio of the outer layer to the inner layer is calculated to be approximately 95:5. In addition, in Fig. 11, when the boron input amount is 1.5 molar part, the boron weight ratio of the outer layer to the inner layer is calculated to be approximately 92:8. Through Fig. 11, it can be confirmed that boron compounds such as lithium borate are coated not only on the surface of the secondary particles of the anode active material but also on the inner grain boundaries, and that the boron content on the surface is more than four times the boron content on the inner grain boundaries.

[0161] Evaluation Example 4: Evaluation of Capacity and High Temperature Life Characteristics

[0162] The batteries prepared in the examples and comparative examples were charged at 25°C with a constant current of 0.2C to an upper limit voltage of 4.25V, and then discharged at 0.2C to a discharge cutoff voltage of 3.0V to measure the initial charge / discharge capacity, and the results are shown in Fig. 12. In Fig. 12, the gray bar graph represents the initial charge capacity and the black bar graph represents the initial discharge capacity. After the initial charge / discharge, the high-temperature life characteristics were evaluated by repeating the charging and discharging at 1C at 45°C in a voltage range of 3.0V to 4.3V at 50 or more times, and the results are shown in Fig. 13. The capacity retention rate at 50 cycles is also indicated by the dotted line graph in Fig. 12.

[0163] Referring to FIGS. 12 and 13, compared to Comparative Example 1, which uses a general secondary particle-shaped positive active material, Comparative Example 2, which uses a boron-coated positive active material using a conventional method, and Comparative Example 3, which uses a positive active material that undergoes additional heat treatment without boron coating, it can be seen that in the case of Example 1, both the initial charge capacity and the initial discharge capacity are high, and at the same time, the high-temperature life characteristics are improved.

[0164] 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

[0165] 11: Secondary particle 12: Interior of the secondary particle 13: Primary particle 14: External part of the secondary particle 100: Lithium secondary battery 112: Negative electrode 113: Separator 114: Anode 120: Battery container 140: Encapsulation member

Claims

Claim 1 A positive electrode active material for a lithium secondary battery comprising a lithium nickel-based composite oxide, wherein a plurality of primary particles are aggregated to form secondary particles in which at least a portion of the primary particles are arranged radially, a boron coating layer comprising lithium borate located on the surface of the secondary particles, and boron doped into the interior of the primary particles exposed on the surface of the secondary particles, wherein the doped boron is located only within a depth range of 10 nm from the outer surface of the primary particles exposed on the surface of the secondary particles, and the positive electrode active material further comprises a grain boundary boron coating portion comprising lithium borate located on the surface of the primary particles inside the secondary particles, wherein, with respect to the total amount of the boron coating layer and the grain boundary boron coating portion, the boron coating layer comprises 70% to 98% by weight and the grain boundary boron coating portion comprises 2% to 30% by weight. Claim 2 delete Claim 3 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the doped boron is located only within a depth range of 5 nm from the outer surface of the primary particle exposed to the surface of the secondary particle. Claim 4 In claim 1, the lithium borate of the boron coating layer is LiBO2, Li3B7O 12 , Li6B4O9, Li3B 11 O 18 , Li2B4O7, Li3BO3, Li8B6O 13 , Li5B3O7, Li4B2O5, Li 10 B4O 11 A positive electrode active material for a lithium secondary battery comprising , Li8B2O7, or a combination thereof. Claim 5 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the content of the lithium borate in the boron coating layer is 0.02 weight% to 0.5 weight% with respect to the positive electrode active material. Claim 6 delete Claim 7 delete Claim 8 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the weight of the boron coating layer is 4 times or more and 49 times or less the weight of the grain boundary boron coating portion. Claim 9 delete Claim 10 A positive electrode active material for a lithium secondary battery according to claim 1, wherein, with respect to the positive electrode active material, the content of the boron coating layer is 0.02 wt% to 0.5 wt% and the content of the grain boundary boron coating portion is 0.001 wt% to 0.05 wt%. Claim 11 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the primary particles have a plate shape, and at least some of the plate-shaped primary particles are arranged radially. Claim 12 A positive electrode active material for a lithium secondary battery according to claim 11, wherein the average major axis length of the plate-shaped primary particle 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 major axis length is 1:2 to 1:

5. Claim 13 A positive electrode active material for a lithium secondary battery according to claim 1, wherein the secondary particle comprises an interior and an exterior surrounding the interior, the interior comprises an irregular porous structure, and the exterior comprises a radial arrangement structure. Claim 14 A positive electrode active material for a lithium secondary battery according to claim 13, wherein the interior of the secondary particle has a larger pore size than the exterior, the interior pore size is 150 nm to 1 μm, and the exterior pore size is less than 150 nm. Claim 15 In claim 1, the secondary particle comprises an open pore of less than 150 nm in size located on the surface of the secondary particle and facing toward the center of the interior, forming a positive electrode active material for a lithium secondary battery. Claim 16 A positive electrode active material for a lithium secondary 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, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr and combinations thereof. Claim 17 A method for manufacturing a positive electrode active material for a lithium secondary battery, comprising mixing and heat-treating a nickel-based hydroxide, a lithium raw material, and a boron raw material, wherein the nickel-based hydroxide is formed by aggregating a plurality of primary particles and is in the form of secondary particles in which at least a portion of the primary particles are arranged radially, to obtain a positive electrode active material according to any one of claims 1, 3 to 5, 8, and 10 to 16. Claim 18 A method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 17, wherein the content of the boron raw material is 0.1 to 5 moles per 100 moles of the nickel-based hydroxide. Claim 19 A method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 17, wherein the heat treatment is carried out at a temperature of 650 ℃ to 850 ℃ for 5 to 20 hours. Claim 20 A lithium secondary battery comprising a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode comprises a positive active material according to any one of claims 1, 3 to 5, 8, and 10 to 16.

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