Positive Electrode Active Material for Lithium Secondary Battery, Method for Producing the Same, and Lithium Secondary Battery

Abstract

To provide a high-nickel positive electrode active material whose initial charging-discharging efficiency and battery safety at a voltage as high as 4.35 V or more are improved, a manufacturing method for the same, and a lithium secondary battery including the same.SOLUTION: A positive electrode active material for a lithium secondary battery according to an embodiment includes a lithium-nickel composite oxide particle containing a molar content of nickel of 80 mol% or more relative to the entire elements excluding lithium and oxygen, and containing one or more elements selected from the group consisting of B, Sb, and Nb, a first coating layer existing on a surface of the particle and containing one or more elements selected from the group consisting of B, Sb, and Nb, and a second coating layer existing on the first coating layer and containing metal phosphate.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same.

Background Art

[0002] As a driving power source for mobile information terminals such as mobile phones, notebook computers, and smart phones, a lithium secondary battery having a high energy density and being easy to carry is mainly used. Recently, research has been actively conducted on using a lithium secondary battery having a high energy density as a driving power source or a power storage power source for hybrid vehicles and electric vehicles.

[0003] In order to meet such applications, positive electrode active materials that can achieve high capacity, high stability, and long life performance have been studied, and generally ternary positive electrode active materials of Ni, Co, Mn or Ni, Co, Al are used. However, recently, as active materials having an even higher energy density are required and the supply amount of rare metals decreases, a high-nickel-based (High-Ni; Ni-rich) positive electrode active material with a reduced proportion of cobalt and an increased proportion of nickel in the positive electrode active material, or a cobalt-free high-nickel-based positive electrode active material has been proposed.

[0004] However, when the proportion of nickel in the positive electrode active material increases, there are problems that the stability of the crystal structure decreases and the residual lithium on the surface of the positive electrode active material increases. As a result, the initial charge-discharge efficiency of the battery decreases, the amount of gas generation increases due to an increase in side reactions in the battery, and the processability deteriorates. In particular, in order to increase the energy density of the high-nickel-based positive electrode active material, the battery is driven under high voltage conditions. In this case, the safety of the battery rapidly decreases due to side reactions between the residual lithium compound on the positive electrode and the electrolyte. This makes it difficult to manufacture a battery that has both high energy and high safety.

[0005] To solve such problems, a technique of doping the cathode active material with a foreign element has been proposed. However, depending on the doping element, there are problems such as a further increase in the residual lithium content and a sharp decrease in the battery safety due to side reactions under severe conditions such as high voltage, and an increase in the resistance of the cathode, resulting in a decrease in the initial charge-discharge efficiency.

[0006] Also, a technique of applying a coating material to the cathode active material to protect the cathode active material for battery safety during high-voltage driving has been proposed. However, in this case, although the life characteristics can be improved, problems frequently occur such as a decrease in the initial efficiency due to an increase in the resistance of the cathode surface.

Summary of the Invention

Problems to be Solved by the Invention

[0007] Provided are a high-nickel cathode active material in which both the initial charge-discharge efficiency and battery safety are improved at a high voltage of 4.35 V or higher, a method for manufacturing the same, and a lithium secondary battery including the same.

Means for Solving the Problems

[0008] In one embodiment, provided is a cathode active material for a lithium secondary battery including lithium nickel-based composite oxide particles in which the molar content of nickel is 80 mol% or more with respect to the total elements excluding lithium and oxygen, and containing one or more elements selected from the group consisting of B, Sb, and Nb; a first coating layer located on the surface of the particles and containing one or more elements selected from the group consisting of B, Sb, and Nb; and a second coating layer located on the first coating layer and containing metal phosphate.

[0009] In another embodiment, a nickel-based composite hydroxide in which the molar content of nickel is 80 mol% or more with respect to all elements excluding oxygen and hydrogen, a raw material containing one or more elements selected from the group consisting of B, Sb, and Nb, and a lithium raw material are mixed and subjected to a first heat treatment to obtain lithium nickel-based composite oxide particles, and (ii) the obtained lithium nickel-based composite oxide particles are mixed with a metal raw material and a phosphorus-based raw material and subjected to a second heat treatment, thereby providing a method for producing a positive electrode active material for a lithium secondary battery.

[0010] In another embodiment, a lithium secondary battery including a positive electrode containing the positive electrode active material, a negative electrode, and an electrolyte is provided.

Advantages of the Invention

[0011] The positive electrode active material for a lithium secondary battery according to one embodiment is a high-nickel layered positive electrode active material, and both the initial charge-discharge efficiency and the battery safety are improved under high voltage conditions.

Brief Description of the Drawings

[0012]

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Mode for Carrying Out the Invention

[0013] Hereinafter, specific embodiments will be described in detail so that those having ordinary knowledge in this technical field can easily implement them. However, the present invention can be realized in various different forms and is not limited to the embodiments described here.

[0014] The terms used here are for illustrative purposes only to describe exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0015] Here, "these combinations" means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of components.

[0016] Here, terms such as "comprising", "including", or "having" are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and it should be understood that they do not preclude in advance the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0017] To clearly represent various layers and regions in the drawings, the thickness is shown enlarged, and the same drawing reference numerals are given to similar parts throughout the specification. When a part such as a layer, film, region, plate, etc. is "on" or "above" another part, this includes not only the case where it is "directly above" the other part but also the case where there are other parts in between. Conversely, when a part is "directly above" another part, it means that there are no other parts in between.

[0018] Also, "layer" includes not only the shape formed on the entire surface but also the shape formed on a partial surface when observed in a plan view.

[0019] In addition, the average particle size can be measured by methods widely known to those skilled in the art. For example, it can be measured with a particle size analyzer, or it can also be measured from optical micrographs such as transmission electron micrographs and scanning electron micrographs. As another method, it can be measured using the dynamic light scattering method, data analysis is performed, the number of particles is counted for each particle size range, and then the average particle size value can be obtained by calculation. Unless otherwise defined, the average particle size can mean the diameter (D50) of the particles with a cumulative volume of 50% in the particle size distribution. Also, the average particle size can be obtained by randomly measuring the sizes (diameter or major axis length) of more than 20 particles from an electron micrograph such as a scanning electron micrograph to obtain a particle size distribution, and taking the diameter (D50) of the particles with a cumulative volume of 50% in the above particle size distribution as the average particle size.

[0020] Here, "or" is not construed in an exclusive sense. For example, "A or B" is construed to include A, B, A + B, etc. "Metal" is a concept that includes common metals, transition metals, and metalloids (semi-metals).

[0021] Positive electrode active material In one embodiment, there is provided a positive electrode active material for a lithium secondary battery, including lithium nickel-based composite oxide particles in which the molar content of nickel is 80 mol% or more with respect to all elements excluding lithium and oxygen, and containing one or more elements selected from the group consisting of B, Sb, and Nb; a first coating layer located on the surface of the particles and containing one or more elements selected from the group consisting of B, Sb, and Nb; and a second coating layer located on the first coating layer and containing a metal phosphate.

[0022] The positive electrode active material can be said to be a high-nickel layered positive electrode active material. The molar content of nickel may be, for example, 85 mol% or more, 88 mol% or more, 90 mol% or more, 92 mol% or more, 100 mol% or less, or 99 mol% or less with respect to all elements excluding lithium and oxygen in the lithium nickel-based composite oxide. It can be said that the positive electrode active material according to one embodiment is an invention that, while being a high-nickel type, improves the stability of the crystal structure, enhances the initial efficiency, and improves the problem of battery safety due to residual lithium or the like.

[0023] Further, the positive electrode active material may be a cobalt-free layered positive electrode active material that does not contain cobalt or contains an extremely small amount of cobalt. Cobalt, which is a rare metal, has problems such as a small reserve, insufficient supply, and high cost. However, since cobalt plays a crucial role in forming the positive electrode active material structure, when cobalt is removed, structural defects may occur, the resistance may increase, it may be difficult to ensure a long life, and the overall battery performance may deteriorate. In addition, the conventionally proposed cobalt-free positive electrode active materials having an olivine-based or spinel crystal structure have limitations in realizing high energy due to a small lithium solubility. In one embodiment, there is provided a positive electrode active material that can realize a high capacity and is a layered high-nickel-based cobalt-free positive electrode active material, while improving the structural stability and realizing excellent battery performance even under high voltage conditions.

[0024] The positive electrode active material is characterized by containing one or more elements selected from the group consisting of B, Sb, and Nb. B, Sb, and Nb can be said to be a kind of doping element. While these elements play a role in improving the stability of the crystal structure of the positive electrode active material, they can be said to be elements that slow down the grain growth rate during high-temperature firing compared to other doping elements. As a result, under the same synthesis conditions, these elements can further reduce the size of the primary particles that form secondary particles. The smaller the size of the primary particles, the shorter the lithium diffusion distance required for the insertion and desorption of lithium, the higher the initial charge-discharge efficiency of the battery, and the better the life characteristics can be improved. However, contrary to such advantages, these elements react with lithium and exist on the surface of the positive electrode active material particles in the form of oxides, which act as residual lithium, and under harsh conditions such as high voltage, the safety of the battery rapidly decreases due to surface side reactions, the positive electrode resistance increases, and as a result, rather, the problem of a decrease in the initial charge-discharge efficiency is caused. That is, in order to improve the initial charge-discharge efficiency, doping elements such as B, Sb, and Nb can be introduced to synthesize secondary particles in which a plurality of primary particles with reduced size are aggregated, but the problem of an increase in residual lithium on the surface occurs.

[0025] In one embodiment, in order to solve the above problem, by introducing doping elements such as B, Sb, and Nb and coating the surface of the positive electrode active material with metal phosphate, the residual lithium is not exposed on the surface, the side reaction between the positive electrode and the electrolyte is suppressed, and the safety of the high-voltage battery is improved. At the same time, it is intended to improve the performance of the battery without the coating acting as a resistance or reducing the capacitance.

[0026] As a result, it can be said that the positive electrode active material according to one embodiment is a high-nickel-based cobalt-free layered positive electrode active material with improved initial charge-discharge efficiency and life characteristics, and at the same time, high-voltage safety is ensured. It can be said to be a positive electrode material in which the size of the primary particles constituting the secondary particles is relatively small and the surface is coated with metal phosphate.

[0027] Lithium nickel-based composite oxide particles The lithium nickel-based composite oxide particles correspond to a kind of core and can be said to be in the form of particles while containing the lithium nickel-based composite oxide.

[0028] The particles can be said to be in the form of secondary particles formed by aggregation of a plurality of primary particles. The secondary particles may be spherical, ellipsoidal, polygonal, amorphous, etc. One embodiment is characterized in that the size of the primary particles is relatively small. This is understood to be because the introduction of doping elements such as B, Sb, and Nb slows down the grain growth rate during high-temperature firing and controls the growth of the primary particles. Compared with the case where no doping element is introduced or other doping elements are introduced, secondary particles with smaller primary particles can be synthesized under the same synthesis conditions.

[0029] The average particle size of the primary particles may be less than 200 nm, for example, 50 nm or more and less than 200 nm, 100 nm or more and less than 200 nm, 50 nm or more and 190 nm or less, or 50 nm or more and 180 nm or less. When the average particle size of the primary particles satisfies the above range, the lithium diffusion path is shortened, the resistance is reduced, and the charge and discharge efficiency can be improved. Here, the average particle size of the primary particles means the size of the primary particles observed on the surface of the secondary particles. After selecting any 20 or more primary particles in the electron micrograph of the surface of the secondary particles and measuring the particle size (or major axis, or the length of the long axis), it can be obtained by calculating the arithmetic average of these.

[0030] The average particle size of the secondary particles may be 5 μm to 25 μm, for example, 5 μm to 20 μm, 7 μm to 20 μm, 10 μm to 20 μm, or 12 μm to 18 μm. Here, the average particle size of the secondary particles may be a value obtained by selecting any 20 or more secondary particles in the electron micrograph of the positive electrode active material, measuring the particle size (or major axis, or the length of the long axis), and then calculating the arithmetic average.

[0031] In one example, the lithium nickel-based composite oxide particles may be in the form of secondary particles in which a plurality of primary particles are aggregated, and at least a part of the primary particles may be arranged radially. In this case, the diffusion degree of lithium increases, the initial charge-discharge efficiency is improved, and it is possible to secure a high capacity. Further, uniform expansion and contraction are possible during the insertion and desorption processes of lithium, and the problem that the positive electrode active material is broken by charge and discharge is improved, and the life characteristics and safety of the battery are improved. Hereinafter, the radial structure will be specifically described.

[0032] At least a part of the primary particles can have a plate shape. FIG. 1 is a schematic diagram showing the plate shape of the primary particles. Referring to FIG. 1, the primary particles can 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, (C) a hexahedron shape, etc.

[0033] In FIG. 1, "a" means the length of the major axis of the primary particle, "b" means the length of the minor axis, and "t" means the thickness. Here, the length of the major axis (a) means the maximum length based on the widest surface of the primary particle. The thickness (t) can be said to be the maximum length of the surface that is substantially perpendicular to the widest surface of the primary particle. The direction including the length of the major axis (a) and the length of the minor axis (b) is defined as the surface direction, and the direction including the thickness (t) is defined as the thickness direction.

[0034] The thickness (t) of the primary particle may be smaller than the length of the major axis (a) and the length of the minor axis (b) which are the lengths in the surface direction. The length of the major axis (a) among the lengths in the surface direction may be longer than or the same as the length of the minor axis (b).

[0035] In the positive electrode active material, at least a part of the primary particles can have a radial arrangement structure. For example, the major axes of the primary particles may be arranged in the radial direction. FIG. 2 is a diagram for explaining the definition of the radial shape. In one embodiment, the radial arrangement structure means that, as shown in FIG. 2, the thickness (t) direction of the primary particles is arranged perpendicular to the direction (R) from the center to the surface of the secondary particle or forms an angle of ±5° with the perpendicular direction.

[0036] When at least a part of the primary particles is arranged radially in this way, the surface side of the secondary particle can have a relatively large number of lithium diffusion paths between the primary particles, and a large number of crystal planes capable of lithium transfer are exposed to the outside, improving the lithium diffusivity and enabling the securing of high initial efficiency and high capacity. Further, when the primary particles are arranged radially, the pores exposed on the surface of the secondary particle are directed toward the center of the secondary particle, and the diffusion of lithium can be further promoted. And, due to the radially arranged primary particles, uniform expansion and contraction are possible during the insertion and desorption of lithium, and pores are present on the side of the Miller index (001) plane direction, which is the direction in which the particles expand during lithium desorption, and this serves as a buffering action. As a result, when the positive electrode active material expands and contracts, the probability of cracks occurring decreases, the internal pores additionally relieve the volume change, the cracks generated between the primary particles during charge and discharge decrease, and ultimately, the life characteristics of the lithium secondary battery are improved and the phenomenon of increased resistance decreases.

[0037] In one example, the secondary particle can include an interior having an irregular porous structure and an exterior surrounding the interior and having a radially oriented structure.

[0038] The irregular porous structure is a structure having primary particles and pores, meaning that the pore size, shape, position, etc. are not regular. That is, the primary particles arranged inside may be arranged irregularly, unlike the primary particles arranged outside. Here, "outside" can mean, for example, a region from 30 length % to 50 length %, for example, up to 40 length % from the outermost surface, of the total distance from the center to the surface of the secondary particle, or a region up to approximately 3 μm deep from the outermost shell of the secondary particle. Also, "inside" can mean a region from 50 length % to 70 length %, for example, up to 60 length % from the center, of the total distance from the center to the surface of the secondary particle, or the remaining region excluding the region up to approximately 3 μm deep from the outermost shell of the secondary particle.

[0039] Moreover, the pores existing inside the secondary particles may be even larger in size than the pores existing outside. For example, the size of the pores existing inside may be 150 nm to 1 μm, and the size of the pores existing outside may be less than 150 nm. When the pore size inside is larger than that outside in this way, compared with secondary particles having the same pore size inside and outside, there is an advantage that the lithium diffusion distance inside the positive electrode active material is shortened, lithium insertion is easy outside, and there is an effect of alleviating the volume change that occurs during charge and discharge. Here, when the pores are spherical or circular, the pore size means the diameter, and when the pores are elliptical or the like, the pore size can mean the length of the major axis, and it may be measured through an electron micrograph of the cross section of the secondary particles.

[0040] The secondary particles can have open pores on the surface. The size of the open pores may be less than about 150 nm, for example, 10 nm to 148 nm. Open pores are pores in which a part of the pore wall is not closed, and are formed by the space between plate-shaped primary particles arranged radially, and are pores deeply connected from the surface of the secondary particles toward the center. Such open pores can be connected to the outside and become a passage through which substances can enter and exit. The open pores may be in a form extending from the surface of the secondary particles toward the center, and can be formed to a depth of, on average, 150 nm or less from the surface of the secondary particles, for example, 0.001 nm to 100 nm, for example, 1 nm to 50 nm. The size and depth of the open pores may be measured by the BJH (Barrett, Joyner and Halenda) method, which is a method derived through the adsorption or desorption content of nitrogen.

[0041] Figure 3 is a schematic diagram showing the cross-sectional structure of the secondary particles of the positive electrode active material. Referring to Figure 3, the secondary particle 11 includes an outer portion 14 having a structure in which primary particles 13 having a plate shape are arranged in a radial direction, and an inner portion 12 in which the primary particles 13 are irregularly arranged. In the inner portion 12, there may be an even more empty space between the primary particles compared to the outside. And the pore size and porosity inside are larger than the pore size and porosity outside, and the shape and the like are irregular. In Figure 3, the arrow indicates the moving direction of lithium ions.

[0042] In the secondary particle, the inner portion has a porous structure, which has the effect of reducing the diffusion distance of lithium ions to the inside, and in the outer portion, the primary particles are arranged radially, making it easy for lithium ions to be inserted into the surface. And the size of the primary particles is small, making it easy to secure a lithium transfer path between the crystal grains. And the size of the primary particles is small, and the pores between the primary particles relieve the volume change that occurs during charge and discharge, minimizing the stress due to the volume change during charge and discharge. Such a positive electrode active material can reduce the resistance of the lithium secondary battery and improve the capacity characteristics and life characteristics.

[0043] The lithium nickel-based composite oxide is characterized by containing one or more elements selected from the group consisting of B, Sb, and Nb while containing a high concentration of nickel. For example, the lithium nickel-based composite oxide can be represented by the following Chemical Formula 1. [Chemical Formula 1] Li x1 Ni a1 M 1 b1 M 2 (1-a1-b1) O2

[0044] In the above Chemical Formula 1, M 1 is one or more elements selected from the group consisting of B, Sb, and Nb, and M 2is one or more elements selected from the group consisting of Al, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mn, Mo, P, S, Si, Sr, Ti, V, W, and Zr, where 0.9 ≦ x1 ≦ 1.2, 0.8 ≦ a1 < 1, and 0 < b1 ≦ 0.2.

[0045] In the chemical formula 1, 0.8 ≦ a1 < 1, 0.85 ≦ a1 < 1, 0.9 ≦ a1 < 1, 0.91 ≦ a1 < 1, or 0.92 ≦ a1 ≦ 0.999 may be satisfied, and 0 < b1 ≦ 0.1, 0 < b1 ≦ 0.05, or 0.001 ≦ b1 ≦ 0.05 may also be satisfied.

[0046] The content of one or more elements selected from the group consisting of B, Sb, and Nb may be 0.01 wt% to 5 wt% based on 100 wt% of the total metal excluding lithium in the lithium nickel-based composite oxide particles, for example, 0.1 wt% to 4 wt%, 0.1 wt% to 3 wt%, 0.1 wt% to 2 wt%, or 0.5 wt% to 1.5 wt%. Also, the content of one or more elements selected from the group consisting of B, Sb, and Nb may be 0.01 mol% to 3 mol% based on 100 mol% of the total metal excluding lithium in the lithium nickel-based composite oxide particles, for example, 0.1 mol% to 2.5 mol%, or 0.1 mol% to 2 mol%. When the above content range is satisfied, one or more elements selected from the group consisting of B, Sb, and Nb can improve the structural stability of the high-nickel cathode active material, reduce the size of the primary particles forming the secondary particles during the high-temperature firing process, increase the lithium diffusion rate, and improve the initial charge-discharge efficiency.

[0047] First coating layer The first coating layer is located on the surface of the lithium nickel-based composite oxide particles and is a layer containing one or more elements selected from the group consisting of B, Sb, and Nb.

[0048] The thickness of the first coating layer may be 10 nm or less, or even 5 nm or less, and may be, for example, 1 nm to 10 nm, 1 nm to 7 nm, or 2 nm to 5 nm. By being formed with such a thin thickness, the first coating layer does not act as a resistor and can appropriately control the growth of primary particles, improving the lithium diffusivity while enhancing the structural stability of the cathode active material.

[0049] The first coating layer can include oxides of one or more elements selected from the group consisting of B, Sb, and Nb; oxides containing one or more elements selected from the group consisting of B, Sb, and Nb and lithium; or combinations thereof. For example, the first coating layer can include boron oxide, lithium borate, antimony oxide, lithium antimonate, niobium oxide, lithium niobate, or combinations thereof.

[0050] It can be said that the first coating layer is a layer formed during the process of doping one or more elements selected from the group consisting of B, Sb, and Nb. Specifically, a lithium nickel-based composite oxide can be produced by mixing a nickel-based composite hydroxide which is a cathode active material precursor, a lithium raw material, and a raw material containing one or more elements selected from the group consisting of B, Sb, and Nb and performing heat treatment, and the first coating layer can be formed during this process.

[0051] Second coating layer The second coating layer is located on the first coating layer and is a layer containing metal phosphate. The second coating layer can serve to prevent the first coating layer, which may become a kind of residual lithium and cause side reactions, from being exposed on the outermost shell of the cathode active material.

[0052] The thickness of the second coating layer may be 20 nm or less, for example, 1 nm to 20 nm, 1 nm to 18 nm, 1 nm to 15 nm, 1 nm to 10 nm, 1 nm to 7 nm, or 2 nm to 5 nm. By being formed with such a thin thickness, the second coating layer does not act as a resistor and can reduce the residual lithium content on the surface, thereby improving the overall performance of the battery.

[0053] In the metal phosphate of the second coating layer, the metal is a concept including general metals, transition metals, and metalloids. For example, it may be one or more elements selected from the group consisting of Al, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Si, Sr, Ti, V, W, Zn, and Zr. In one example, the metal may be one or more elements selected from the group consisting of Al and Mg. In this case, residual lithium can be effectively reduced without degrading battery performance.

[0054] The metal phosphate can further contain a lithium element. In this case, the metal phosphate can be expressed as lithium-metal-phosphate. In the second coating layer, a state in which the metal phosphate and lithium-metal-phosphate are mixed may exist.

[0055] The content of the metal phosphate may be 0.1 wt% to 3 wt% based on 100 wt% of the total metal excluding lithium in the lithium nickel-based composite oxide particles. For example, it may be 0.1 wt% to 2 wt%, or 0.5 wt% to 1.5 wt%. Also, the content of the metal phosphate may be 0.1 mol% to 3 mol% based on 100 mol% of the total metal excluding lithium in the lithium nickel-based composite oxide particles. For example, it may be 0.1 mol% to 2 mol%, or 0.5 mol% to 1.5 mol%. When the above content range is satisfied, the metal phosphate does not act as a resistor and exists on the surface with a very thin thickness, and can play a role of a kind of protective layer.

[0056] The positive electrode active material has reduced residual lithium on the surface by the second coating layer. For example, the content of residual lithium on the surface of the positive electrode active material may be less than 0.2% by weight based on 100% by weight of the positive electrode active material, specifically, it may be 0.001% by weight or more and less than 0.2% by weight, or 0.001% by weight or more and 0.19% by weight or less. When the content range of residual lithium in the high-nickel positive electrode active material is within the above range, side reactions at the interface between the positive electrode and the electrolyte are suppressed, and the safety of the battery can be improved.

[0057] Method for producing positive electrode active material In one embodiment, a method for manufacturing the above-mentioned positive electrode active material is provided. Specifically, the method for manufacturing a positive electrode active material according to one embodiment includes: (i) mixing a nickel-based composite hydroxide in which the molar content of nickel is 80 mol% or more based on the total elements excluding oxygen and hydrogen, a raw material containing one or more elements selected from the group consisting of B, Sb, and Nb, and a lithium raw material, and performing a first heat treatment to obtain lithium nickel-based composite oxide particles; and (ii) mixing the obtained lithium nickel-based composite oxide particles with a metal raw material and a phosphorus-based raw material and performing a second heat treatment.

[0058] The nickel-based composite hydroxide may be a high-nickel-based composite hydroxide, and the molar content of nickel may be 85 mol% or more, 88 mol% or more, 90 mol% or more, 92 mol% or more based on the total elements excluding oxygen and hydrogen, and may be 100 mol% or less or 99 mol% or less.

[0059] The nickel-based composite hydroxide can be represented, for example, by the following Chemical Formula 11. [Chemical Formula 11] Ni a11 M 11 b11 (OH)2

[0060] In the above Chemical Formula 11, M 11 is one or more elements selected from the group consisting of Al, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mn, Mo, P, S, Si, Sr, Ti, V, W, and Zr, and 0.8 ≦ a11 ≦ 1 and 0 ≦ b11 ≦ 0.2.

[0061] In the chemical formula 11, 0.8 ≦ a11 < 1, 0.85 ≦ a11 ≦ 1, 0.9 ≦ a11 ≦ 1, 0.91 ≦ a11 ≦ 1, or 0.92 ≦ a11 ≦ 0.999 may be satisfied, and 0 ≦ b11 ≦ 0.1, 0 ≦ b11 ≦ 0.05, or 0.001 ≦ b11 ≦ 0.05 may be satisfied.

[0062] For 100 mol parts of the total metal of the nickel-based composite hydroxide, 0.01 mol part to 3 mol parts of a raw material containing one or more elements selected from the group consisting of B, Sb, and Nb may be mixed, and 90 mol parts to 120 mol parts of a lithium raw material may be mixed. When the input content range is satisfied, lithium nickel-based composite hydroxide particles having a structure that is stable and in which the size of the primary particles forming the secondary particles is appropriately reduced can be synthesized. Here, the content of the raw material containing one or more elements selected from the group consisting of B, Sb, and Nb may be such that the content of the B, Sb, or Nb element is 0.01 mol part to 3 mol parts with respect to 100 mol parts of the total metal of the nickel-based composite hydroxide, and for example, the raw material may be input so as to be 0.01 mol part to 2 mol parts, or 0.1 mol part to 1.5 mol parts. The raw material containing one or more elements selected from the group consisting of B, Sb, and Nb may be an oxide containing B, Sb, or Nb, and for example, it may be B2O3, Sb2O3, or Nb2O5, but is not limited thereto.

[0063] The first heat treatment is a high-temperature firing process for substantially synthesizing the positive electrode active material, and can be performed in a temperature range of 600°C to 1000°C. For example, it can be performed at 600°C to 900°C, or 650°C to 800°C, and can be performed for 5 hours to 25 hours.

[0064] The lithium nickel-based composite oxide particles obtained after the first heat treatment are in the form of secondary particles formed by aggregation of a plurality of primary particles, and the average particle size of the primary particles can be characterized by being less than 200 nm. As described above, by introducing one or more elements selected from the group consisting of B, Sb, and Nb as doping elements, the grain growth rate becomes slow in the first heat treatment process, and thereby the size of the primary particles becomes small and can exhibit a size of less than about 200 nm. Since the content regarding the primary particles and the secondary particles is as described above, detailed description thereof is omitted.

[0065] The lithium nickel-based composite oxide particles obtained after the first heat treatment refer to those containing a lithium nickel-based composite oxide and having a particle form. The particles can include a first coating layer containing one or more elements selected from the group consisting of B, Sb, and Nb and located on the surface of the particles. The lithium nickel-based composite oxide can be represented by Chemical Formula 1 or the like as described above. The content regarding the first coating layer is also as described above.

[0066] The step (ii) after the first heat treatment is a process for forming a second coating layer containing metal phosphate. With respect to 100 mol parts of the total metal excluding lithium in the lithium nickel-based composite oxide, the metal raw material and the phosphorus-based raw material can be mixed in an amount of 0.1 mol part to 3 mol parts, respectively, for example, 0.1 mol part to 2 mol parts, or 0.5 mol part to 1.5 mol parts.

[0067] The metal raw material means a metal raw material for forming metal phosphate, and here the metal may be one or more elements selected from the group consisting of Al, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Si, Sr, Ti, V, W, Zn, and Zr as described above.

[0068] The second heat treatment can be carried out, for example, in a temperature range of 500°C to 700°C, and can be carried out, for example, at 550°C to 650°C. A second coating layer with a very thin thickness can be stably formed by heat treatment in the above temperature range. The content of the second coating layer is as described above.

[0069] The residual lithium content on the surface of the lithium nickel-based composite oxide particles obtained after the first heat treatment tends to increase due to the introduction of the doping element. For example, it may be 0.9 wt% or more based on 100 wt% of the lithium nickel-based composite oxide. Then, the residual lithium content on the surface of the cathode active material particles obtained after the second heat treatment is effectively reduced by the formation of the second coating layer. For example, it may be less than 0.2 wt% based on 100 wt% of the cathode active material.

[0070] Positive electrode In one embodiment, a cathode for a lithium secondary battery including the above-described cathode active material is provided. The cathode for a lithium secondary battery includes a current collector and a cathode active material layer located on the current collector. The cathode active material layer includes the above-described cathode active material and may further include a binder and / or a conductive material.

[0071] The binder serves to adhere the cathode active material particles well to each other and to adhere the cathode active material well to the current collector. Typical examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0072] In the cathode active material layer, the content of the binder may be approximately 1 wt% to 5 wt% based on the total weight of the cathode active material layer.

[0073] The conductive material is used to impart conductivity to the electrode. In the battery being configured, any material can be used as long as it is an electron conductive material that does not cause a chemical change. Examples thereof include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based substances in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or a conductive material containing a mixture thereof can be used.

[0074] In the positive electrode active material layer, the content of the conductive material may be 1 wt% to 5 wt% with respect to the total weight of the positive electrode active material layer.

[0075] As the positive electrode current collector, aluminum foil can be used, but it is not limited thereto.

[0076] Lithium secondary battery In one embodiment, a lithium secondary battery including a positive electrode containing the aforementioned positive electrode active material, a negative electrode, a separator located between the positive electrode and the positive electrode, and an electrolyte is provided.

[0077] FIG. 4 is a schematic view showing a lithium secondary battery according to one embodiment. Referring to FIG. 4, a lithium secondary battery 100 according to one embodiment includes a positive electrode 114, a negative electrode 112 located opposite to the positive electrode 114, a separator 113 disposed between the positive electrode 114 and the negative electrode 112, and a battery cell including a lithium secondary battery electrolyte that impregnates the positive electrode 114, the negative electrode 112, and the separator 113, a battery container 120 in which the battery cell is housed, and a sealing member 140 that seals the battery container 120.

[0078] Negative electrode The negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer contains a negative electrode active material and may further contain a binder and / or a conductive material.

[0079] The negative electrode active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0080] As the material capable of reversibly intercalating / deintercalating lithium ions, a carbon-based negative electrode active material can be used, which can include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0081] As the alloy of lithium metal, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0082] As the material capable of doping and undoping lithium, an Si-based negative electrode active material or an Sn-based negative electrode active material can be used. As the Si-based negative electrode active material, silicon, a silicon-carbon composite, SiO x(0 < x < 2), Si-Q alloy (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), examples of Sn-based negative electrode active materials include Sn, SnO2, Sn-R alloy (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), etc., and at least one of these can also be mixed with SiO2 and used. As elements Q and R, 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 those selected from the group consisting of combinations thereof can be used.

[0083] The silicon-carbon composite may be, for example, a silicon-carbon composite including a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of this 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, polyimide resin can be used. At this time, the content of silicon may be 10% by weight to 50% by weight based on the total weight of the silicon-carbon composite. Also, the content of crystalline carbon may be 10% by weight to 70% by weight based on the total weight of the silicon-carbon composite, and the content of amorphous carbon may be 20% by weight to 40% by weight based on the total weight of the silicon-carbon composite. Also, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle diameter (D50) of the silicon particles may be 10 nm to 20 μm. The average particle diameter (D50) of the silicon particles may preferably be 10 nm to 200 nm. The silicon particles exist in an oxidized form, and at this time, the atomic content ratio of Si:O in the silicon particles indicating the degree of oxidation may be 99:1 to 33:67. The silicon particles may be SiO x particles, and at this time, SiO x In, the x range may be greater than 0 and less than 2. In this specification, unless otherwise defined, the average particle diameter (D50) means the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution.

[0084] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with the carbon-based negative electrode active material. When the Si-based negative electrode active material or the 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 as a weight ratio.

[0085] In the negative electrode active material layer, the content of the negative electrode active material may be 95% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

[0086] In one embodiment, the negative electrode active material layer may further contain a binder and optionally further contain a conductive material. In the negative electrode active material layer, the content of the binder may be 1 wt% to 5 wt% based on the total weight of the negative electrode active material layer. Further, when further containing a conductive material, the negative electrode active material layer may contain 90 wt% to 98 wt% of the negative electrode active material, 1 wt% to 5 wt% of the binder, and 1 wt% to 5 wt% of the conductive material.

[0087] The binder serves to make the negative electrode active material particles adhere well to each other and also make the negative electrode active material adhere well to the current collector. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof can be used.

[0088] Examples of the water-insoluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, an ethylene-propylene copolymer, polystyrene, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0089] Examples of the water-soluble binder include a rubber-based binder or a polymer resin binder. The rubber-based binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymer resin binder may be selected from polyethylene oxide, polyvinyl pyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, ethylene-propylene-diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0090] When using a water-soluble binder as the negative electrode binder, it can further contain a cellulose-based compound that can impart viscosity as a kind of thickener. As this cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or their alkali metal salts can be mixed and used. As the alkali metal, Na, K, or Li can be used. The content of such a thickener used may be 0.1 to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

[0091] The conductive material is used to impart conductivity to the electrode, and in the configured battery, any material can be used as long as it is an electron conductive material that does not cause a chemical change. Examples thereof include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials including copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or conductive materials containing mixtures thereof can be used.

[0092] As the negative electrode current collector, those 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 can be used.

[0093] Electrolyte The electrolyte contains a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. As the non-aqueous organic solvent, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents can be used. As the carbonate-based solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used. As the ester-based solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, etc. can be used. As the ether-based solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. can be used, and as the ketone-based solvent, cyclohexanone, etc. can be used. Also, as the alcohol-based solvent, ethyl alcohol, isopropyl alcohol, etc. can be used, and as the aprotic solvent, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms and can contain a double bond, aromatic ring, or ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc. can be used.

[0094] The non-aqueous organic solvent can 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 intended battery performance, which should be widely understood by those skilled in the art.

[0095] Also, in the case of carbonate solvents, cyclic carbonates and chain carbonates can be mixed and used. In this case, when the cyclic carbonate and the chain carbonate are mixed and used at a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte will be excellent.

[0096] The non-aqueous organic solvent can further contain an aromatic hydrocarbon organic solvent in the carbonate solvent. At this time, the carbonate solvent and the aromatic hydrocarbon organic solvent can be mixed at a volume ratio of about 1:1 to about 30:1.

[0097] As the aromatic hydrocarbon solvent, an aromatic hydrocarbon compound of the following Chemical Formula I can be used.

[0098]

Chemical formula

[0099] In the above Chemical Formula I, R 4 ~R 9 are the same as or different from each other and are selected from the group consisting of hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, a haloalkyl group having 1 to 10 carbon atoms, and combinations thereof.

[0100] Specific examples of the aromatic hydrocarbon solvent 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, 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, or a combination thereof.

[0101] The electrolytic solution may further contain vinylene carbonate or an ethylene carbonate compound represented by the following Chemical Formula II as a life improvement additive in order to improve the battery life.

[0102] [Chemical formula]

[0103] In the above Chemical Formula II, R 10 and R 11 are the same as or different from each other and are selected from the group consisting of hydrogen, a halogen group, a cyano group, a nitro group, and a fluorinated alkyl group having 1 to 5 carbon atoms, and at least one of the R 10 and R 11 is selected from the group consisting of a halogen group, a cyano group, a nitro group, and a fluorinated alkyl group having 1 to 5 carbon atoms, provided that R10 and R 11 are not all hydrogen.

[0104] Typical examples of ethylene carbonate compounds include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate, etc. When such a life-improving additive is further used, its usage amount can be appropriately adjusted.

[0105] The lithium salt is dissolved in a non-aqueous organic solvent, acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode.

[0106] Typical 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, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2)(where x and y are natural numbers, for example, integers from 1 to 20), lithium difluoro(bisoxalato)phosphate, LiCl, LiI, LiB(C2O4)2 (lithium bis(oxalato)borate, LiBOB), and lithium difluoro(oxalato)borate (LiDFOB), and one or more selected from the group consisting thereof.

[0107] The concentration of the lithium salt is preferably used within the range of 0.1 M to 2.0 M. If the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0108] Separator The separator 113 separates the positive electrode 114 and the negative electrode 112 and provides a migration path for lithium ions, and any separator can be used as long as it is commonly used in lithium-ion batteries. As the separator, one having low resistance to ion migration of the electrolyte and excellent electrolyte moisture retention ability can be used. For example, the separator can include glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, and may be in a non-woven or woven form. For example, polyolefin-based polymer separators such as polyethylene and polypropylene are mainly used in lithium-ion batteries, and a coated separator containing a ceramic component or a polymer substance to ensure heat resistance or mechanical strength can also be used, and it can be selectively used in a single-layer or multi-layer structure.

[0109] Lithium secondary batteries can be classified into lithium-ion batteries, lithium-ion polymer batteries, and lithium polymer batteries according to the types of separators and electrolytes used, can be classified into cylindrical, rectangular, coin-shaped, pouch-shaped, etc. according to the form, and can be classified into bulk type and thin film type according to the size. Since the structures and manufacturing methods of these batteries are widely known in this field, detailed descriptions are omitted.

[0110] The lithium secondary battery according to one embodiment realizes high capacity, is excellent in storage stability, life characteristics, high rate characteristics, etc. at high temperatures, can be used in electric vehicles (EVs), can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs), and can be used in portable electronic devices and the like.

[0111] Hereinafter, examples and comparative examples of the present invention will be described. The following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

Examples

[0112] Example 1 1. Production of positive electrode active material (1) Production of nickel-based composite hydroxide Nickel-based composite hydroxide Ni(OH)₂ was synthesized through the coprecipitation method described later. A metal solution in which nickel sulfate (NiSO₄·6H₂O) was dissolved in a distilled water solvent was prepared as a metal raw material, and aqueous ammonia (NH₄OH) for forming a complex compound and sodium hydroxide (NaOH) as a precipitant were prepared.

[0113] [First stage: 2.5 kW / m 3 , NH₄OH 0.40 M, pH 10.5 - 11.5, reaction time 6 hours] First, aqueous ammonia with a concentration of 0.40 M was put into the reactor. With a stirring power of 2.5 kW / m 3 , at a reaction temperature of 50°C, the metal raw material and the complexing agent (NH₄OH) were respectively introduced at a rate of 85 ml / min and 10 ml / min to start the reaction. The reaction was carried out for 6 hours while adding NaOH to maintain the pH. As a result of the reaction, it was confirmed that the average size of the obtained core particles was in the range of about 6.5 μm to 7.5 μm, and the second stage was carried out as follows.

[0114] [Second stage: 2.0 kW / m 3 , NH₄OH 0.45 M, pH 10.5 - 11.5, reaction time 18 hours] While maintaining the reaction temperature at 50 °C, the metal raw material and the complexing agent were respectively changed to the feeding rates of 85 ml / min and 12 ml / min and fed in, and the concentration of the complexing agent was maintained at 0.45 M. The reaction was carried out for 18 hours while adding NaOH to maintain the pH. At this time, the stirring power was lowered to 2.0 kW / m which was lower than that of the first stage and the reaction was carried out. By carrying out such a reaction, it was confirmed that the average size of the product particles including the core and the intermediate layer was 13.5 μm to 14 μm, and the third stage was carried out as follows. 3 The reaction was carried out with the stirring power lowered to 3

[0115] [Third stage: 1.5 kW / m 3 , 0.45 M NH4OH, pH 10.5 - 11.5, reaction time 14 hours] While maintaining the reaction temperature at 50 °C, the feeding rates of the metal raw material and the complexing agent and the concentration of the complexing agent were made the same as those in the second stage. The reaction was carried out for 14 hours while adding NaOH to maintain the pH. At this time, the stirring power was lowered to 1.5 kW / m which was lower than that of the second stage and the reaction was carried out. 3 [Post - process] After washing the resultant, it was dried with hot air at about 150 °C for 24 hours to obtain nickel - based composite hydroxide (Ni(OH)2).

[0116] (2) Production of positive electrode active material

[0117] For 100 mole parts of nickel in the obtained Ni(OH)2, B2O3 was prepared so that the content of boron was 1 mole part, and 100 mole parts of lithium hydroxide were prepared. These were mixed with Ni(OH)2 and put into a firing furnace, and the first heat treatment was carried out at a temperature of 700 °C for 10 hours in an oxygen atmosphere. Thereby, an intermediate (B - LMO) was obtained in which a first coating layer containing boron was formed on the surface of the boron - doped lithium nickel - based composite oxide particles.​Disperse the intermediate in ethanol. After dissolving Al(NO3)3·9H2O and (NH4)2HPO4 in 5 ml of distilled water so that the content of AlPO4 becomes 1 mole part with respect to 100 mole parts of nickel in the intermediate, add it to the ethanol dispersion, mix, and evaporate the solvent. Then, perform a second heat treatment at 600 °C. Thereby, a second coating layer containing aluminum phosphate is formed on the surface of the first coating layer.

[0118] 2. Production of lithium secondary battery Mix 95% by weight of the prepared cathode active material, 3% by weight of a polyvinylidene fluoride binder, and 2% by weight of a carbon nanotube conductive material in an N-methylpyrrolidone solvent to produce a cathode active material slurry. Apply the cathode active material slurry to an aluminum current collector, dry it, and then roll it to prepare a cathode.

[0119] Using the prepared cathode and a lithium metal counter electrode, with a separator having a polyethylene-polypropylene multilayer structure interposed therebetween, inject an electrolyte in which 1.0 M of LiPF6 lithium salt is added to a solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 50:50 to produce a coin half cell.

[0120] Example 2 In the production of the cathode active material, except that Sb2O3 is used instead of B2O3 and added so that the content of antimony (Sb) becomes 1 mole part with respect to 100 mole parts of nickel in Ni(OH)2, producing an intermediate in which an Sb-containing first coating layer is formed on the surface of lithium nickel-based composite oxide particles doped with Sb, the cathode active material and the coin half cell are produced in the same manner as in Example 1.

[0121] Example 3 In the production of the positive electrode active material, except for manufacturing an intermediate in which a Nb-containing first coating layer is formed on the surface of Nb-doped lithium nickel-based composite oxide particles by using Nb2O5 instead of B2O3 and adding it so that the content of niobium (Nb) becomes 1 mol part with respect to 100 mol parts of nickel in Ni(OH)2, the positive electrode active material and the coin half cell are manufactured in the same manner as in Example 1.

[0122] Comparative Example 1 In the production of the positive electrode active material, except for not adding B2O3 and not performing AlPO4 coating, that is, except for applying LiNiO2 as the positive electrode active material, the positive electrode active material and the coin half cell are manufactured in the same manner as in Example 1.

[0123] Comparative Example 2 In the production of the positive electrode active material, except for not performing AlPO4 coating, that is, except for applying, as the positive electrode active material, a material in which a boron-containing first coating layer is formed on the surface of boron-doped lithium nickel-based composite oxide particles, the positive electrode active material and the coin half cell are manufactured in the same manner as in Example 1.

[0124] Comparative Example 3 In the production of the positive electrode active material, except for not adding B2O3, that is, except for applying, as the positive electrode active material, a material in which only an AlPO4-containing second coating layer is formed on the surface of LiNiO2, the positive electrode active material and the coin half cell are manufactured in the same manner as in Example 1.

[0125] Comparative Example 4 In the production of the positive electrode active material, except for adding aluminum nitrate instead of B2O3 and not performing AlPO4 coating, that is, except for applying, as the positive electrode active material, a material in which only an Al-containing first coating layer is formed on the surface of Al-doped lithium nickel-based composite oxide particles, the positive electrode active material and the coin half cell are manufactured in the same manner as in Example 1.

[0126] Evaluation Example 1: Confirmation of the first coating layer and the second coating layer The intermediate (B-LMO) prepared in Example 1 was subjected to a depth profile analysis using Time-of-flight secondary ion mass spectrometry (TOF-SIMS). The Ni content was determined by depth from the particle surface to the interior. - and BO2 - The concentration of BO2 was analyzed and the results are shown in Figure 5. - The image of the ion concentration mapping is shown in Figure 6. Referring to Figure 5, it can be seen that a first boron-containing coating layer was formed on the particle surface to a thickness of about 5 nm. Figure 6 shows that the compound located on the particle surface is BO2 - The first coating layer is lithium-boron-oxide (Li x BO y ), which is believed to be the cause of the increased residual lithium.

[0127] The final cathode active material prepared in Example 1 was subjected to SEM-EDS (Scanning Electron Microscope-Energy Dispersive X-ray Spectrometry) analysis, and the resulting mapping images of Al, P, and Ni elements are shown in Figure 7. The results of line scanning in the direction of the arrow in Figure 7 are shown in Figure 8. Referring to Figure 8, it can be seen that Ni is located in the center, while Al and P are located on the outer surface, and that an AlPO4-containing second coating layer with a thickness of approximately 20 nm or less was formed on the outermost shell of the active material.

[0128] Evaluation Example 2: Confirmation of the change in the size of primary particles FIG. 9 shows a scanning electron microscope (SEM) image of the surface of the positive electrode active material prepared in Comparative Example 1, and FIG. 10 shows an SEM image of a cross section of the positive electrode active material.

[0129] The SEM image of the surface of the positive electrode active material produced in Comparative Example 4 is shown in Fig. 11, and the SEM image of the cross section of the positive electrode active material is shown in Fig. 12.

[0130] The SEM image of the surface of the intermediate (B-LNO) of the positive electrode active material produced in Example 1 is shown in Fig. 13, and the SEM image of the cross section of the positive electrode active material intermediate is shown in Fig. 14.

[0131] The SEM image of the surface of the intermediate (Sb-LNO) of the positive electrode active material produced in Example 2 is shown in Fig. 15. Finally, the SEM image of the surface of the intermediate (Nb-LNO) of the positive electrode active material produced in Example 3 is shown in Fig. 16.

[0132] Comparing with the images of Comparative Example 1 in Figs. 9 and 10, in the case of Comparative Example 4 in Figs. 11 and 12, it can be confirmed that the particle size of the primary particles became even larger by doping with Al. On the contrary, in the cases of Example 1 in Figs. 13 and 14, Example 2 in Fig. 15, and Example 3 in Fig. 16, it can be confirmed that the particle size of the primary particles became smaller compared to Comparative Example 1 by doping with B, Sb, and Nb, respectively. It is understood that the doping element appropriately suppresses the growth of primary particles during the first heat treatment. When the size of the primary particles decreases in this way, the lithium diffusion path is shortened, the resistance decreases, and the initial charge-discharge efficiency of the battery is improved, which will be analyzed in Evaluation Example 4 described later.

[0133] Evaluation Example 3: Residual lithium evaluation The content of unreacted residual lithium on the surface of the positive electrode active materials of Comparative Example 1 and Comparative Example 4 and the positive electrode active material intermediates of Examples 1 to 3 was evaluated, and the results are shown in Table 1.

[0134] The measurement method of the residual lithium content is as follows. 10 g of the positive electrode active material (or intermediate) is put into 100 ml of distilled water and stirred at a speed of 300 rpm for 30 minutes, and then the pH change is measured while adding HCl. For example, when the residual lithium exists in the form of Li2CO3, LiOH, etc., when adding HCl, H + and CO32- reacts or H+ and OH - react to perform titration. The residual lithium content is calculated through the amount of HCl introduced until the titration is completed. The unit ppm is based on weight. For example, 4000 ppm means 0.4% by weight with respect to 100% by weight of the positive electrode active material (or intermediate).

[0135]

Table 1

[0136] Referring to Table 1, when the size of the primary particles increases due to Al doping as in Comparative Example 4, the residual lithium decreases. On the contrary, when the size of the primary particles decreases by doping with B, Sb, and Nb respectively as in Examples 1 to 3, it can be confirmed that the residual lithium increases. Therefore, in the case of the examples, although the size of the primary particles can be decreased to improve the initial charge-discharge efficiency, it can be confirmed that there is a problem that the side reaction increases due to the increase in residual lithium, the gas generation amount increases, and the battery stability at high voltage decreases.

[0137] Therefore, in one embodiment, after doping with B, Sb, or Nb, coating with metal phosphate has successfully improved the battery performance without increasing resistance or decreasing capacity while reducing the content of residual lithium. The residual lithium content was measured for the final positive electrode active materials in Examples 1 to 3 in the same manner as described above, and the results are shown in Table 2 below.

[0138]

Table 2

[0139] Referring to Table 2 above, in the case of Examples 1 to 3, it can be confirmed that after the formation of the metal phosphate-containing second coating layer, the residual lithium content on the surface decreased to less than 2000 ppm. Thus, in the case of the cathode active material according to the examples, the size of the primary particles becomes smaller by doping, improving the initial charge-discharge efficiency of the battery. At the same time, it is understood that the high-voltage stability can be improved by reducing the residual lithium content with the second coating layer.

[0140] Evaluation Example 4: Electrical performance evaluation The coin half-cells manufactured in Example 1 and Comparative Examples 1 to 4 were charged at room temperature under 0.2C conditions from 3.0V to the upper limit of 4.35V (vs. Li / Li + ) and then rested for 10 minutes, and then discharged until 3.0V under 0.2C conditions to perform initial charge and discharge. At this time, the initial discharge capacity was measured and shown in Table 3 below, and the ratio of the initial discharge capacity to the initial charge capacity was denoted as the initial efficiency and shown in Table 3 below.

[0141] Thereafter, charge and discharge were repeated 50 times in the range of 3.0V to 4.35V at 1C at room temperature. The ratio of the discharge capacity at 50 cycles to the initial discharge capacity was denoted as the 50-cycle life and shown in Table 3 below.

[0142]

Table 3

[0143] Referring to Table 3 above, in the case of Comparative Example 1 where doping and coating were not performed, the life characteristics were significantly low. In the case of Comparative Example 2 where only boron doping was performed, it was confirmed that the initial efficiency and life characteristics decreased somewhat. As described above, it is understood that the residual lithium was high and the high-voltage safety became a problem.

[0144] In the case of Comparative Example 3 where only a metal phosphate coating was performed without doping such as boron, although the coating had the effect of reducing residual lithium, there was no effect of doping, resulting in a decrease in the initial efficiency, and the coating layer acted as a resistance, leading to a decrease in the life characteristics. Also, in the case of Comparative Example 4 where only aluminum doping was performed, as described above, while the size of the primary particles increased, it was confirmed that the initial efficiency and life characteristics were somewhat lower compared to Example 1.

[0145] On the contrary, in the case of Example 1, it was confirmed that the residual lithium was very low at a level of less than 2000 ppm, ensuring high-voltage safety, the initial capacity was high, and all of the initial charge-discharge efficiency and life characteristics were improved.

[0146] As described above, the preferred embodiments have been described in detail. However, the scope of the rights 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 also belong to the scope of the rights of the present invention.

Explanation of Reference Numerals

[0147] 11: Secondary particle 12: Inside of the secondary particle 13: Primary particle 14: Outside of the secondary particle 100: Lithium secondary battery 112: Negative electrode 113: Separator 114: Positive electrode 120: Battery container 140: Encapsulating member

Claims

1. Lithium nickel-based composite oxide particles in which the molar content of nickel is 80 mol% or more with respect to all elements excluding lithium and oxygen, and containing one or more elements selected from the group consisting of B and Sb, a first coating layer located on the surface of the particles and containing one or more elements selected from the group consisting of B and Sb, and a second coating layer located on the first coating layer and containing a metal phosphate, for a positive electrode active material for a lithium secondary battery (however, excluding the case where the positive electrode active material for a lithium secondary battery contains Nb).

2. The positive electrode active material for a lithium secondary battery according to Claim 1, wherein the lithium nickel-based composite oxide particles include a layered cobalt-free lithium nickel-based composite oxide.

3. The lithium nickel-based composite oxide particles are in the form of secondary particles formed by aggregation of a plurality of primary particles, and the average particle diameter of the primary particles is less than 200 nm, for the positive electrode active material for a lithium secondary battery according to Claim 1.

4. The positive electrode active material for a lithium secondary battery according to Claim 3, wherein the average particle diameter of the secondary particles is 5 μm to 25 μm.

5. The lithium nickel-based composite oxide particles are formed by aggregation of a plurality of primary particles, and at least a part of the primary particles has a secondary particle form having a radial arrangement structure, for the positive electrode active material for a lithium secondary battery according to Claim 1.

6. The secondary particles according to Claim 5 include an interior having an irregular porous structure and an exterior surrounding the interior and having a radial arrangement structure.

7. At least a part of the primary particles has a plate shape, the secondary particles include open pores on the surface, and the open pores are formed by the space between plate-shaped primary particles arranged radially and are pores connected in the central direction on the surface of the secondary particles, for the positive electrode active material for a lithium secondary battery according to Claim 5.

8. The lithium nickel-based composite oxide particles according to Claim 1 include a compound represented by the following Chemical Formula 1: 【Chemical Formula 1】 Li ｘ１ Ni ａ１ M １ ｂ１ M ２ （１－ａ１－ｂ１） O ２ In the above Chemical Formula 1, M １ is one or more elements selected from the group consisting of B and Sb, and M ２ is one or more elements selected from the group consisting of Al, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mn, Mo, P, S, Si, Sr, Ti, V, W, and Zr, where 0.9 ≤ x1 ≤ 1.2, 0.8 ≤ a1 < 1, and 0 < b1 ≤ 0.

2.

9. The content of one or more elements selected from the group consisting of B and Sb is 0.01 wt% to 5 wt% with respect to 100 wt% of the total metal excluding lithium in the lithium nickel-based composite oxide particles, for the positive electrode active material for a lithium secondary battery according to Claim 1.

10. The thickness of the first coating layer is 1 nm to 10 nm, and the positive electrode active material for a lithium secondary battery according to claim 1.

11. The first coating layer includes an oxide of one or more elements selected from the group consisting of B and Sb; an oxide containing one or more elements selected from the group consisting of B and Sb and lithium; or a combination thereof, and the positive electrode active material for a lithium secondary battery according to claim 1.

12. The thickness of the second coating layer is 1 nm to 20 nm, and the positive electrode active material for a lithium secondary battery according to claim 1.

13. In the metal phosphate of the second coating layer, the metal is one or more elements selected from the group consisting of Al, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Si, Sr, Ti, V, W, Zn, and Zr, and the positive electrode active material for a lithium secondary battery according to claim 1.

14. The metal is one or more elements selected from the group consisting of Al and Mg, and the positive electrode active material for a lithium secondary battery according to claim 13.

15. The content of the metal phosphate is 0.1 wt% to 3 wt% based on the total metal excluding lithium in the lithium nickel-based composite oxide particles, and the positive electrode active material for a lithium secondary battery according to claim 1.

16. The content of residual lithium on the surface of the positive electrode active material for a lithium secondary battery is less than 0.2 wt% based on 100 wt% of the positive electrode active material for a lithium secondary battery, and the positive electrode active material for a lithium secondary battery according to claim 1.

17. A nickel-based composite hydroxide in which the molar content of nickel is 80 mol% or more based on the total elements excluding oxygen and hydrogen, a raw material containing one or more elements selected from the group consisting of B and Sb, and a lithium raw material are mixed and first heat-treated to obtain lithium nickel-based composite oxide particles. A method for manufacturing a positive electrode active material for a lithium secondary battery, including mixing the obtained lithium nickel-based composite oxide particles with a metal raw material and a phosphorus-based raw material and performing a second heat treatment (however, excluding the case where the positive electrode active material for a lithium secondary battery contains Nb).

18. The nickel-based composite hydroxide is represented by the following Chemical Formula 11, and the method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 17: [Chemical Formula 11] Ni ａ１１ M １１ ｂ１１ (OH) ２ In the above Chemical Formula 11, M １１ is one or more elements selected from the group consisting of Al, Ba, Ca, Ce, Cr, Cu, F, Fe, Mg, Mn, Mo, P, S, Si, Sr, Ti, V, W, and Zr, where 0.8 ≤ a11 ≤ 1 and 0 ≤ b11 ≤ 0.

2.

19. Based on 100 mol parts of the total metal of the nickel-based composite hydroxide. A raw material containing one or more elements selected from the group consisting of B and Sb is mixed in an amount of 0.01 to 3 mol parts, The method for producing a positive electrode active material for a lithium secondary battery according to claim 17, wherein the lithium raw material is mixed in an amount of 90 to 120 mol parts.

20. The method for producing a positive electrode active material for a lithium secondary battery according to claim 17, wherein the first heat treatment is performed in a temperature range of 600°C to 1000°C.

21. The method for producing a positive electrode active material for a lithium secondary battery according to claim 17, wherein the lithium nickel-based composite oxide particles obtained after the first heat treatment are in the form of secondary particles formed by aggregation of a plurality of primary particles, and the average particle diameter of the primary particles is less than 200 nm.

22. The lithium nickel-based composite oxide particles obtained after the first heat treatment, include a first coating layer located on the surface of the particles and containing one or more elements selected from the group consisting of B and Sb, The method for producing a positive electrode active material for a lithium secondary battery according to claim 17, wherein the thickness of the first coating layer is 1 nm to 10 nm.

23. The method for producing a positive electrode active material for a lithium secondary battery according to claim 22, wherein the first coating layer includes an oxide of one or more elements selected from the group consisting of B and Sb; an oxide containing one or more elements selected from the group consisting of B and Sb and lithium; or a combination thereof.

24. With respect to 100 mol parts of the total metal excluding lithium in the lithium nickel-based composite oxide, The method for producing a positive electrode active material for a lithium secondary battery according to claim 17, wherein the metal raw material and the phosphorus-based raw material are each mixed in an amount of 0.1 to 3 mol parts.

25. The method for producing a positive electrode active material for a lithium secondary battery according to claim 17, wherein the metal raw material is a compound containing one or more metal elements selected from the group consisting of Al, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Si, Sr, Ti, V, W, Zn, and Zr.

26. The method for producing a positive electrode active material for a lithium secondary battery according to claim 17, wherein the second heat treatment is performed in a temperature range of 500°C to 700°C.

27. Through the second heat treatment, a positive electrode active material for a lithium secondary battery is obtained, which includes the lithium nickel-based composite oxide particles obtained by the first heat treatment and a second coating layer containing metal phosphate located on the surface of the particles. The method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 17, wherein the thickness of the second coating layer is 1 nm to 20 nm.

28. The residual lithium content on the surface of the lithium nickel-based composite oxide particles obtained after the first heat treatment is 0.9% by weight or more with respect to 100% by weight of the lithium nickel-based composite oxide. The method for manufacturing a positive electrode active material for a lithium secondary battery according to claim 17, wherein the residual lithium content on the surface of the positive electrode active material particles obtained after the second heat treatment is less than 0.2% by weight with respect to 100% by weight of the positive electrode active material.

29. A positive electrode containing a positive electrode active material according to any one of claims 1 to 16, a negative electrode, and an electrolyte, a lithium secondary battery.

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