KR20240085142A - Positive active material for rechargeable lithium battery, preparing method thereof and rechargeable lithium battery including the same - Google Patents

Abstract

The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery comprising the same, comprising a first positive electrode active material in the form of a secondary particle formed by agglomeration of a plurality of primary particles, and a second positive electrode active material in the form of a single particle, wherein the first positive electrode active material and the second positive electrode active material each comprise a lithium nickel-based composite oxide having a nickel content of 70 mol% or more with respect to all elements excluding lithium and oxygen, the first positive electrode active material comprises a coating portion present in the form of a film on the surface of the secondary particle, the second positive electrode active material comprises a coating portion present in the form of a film on the surface of the single particle, the coating portion of the first positive electrode active material and the coating portion of the second positive electrode active material each comprise lithium cobalt oxide and cobalt oxyhydroxide.

Description

Positive active material for lithium secondary battery, manufacturing method thereof, and lithium secondary battery including same {POSITIVE ACTIVE MATERIAL FOR RECHARGEABLE LITHIUM BATTERY, PREPARING METHOD THEREOF AND RECHARGEABLE LITHIUM BATTERY INCLUDING THE SAME}

It relates to a positive electrode active material for lithium secondary batteries, a method of manufacturing the same, and a lithium secondary battery containing the same.

Lithium secondary batteries, which have high energy density and are easy to carry, are mainly used as a driving power source for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, research is being actively conducted to use lithium secondary batteries with high energy density as a driving power source or power storage power source for hybrid vehicles or electric vehicles.

In order to implement a lithium secondary battery suitable for these purposes, various positive electrode active materials are being reviewed. Among them, lithium nickel-based oxide, lithium nickel manganese cobalt composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium cobalt oxide are mainly used as positive electrode active materials. However, as these positive electrode active materials are repeatedly charged and discharged, the structure collapses or cracks occur, which reduces the long-term lifespan of the lithium secondary battery and increases resistance, causing problems such that it does not exhibit satisfactory capacity characteristics. Accordingly, the development of new positive electrode active materials that can achieve high capacity and high energy density while securing long-life characteristics is required.

It increases the energy density of high-nickel-based positive electrode active materials and improves long life characteristics and thermal stability characteristics.

In one embodiment, a positive electrode active material for a lithium secondary battery includes a first positive electrode active material in the form of secondary particles made by agglomerating a plurality of primary particles, and a second positive electrode active material in the form of single particles, the first positive electrode active material and the second positive electrode. The active material includes a lithium nickel-based composite oxide having a nickel content of 70 mol% or more based on the total elements excluding lithium and oxygen, and the first positive electrode active material includes a coating portion present in the form of a film on the surface of the secondary particle, , the second positive electrode active material includes a coating portion present in the form of a film on the surface of the single particle, and the coating portion of the first positive electrode active material and the coating portion of the second positive electrode active material each include lithium cobalt oxide and cobalt oxyhydroxide. Provides a positive electrode active material for lithium secondary batteries.

In another embodiment, a first positive electrode active material in the form of secondary particles, lithium, which contains a lithium nickel-based composite oxide with a nickel content of 70 mol% or more relative to the total elements excluding lithium and oxygen, and which is formed by agglomerating a plurality of primary particles. A second positive electrode active material in the form of single particles, cobalt sulfate, and sodium hydroxide containing a lithium nickel-based complex oxide having a nickel content of 70 mol% or more based on all elements excluding oxygen and added to a solvent are mixed; Remove solvent; Adding lithium raw material to the obtained product; By heat treatment; Provided is a method for producing a positive electrode active material for a lithium secondary battery, including obtaining the above-mentioned positive electrode active material.

Another embodiment provides a lithium secondary battery including a positive electrode including the positive electrode active material, a negative electrode, and an electrolyte.

According to one embodiment, a cathode active material for a lithium secondary battery has improved stability while realizing high capacity and high energy density, and a lithium secondary battery containing the same has improved high-temperature long-life characteristics and thermal stability.

Figure 1 is a schematic diagram showing a lithium secondary battery according to one embodiment.
Figure 2 is an X-ray diffraction (XRD) analysis graph of the positive electrode active material prepared in Example 1, the positive electrode plate before life, and the positive electrode plate after life.
FIG. 3 is an enlarged view of the graph at around 20° in FIG. 2.
Figure 4 is an enlarged view of the graph near 40° in Figure 2.
Figure 5 is an X-ray diffraction analysis graph for Co(OH) ₂ , CoOOH, and Co ₃ O ₄ .
Figure 6 is an image highlighting the cobalt element through SEM-EDS analysis of the fracture surface of the first positive electrode active material of Example 1.
Figure 7 is an image highlighting the cobalt element through SEM-EDS analysis of the fracture surface of the second positive electrode active material of Example 1.
Figure 8 is a graph of lifespan characteristics evaluation for coated half-cells manufactured in Example 1, Comparative Example 1, and Comparative Example 2.

Hereinafter, specific implementation examples will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein.

The terminology used herein is for the purpose of describing example implementations only and is not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

Here, “a combination thereof” means a mixture of constituents, a laminate, a composite, a copolymer, an alloy, a blend, a reaction product, etc.

Here, terms such as “comprise,” “comprise,” or “have” are intended to designate the presence of implemented features, numbers, steps, components, or a combination thereof, but not one or more other features, numbers, or steps. , components, or combinations thereof should be understood as not excluding in advance the existence or possibility of addition.

In the drawings, the thickness is enlarged to clearly express various layers and regions, and similar reference numerals are given to similar parts throughout the specification. When a part of a layer, membrane, region, plate, etc. is said to be “on” or “on” another part, this includes not only cases where it is “directly on” another part, but also cases where there is another part in between. Conversely, when a part is said to be “right on top” of another part, it means that there is no other part in between.

Also, here, “layer” includes not only the shape formed on the entire surface when observed in plan view, but also the shape formed on some surfaces.

In addition, the average particle size can be measured by a method well known to those skilled in the art, for example, by using a particle size analyzer, or by transmission electron micrograph or scanning electron micrograph. Alternatively, the average particle diameter value can be obtained by measuring using dynamic light scattering method, performing data analysis, counting the number of particles for each particle size range, and then calculating from this. Unless otherwise defined, the average particle diameter may mean the diameter (D50) of particles with a cumulative volume of 50% by volume in the particle size distribution.

Here, “or” is not interpreted in an exclusive sense; for example, “A or B” is interpreted as including A, B, A+B, etc.

positive electrode active material

In one embodiment, a positive electrode active material for a lithium secondary battery is provided, including a first positive electrode active material in the form of secondary particles made by agglomerating a plurality of primary particles, and a second positive electrode active material in the form of single particles.

The first positive electrode active material and the second positive electrode active material each include a lithium nickel-based composite oxide having a nickel content of 70 mol% or more based on the total elements excluding lithium and oxygen. That is, the first and second positive electrode active materials can be said to be high nickel-based positive electrode active materials.

Additionally, the first positive electrode active material includes a coating portion that exists in the form of a film on the surface of the secondary particle, and the second positive electrode active material includes a coating portion that exists in the form of a film on the surface of the single particle. Here, the coating portion of the first positive electrode active material and the coating portion of the second positive electrode active material are characterized in that they include lithium cobalt oxide (LiCoO ₂ ) and cobalt oxyhydroxide (CoOOH), respectively.

The cobalt oxyhydroxide in the coating portion has an R-3m crystal structure, and has less structural heterogeneity with the lithium nickel-based composite oxide, thereby facilitating lithium movement and thereby improving the performance of the lithium secondary battery.

It can be said that the coating part includes a composite phase of lithium cobalt oxide and cobalt oxyhydroxide. Through this composite phase, the surface structure of the positive electrode active material can be strengthened, thereby suppressing side reactions between the positive electrode active material and the electrolyte solution, and improving the lifespan characteristics, overcharge characteristics, and high temperature storage characteristics of the lithium secondary battery. Through the above composite phase, it is possible to overcome the unstable structure of high-nickel-based positive electrode active materials and secure stable characteristics at the level of low-nickel-based positive electrode active materials.

The composite phase can be confirmed through X-ray diffraction analysis of the positive electrode active material or the positive electrode plate. For example, the positive electrode active material may exhibit peaks at 19.5° to 20.5° and 39° to 40° in X-ray diffraction analysis, and these peaks may indicate the presence of cobalt oxyhydroxide.

The coating part exists in the form of a film and may be in the form of a continuous coating layer or in the form of an island, which is different from that existing in the form of particles.

The thickness of each of the coating portion of the first positive electrode active material and the coating portion of the second positive electrode active material may be 1 nm to 500 nm, for example, 1 nm to 400 nm, 1 nm to 300 nm, 1 nm to 200 nm. , 1 nm to 100 nm, 5 nm to 50 nm, or 5 nm to 40 nm. By forming the coating portion in this thickness range, the performance of the lithium secondary battery can be improved by stabilizing the structure of the positive electrode active material and suppressing side reactions with the electrolyte without acting as resistance or deteriorating battery performance. Here, the thickness of the coating portion can be measured using SEM, TEM, TOF-SIMS, XPS, or EDS, and for example, can be measured through an SEM image of the cross section of the positive electrode active material.

The cobalt content of the coating portion of the positive electrode active material may be about 0.5 mol% to 5 mol%. Specifically, in the entire positive electrode active material, the content of cobalt on the surface relative to 100 mol% of elements excluding lithium and oxygen in the lithium nickel-based composite oxide may be 0.5 mol% to 5 mol%, for example, 0.5 mol% to 5 mol%. It may be 4 mol%, or 1 mol% to 3 mol%. By being coated with cobalt at the above content, the structure of the positive electrode active material can be stabilized without reducing capacity and the efficiency and lifespan characteristics of the battery can be improved.

Meanwhile, according to one embodiment, the content of cobalt (at%) compared to the total amount of nickel and cobalt in the coating portion of the first positive electrode active material relative to the content (at%) of cobalt relative to the total amount of nickel and cobalt in the coating portion of the second positive electrode active material. ) the ratio may be 1.45 to 1.60. When coating portions are formed on each positive electrode active material in the form of a mixture of a first positive electrode active material in the form of secondary particles and a second positive electrode active material in the form of single particles, coating imbalance occurs between the two particles. For example, when two types of particles are mixed and wet coating is performed at the same time, more coating material tends to react and coat single particles with a relatively high specific surface area. As a result, the secondary particles do not achieve sufficient coating effect, causing structural collapse or side reactions on the surface, accelerating deterioration, and the uneven presence of coating particles on the surface causes gas generation, and excessive coating on single particles causes resistance. This has a negative effect on battery performance. On the other hand, according to one embodiment, the performance of lithium secondary batteries, such as high-temperature long-term life characteristics, is improved by strengthening the coating of secondary particles while suppressing excessive coating on single particles, that is, by appropriately controlling the coating content relationship between the two types of particles. can do. For example, when the ratio of the cobalt coating content of the first positive electrode active material to the cobalt coating content of the second positive electrode active material satisfies 1.45 to 1.60, high capacity and high energy density are realized while simultaneously improving high temperature long life characteristics and high temperature storage. It can suppress gas generation and improve initial charge/discharge efficiency. The ratio may be, for example, 1.45 times to 1.55 times, or 1.50 times to 1.60 times.

First positive electrode active material

The first positive electrode active material is in a polycrystal form and includes secondary particles in which at least two or more primary particles are aggregated. The first positive electrode active material according to one embodiment includes a coating portion that exists in the form of a film along the surface of the secondary particle, and includes a composite phase of lithium cobalt oxide and cobalt oxyhydroxide.

The content of cobalt relative to the total amount of nickel and cobalt in the cobalt coating portion of the first positive electrode active material may be 55 at% to 70 at%, for example, 55 at% to 68 at%, 55 at% to 65 at%, 55 at% to 68 at%, at% to 63 at%, 57 at% to 70 at%, 59 at% to 70 at%, 60 at% to 70 at%, 60 at% to 65 at%, or 61 at% to 63 at%. . When the cobalt coating content of the first positive electrode active material satisfies the above range and is 1.45 to 1.60 times the cobalt coating content of the second positive electrode active material, coating unevenness between particles is resolved and a uniform coating is formed on the surface of the first positive electrode active material. As a single coating is formed, gas generation is suppressed, and initial charge/discharge efficiency and long-term life characteristics can be improved.

The first positive electrode active material according to one embodiment may further include a grain boundary cobalt coating portion located on the surface of the primary particles inside the secondary particles. The grain boundary cobalt coating exists on the inside of the secondary particle rather than on the surface, and can be said to be coated along the interface of the primary particles inside the secondary particle, and thus can be expressed as being coated at the grain boundary. Here, the interior of the secondary particle refers to the entire interior excluding the surface, and for example, it may mean the area from approximately 10 nm depth to the entire inside surface, or from a depth of 10 nm to a depth of approximately 2 ㎛. . The first positive electrode active material according to one embodiment further includes a grain boundary cobalt coating portion, thereby enhancing structural stability, inducing a uniform and even coating on the surface, and adjusting the coating content on the surface appropriately to increase initial charge/discharge efficiency and increase the resistance without increasing resistance. Lifespan characteristics can be improved.

The average particle diameter of the first positive electrode active material, that is, the average particle diameter of the secondary particles, may be 5 ㎛ to 20 ㎛. For example, it may be 7 μm to 20 μm, 10 μm to 20 μm, or 12 μm to 18 μm. The average particle diameter of the secondary particles of the first positive electrode active material may be larger than the average particle diameter of the second positive electrode active material of single particles, which will be described later. The positive electrode active material according to one embodiment may be a mixture of a first positive electrode active material, which is a polycrystalline and opposing material, and a second positive active material, which is a single particle and elementary particles. Accordingly, the mixture density can be improved, and high capacity and high energy density can be achieved. It can be implemented. Here, the average particle diameter of the first positive electrode active material is measured by randomly selecting about 20 active materials in the form of secondary particles from electron micrographs of the positive electrode active material, and the diameter of the particles with a cumulative volume of 50% by volume from the particle size distribution ( D50) may be taken as the average particle diameter.

The first positive electrode active material may be a high nickel-based positive electrode active material containing a high content of nickel. The nickel content in the lithium nickel-based composite oxide may be 70 mol% or more, for example, 75 mol% or more, 80 mol% or more, 85 mol% or more, or 90 mol% or more based on the total amount of elements excluding lithium and oxygen. and may be 99.9 mol% or less, or 99 mol% or less. This high-nickel-based first positive electrode active material can achieve high capacity and high performance.

Second positive active material

The second positive electrode active material is in the form of a single particle, which means that it exists alone without a grain boundary within the particle and consists of a single particle, and is an independent phase in which the particles are not agglomerated with each other in terms of morphology. It may mean a single particle that exists in a phase, a monolith structure, a monolithic structure, or a non-agglomerated particle, and for example, it may be a single crystal. The positive electrode active material according to one embodiment includes the second positive active material in the form of single particles, thereby realizing high capacity and high energy density and exhibiting improved lifespan characteristics.

The second positive electrode active material according to one embodiment includes a coating portion in the form of a film formed along the surface of a single particle, and the coating portion includes a composite phase of lithium cobalt oxide and cobalt oxyhydroxide.

The content of cobalt relative to the total amount of nickel and cobalt in the coating portion of the second positive electrode active material may be 39 at% to 45 at%, for example, 39 at% to 44 at%, 39 at% to 43 at%, and 39 at%. % to 42 at%, 40 at% to 45 at%, or 41 at% to 45 at%. When the cobalt coating content of the second positive electrode active material satisfies the above range and the ratio of the cobalt coating content of the first positive electrode active material to this satisfies 1.45 to 1.60, coating unevenness between particles is resolved, and the second positive electrode active material Excessive coating is suppressed and uniform coating is induced, thereby reducing resistance and improving initial charge/discharge efficiency and long-term life characteristics.

Meanwhile, in one embodiment, the method of measuring the content of cobalt relative to the total amount of nickel and cobalt on the surface of the positive electrode active material is to perform scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) on the surface of the positive electrode active material and perform quantitative analysis. It may be obtained by calculating the respective contents of nickel and cobalt through analysis and then calculating the ratio of the cobalt content to the sum. In addition to SEM-EDS, methods for measuring cobalt content include Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) or Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). This can be used.

The average particle diameter of the second positive electrode active material, that is, the average particle diameter of a single particle, may be 0.1 ㎛ to 10 ㎛, for example, 0.1 ㎛ to 7 ㎛, 0.5 ㎛ to 6 ㎛, or 1 ㎛ to 5 ㎛. The particle size of the second positive electrode active material may be smaller than that of the first positive electrode active material, and thus the density of the positive electrode active material can be further increased. Here, the average particle diameter of the second positive electrode active material is measured by randomly selecting about 20 active materials in the form of single particles from electron micrographs of the positive electrode active material, and the diameter of the particles with a cumulative volume of 50% by volume from the particle size distribution (D50 ) may be taken as the average particle diameter.

The second positive electrode active material may be a high nickel-based positive electrode active material containing a high content of nickel. The nickel content in the lithium nickel-based composite oxide may be 70 mol% or more, for example, 75 mol% or more, 80 mol% or more, 85 mol% or more, or 90 mol% or more based on the total amount of elements excluding lithium and oxygen. It may be 99.9 mol% or less, or 99 mol% or less. This high-nickel-based second positive electrode active material can achieve high capacity and high performance.

Specifically, the first positive electrode active material and the second positive electrode active material may each independently include a lithium nickel-based composite oxide represented by Formula 1 below.

[Formula 1]

Li _a1 Ni _x1 M ¹ _y1 M ² _z1 O _{2- b1}

In Formula 1, 0.9≤a1≤1.8, 0.7≤x1≤1, 0≤y1≤0.3, 0≤z1≤0.2, 0.9≤x1+y1+z1≤1.1, and 0≤b1≤0.1, M ¹ and M ² is each independently selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr. is one or more elements, and X is one or more elements selected from the group consisting of F, P and S.

In Formula 1, it may be 0.8≤x1≤1, 0≤y1≤0.2, and 0≤z1≤0.15, or 0.9≤x1≤1, 0≤y1≤0.1, and 0≤z1≤0.1.

For example, the first positive electrode active material and the second positive electrode active material may each independently include a lithium nickel-based composite oxide represented by Formula 2 below. The compound represented by Formula 2 can be said to be a lithium nickel cobalt-based complex oxide.

[Formula 2]

Li _a2 Ni _x2 Co _y2 M ³ _z2 O _{2- b2}

In Formula 2, 0.9≤a2≤1.8, 0.7≤x2<1, 0<y2≤0.3, 0≤z2≤0.2, 0.9≤x2+y2+z2≤1.1, and 0≤b2≤0.1, and M ³ is Al. , B, Ba, Ca, Ce, Cr, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr, and It is one or more elements selected from the group consisting of S.

In Formula 2, it may be 0.8≤x2≤0.99, 0.01≤y2≤0.2, and 0.01≤z2≤0.15, or 0.9≤x2≤0.99, 0.01≤y2≤0.1, and 0.01≤z2≤0.1.

As an example, the first positive electrode active material and the second positive electrode active material may each independently include a lithium nickel-based composite oxide represented by Chemical Formula 3 below. The compound of Formula 3 can be called lithium nickel-cobalt-aluminum oxide or lithium nickel-cobalt-manganese oxide.

[Formula 3]

Li _a3 Ni _x3 Co _y3 M ⁴ _z3 M ⁵ _w3 O _{2- b3}

In Formula 3, 0.9≤a3≤1.8, 0.7≤x3≤0.98, 0.01≤y3≤0.29, 0.01≤z3≤0.29, 0≤w3≤0.19, 0.9≤x3+y3+z3+w3≤1.1, and 0≤ b3≤0.1, M ⁴ is one or more elements selected from the group consisting of Al and Mn, and M ⁵ is B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sr, Ti, It is one or more elements selected from the group consisting of V, W, and Zr, and X is one or more elements selected from the group consisting of F, P, and S.

In Formula 3, 0.85≤x3≤0.98, 0.01≤y3≤0.14, 0.01≤z3≤0.14, and 0≤w3≤0.14, or 0.9≤x3≤0.98, 0.01≤y3≤0.09, 0.01≤z3≤0.09, and It may be 0≤w3≤0.09.

In the positive electrode active material according to one embodiment, the first positive electrode active material is included in an amount of 50% to 90% by weight, and the second positive electrode active material is included in an amount of 10% to 50% by weight, based on the total amount of the first positive electrode active material and the second positive electrode active material. It can be included as a percentage. For example, the first positive electrode active material may be included in an amount of 60% to 90% by weight, or 70% to 90% by weight, and the second positive electrode active material may be included in an amount of 10% to 40% by weight, or 10% to 30% by weight. can be included. When the content ratio of the first and second positive electrode active materials is the same, the positive electrode active material containing the same can achieve high capacity, improve mixture density, and exhibit high energy density.

Method for producing positive electrode active material

In one embodiment, the first positive electrode active material in the form of secondary particles, lithium and A second positive electrode active material in the form of a single particle containing a lithium nickel-based composite oxide with a nickel content of 70 mol% or more relative to all elements excluding oxygen, cobalt sulfate (CoSO ₄ ·7H ₂ O(OH) ₂ ), and sodium hydroxide (NaOH) was added to the solvent and mixed; Remove solvent; Adding lithium raw material to the obtained product; By heat treatment; A method for producing a positive electrode active material for a lithium secondary battery is provided, including obtaining the above-mentioned positive electrode active material.

Through the above manufacturing method, a first positive electrode active material including a coating portion present in the form of a film on the surface of the secondary particle and a second positive electrode active material including a coating portion present in the form of a film on the surface of the single particle are mixed. A positive electrode active material can be obtained. The coating part is characterized in that it includes a composite phase of lithium cobalt oxide and cobalt oxyhydroxide.

The description of the lithium nickel-based composite oxide is the same as described above and is therefore omitted. The solvent may be an aqueous solvent such as water or an alcohol-based solvent.

The first positive electrode active material and the second positive electrode active material may be mixed at a weight ratio of 9:1 to 5:5, for example, 8:2 to 6:4. In this case, it is advantageous to realize high capacity and high energy density.

The cobalt sulfate can be said to be a coating raw material added to manufacture the positive electrode active material according to one embodiment. The cobalt sulfate may be mixed so that the content of cobalt relative to elements other than lithium and oxygen in the entire lithium nickel-based composite oxide of the first positive electrode active material and the lithium nickel-based composite oxide of the second positive electrode active material is 0.5 mole part to 5 mole part. For example, it may be mixed to 0.5 mole part to 4 mole part, or 1 mole part to 3 mole part.

The sodium hydroxide may act as a precipitant and/or pH adjuster. If sodium hydroxide is not added, the coating may not be formed effectively or the desired content of cobalt may not be coated, and the CoOOH phase may not appear in the coating on the surface of the final positive electrode active material.

The sodium hydroxide is added so that the sodium content is 1 to 10 mole parts based on 100 mole parts of all elements excluding lithium and oxygen in the lithium nickel-based composite oxide of the first positive electrode active material and the lithium nickel-based composite oxide of the second positive electrode active material. For example, it may be added in an amount of 3 to 9 mole parts, or 5 mole parts to 8 mole parts. When the content of sodium added satisfies the above range, a coating portion in the form of a film containing LiCoO ₂ and CoOOH can be effectively formed.

Additionally, the ratio of the cobalt molar content of cobalt sulfate and the sodium molar content of sodium hydroxide may be 1:1.1 to 1:5, for example, 1:1.5 to 1:4, or 1:2 to 1:3. . When the molar ratio of cobalt and sodium added satisfies the above range, it is advantageous to form a coating in the form of a film containing LiCoO ₂ and CoOOH.

After removing the solvent, lithium raw material is added to the obtained product, where the lithium raw material may be, for example, Li ₂ CO ₃ , LiOH, hydrates thereof, or a combination thereof. The lithium raw material may be added so that the content of lithium relative to elements other than lithium and oxygen in the entire lithium nickel-based composite oxide of the first positive electrode active material and the lithium nickel-based composite oxide of the second positive electrode active material is 0.1 mole part to 10 mole part. For example, it can be added at 0.1 mole part to 8 mole part, or 1 mole part to 6 mole part. In the process of washing and coating the positive electrode active material in a solvent, damage may occur on the surface of the lithium nickel-based composite oxide particles, resulting in a decrease in capacity and rate characteristics and an increase in resistance when stored at high temperatures. As such, lithium nickel-based composite oxide particles may be damaged during heat treatment. By adding raw materials, surface damage can be repaired and capacity and rate characteristics can be improved.

The heat treatment may be performed in an oxidizing gas atmosphere such as oxygen or air, and may be performed at 650°C to 900°C, or 650°C to 800°C. The heat treatment time varies depending on the heat treatment temperature, etc., but may be performed for, for example, 5 to 30 hours or 10 to 24 hours. By heat treatment under the above conditions, a coating portion in which a composite phase of lithium cobalt oxide and cobalt oxyhydroxide is present can be formed.

According to one embodiment, mixing the first positive electrode active material, the second positive active material, cobalt sulfate, and sodium hydroxide in a solvent includes adding the second positive electrode active material cobalt sulfate, and sodium hydroxide to the solvent and mixing them. After performing the process, a second process of adding and mixing the first positive electrode active material, cobalt sulfate, and sodium hydroxide may be sequentially performed. According to this method, excessive coating on single particles is suppressed and the coating of secondary particles is strengthened, that is, the coating content relationship between the two types of particles is appropriately adjusted, thereby improving lithium secondary properties such as high-temperature long-term lifespan characteristics, initial charge/discharge efficiency, and high-temperature storage performance. Battery performance can be improved. For example, according to the sequential process, the content (at%) of cobalt relative to the total amount of nickel and cobalt in the cobalt coating portion of the second positive electrode active material is compared to the total amount of nickel and cobalt in the cobalt coating portion of the first positive electrode active material. A positive electrode active material having a content (at%) ratio of 1.45 to 1.60 can be manufactured.

Here also, the time required for the first process may be from about 10 minutes to about 100 minutes, and the time required for the second process may be from about 10 minutes to about 100 minutes. Additionally, the ratio of the time required for the first process (minutes) to the time required for the second process (minutes) may be 50:50 to 75:25, for example, 65:35 to 75:25. there is. By designing at this time ratio, it is possible to optimize the coating content of each of the first and second positive electrode active materials.

anode

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

The binder serves to attach the positive electrode active material particles to each other well and also to attach the positive electrode active material to the current collector. Representative examples include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and polyvinyl alcohol. Chloride, carboxylated polyvinylchloride, polyvinylfluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene- Butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. can be used, but are not limited thereto.

The content of the binder in the positive electrode active material layer may be approximately 1% by weight to 5% by weight based on the total weight of the positive active material layer.

The conductive material is used to provide conductivity to the electrode, and in the battery being constructed, any electronically conductive material can be used as long as it does not cause chemical change. Examples include natural graphite, artificial graphite, carbon black, acetylene black, and Ketjen. Carbon-based materials such as black, carbon fiber, carbon nanofiber, and carbon nanotube; Metallic substances containing copper, nickel, aluminum, silver, etc. and in the form of metal powder or metal fiber; Conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material containing a mixture thereof may be used.

The content of the conductive material in the positive electrode active material layer may be 1% by weight to 5% by weight based on the total weight of the positive active material layer.

Aluminum foil may be used as the positive electrode current collector, but is not limited thereto.

cathode

A 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 includes a negative electrode active material and may further include a binder and/or a conductive material.

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 dedoping lithium, or a transition metal oxide.

The material capable of reversibly intercalating/deintercalating lithium ions is a carbon-based negative electrode active material, and may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-shaped, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, and mesophase pitch carbide. , calcined coke, etc.

The lithium metal alloy includes lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn. Any alloy of metals of choice may be used.

As the material capable of doping and dedoping lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used, and the Si-based negative electrode active material includes silicon, 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, but not Si. ), the Sn-based negative electrode active materials include Sn, SnO ₂ , and Sn-R alloy (where R is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and elements selected from the group consisting of combinations thereof, but not Sn), and the like, and at least one of these may be mixed with SiO ₂ . The elements Q and R include 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, One selected from the group consisting of S, Se, Te, Po, and combinations thereof can be used.

For example, the silicon-carbon composite may be a silicon-carbon composite including a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. As the amorphous carbon precursor, coal-based pitch, mesophase pitch, petroleum-based pitch, coal-based oil, petroleum-based heavy oil, or polymer resin such as phenol resin, furan resin, and 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. In addition, the content of the 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 the amorphous carbon may be 20% by weight to 40% by weight based on the total weight of the silicon-carbon composite. there is. Additionally, 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 may exist in an oxidized form, and in this case, the atomic content ratio of Si:O in the silicon particles, which indicates the degree of oxidation, may be 99:1 to 33:67. The silicon particles may be SiO _x particles, and in this case, the SiO _x x range may be greater than 0 and less than 2. In this specification, unless otherwise defined, the average particle diameter (D50) refers to the diameter of particles with a cumulative volume of 50% by volume in the particle size distribution.

The Si-based negative electrode active material or Sn-based negative electrode active material may be used by mixing with a carbon-based negative electrode active material. When using a mixture of Si-based negative electrode active material or Sn-based negative electrode active material and carbon-based negative electrode active material, the mixing ratio may be 1:99 to 90:10 by weight.

The content of the negative electrode active material in the negative electrode active material layer may be 95% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

In one embodiment, the negative electrode active material layer further includes a binder and, optionally, may further include a conductive material. The content of the binder in the negative electrode active material layer may be 1% to 5% by weight based on the total weight of the negative electrode active material layer. In addition, when a conductive material is further included, the negative electrode active material layer may include 90% to 98% by weight of the negative electrode active material, 1% to 5% by weight of the binder, and 1% to 5% by weight of the conductive material.

The binder serves to adhere the negative electrode active material particles to each other and also helps the negative electrode active material to adhere to the current collector. The binder may be a water-insoluble binder, a water-soluble binder, or a combination thereof.

The water-insoluble binder includes polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, ethylene propylene copolymer, polystyrene, polyvinylpyrrolidone, polyurethane, and polytetrafluoride. Ethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamidoimide, polyimide, or combinations thereof may be mentioned.

Examples of the water-soluble binder include a rubber 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, fluorine rubber, and combinations thereof. The polymer resin binder is polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, poly It may be selected from ester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

When a water-soluble binder is used as the negative electrode binder, it may further include a cellulose-based compound capable of imparting viscosity. As this cellulose-based compound, one or more types of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof can be used. Na, K, or Li can be used as the alkali metal. The amount of the thickener used may be 0.1 to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

The conductive material is used to provide conductivity to the electrode, and in the battery being constructed, any electronically conductive material can be used as long as it does not cause chemical change. Examples include natural graphite, artificial graphite, carbon black, acetylene black, and Ketjen. Carbon-based materials such as black, carbon fiber, carbon nanofiber, and carbon nanotube; Metallic substances containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; Conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material containing a mixture thereof may be used.

The negative electrode current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof. .

lithium secondary battery

Another embodiment provides a lithium secondary battery including a positive electrode, a negative electrode, a separator positioned between the positive electrode and the positive electrode, and an electrolyte.

Figure 1 is a schematic diagram showing a lithium secondary battery according to one embodiment. Referring to FIG. 1, the lithium secondary battery 100 according to one embodiment is disposed between the positive electrode 114, the negative electrode 112 located opposite the positive electrode 114, and the positive electrode 114 and the negative electrode 112. A battery cell containing an electrolyte for a lithium secondary battery impregnating the separator 113 and the positive electrode 114, the negative electrode 112 and the separator 113, a battery container 120 containing the battery cell, and the battery container ( It includes a sealing member 140 that seals 120).

The electrolyte includes 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. The non-aqueous organic solvent may be carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent. The carbonate-based solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used. The ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, and mevalono. Lactone (mevalonolactone), caprolactone, etc. may be used. The ether-based solvent may be dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc., and the ketone-based solvent may include cyclohexanone. there is. In addition, the alcohol-based solvent may be ethyl alcohol, isopropyl alcohol, etc., and the aprotic solvent may be R-CN (where R is a C2 to C20 straight-chain, branched, or ring-structured hydrocarbon group. , may contain a double bond, an aromatic ring, or an ether bond), nitriles such as amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes may be used. .

The non-aqueous organic solvents can be used alone or in a mixture of one or more, and when used in a mixture of more than one, the mixing ratio can be appropriately adjusted according to the desired battery performance, which is widely understood by those working in the field. It can be.

Additionally, in the case of the carbonate-based solvent, a mixture of cyclic carbonate and chain carbonate can be used. In this case, when cyclic carbonate and chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9, the electrolyte can exhibit excellent performance.

The non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent in addition to the carbonate-based solvent. At this time, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed at a volume ratio of about 1:1 to about 30:1.

As the aromatic hydrocarbon-based solvent, an aromatic hydrocarbon-based compound of the following formula (I) may be used.

[Formula I]

In the above formula (I), R ⁴ to R ⁹ are the same or different from each other and are selected from the group consisting of hydrogen, halogen, alkyl group with 1 to 10 carbon atoms, haloalkyl group with 1 to 10 carbon atoms, and combinations thereof.

Specific examples of the aromatic hydrocarbon solvent include benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, and 1,2,3-trifluo. Robenzene, 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-trifluoro Toluene, 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, It is selected from the group consisting of 5-triiodotoluene, xylene, and combinations thereof.

In order to improve battery life, the electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound of the following formula (II) as a life-enhancing additive.

[Formula II]

In Formula II, R ¹⁰ and R ¹¹ are the same 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. Among R ¹⁰ and R ¹¹ At least one 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 neither R ¹⁰ nor R ¹¹ is hydrogen.

Representative examples of the ethylene carbonate-based compounds include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. You can. When using more of these life-enhancing additives, the amount used can be adjusted appropriately.

The lithium salt is a substance that dissolves in a non-aqueous organic solvent and acts as a source of lithium ions in the battery, enabling the operation of a basic lithium secondary battery and promoting the movement of lithium ions between the positive and negative electrodes. .

Representative examples of lithium salts include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiN(SO ₃ C ₂ F ₅ ) ₂ , Li (FSO ₂ ) ₂ N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiPO ₂ F ₂ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (where x and y are natural numbers, for example, integers from 1 to 20), lithium difluorobisoxalatophosphate (lithium difluoro( bisoxalato) phosphate), LiCl, LiI, LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate; LiBOB), and lithium difluoro(oxalato)borate (LiDFOB) One or two or more selected from the group consisting of may be mentioned.

It is recommended that the concentration of lithium salt be used within the range of 0.1M to 2.0M. When the concentration of lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so excellent electrolyte performance can be achieved and lithium ions can move effectively.

The separator 113 separates the positive electrode 114 and the negative electrode 112 and provides a passage for lithium ions, and any type commonly used in lithium ion batteries can be used.　 That is, one that has low resistance to ion movement in the electrolyte and has excellent electrolyte moisturizing ability can be used.　 For example, the separator 113 may include glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, and may be in the form of non-woven or woven fabric. For example, in lithium ion batteries, polyolefin-based polymer separators such as polyethylene and polypropylene are mainly used, and coated separators containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and can optionally be single-layer or multi-layer. It can be used as a structure.

Lithium secondary batteries can be classified into lithium ion batteries, lithium ion polymer batteries, and lithium polymer batteries depending on the type of separator and electrolyte used, and can be classified into cylindrical, prismatic, coin, pouch, etc. depending on their shape. Depending on the size, it can be divided into bulk type and thin film type. The structures and manufacturing methods of these batteries are widely known in this field, so detailed descriptions are omitted.

A lithium secondary battery according to one embodiment has high capacity and has excellent storage stability, lifespan characteristics, and high rate characteristics at high temperatures, so it can be used in electric vehicles (EV) and plug-in hybrid electric vehicles. It can be used in hybrid vehicles such as vehicle, PHEV), and can also be used in portable electronic devices.

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

Example 1

1. Preparation of primary lithium nickel-based composite oxide in the form of secondary particles

As metal raw materials, nickel sulfate (NiSO ₄ ·6H ₂ O), cobalt sulfate (CoSO ₄ ·7H ₂ O), and aluminum sulfate (Al ₂ (SO ₄ ) ₃ ·18H ₂ O) are mixed in a solvent at a molar ratio of 91:8:1. A mixed solution was prepared by dissolving it in distilled water, and ammonia water (NH ₄ OH) and sodium hydroxide (NaOH) as a precipitant were prepared to form a complex.

After adding a diluted ammonia solution to the continuous reactor, a mixed solution of metal raw materials is continuously added, and sodium hydroxide is added to maintain the pH inside the reactor. The reaction proceeds slowly for approximately 80 hours, and when the reaction is stabilized, the overflowing product is collected and washed and dried to obtain the final precursor. Accordingly, the first nickel-based hydroxide (Ni _0.91 Co _0.08 Al _0.01 (OH) ₂ ) in the form of secondary particles in which primary particles are aggregated is obtained, washed and dried.

The first nickel-based hydroxide and LiOH are mixed so that the molar ratio of lithium to the total amount of metal in the first nickel-based hydroxide is 1.04, and a first heat treatment is performed at about 750° C. for 15 hours in an oxygen atmosphere, thereby producing the first lithium nickel-based Oxide (LiNi _0.91 Co _0.08 Al _0.01 O ₂ ) is obtained. The average particle diameter of the obtained first lithium nickel-based oxide is approximately 15 ㎛, and is in the form of secondary particles in which primary particles are aggregated.

2. Preparation of secondary lithium nickel-based composite oxide in single particle form

Prepare a mixed solution by dissolving nickel sulfate, cobalt sulfate, and manganese sulfate (MnSO ₄ ·H ₂ O) in distilled water as a solvent at a molar ratio of 95:4:1. To form a complex, prepare diluted ammonia water (NH ₄ OH) and sodium hydroxide (NaOH) as a precipitant. Afterwards, the metal raw material mixed solution, aqueous ammonia, and sodium hydroxide are each added into the reactor. Next, the reaction proceeds for about 20 hours while stirring. Thereafter, the slurry solution in the reactor is filtered, washed with high-purity distilled water, and dried for 24 hours to obtain a second nickel-based hydroxide (Ni _0.95 Co _0.04 Mn _0.01 (OH) ₂ ) powder. The obtained second nickel-based hydroxide powder had an average particle diameter of about 4.0 ㎛, and a specific surface area measured by the BET measurement method of about 15 m ² /g.

The obtained second nickel-based hydroxide, LiOH satisfying Li/(Ni+Co+Mn) = 1.05, and Al, Zr, and Mg components as dopants were mixed together and put into a sintering furnace, and heated at 820° C. in an oxygen atmosphere for 10 days. A second heat treatment is performed for a period of time. Thereafter, the obtained product is pulverized for about 30 minutes to separate/disperse into a plurality of secondary lithium nickel-based oxides in the form of single particles. The average particle diameter of the obtained single-particle second lithium nickel-based oxide was about 3.7㎛.

3. Preparation of cobalt coating and final positive electrode active material

A distilled water solvent and cobalt sulfate (CoSO ₄ ·7H ₂ O) are added to the mixer, and the prepared second lithium nickel-based composite oxide is added and mixed to proceed with the first process. The cobalt sulfate is added so that the cobalt content relative to all elements excluding lithium and oxygen in the second lithium nickel-based composite oxide is 3.0 molar parts. In the first process, the second lithium nickel-based complex oxide is added, and then sodium hydroxide, which acts as a precipitant and a pH adjuster, is added and mixed. Sodium hydroxide is added so that the sodium content in the second lithium nickel-based composite oxide is 6.0 mole parts based on 100 mole parts of all elements excluding lithium and oxygen.

After the first process is performed for 30 minutes, the second process is performed in which cobalt sulfate is added and then the first lithium nickel-based composite oxide is added and mixed. The first lithium nickel-based composite oxide is added so that the weight ratio of the first lithium nickel-based composite oxide and the previously added second lithium nickel-based composite oxide is 7:3. The cobalt sulfate is added so that the cobalt content relative to all elements excluding lithium and oxygen in the first lithium nickel-based composite oxide is 3.0 molar parts. In the second process, after adding the first lithium nickel-based complex oxide, sodium hydroxide is added and mixed together. Sodium hydroxide is added so that the sodium content in the first lithium nickel-based composite oxide is 6.0 mole parts based on 100 mole parts of all elements excluding lithium and oxygen.

After the second process is performed for 30 minutes, it is filtered and dried at 200°C for 10 hours. Afterwards, the obtained product and lithium hydroxide are mixed, placed in a sintering furnace, and heat treated at about 700° C. for 15 hours in an oxygen atmosphere. At this time, lithium hydroxide is added so that the content of lithium is 6 mole parts based on the total elements excluding lithium and oxygen in the obtained product. Thereafter, the furnace is cooled to room temperature, and the first positive electrode active material in which a film-shaped coating is formed on the surface of the secondary particles made of the first lithium nickel-based composite oxide, and the surface of the single particles made of the second lithium nickel-based composite oxide The final positive electrode active material is obtained by mixing the second positive electrode active material with a film-shaped coating formed thereon.

4. Preparation of anode

95% by weight of the final positive electrode active material, 3% by weight of polyvinylidene fluoride binder, and 2% by weight of the carbon nanotube conductive material are mixed in N-methylpyrrolidone solvent to prepare a positive electrode active material slurry. The positive electrode active material slurry is applied to an aluminum current collector, dried, and rolled to prepare a positive electrode.

5. Manufacturing of lithium secondary battery

Using the prepared positive electrode and the lithium metal counter electrode, a separator having a polyethylene polypropylene multilayer structure was interposed between them, and 1.0 M of LiPF ₆ lithium salt was added to a solvent mixed with ethylene carbonate and diethyl carbonate in a 50:50 volume ratio. A coin half cell is manufactured by injecting electrolyte.

Comparative Example 1

“3.” of Example 1. In “Manufacture of cobalt coating and final positive electrode active material,” the positive electrode active material, positive electrode, and coin half were prepared in the same manner as in Example 1, except that sodium hydroxide, which acts as a precipitant and pH adjuster, was not added in the first and second processes. Manufacture cells.

Comparative Example 2

“3.” of Example 1. In “Cobalt coating and production of final positive electrode active material,” coating is performed dry rather than wet. That is, the first lithium nickel-based composite oxide, the second lithium nickel-based composite oxide, cobalt hydroxide, and lithium hydroxide are mixed in a sintering furnace and heat treated at 700° C. for 15 hours. At this time, cobalt hydroxide was added so that the cobalt content relative to all elements excluding lithium and oxygen in the first lithium nickel-based composite oxide and the second lithium nickel-based composite oxide was 3.0 mole parts, and hydroxide was added so that the lithium content was 6.0 mole parts. Add lithium. Otherwise, the positive electrode active material, positive electrode, and coin half cell were manufactured in the same manner as in Example 1.

Evaluation Example 1: X-ray diffraction analysis

(i) the final positive electrode active material prepared in Example 1, (ii) the positive electrode plate obtained by disassembling the battery immediately before driving the coin half-cell of Example 1, and (iii) the coin half-cell of Example 1 for 150 cycles. After this, X-ray diffraction analysis was performed on the positive electrode plate obtained by disassembling the battery, and the results are shown in Figure 2.

In (iii) above, the coin half-cell of Example 1 was initially charged under constant current (0.2 C) and constant voltage (4.25 V, 0.05 C cut-off) conditions, rested for 10 minutes, and then charged to 3.0 under constant current (0.2 C) conditions. After initial discharge was performed until V, charging and discharging were repeated 150 times at 0.5C/0.5C at 45°C.

FIG. 3 is an enlarged view of the graph at around 20° in FIG. 2, and FIG. 4 is an enlarged view of the graph at around 40° in FIG. 2. Figure 5 is an X-ray diffraction analysis graph for Co(OH) ₂ , CoOOH, and Co ₃ O ₄ for comparison.

Referring to Figures 2 to 5, the positive electrode active material according to Example 1 shows a peak at 19.5° to 20.5° and a peak at 39° to 40°, confirming that CoOOH exists on the surface. That is, it can be confirmed that the positive electrode active material of Example 1 has a LiCoO ₂ -like structure and a composite phase of CoOOH in the surface coating portion. This complex phase is captured not only in the manufactured positive electrode active material, but also after manufacturing the positive electrode plate and after battery operation.

The same X-ray diffraction analysis was performed on Comparative Example 1 and Comparative Example 2, but in the case of Comparative Example 1, quantitative coating was not performed and the CoOOH phase was not confirmed in the X-ray diffraction graph. In Comparative Example 2, continuous coating was not performed on the surface of the positive electrode active material, and the CoOOH phase was not confirmed in the X-ray diffraction graph.

Evaluation Example 2: SEM-EDS analysis of cross section of positive electrode active material

Figure 6 is a SEM-EDS analysis image of the cross section of particles corresponding to the first positive electrode active material in the final positive electrode active material prepared in Example 1. Figure 7 is a SEM-EDS analysis image of the cross section of particles corresponding to the second positive electrode active material in the final positive electrode active material prepared in Example 1. The highlighted portion in FIGS. 6 and 7 represents cobalt.

Referring to Figure 6, it can be seen that a coating containing cobalt exists in the form of a film on the surface of the secondary particle, and that cobalt is also coated at the grain boundary, which is the surface of the primary particles present inside the secondary particle. Referring to Figure 7, it can be seen that a coating containing cobalt was formed in the form of a film on the surface of the single particle.

Evaluation Example 3: Analysis of cobalt coating content of positive electrode active material

The cobalt content (Co/(Ni+Co), at%) on the surface of each of the first and second positive electrode active materials was measured through the SEM-EDS analysis performed in Evaluation Example 2 above, and the results are shown in Table 1 below. indicated.

First positive electrode active material coating content (A) Second positive electrode active material coating content (B) A/B Example 1 61.8 40.4 1.53

Evaluation Example 4: Battery performance evaluation

Three samples each of the lithium secondary batteries manufactured in Example 1, Comparative Example 1, and Comparative Example 2 were prepared, initially charged under constant current (0.2 C) and constant voltage (4.25 V, 0.05 C cut-off) conditions, and 10 After resting for a minute, initial charging and discharging is performed by discharging until it reaches 3.0 V under constant current (0.2 C) conditions. Afterwards, charging and discharging were repeated 50 times at 0.5C/0.5C at 45°C to evaluate lifespan characteristics, and the capacity maintenance rate in each cycle compared to the initial discharge capacity is shown in FIG. 8.

Referring to FIG. 8, it can be seen that Example 1 has superior lifespan characteristics compared to Comparative Examples 1 and 2.

Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept defined in the following claims are also within the scope of the present invention. It belongs.

100: lithium secondary battery 112: negative electrode
113: Separator 114: Anode
120: Battery container 140: Encapsulation member

Claims (22)

A first positive electrode active material in the form of secondary particles made by agglomerating a plurality of primary particles, and
A positive electrode active material for a lithium secondary battery comprising a second positive electrode active material in the form of a single particle,
The first positive electrode active material and the second positive electrode active material each include a lithium nickel-based composite oxide having a nickel content of 70 mol% or more based on the total elements excluding lithium and oxygen,
The first positive electrode active material includes a coating that exists in the form of a film on the surface of the secondary particle,
The second positive electrode active material includes a coating portion present in the form of a film on the surface of the single particle,
The positive electrode active material for a lithium secondary battery, wherein the coating portion of the first positive electrode active material and the coating portion of the second positive electrode active material include lithium cobalt oxide and cobalt oxyhydroxide, respectively. In paragraph 1:
In the coating portion of the first positive electrode active material and the coating portion of the second positive electrode active material, the lithium cobalt oxide and the cobalt oxyhydroxide exist in a composite phase. In paragraph 1:
The positive electrode active material is a positive electrode active material for a lithium secondary battery that exhibits peaks at 19.5° to 20.5° and 39° to 40° in X-ray diffraction analysis. In paragraph 1:
A cathode active material for a lithium secondary battery, wherein the coating portion of the first cathode active material and the coating portion of the second cathode active material each have a thickness of 1 nm to 500 nm. In paragraph 1:
A positive electrode active material for a lithium secondary battery in which, in the entire positive electrode active material, the content of cobalt on the surface is 0.5 mol% to 5 mol% based on 100 mol% of elements excluding lithium and oxygen in the lithium nickel-based composite oxide. In paragraph 1:
The ratio of the content of cobalt (at%) relative to the total amount of nickel and cobalt in the coating portion of the second positive electrode active material to the content (at%) of cobalt relative to the total amount of nickel and cobalt in the coating portion of the first positive electrode active material is 1.45 to 1.60. Cathode active material for lithium secondary batteries. In paragraph 1:
A cathode active material for a lithium secondary battery in which the content of cobalt relative to the total amount of nickel and cobalt in the coating portion of the first cathode active material is 55 at% to 70 at%. In paragraph 1:
A cathode active material for a lithium secondary battery in which the content of cobalt relative to the total amount of nickel and cobalt in the coating portion of the second cathode active material is 39 at% to 45 at%. In paragraph 1:
The first positive electrode active material further includes a grain boundary coating located on the surface of the primary particles inside the secondary particles,
The grain boundary coating portion is a positive electrode active material for a lithium secondary battery comprising lithium cobalt oxide and cobalt oxyhydroxide. In paragraph 1:
The average particle diameter of the first positive electrode active material is 5 ㎛ to 20 ㎛,
A cathode active material for a lithium secondary battery wherein the second cathode active material has an average particle diameter of 0.1 ㎛ to 10 ㎛. In paragraph 1:
A positive electrode active material for a lithium secondary battery comprising 50% to 90% by weight of the first positive electrode active material and 10% to 50% by weight of the second positive electrode active material, relative to the total amount of the first and second positive electrode active materials. In paragraph 1:
The lithium nickel-based composite oxide of the first positive electrode active material and the lithium nickel-based composite oxide of the second positive electrode active material are each independently represented by the following formula (1):
[Formula 1]
Li _a1 Ni _x1 M ¹ _y1 M ² _z1 O _{2- b1}
In Formula 1, 0.9≤a1≤1.8, 0.7≤x1≤1, 0≤y1≤0.3, 0≤z1≤0.2, 0.9≤x1+y1+z1≤1.1, and 0≤b1≤0.1, M ¹ and M ² is each independently selected from the group consisting of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sr, Ti, V, W, and Zr. is one or more elements, and X is one or more elements selected from the group consisting of F, P and S. A first positive electrode active material in the form of secondary particles, which contains a lithium nickel-based complex oxide with a nickel content of 70 mol% or more relative to the total elements excluding lithium and oxygen, and is made by agglomerating a plurality of primary particles. Containing a lithium nickel-based complex oxide with a nickel content of 70 mol% or more relative to the total, a second positive electrode active material in the form of single particles, cobalt sulfate, and sodium hydroxide are added to a solvent and mixed;
Remove solvent;
Adding lithium raw material to the obtained product;
By heat treatment;
A method for producing a positive electrode active material for a lithium secondary battery, comprising obtaining the positive electrode active material according to any one of claims 1 to 12. In paragraph 13:
A method of producing a positive electrode active material for a lithium secondary battery, wherein the first positive electrode active material and the second positive electrode active material are mixed at a weight ratio of 9:1 to 5:5. In paragraph 13:
The cobalt sulfate is mixed so that the cobalt content is 0.5 mole parts to 5 mole parts with respect to 100 mole parts of all elements excluding lithium and oxygen in the lithium nickel-based composite oxide of the first positive electrode active material and the lithium nickel-based composite oxide of the second positive electrode active material. A method for producing a positive electrode active material for a lithium secondary battery. In paragraph 13:
The sodium hydroxide is mixed with the lithium nickel-based composite oxide of the first positive electrode active material and the lithium nickel-based composite oxide of the second positive electrode active material so that the sodium content is 1 mole part to 10 mole parts based on 100 mole parts of all elements excluding lithium and oxygen. A method for producing a positive electrode active material for a lithium secondary battery. In paragraph 13:
A method for producing a positive electrode active material for a lithium secondary battery, wherein the ratio of the molar content of cobalt in the cobalt sulfate and the molar content of sodium in the sodium hydroxide is 1:1.1 to 1:5. In paragraph 13:
The lithium raw material is added so that the content of lithium relative to elements other than lithium and oxygen in the entire lithium nickel-based composite oxide of the first positive electrode active material and the lithium nickel-based composite oxide of the second positive electrode active material is 0.1 mole part to 10 mole part. Method for manufacturing cathode active material for lithium secondary battery. In paragraph 13:
A method of producing a positive electrode active material for a lithium secondary battery, wherein the heat treatment is carried out in a temperature range of 650 ℃ to 900 ℃. In paragraph 13:
Mixing the first positive electrode active material, the second positive active material, cobalt sulfate, and sodium hydroxide in a solvent,
A first process of adding and mixing the second positive electrode active material, cobalt sulfate, and sodium hydroxide to the solvent is performed, and then a second process of adding and mixing the first positive electrode active material, cobalt sulfate, and sodium hydroxide is sequentially performed. A method for manufacturing a positive electrode active material for a lithium secondary battery. In paragraph 20:
A method for producing a positive electrode active material for a lithium secondary battery, wherein the ratio of the time (minutes) required for the first process and the time (minutes) required for the second process is 50:50 to 75:25. A lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte containing the positive electrode active material according to any one of claims 1 to 12.