KR20220070728A - Positive active material for rechareable lithium battery, preparing method thereof, and rechareable lithium battery comprising positive electrode including positive active material - Google Patents

Abstract

The present invention provides a positive electrode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including a positive electrode including the same, wherein the positive electrode active material for a lithium secondary battery includes: a first positive electrode active material including secondary particles which are formed by aggregating at least two primary particles and in which at least a part of the primary particles has a radial arrangement structure; and a second positive electrode active material having a monolithic structure, the first positive electrode active material and the second positive electrode active material are both nickel-based positive electrode active materials, and the surface of the second positive electrode active material is coated with a boron-containing compound.

Description

A cathode active material for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including a cathode comprising the same

It relates to a lithium secondary battery including a positive electrode active material for a lithium secondary battery, a method for manufacturing the same, and a positive electrode comprising the same.

With the development of portable electronic devices and communication devices, there is a high need for the development of a lithium secondary battery having a high energy density.

As a cathode active material of a lithium secondary battery, lithium nickel manganese cobalt composite oxide, lithium cobalt oxide, and the like are used. In the case of using such a positive electrode active material, the long-term lifespan of the lithium secondary battery is reduced due to cracks generated in the positive electrode active material as charging and discharging are repeated, resistance increases, and the capacity characteristics do not reach a satisfactory level, so improvement is required.

To provide a positive electrode active material for a lithium secondary battery in which the structural collapse and cracking of the positive electrode active material due to repeated charging and discharging is small and the side reaction between the positive electrode active material and the electrolyte is suppressed, and a method for manufacturing the same A lithium secondary battery is provided.

According to one embodiment, at least two or more primary particles are formed by aggregation, at least a portion of the primary particles are a first positive electrode active material including secondary particles having a radially arranged structure; and a second positive electrode active material having a monolith structure, wherein the first positive electrode active material and the second positive electrode active material are both nickel-based positive electrode active materials, and the surface of the second positive electrode active material is coated with a boron-containing compound A cathode active material for a lithium secondary battery is provided.

According to another embodiment, a first heat treatment is performed on the first precursor in an oxidizing gas atmosphere to obtain a first nickel-based oxide, a second heat treatment is performed on the second precursor in an oxidizing gas atmosphere to obtain a second nickel-based oxide, and the second nickel-based oxide is obtained. A second nickel-based oxide coated with a boron-containing compound is obtained by mixing a nickel-based oxide and a boron-containing precursor and heat treatment, and the first nickel-based oxide and a second nickel-based oxide coated with the boron-containing compound are mixed, 1 A method for manufacturing a positive electrode active material for a lithium secondary battery comprising obtaining a positive electrode active material comprising a positive electrode active material and a second positive electrode active material coated with a boron-containing compound, wherein the second nickel-based oxide includes particles having a monolith structure.

According to another embodiment, there is provided a lithium secondary battery including a positive electrode including the above-described positive electrode active material for a lithium secondary battery, a negative electrode, and an electrolyte interposed between the positive electrode and the negative electrode.

The positive electrode active material for a lithium secondary battery according to an embodiment has less structural collapse and cracking due to repeated charging and discharging, and suppresses side reactions with the electrolyte. In addition, by providing a material of a monolithic structure that does not reduce capacity, a lithium secondary battery including the same has a high capacity and is very excellent in capacity retention and lifespan characteristics.

1 is a schematic diagram showing the shape of a primary particle according to an embodiment;
2 is a diagram for explaining the definition of a radial in secondary particles according to an embodiment;
3 is a schematic diagram showing a cross-sectional structure of a secondary particle according to an embodiment;
4 schematically shows the structure of a lithium secondary battery having a positive electrode including a positive electrode active material for a lithium secondary battery according to an embodiment.

Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and the same reference numerals are given to the same or similar components throughout the specification.

In various embodiments, the same reference numerals are used to represent components having the same configuration in one embodiment, and only configurations different from the one embodiment will be described in other embodiments.

In one embodiment, regarding the size, particle diameter, length, etc. of various particles, there is a method of expressing the average size of a group by quantifying it by a metrology method, but it is universally used and the mode diameter and integral distribution curve showing the maximum value of the distribution There are median diameters corresponding to the median of , and various average diameters (number average, length average, area average, mass average, volume average, etc.). In the present invention, unless otherwise specified, the average size, average particle diameter, and average length may be a volume average value, or may mean a measurement of D50 (particle diameter at a point where the distribution ratio is 50%). This may mean measured through a particle size analyzer that analyzes the size of particles according to diffraction, or may mean measured through a scanning electron micrograph or the like.

In one embodiment, the term "monolith" structure refers to a structure in which each particle of a morphology phase is separated and/or dispersed from each other as independent phases that are distinguished from each other.

Hereinafter, a cathode active material for a lithium secondary battery according to an embodiment will be described with reference to FIGS. 1 to 3 .

The positive electrode active material for a lithium secondary battery according to an embodiment includes a first positive electrode active material including secondary particles formed by aggregation of at least two or more primary particles, and a second positive electrode active material having a monolith structure. At least a portion of the secondary particles has a radially arranged structure, and both the first positive electrode active material and the second positive electrode active material are nickel-based positive electrode active materials. The surface of the second positive electrode active material is coated with a boron-containing compound.

Hereinafter, the first positive electrode active material according to the present embodiment will be described.

The first positive electrode active material includes secondary particles in which at least two or more primary particles are aggregated. At least some of the primary particles may have a plate shape. The primary particle may be formed to have a thickness smaller than the major axis length (planar direction). Here, the long axis length may mean a maximum length based on the widest surface of the primary particle. That is, the primary particles may have a structure in which the length t in one axial direction (ie, the thickness direction) is smaller than the long axis length (a) in the other direction (ie, the plane direction).

1 is a schematic diagram showing the shape of a primary particle according to an embodiment.

Referring to FIG. 1 , the primary particles according to one embodiment have a basic plate-like structure, such as (A) a polygonal nanoplate shape such as a hexagon, (B) a nanodisk shape, and (C) a rectangular parallelepiped shape, while having various detailed shapes can have 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.

On the other hand, the thickness t of the primary particles may be formed smaller than the lengths a and b in the plane direction. The length a in the plane direction may be longer or the same as that of b. In one embodiment, the direction in which the thickness t is defined in the primary particle is defined as the thickness direction, and the direction containing the lengths a and b is defined as the plane direction.

The first positive electrode active material according to an embodiment may have irregular porous pores inside and outside the secondary particles, respectively. "Irregular porous structure" means a structure having pores that are not regular in pore size and shape and have no uniformity. The interior containing the irregular porous structure contains primary particles as well as the exterior. The primary particles disposed inside may be arranged without regularity, unlike primary particles disposed outside.

Herein, the term "outside" refers to an area of 30% to 50% in length, for example, 40% in length from the outermost surface of the total distance from the center of the secondary particle to the surface, or within 2 μm from the outermost surface of the secondary particle. say area. In addition, "inside" refers to an area of 50 length % to 70 length %, for example 60 length %, from the center of the total distance from the center of the secondary particle to the surface, or within 2 μm from the outermost surface of the secondary particle, or It refers to the remaining area excluding the area within 4 μm or within 6 μm.

Meanwhile, the secondary particles of the first positive electrode active material according to an exemplary embodiment may have open pores having a size of less than 150 nm, for example, 10 nm to 148 nm toward the inner center. An open pore is an exposed pore through which the electrolyte can enter and exit. According to one embodiment, the open pores may be formed from the surface of the secondary particles to a depth of 150 nm or less on average, for example, 0.001 nm to 100 nm, for example 1 nm to 50 nm.

The first positive electrode active material according to an embodiment may include secondary particles formed by arranging at least some of the long axes of the primary particles in a radial direction. At least a portion of the primary particles may have a radially arranged structure. 2 is a diagram for explaining the definition of a radial in secondary particles according to an embodiment.

In one embodiment, the "radial" arrangement structure means that the thickness (t) direction of the primary particles is perpendicular to the direction (R) from the secondary particles to the center or forms an angle of ±5° with the direction perpendicular to the direction as shown in FIG. 2 means to be arranged.

Meanwhile, the average length of the primary particles constituting the secondary particles may be 0.01 μm to 5 μm. For example, it may be 0.01 μm to 2 μm, 0.01 μm to 1 μm, more specifically 0.02 μm to 1 μm, and 0.05 μm to 0.5 μm. Here, "average length" means an average length of an average major axis length and an average minor axis length in the plane direction of the primary particles, or an average particle diameter when the primary particles are spherical.

The average thickness of the primary particles constituting the secondary particles is, for example, 50 nm or more, for example 100 nm or more, for example 200 nm or more, for example 300 nm or more, for example 400 nm or more, for example 500 nm or greater, such as 600 nm or greater, such as 700 nm or greater, such as 800 nm or greater, such as 900 nm or greater, such as 1 μm or greater, such as 1.2 μm or greater, such as 1.4 μm or greater. or more, for example 13 μm or less, such as 12 μm or less, such as 11 μm or less, such as 10 μm or less, such as 9 μm or less, such as 8 μm or less, such as 7 μm or less, such as 6 μm or less, such as 5 μm or less, such as 4 μm or less, such as 3 μm or less, such as 2 μm or less. And the ratio of the average thickness to the average length is 1:1 to 1:10, for example 1:1 to 1:8, for example 1:1 to 1:6.

As such, the average length of the primary particles, the average thickness, and the ratio of the average thickness to the average length satisfies the above-mentioned ratio, and when the primary particles are small and the primary particles are radially arranged from the outside, relative to the surface side As a result, lithium diffusion pathways between many grain boundaries and a large number of crystal planes capable of transferring lithium to the outside are exposed, which improves lithium diffusion, enabling high initial efficiency and capacity to be secured. In addition, when the primary particles are arranged radially, the pores exposed from the surface in between are also directed toward the center, thereby promoting lithium diffusion from the surface. By means of the radially arranged primary particles, uniform contraction and expansion are possible during lithium desorption and/or insertion, and pores exist in the (001) direction, which is the direction in which the particles expand during lithium desorption, to provide a buffering action, Because the size of the plate-type primary particles is small, the probability of cracks occurring during contraction and expansion is lowered, and the internal pores further relieve volume changes to reduce cracks occurring between primary particles during charging and discharging, improving lifespan characteristics and increasing resistance can be reduced

Closed pores may exist inside the secondary particle and closed pores and/or open pores may exist outside the secondary particle. Closed pores are difficult to contain electrolytes, etc., whereas open pores may contain electrolytes or the like in the pores. In the present specification, closed pores are independent pores that are not connected to other pores because all of the walls of the pores are formed in a closed structure, and open pores are continuous pores connected to the outside of the particle because at least some of the walls of the pores are formed in an open structure. .

The positive electrode active material for a lithium secondary battery according to an embodiment minimizes direct contact between the cracked surface and the electrolyte solution even when cracks occur by including the first positive electrode active material as described above, thereby suppressing an increase in surface resistance.

3 is a schematic diagram showing a cross-sectional structure of a secondary particle according to an embodiment.

Referring to FIG. 3, the secondary particles 11 have an outer 14 having a structure in which the primary particles 13 having a plate shape are arranged in a radial direction, and an inner 12 in which the primary particles 13 are irregularly arranged. contains

The interior 12 may have more empty spaces between the primary particles than the exterior. In addition, the pore size and porosity inside are large and irregular compared to the pore size and porosity outside. In FIG. 3, arrows indicate the movement direction of lithium ions.

The secondary particle according to an embodiment of the present invention has a porous structure inside, so that the diffusion distance of lithium ions to the inside is reduced, and the outside is arranged in a radial direction toward the surface to facilitate insertion of lithium ions into the surface. In addition, the size of the primary particles of the cathode active material for a lithium secondary battery is small, so that it is easy to secure a lithium transfer path between the crystal grains. In addition, since the size of the primary particles is small and the pores between the primary particles alleviate the volume change that occurs during charging and discharging, the stress received during the volume change during charging and discharging is minimized.

The secondary particles according to an embodiment of the present invention may have an average particle diameter of 1 μm to 20 μm. For example, 1 μm to 18 μm, or 1 μm to 16 μm, or 1 μm to 15 μm, or 1 μm to 10 μm, or 5 μm to 20 μm, or 5 μm to 18 μm, or 5 μm to 15 μm. For example, it may be 1 μm to 5 μm or 10 μm to 20 μm.

The secondary particles according to an embodiment may include radial primary particles and non-radiative primary particles. The content of the non-radiative primary particles is 20% by weight or less, for example, 0.01% to 10% by weight, specifically 0.1% to 5% by weight based on 100 parts by weight of the total weight of the radial primary particles and the non-radiative primary particles. can When the non-radiative primary particles in the secondary particles are included in the above-described content range in addition to the radial primary particles, lithium secondary batteries having improved lifespan characteristics can be manufactured by facilitating the diffusion of lithium.

Hereinafter, the second positive electrode active material according to the present embodiment will be described.

The second positive electrode active material according to an embodiment has a monolith structure. That is, the second positive electrode active material has a form in which a plurality of crystal particles are separated and/or dispersed from each other to form an independent and/or separated phase for each particle rather than an agglomerated form, but two or three particles are It may also include a form attached to each other.

The shape of the second cathode active material is not particularly limited, and may have a random shape, such as a spherical shape, an oval shape, a plate shape, a rod shape, or the like.

The surface of the second positive electrode active material is coated with a boron-containing compound. The boron-containing compound may be, for example, boron oxide, lithium borate, or a combination thereof, for example, B ₂ O ₃ , LiBO ₂ , Li ₃ B ₇ O ₁₂ , Li ₆ B ₄ O ₉ , Li ₃ B ₁₁ O ₁₈ , Li ₂ B ₄ O ₇ , Li ₃ BO ₃ , or a combination thereof.

In general, the structure of a positive electrode active material may collapse due to repeated charging and discharging, and in particular, a nickel-based positive electrode active material may cause structural collapse as NiO is formed on the surface. When the structure of the positive electrode active material is collapsed, cation mixing may occur, which may cause gas generation or deterioration of lifespan characteristics. In addition, the cathode active material may be cracked due to repeated charging and discharging, which leads to an increase in side reactions between the cathode active material and the electrolyte, which leads to a decrease in battery capacity and poor lifespan characteristics. However, in the second positive electrode active material coated with the boron-containing compound, separation of oxygen atoms from the surface of the positive electrode active material is prevented, structural collapse is suppressed, and cracking caused by repeated charging and discharging is suppressed. In addition, even if the cathode active material is broken, a side reaction with the electrolyte may be suppressed. In addition, by the boron-containing compound present on the surface of the second positive electrode active material, lithium ions present in the electrolyte can be easily received into the particles, thereby improving the discharge capacity. Accordingly, the lithium secondary battery according to the embodiment in which the second positive electrode active material coated with the boron-containing compound is introduced may exhibit excellent capacity retention and lifespan characteristics while having a high capacity.

The boron-containing compound may be continuously coated on the entire surface of the second positive electrode active material, or may be coated in an island form.

The content of boron with respect to the total weight of the second positive electrode active material may be 0.3 mol% or less, for example, 0.01 mol% to 0.3 mol%, or 0.1 mol% to 0.3 mol%. In the case of including the second positive electrode active material having a monolithic structure, it is possible to effectively suppress structural collapse and cracking of the positive electrode active material that occurs while charging and discharging are repeated, and it is possible to prevent side reactions between the positive electrode active material and the electrolyte, and thus lithium secondary battery It is possible to improve the capacity retention rate and lifespan characteristics while increasing the capacity of the On the other hand, the monolith structure makes it difficult to diffuse lithium into the particle. By coating the surface with a boron-containing compound, the diffusion of lithium can be facilitated and the release of oxygen atoms from the surface of the positive electrode active material can be effectively prevented. When the content of boron is within the above range, this effect can be maximized. On the other hand, when the content of boron is higher than 0.3 mol%, high-temperature lifespan characteristics of the battery may deteriorate.

The second cathode active material according to an embodiment may be included in an amount of 10 wt% to 50 wt%, based on the total weight of the cathode active material for a lithium secondary battery. For example, 10% by weight or more, 15% by weight or more, 20% by weight or more, 25% by weight or more may be contained, for example, 50% by weight or less, 45% by weight or less, 40% by weight or less, 35% by weight or less may contain.

In one embodiment, the primary particles and the second positive electrode active material in the first positive electrode active material have different sizes. The average particle diameter of the second positive electrode active material may be 0.05 μm to 10 μm. for example from 0.1 μm to 10 μm, or from 0.1 μm to 8 μm, or from 0.1 μm to 7 μm, or from 0.1 μm to 6 μm, or from 0.1 μm to 5 μm, or from 1 μm to 4 μm. As described above, since the primary particles of the first positive electrode active material and the second positive electrode active material have different sizes, the density of the positive electrode active material for a lithium secondary battery according to an embodiment can be further increased.

On the other hand, the first positive electrode active material and the second positive electrode active material according to an embodiment are each a nickel-based positive electrode active material represented by the following formula (1).

[Formula 1]

Li _a (Ni _1-xyz Co _x Mn _y M _z )O ₂

In Formula 1, M is boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe) ), copper (Cu), zirconium (Zr), and an element selected from the group consisting of aluminum (Al),

0.95≤a≤1.3, x≤(1-x-y-z), y≤(1-x-y-z), 0 <x<1, 0≤y<1, 0≤z<1. As such, in the nickel-based positive electrode active material of Formula 1, the content of nickel is greater than the content of cobalt, the content of nickel is greater than the content of manganese, and the content of nickel is greater than the content of the element corresponding to M.

In Formula 1, 0.95≤a≤1.3, for example, 1.0≤a≤1.1, 0<x≤0.33, for example, may be 0.1≤x≤0.33, 0≤y≤0.5, for example 0.05≤y≤0.3 , 0≤z≤0.05, 0.33≤(1-x-y-z) ≤0.95, and 0.33≤(1-x-y-z) ≤0.95.

For example, in Formula 1, 0≤z≤0.05, 0<x≤0.33, and 0≤y≤0.33.

For example, in Formula 1, (1-x-y-z)≥0.4, for example, (1-x-y-z)≥0.5, for example, (1-x-y-z)≥0.6.

The content of nickel in the nickel-based positive electrode active material may be 50 mol% or more, for example 55 mol% or more, for example 60 mol% or more, based on the total content of transition metals (Ni, Co, or Mn, etc.) , for example 95 mol% or less, such as 90 mol% or less, such as 80 mol% or less, such as 70 mol% or less, such as 60 mol% or less, such as 63 mol% or less, and , for example from 50 mol% to 95 mol%, for example from 70 mol% to 95 mol%, for example from 80 mol% to 95 mol%. In the nickel-based positive electrode active material, nickel has a higher content than the content of aluminum or manganese and the content of cobalt.

The content of nickel in the nickel-based positive electrode active material is greater than that of each other transition metal based on 1 mole of the total transition metal. As described above, when a nickel-based positive electrode active material having a large nickel content is used as the first positive electrode active material and the second positive electrode active material, when a lithium secondary battery employing a positive electrode including the same is used, lithium diffusion is high, conductivity is good, and at the same voltage Higher doses can be obtained.

According to one embodiment, the press density of the positive electrode active material for a lithium secondary battery including the above-described first positive electrode active material and the second positive electrode active material is, for example, 3.3 g/cc or more, 3.35 g/cc or more, 3.4 g/cc or more, 3.45 g/cc or more, or 3.5 g/cc or more. In one embodiment, the compressed density of the positive electrode active material for a lithium secondary battery may be obtained by inserting 3 g of the positive electrode active material for a lithium secondary battery into a compressed density meter, and then compressing the positive electrode active material with a force of 3 tons for 30 seconds. Accordingly, even if the positive electrode active material for a lithium secondary battery according to an embodiment includes the first positive electrode active material and the second positive electrode active material having different sizes, it is possible to secure a positive electrode having an excellent level of electrode plate density.

Hereinafter, a cathode active material for a lithium secondary battery according to another embodiment of the present invention will be described.

A positive electrode active material for a lithium secondary battery according to this embodiment includes a first positive electrode active material including secondary particles formed by aggregation of two or more primary particles, and at least a portion of the primary particles including secondary particles forming a radially arranged structure; and a second positive electrode active material having a monolithic structure on which a boron-containing compound is coated. In addition, the secondary particles of the present embodiment may further include particles having a monolithic structure. The positive electrode active material of this embodiment includes substantially the same configuration as the one embodiment of the present invention, except that the secondary particles of the first positive electrode active material further include particles having a monolithic structure. Accordingly, detailed descriptions of substantially the same components will be omitted hereinafter.

Specifically, in the first positive electrode active material, particles having a monolithic structure may be attached to the outside of the secondary particle or dispersed therein. For example, the particle having the monolithic structure is agglomerated (physically and/or chemically bound) with the secondary particle, or fills the pores formed in the secondary particle without forming a physical and/or chemical bond with the secondary particle, or may be in contact with the pore wall.

Hereinafter, the structure and manufacturing method of a lithium secondary battery having a positive electrode including a positive electrode active material for a lithium secondary battery according to an embodiment will be described with reference to FIG. 4 .

4 schematically shows the structure of a lithium secondary battery having a positive electrode including a positive electrode active material for a lithium secondary battery according to an embodiment.

Referring to FIG. 4 , the lithium secondary battery 21 includes a positive electrode 23 , a negative electrode 22 , and a separator 24 containing a positive electrode active material for a lithium secondary battery according to an exemplary embodiment.

The positive electrode 23 and the negative electrode 22 are manufactured by respectively coating and drying a composition for forming a positive electrode active material layer and a composition for forming a negative electrode active material layer on a current collector.

The composition for forming a positive electrode active material is prepared by mixing a positive electrode active material, a conductive agent, a binder and a solvent, and the nickel-based active material represented by Chemical Formula 1 described above is used as the positive electrode active material.

The binder is a component that assists in bonding between the active material and the conductive agent and bonding to the current collector, and is added in an amount of 1 to 50 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material. Non-limiting examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro ethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, various copolymers, and the like. The content is used in an amount of 2 to 5 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material. When the content of the binder is within the above range, the binding force of the active material layer to the current collector is good.

The conductive agent is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The amount of the conductive agent is 2 to 5 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material. When the content of the conductive agent is within the above range, the conductivity characteristics of the finally obtained electrode are excellent.

As a non-limiting example of the solvent, N-methylpyrrolidone and the like are used.

The amount of the solvent is 1 to 10 parts by weight based on 100 parts by weight of the positive electrode active material. When the content of the solvent is within the above range, the operation for forming the active material layer is easy.

The positive electrode current collector has a thickness of 3 to 500 μm, and is not particularly limited as long as it has high conductivity without causing chemical change in the battery, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, Alternatively, a surface treated with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. The current collector may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface thereof, and various forms such as a film, sheet, foil, net, porous body, foam body, and non-woven body are possible.

Separately, a composition for forming a negative electrode active material layer is prepared by mixing a negative electrode active material, a binder, a conductive agent, and a solvent.

As the negative electrode active material, a material capable of occluding and releasing lithium ions is used. Non-limiting examples of the negative active material include graphite, carbon-based materials such as carbon, lithium metal, alloys thereof, silicon oxide-based materials, and the like. According to an embodiment of the present invention, silicon oxide is used.

The binder is added in an amount of 1 to 50 parts by weight based on 100 parts by weight of the total weight of the negative electrode active material. As a non-limiting example of such a binder, the same type as the positive electrode may be used.

The conductive agent is used in an amount of 1 to 5 parts by weight based on 100 parts by weight of the total weight of the negative electrode active material. When the content of the conductive agent is within the above range, the conductivity characteristics of the finally obtained electrode are excellent.

The amount of the solvent is 1 to 10 parts by weight based on 100 parts by weight of the total weight of the negative electrode active material. When the content of the solvent is within the above range, the operation for forming the anode active material layer is easy.

The conductive agent and the solvent may be the same type of material as that of the positive electrode.

As the negative electrode current collector, it is generally made to have a thickness of 3 to 500 μm. Such a negative current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or a surface of copper or stainless steel. Carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, etc. may be used. In addition, like the positive electrode current collector, the bonding strength of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven body, and the like.

A separator is interposed between the positive electrode and the negative electrode manufactured according to the above process.

The separator has a pore diameter of 0.01 to 10 μm and a thickness of generally 5 to 300 μm. Specific examples include olefinic polymers such as polypropylene and polyethylene; Alternatively, a sheet or non-woven fabric made of glass fiber is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The lithium salt-containing non-aqueous electrolyte consists of a non-aqueous electrolyte solution and a lithium salt. As the non-aqueous electrolyte, a non-aqueous electrolyte, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used.

Examples of the non-aqueous electrolyte include, but are not limited to, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2- Dimethoxyethane, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, N,N-dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, Phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, pyropionic acid An aprotic organic solvent such as methyl or ethyl propionate may be used.

Examples of the organic solid electrolyte include, but are not limited to, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and the like.

Examples of the inorganic solid electrolyte include, but are not limited to, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ and the like may be used.

The lithium salt is a material readily soluble in the non-aqueous electrolyte, and includes, but is not limited to, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborate, lower aliphatic lithium carboxylate, lithium tetraphenyl borate, imide etc. may be used.

As described above, the positive electrode 23 , the negative electrode 22 , and the separator 24 are wound or folded and accommodated in the battery case 25 . Next, an organic electrolyte is injected into the battery case 25 and sealed with a cap assembly 26 , thereby completing the lithium secondary battery 21 as shown in FIG. 4 .

The battery case 25 may have a cylindrical shape, a square shape, a thin film shape, or the like. For example, the lithium secondary battery 20 may be a large thin film type battery. The lithium secondary battery may be a lithium ion battery. A separator may be disposed between the positive electrode and the negative electrode to form a battery structure. After the battery structure is stacked in a bi-cell structure, it is impregnated with an organic electrolyte, and the obtained result is accommodated and sealed in a pouch, thereby completing a lithium ion polymer battery. In addition, a plurality of the battery structures are stacked to form a battery pack, and the battery pack can be used in any device requiring high capacity and high output. For example, it can be used in a laptop computer, a smart phone, an electric vehicle, and the like.

In addition, since the lithium secondary battery has excellent storage stability, lifespan characteristics, and high rate characteristics at high temperatures, it can be used in electric vehicles (EVs). For example, it may be used in a hybrid vehicle such as a plug-in hybrid electric vehicle (PHEV).

The lithium secondary battery according to an embodiment has excellent electrode plate density by using the above-described positive electrode active material for lithium secondary battery, and thus has excellent electrochemical properties.

Hereinafter, a method of manufacturing a cathode active material for a lithium secondary battery according to the above-described embodiment will be described.

In the method for manufacturing a cathode active material for a lithium secondary battery according to an embodiment, a first nickel-based oxide is formed through a first precursor, a second nickel-based oxide is obtained using a second precursor, and the second nickel-based oxide and boron The precursor containing the precursor is mixed and subjected to a third heat treatment to obtain a second nickel-based oxide coated with a boron-containing compound, and the first nickel-based oxide and the second nickel-based oxide coated with the boron-containing compound are mixed to contain the first positive electrode active material and boron It may include obtaining a positive electrode active material including a second positive electrode active material coated with the compound. Hereinafter, it will be described in detail.

First, a first nickel-based oxide may be obtained by subjecting the first precursor to a first heat treatment in an oxidizing gas atmosphere.

Specifically, the oxidizing gas atmosphere may use an oxidizing gas such as oxygen or air. The first heat treatment may be performed, for example, at 800 °C to 900 °C. The first heat treatment time is variable depending on the heat treatment temperature and the like, but is performed for, for example, 5 to 15 hours.

The first precursor according to an embodiment includes Li, Ni, Co, Mn, optionally boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), and vanadium. (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr) and an element selected from the group consisting of aluminum (Al) in a predetermined molar ratio within a range that satisfies the stoichiometric ratio, respectively. may contain.

Meanwhile, the first precursor may be obtained by mixing the first composite metal hydroxide with a lithium-based material.

The first composite metal hydroxide may be one in which elements including at least nickel among elements selected from the group described above and a hydroxyl group are combined within a range that satisfies a stoichiometric ratio. For example, the first composite metal hydroxide may be a nickel-based composite metal hydroxide, for example nickel-cobalt-aluminum hydroxide, or nickel-cobalt-manganese hydroxide.

The lithium-based material is a lithium source for the positive electrode active material for a lithium secondary battery according to an embodiment to function as a positive electrode active material. The type of the lithium-based material according to the exemplary embodiment is not particularly limited, and for example, Li ₂ CO ₃ , LiOH, a hydrate thereof, or a combination thereof may be used.

That is, the first precursor may be a mixture of a nickel-based composite metal hydroxide and a lithium-based material. The first nickel-based oxide obtained by subjecting the first precursor to a first heat treatment in an oxidizing gas atmosphere may be a lithium nickel-based composite oxide, for example, lithium nickel-cobalt-aluminum oxide, lithium nickel-cobalt-manganese oxide. have.

Meanwhile, by separately performing a second heat treatment on the second precursor in an oxidizing gas atmosphere, and pulverizing the resultant, a second nickel-based oxide including monolithic particles can be obtained. This is mixed with a material containing boron and subjected to a third heat treatment to obtain a second nickel-based oxide coated with a boron-containing compound.

Specifically, the oxidizing gas atmosphere may use an oxidizing gas such as oxygen or air. The second heat treatment may be performed, for example, at 800 °C to 1000 °C. The second heat treatment time is variable depending on the heat treatment temperature and the like, but is performed for, for example, 5 to 20 hours. The second precursor may be obtained by mixing the second composite metal hydroxide with the lithium-based material as described above.

The second composite metal hydroxide is, like the above-described first composite hydroxide, Li, Ni, Co, Mn, optionally boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) , titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr) and an element selected from the group consisting of aluminum (Al) satisfies the stoichiometric ratio, respectively. It may be contained in a predetermined molar ratio within the range, and among them, elements including at least nickel and a hydroxyl group may be combined within a range that satisfies a stoichiometric ratio. The second composite metal hydroxide may be, for example, a nickel-based composite metal hydroxide, for example nickel-cobalt-aluminum hydroxide, or nickel-cobalt-manganese hydroxide.

The second composite metal hydroxide has an average particle diameter of, for example, 0.5 µm or more, 1.0 µm or more, 1.5 µm or more, 2.0 µm or more, for example, 10 µm or less, 8 µm or less, 6 µm or less, 5 µm or less, 4 µm or less. The following can be used.

In one embodiment, the specific surface area of the second composite metal hydroxide measured by the BET measurement method may be 1 m ² /g to 30 m ² /g. For example, it may be 2 m ² /g to 25 m ² /g, specifically 5 m ² /g to 25 m ² /g. When the specific surface area of the second composite metal hydroxide satisfies the above range, the second nickel-based oxide may be finely pulverized into particles having a monolithic structure and having a monolithic structure in the above-mentioned average particle size range in the pulverization process, and the content of residual lithium is reduced can do.

The second nickel-based oxide obtained by subjecting the second precursor to a second heat treatment in an oxidizing gas atmosphere may be a lithium nickel-based composite oxide, for example, lithium nickel-cobalt-aluminum oxide or lithium nickel-cobalt-manganese oxide. .

Thereafter, by pulverizing the second heat-treated material, a second nickel-based oxide including particles having a monolithic structure falling within the aforementioned average particle diameter range is obtained. The second nickel-based oxide has a smaller average particle diameter than the above-described first nickel-based oxide. The grinding process may be performed using a known grinding device, such as a jet mill.

The obtained monolithic particles fall within the above-mentioned average particle diameter range, and as described above, may exist dispersed without agglomeration for each particle. Meanwhile, in one embodiment, the input amount and/or the mixing ratio of the lithium-based material and the second composite metal hydroxide are not particularly limited, but the conditions for forming the second positive electrode active material having a monolithic structure are satisfied, and at the same time, the nickel-based material Excessive lithium salts and unreacted lithium-based materials may be adjusted within a range capable of minimizing residuals after the preparation of the active material.

In one embodiment, the molar ratio (Li/Me) of lithium (Li) to the remaining metal elements (Me) other than lithium in the second precursor is, for example, 0.8 or more, 0.85 or more, 0.9 or more, 0.95 or more, for example For example, it may be 1.0 or more, for example, 1.2 or less, for example, 1.1 or less, for example, 1.05 or less.

On the other hand, the molar ratio between Ni, Co, Mn, and optional elements in the first composite metal hydroxide and the second composite metal hydroxide can be freely selected within the range for finally preparing the nickel-based positive electrode active material represented by the above-mentioned formula (1). However, at least the molar ratio of Ni may be controlled to be large compared to the molar ratio of each of Co, Mn, and optional other elements. Alternatively, the second precursor according to an embodiment may be adjusted to have the same molar ratio as the above-described first precursor.

Thereafter, a process of coating the boron-containing compound on the second nickel-based oxide is performed by mixing the second nickel-based oxide of the monolith structure with the boron-containing precursor and performing a third heat treatment. Here, the boron-containing precursor refers to a material that may exist as a boron-containing compound on the surface of the second nickel-based oxide through a heat treatment process. For example, the boron-containing precursor is boric acid (H ₃ BO ₃ ), B ₂ O ₃ , C ₆ H ₅ B(OH) ₂ , (C ₆ H ₅ O) ₃ B, [CH ₃ (CH ₂ ) ₃ O ] ₃ B, C ₁₃ H ₁₉ BO ₃ , C ₃ H ₉ B ₃ O ₆ , (C ₃ H ₇ O) ₃ B, or a combination thereof.

The temperature for the third heat treatment by mixing the second nickel-based oxide and the boron-containing precursor may be about 300°C to about 500°C. The third heat treatment time is variable depending on the heat treatment temperature and the like, but may be, for example, 3 to 15 hours. When the third heat treatment is performed in this temperature range and time range, a second nickel-based oxide coated with a boron-containing compound uniformly may be obtained.

The content of the boron-containing precursor relative to 100 parts by weight of the second nickel-based oxide may be 0.01 parts by weight to 0.35 parts by weight, or 0.1 parts by weight to 0.35 parts by weight, or 0.1 parts by weight to 0.3 parts by weight. In the case of coating in this content range, a second nickel-based oxide coated with a boron-containing compound uniformly may be obtained.

Thereafter, a process of mixing the first nickel-based oxide and the second nickel-based oxide coated with the boron-containing compound is performed. In one embodiment, the mixing ratio of the first nickel-based oxide and the second nickel-based oxide coated with the boron-containing compound is, for example, 9:1 to 5:5, for example, 8:2 to 5: based on the weight ratio. 5, eg 8:2 to 6:4, eg 7:3.

The prepared positive electrode active material for a lithium secondary battery includes a first positive electrode active material including secondary particles formed by aggregation of primary particles as described above, and a second positive electrode active material having a monolithic structure and coated with a boron-containing compound, the first At least some of the primary particles in the secondary particles of the positive electrode active material are radially arranged. The positive electrode active material prepared in this way and the lithium secondary battery including the same have excellent stability and electrochemical properties as described above.

Hereinafter, specific embodiments of the present invention are presented. However, the examples described below are only for specifically illustrating or explaining the present invention, and the present invention is not limited thereto.

Example 1

1. Complex metal hydroxide manufacturing process

(1) First composite metal hydroxide manufacturing process

First, a nickel-based active material precursor (Ni _0.945 Co _0.04 Al _0.015 OH) was synthesized through a co-precipitation method to be described later in order to prepare the first nickel-based oxide. Nickel sulfate, cobalt sulfate and aluminum nitrate were used as metal raw materials for forming the nickel-based active material precursor in the following manufacturing process.

[Step 1: 2.5kW/㎥, NH ₄ OH 0.40M, pH 10.5 to 11.5, reaction time 6 hours]

First, ammonia water having a concentration of 0.40M was put into the reactor. At a stirring power of 2.5 kW/m 3 and a reaction temperature of 50° C., the reaction was started while the metal raw material and the complexing agent were added at rates of 85 ml/min and 10 ml/min, respectively.

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 step was performed as follows.

[Step 2: 2.0kW/㎥, NH ₄ OH 0.45M, pH 11-12, reaction time 18 hours]

While maintaining the reaction temperature of 50 ℃, the metal raw material and the complexing agent were added at a rate of 85 ml/min and 12 ml/min, respectively, so that the concentration of the complexing agent was maintained at 0.45M. The reaction was carried out for 6 hours while adding NaOH to maintain the pH. At this time, the stirring power was lowered to 2.0kW/m3, which is lower than the first stage, and the reaction proceeded. It was confirmed that the average size of the product particles containing the core and the intermediate layer obtained by performing this reaction was 13.5 μm to 14 μm, and the third step was performed as follows.

[Step 3: 1.5kW/㎥, NH ₄ OH 0.45M, pH 10.5~11.5, reaction time 14 hours]

While maintaining the reaction temperature of 50 ℃, the input rate of the metal raw material and the complexing agent and the concentration of the complexing agent were the same as in step 2 above. The reaction was carried out for 14 hours while adding NaOH to maintain the pH. At this time, the stirring power was lowered to 1.5kW/m3, which is lower than the second stage, and the reaction was carried out.

[Post-process]

After washing the resultant, the washed resultant was dried with hot air at about 150° C. for 24 hours to obtain a first composite metal hydroxide (Ni _0.945 Co _0.04 Al _0.015 OH).

(2) Second composite metal hydroxide manufacturing process

Separately, nickel sulfate (NiSO ₄ .6H ₂ O), cobalt sulfate (CoSO ₄ .7H ₂ O) and manganese sulfate (MnSO ₄ .H ₂ O) were dissolved in distilled water as a solvent in a molar ratio of 88:8:4. Prepare the mixed solution. To form a complex compound, a dilute aqueous ammonia (NH ₄ OH) solution and sodium hydroxide (NaOH) as a precipitating agent are prepared. Thereafter, the metal raw material mixed solution, aqueous ammonia, and sodium hydroxide are respectively introduced into the reactor. Next, the reaction proceeds for about 20 hours while stirring. Thereafter, the slurry solution in the reactor is filtered and washed with distilled water of high purity, and then dried for 24 hours to obtain a second composite metal hydroxide (Ni _0.88 Co _0.08 Mn _0.04 (OH) ₂ ) powder. The obtained second composite metal hydroxide powder had an average particle diameter of 4.0 μm, and a specific surface area measured by the BET measurement method was 15 m ² /g.

2. Cathode active material manufacturing process

(1) First Nickel-Based Oxide Manufacturing Process

A first precursor is obtained by mixing the obtained first composite metal hydroxide and LiOH in a molar ratio of 1:1 to prepare the first nickel-based oxide, and by performing a first heat treatment for this at about 700° C. for 10 hours in an oxygen atmosphere, the first A nickel-based oxide (LiNi _0.945 Co _0.04 Al _0.015 O ₂ ) was obtained.

The average particle diameter of the obtained 1st nickel-type oxide was 13.8 micrometers.

(2) Second Nickel-Based Oxide Manufacturing Process

Thereafter, the obtained second composite metal hydroxide and LiOH were mixed to satisfy Li/(Ni+Co+Mn) = 1.05 to obtain a second precursor, which was put into a kiln, and the second precursor was put in an oxygen atmosphere at 910° C. for 8 hours. Heat treatment was performed to obtain a second nickel-based oxide (LiNi _0.88 Co _0.08 Mn _0.04 O ₂ ). Thereafter, the obtained second nickel-based oxide is pulverized for about 30 minutes to separate/disperse into a plurality of second nickel-based oxides having a monolithic structure.

The average particle diameter of the obtained second nickel-based oxide having a monolithic structure was 3.7 µm.

(3) Boron coating process of the second nickel-based oxide

The obtained second nickel-based oxide having a monolithic structure and boric acid were mixed at 0.19 wt% (or 0.3 mol%) by a dry mixer, followed by a third heat treatment at 350°C for 8 hours. As a result, a second nickel-based oxide having a monolithic structure in which boron oxide and lithium borate are coated on the surface is obtained.

(4) First nickel-based oxide and second nickel-based oxide mixing step

A positive active material including a first positive active material and a second positive active material coated with a boron-containing compound is prepared by mixing the first nickel-based oxide and the second nickel-based oxide coated with a boron-containing compound in a weight ratio of 8:2 did

Comparative Example 1

A positive electrode active material was prepared in the same manner as in Example 1, except that the boron-containing compound was not coated on the second nickel-based oxide in Example 1.

Comparative Example 2

A positive electrode active material was prepared in the same manner as in Example 1, except that in Example 1, the manufacturing process of the second nickel-based oxide was as follows, and the boron-containing compound was not coated.

(2) Second Nickel-Based Oxide Manufacturing Process

Then, after mixing the obtained second composite metal hydroxide and LiOH to satisfy Li/(Ni+Co+Mn) = 1.00, the mixture was put into a kiln, and a second heat treatment was performed at 725° C. for 20 hours in an oxygen atmosphere. A nickel-based oxide (LiNi _0.88 Co _0.08 Mn _0.04 O ₂ ) was obtained.

The average particle diameter of the obtained 1st nickel-type oxide was 4.6 micrometers.

Comparative Example 3

A positive electrode active material was prepared in the same manner as in Example 1, except that the manufacturing process of the first nickel-based oxide was as follows.

(1) First Nickel-Based Oxide Manufacturing Process

In order to prepare the first nickel-based oxide, a first precursor is obtained by dry mixing the obtained first composite metal hydroxide and LiOH in a 1:1 molar ratio and boric acid in an amount of 0.084 wt% (or 0.125 mol%), and this is used in an oxygen atmosphere. By the first heat treatment at about 700 ° C. for 10 hours, the first nickel-based oxide (LiNi _0.945 Co _0.04 Al _0.015 O ₂ ) coated with a boron-containing compound on the surface was obtained.

The average particle diameter of the obtained 1st nickel-type oxide was 13.8 micrometers.

Manufacturing of Coin Half Cells

For each of Example 1, Comparative Example 1, and Comparative Example 2, each coin half cell was manufactured through the following process.

A mixture of 96 g of the obtained cathode active material for a lithium secondary battery, 2 g of polyvinylidene fluoride, 137 g of N-methylpyrrolidone as a solvent, and 2 g of carbon black as a conductive agent was removed by using a mixer to remove air bubbles and uniformly dispersed. A slurry for forming the positive electrode active material layer is prepared.

The slurry for forming the positive electrode active material layer is coated on an aluminum foil to form a thin electrode plate, dried at 135° C. for at least 3 hours, and then subjected to rolling and vacuum drying processes to manufacture a positive electrode.

A 2032 type coin half cell is manufactured using the positive electrode and the lithium metal counter electrode as the counter electrode. A separator (thickness: about 16 μm) made of a porous polyethylene (PE) film is interposed between the positive electrode and the lithium metal counter electrode, and electrolyte is injected to fabricate a 2032 type coin cell. At this time, as the electrolyte, a solution containing 1.1M LiPF ₆ dissolved in a solvent in which ethylene carbonate (EC) and ethylmethyl carbonate (EMC) are mixed in a volume ratio of 3:5 is used.

Evaluation Example 1: Charging/discharging capacity, charging/discharging efficiency and lifespan characteristics

에서 1C의 정전류로 상한전압 4.3V까지 충전한 후 방전 종지 전압 3.0V까지 1C로 방전하여 초기 방전용량을 측정하였고, 계속하여 50회 사이클까지의 방전용량을 측정하여 용량유지율을 평가하였으며 그 결과를 아래 표 1에 나타내었다.45 of the prepared Example 1 and Comparative Examples 1 to 3 coin half cells

After charging to the upper limit voltage of 4.3V with a constant current of 1C, the initial discharge capacity was measured by discharging at 1C until the final discharge voltage of 3.0V. It is shown in Table 1 below.

Initial discharge capacity (mAh/g) 50 dose retention rate (%) capacity per volume
(mAh/cc) Example 1 214.4 92.7 755 Comparative Example 1 211.4 90.0 744 Comparative Example 2 214.6 88.6 734 Comparative Example 3 204.2 - 673

Referring to Table 1, in the case of Comparative Example 1 using the second positive electrode active material having a monolith structure, 50 times compared to Comparative Example 2 using a general nickel-based oxide having a structure in which primary particles are assembled, not a monolith structure It can be seen that the capacity retention rate is improved, but the initial discharge capacity is reduced.

However, in Example 1 in which the second positive electrode active material having a monolithic structure coated with boron-containing compound is used, unlike Comparative Example 1, the capacity retention rate of 50 times can be improved without reducing the initial discharge capacity. In addition, the capacity per volume can be further improved by mixing the second nickel-based oxide having a monolithic structure.

Comparative Example 3 is a battery to which a first cathode active material coated with a boron-containing compound and a second cathode active material having a monolith structure coated with a boron-containing compound are applied. Referring to Table 1, compared to Example 1, the initial discharge capacity and capacity per volume It can be seen that this is significantly lower.

Meanwhile, in order to confirm the coating effect of boron on the second nickel-based oxide having a monolithic structure, batteries of Examples 2 to 6 and Comparative Example 4 in which only the second nickel-based oxide was applied as a positive electrode active material were prepared as follows.

Example 2

(i) In the boron coating process of the second nickel-based oxide of Example 1, 0.06 wt% (or 0.1 mol%) of the second nickel-based oxide and boric acid were mixed with a dry mixer, followed by heat treatment at 325 ° C. for 8 hours and (ii) a coin half cell was prepared in the same manner as in Example 1, except that only the second nickel-based oxide having a monolith structure coated with boron-containing compound was used as a positive electrode active material.

Comparative Example 4

A coin half cell was manufactured in the same manner as in Comparative Example 1, except that only the second nickel-based oxide having a monolith structure that was not coated with the boron-containing compound prepared in Comparative Example 1 was used as the positive electrode active material.

Example 3

(i) In the boron coating process of the second nickel-based oxide of Example 1, 0.06 wt% (or 0.1 mol%) of the second nickel-based oxide and boric acid were mixed with a dry mixer, followed by heat treatment at 350° C. for 8 hours and (ii) a coin half cell was prepared in the same manner as in Example 1, except that only the second nickel-based oxide having a monolith structure coated with boron-containing compound was used as a positive electrode active material.

Example 4

A coin half cell was manufactured in the same manner as in Example 1, except that only the second nickel-based oxide having a monolith structure coated with the boron-containing compound prepared in Example 1 was used as the cathode active material.

Example 5

(i) In the boron coating process of the second nickel-based oxide of Example 1, 0.32 wt% (or 0.5 mol%) of the second nickel-based oxide and boric acid were mixed with a dry mixer, followed by heat treatment at 350° C. for 8 hours and (ii) a coin half cell was prepared in the same manner as in Example 1, except that only the second nickel-based oxide having a monolith structure coated with boron-containing compound was used as a positive electrode active material.

Example 6

(i) In the boron coating process of the second nickel-based oxide of Example 1, 0.06 wt% (or 0.1 mol%) of the second nickel-based oxide and boric acid were mixed with a dry mixer, followed by heat treatment at 375° C. for 8 hours and (ii) a coin half cell was prepared in the same manner as in Example 1, except that only the second nickel-based oxide having a monolith structure coated with boron-containing compound was used as a positive electrode active material.

Evaluation Example 2: Charging/discharging capacity, charging/discharging efficiency, and lifespan characteristics

에서 1C의 정전류로 상한전압 4.3V까지 충전한 후 방전 종지 전압 3.0V까지 1C로 방전하여 초기 방전용량을 측정하였고, 계속하여 50회 사이클까지의 방전용량을 측정하여 용량유지율을 평가하였으며, 그 결과를 아래 표 2에 나타내었다. 45 coin half cells of Examples 2 to 6 and Comparative Example 4

After charging to the upper limit voltage of 4.3V with a constant current of 1C, the initial discharge capacity was measured by discharging at 1C until the final discharge voltage of 3.0V, and the capacity retention rate was evaluated by measuring the discharge capacity up to 50 cycles. is shown in Table 2 below.

Third heat treatment temperature (℃) boron coating
mol%) Mars Capacity retention rate Charge (mAh/g) Discharge
(mAh/g) efficiency(%) 50 times (%) Example 2 325 0.1 230.9 207.2 89.7% 96.0% Comparative Example 4 350 Bare 230.7 204.4 88.6% 95.5% Example 3 0.1 232.5 207.8 89.4% 95.4% Example 4 0.3 232.2 207.8 89.5% 94.4% Example 5 0.5 234.0 208.5 89.1% 92.1% Example 6 375 0.1 232.7 208.3 89.5% 96.6%

Referring to Table 2, when the content of boron to be added is 0.1 mol%, it can be seen that all of the discharge capacity is improved during heat treatment at 325°C to 375°C, compared to heat treatment without coating the boron of Comparative Example 4. The charging and discharging efficiency of Example 4 in which 0.3 mol% of boron was coated at 350°C was the best. On the other hand, it can be seen that the capacity retention rate of 50 times at 45° C. tends to decrease rapidly when more than 0.3 mol% of boron is added.

In the above, the present invention has been described through preferred embodiments as described above, but the present invention is not limited thereto and various modifications and variations are possible without departing from the concept and scope of the following claims. Those skilled in the art to which the invention pertains will readily understand.

21: lithium secondary battery 22: negative electrode
23: positive electrode 24: separator
25: battery case 26: cap assembly

Claims (20)

A first positive electrode active material comprising at least two or more primary particles agglomerated and including secondary particles in which at least a portion of the primary particles have a radially arranged structure; and
A second positive electrode active material having a monolith structure,
The first positive electrode active material and the second positive electrode active material are both nickel-based positive electrode active materials,
A positive electrode active material for a lithium secondary battery, wherein the surface of the second positive electrode active material is coated with a boron-containing compound. In claim 1,
In the second positive electrode active material, the boron-containing compound is boron oxide, lithium borate, or a combination thereof. In claim 1,
In the second cathode active material, the boron-containing compound is B ₂ O ₃ , LiBO ₂ , Li ₃ B ₇ O ₁₂ , Li ₆ B ₄ O ₉ , Li ₃ B ₁₁ O ₁₈ , Li ₂ B ₄ O ₇ , Li ₃ BO ₃ , or a combination thereof, a cathode active material for a lithium secondary battery. In claim 1,
The content of boron with respect to the total weight of the second positive electrode active material is 0.01 mol% to 0.3 mol% of a positive electrode active material for a lithium secondary battery. In claim 1,
The second cathode active material is contained in an amount of 10% to 50% by weight based on the total weight of the cathode active material for a lithium secondary battery, a cathode active material for a lithium secondary battery. In claim 1,
The second positive electrode active material has an average particle diameter of 0.05 μm to 10 μm, a positive electrode active material for a lithium secondary battery. In claim 1,
In the first positive electrode active material, the secondary particles include a radially arranged structure, or
A positive electrode active material for a lithium secondary battery, comprising an interior including an irregular porous structure and an exterior including a radially arranged structure. In claim 1,
In the first positive electrode active material, the primary particles have a plate shape,
At least some of the primary particles have a long axis arranged in a radial direction, a cathode active material for a lithium secondary battery. In claim 1,
An average length of the primary particles in the first positive electrode active material is 0.01 μm to 5 μm, a positive electrode active material for a lithium secondary battery. In claim 1,
An average particle diameter of the secondary particles in the first positive electrode active material is 1 μm to 20 μm, a positive electrode active material for a lithium secondary battery. In claim 1,
The first positive electrode active material is a positive electrode active material for a lithium secondary battery, which is represented by the following formula (1):
[Formula 1]
Li _a (Ni _1-xyz Co _x Mn _y M _z )O ₂
In Formula 1, M is boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe) ), copper (Cu), zirconium (Zr), and an element selected from the group consisting of aluminum (Al),
0.95≤a≤1.3, x≤(1-xyz), y≤(1-xyz), 0<x<1, 0≤y<1, 0≤z<1. In claim 1,
The second positive active material is a positive electrode active material for a lithium secondary battery, which is represented by the following formula (1):
[Formula 1]
Li _a (Ni _1-xyz Co _x Mn _y M _z )O ₂
In Formula 1, M is boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe) ), copper (Cu), zirconium (Zr), and an element selected from the group consisting of aluminum (Al),
0.95≤a≤1.3, x≤(1-xyz), y≤(1-xyz), 0<x<1, 0≤y<1, 0≤z<1. subjecting the first precursor to a first heat treatment in an oxidizing gas atmosphere to obtain a first nickel-based oxide;
subjecting the second precursor to a second heat treatment in an oxidizing gas atmosphere to obtain a second nickel-based oxide, wherein the second nickel-based oxide has a monolithic structure;
mixing the second nickel-based oxide and the boron-containing precursor and performing a third heat treatment to obtain a second nickel-based oxide coated with a boron-containing compound; and
By mixing the first nickel-based oxide and the second nickel-based oxide coated with the boron-containing compound, the cathode active material comprising a first cathode active material and a second cathode active material coated with a boron-containing compound while having a monolith structure including getting
is a method of manufacturing a cathode active material for a lithium secondary battery. In claim 13,
The boron-containing precursor is H ₃ BO ₃ , B ₂ O ₃ , C ₆ H ₅ B(OH) ₂ , (C ₆ H ₅ O) ₃ B, [CH ₃ (CH ₂ ) ₃ O] ₃ B, C ₁₃ H ₁₉ BO ₃ , C ₃ H ₉ B ₃ O ₆ , (C ₃ H ₇ O) ₃ B, or a combination thereof, a method of manufacturing a cathode active material for a lithium secondary battery. In claim 13,
The content of the boron-containing precursor relative to 100 parts by weight of the second nickel-based oxide is 0.01 parts by weight to 0.35 parts by weight of a method of manufacturing a cathode active material for a lithium secondary battery. In claim 13,
The third heat treatment temperature by mixing the second nickel-based oxide and boron-containing precursor is 300 ℃ to 500 ℃ method for producing a cathode active material for a lithium secondary battery. In claim 13,
Obtaining the second nickel-based oxide includes pulverizing a resultant obtained by subjecting the second precursor to the second heat treatment to form particles having a monolithic structure,
A method of manufacturing a cathode active material for a lithium secondary battery. In claim 13,
The second precursor is obtained by mixing a second composite metal hydroxide having a specific surface area of 1 m ² /g to 30 m ² /g measured by a BET measurement method with a lithium-based material, a method for producing a cathode active material for a lithium secondary battery . In claim 13,
The mixing ratio of the first nickel-based oxide and the second nickel-based oxide coated with the boron-containing compound is 9:1 to 5:5 based on a weight ratio, a cathode active material for a lithium secondary battery. A positive electrode comprising the positive electrode active material for a lithium secondary battery of any one of claims 1 to 12;
cathode; and
A lithium secondary battery comprising an electrolyte interposed between the positive electrode and the negative electrode.

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