WO2026079774A1 - Positive electrode active material, and positive electrode and lithium secondary battery comprising same - Google Patents

Abstract

The present invention relates to a single-particle positive electrode active material that enables optimal battery performance, and, more particularly, the present invention relates to: a positive electrode active material which comprises a single-particle lithium composite transition metal oxide composed of no more than 10 primary particles, the positive electrode active material having a degree of micronization of 4.5 to 6.0 as defined by equation 1 described in the present specification; and a positive electrode and a lithium secondary battery comprising the positive electrode active material.

Description

Cathode active material, a cathode including the same, and a lithium secondary battery

Cross-citation with related applications

This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0138030 filed on October 10, 2024, and all contents disclosed in the document of said Korean Patent Application are incorporated herein as part of this specification.

Technology field

The present invention relates to a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery, and more specifically, to a positive electrode active material in the form of a single particle, a positive electrode containing the same, and a lithium secondary battery.

With the recent increase in technological development and demand for mobile devices and electric vehicles, the demand for rechargeable batteries as an energy source is rapidly rising. Among these rechargeable batteries, lithium-ion batteries, which possess high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

Lithium transition _metal oxides such as lithium cobalt oxide like _LiCoO2 , lithium nickel oxide like _LiNiO2 , lithium manganese oxide like _LiMnO2 or _LiMn2O4 , and lithium iron phosphate oxide like _LiFePO4 have been developed as positive electrode active materials for lithium secondary batteries, and recently, lithium composite transition metal oxides containing two or more transition metals such as Li[Ni _{a Co b} Mn _c ] _O2 , Li[Ni _{a Co b Al} c ] _O2 , and Li[Ni _a Co b Mn _c Al _d ]O2 have been developed _and are widely used.

Lithium composite transition metal oxides containing two or more transition metals developed to date are typically manufactured in the form of spherical secondary particles formed by the aggregation of tens to hundreds of primary particles. Recently, however, the development of single-particle cathode active materials is accelerating in order to address structural and thermal stability issues inherent to the secondary particle form of cathode active materials. Specifically, when secondary particle cathode active materials are applied to lithium secondary batteries, they generate a large amount of gas, which causes the battery volume to expand. Additionally, increasing the nickel content in the cathode active material to achieve high capacity increases the risk of fire. Consequently, there is a growing demand for the development of single-particle cathode active materials with excellent stability.

A single-particle cathode active material is a concept that contrasts with a spherical secondary particle cathode active material formed by the aggregation of tens to hundreds of primary particles manufactured by conventional methods. It is a cathode active material composed of 10 or fewer primary particles, and since the size of the primary particles in a single-particle cathode active material has a very large influence on the performance of the cathode active material, it is necessary to control this well.

Meanwhile, when manufacturing a lithium secondary battery using the aforementioned single-particle cathode active material, cracking and disintegration of the cathode active material particles are prone to occur during the rolling process after coating the material onto the cathode current collector. Consequently, during the charging and discharging process of the lithium secondary battery, gas is generated due to side reactions between the cathode active material and the electrolyte, and swelling occurs, leading to a problem where battery characteristics deteriorate.

Therefore, there is a need to develop single-particle cathode active materials capable of exhibiting optimal battery performance.

The present invention aims to solve the aforementioned problems and provides a single-particle type positive electrode active material capable of exhibiting optimal battery performance.

In addition, the present invention aims to provide a lithium secondary battery with improved performance by including the above-mentioned positive electrode active material.

To solve the above problem, the present invention provides a positive electrode active material, a positive electrode, and a lithium secondary battery.

(1) The present invention provides a positive electrode active material comprising a single-particle lithium composite transition metal oxide composed of 10 or fewer primary particles, and having a degree of small particle size according to Formula 1 below of 4.5 to 6.0.

[Equation 1]

Small particle magnetization = A/B

When the above positive active material was analyzed using a PSA (particle size analyzer),

The above A is the ratio (%) of the number of particles with a diameter of 1㎛ to 2㎛ to the total number of particles, and

The above B is the ratio (%) of the number of particles with a diameter of 3㎛ to 4㎛ to the total number of particles.

(2) The present invention provides a positive active material according to (1), wherein the positive active material has a D ₅₀ of 3.0 μm to 5.0 μm as measured by a PSA (particle size analyzer).

(3) The present invention provides a positive electrode active material in which, in (1) or (2), the lithium composite transition metal oxide is doped with Zr, Y, or a combination thereof.

(4) The present invention provides a positive electrode active material in any one of (1) to (3), wherein the lithium composite transition metal oxide has a composition represented by the following chemical formula 1.

[Chemical Formula 1]

Li _1+x Ni _a1 Co _b1 M ¹ _c1 M ² _d1 M ³ _e1 O _2-y A _y

In the above chemical formula 1,

M ¹ is Mn, Al, or a combination thereof, and

M ² is Zr, Y, or a combination thereof, and

^M3 is one or more selected from the group consisting of W, Cu, Sr, Ti, Mg, Mo, B, Sn, Fe, Zn, and Si, and

A is one or more selected from F, Cl, Br, I, and S, and

-0.1≤x≤0.1, 0.6≤a1<1, 0<b1<0.4, 0<c1<0.4, 0<d1<0.01, 0≤e1<0.1, 0≤y≤0.2, a1+b1+c1+d1+e1=1.

(5) The present invention provides a positive electrode active material in any one of (1) to (4), wherein the lithium composite transition metal oxide is doped with Zr at 1,000 ppm to 4,000 ppm and Y at 800 ppm to 4,000 ppm.

(6) The present invention provides a positive electrode active material in any one of (1) to (5), wherein the positive electrode active material further comprises a coating portion formed on the lithium composite transition metal oxide, and the coating portion comprises Al, W, or a combination thereof.

(7) The present invention provides a positive electrode active material in any one of (1) to (6), wherein the coating portion contains Al in an amount of 1,000 ppm to 2,000 ppm relative to the total weight of the positive electrode active material and W in an amount of 2,000 ppm to 4,000 ppm relative to the total weight of the positive electrode active material.

(8) The present invention provides a positive active material having a press density of 2.8 g/cc or more and 3.0 g/cc or less in any one of (1) to (7).

(9) The present invention provides a positive electrode comprising a positive electrode active material according to any one of (1) to (8).

(10) The present invention provides a lithium secondary battery comprising a positive electrode according to (9) above.

The positive active material of the present invention satisfies a specific range of the degree of small particle size according to Formula 1 described in this specification, thereby improving rolling density and improving the capacity characteristics, initial efficiency, and lifespan characteristics of a lithium secondary battery.

In addition, according to the method for manufacturing a positive electrode active material of the present invention, the above-described positive electrode active material can be effectively manufactured.

The positive electrode and lithium secondary battery according to the present invention may have excellent capacity, initial efficiency, resistance performance, etc.

Figure 1 is an SEM image of the positive electrode active material of Example 1.

Figure 2 is an SEM image of the positive electrode active material of Example 2.

Figure 3 is an SEM image of the positive electrode active material of Comparative Example 1.

Figure 4 is an SEM image of the positive electrode active material of Comparative Example 2.

Figure 5 is an SEM image of the positive electrode active material of Comparative Example 3.

Figure 6 is an SEM image of the positive electrode active material of Comparative Example 4.

Figure 7 is SEM-EDS mapping data of the cathode active material prepared in Example 1.

Hereinafter, the present invention will be described in more detail to aid in understanding the invention.

Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

In this specification, terms such as 'comprising,' 'having,' or 'having' are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

In this specification, the term "on" means not only cases where one configuration is formed on the immediate upper surface of another configuration, but also cases where a third configuration is interposed between these configurations.

In this specification, the term 'single particle form' refers to a form composed of 10 or fewer primary particles, as opposed to a spherical secondary particle form formed by the aggregation of tens to hundreds of primary particles manufactured by conventional methods. Specifically, in the present invention, the single particle form may be a single particle composed of one primary particle, or a secondary particle form formed by the aggregation of 2 to 10 primary particles.

'Primary particles' refer to the smallest unit of particles recognized when observing the positive electrode active material through a scanning electron microscope, and 'secondary particles' refer to a secondary structure formed by the aggregation of multiple primary particles.

In this specification, 'D ₅₀ measured by PSA (particle size analyzer)' refers to the particle size at the 50% point of the volume cumulative distribution according to particle size. The D ₅₀ can be measured by dispersing the powder to be measured in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac's S3500), measuring the difference in diffraction patterns according to particle size as the particles pass through a laser beam to calculate the particle size distribution, and calculating the particle diameter at the point that is 50% of the volume cumulative distribution according to particle size in the measuring device.

In this specification, the press density can be obtained by taking a certain amount of positive active material (powder), placing it into a mold with an inner diameter of 22 mm, pressing it with 2 tons for 3 seconds to measure the thickness of the formed pellet, calculating the volume of the pellet, and then calculating the weight (g) of the active material per unit volume ( ^cm³ ) of the pellet after pressing.

positive electrode active material

The present invention provides a positive electrode active material comprising a lithium composite transition metal oxide in a single-particle form consisting of 10 or fewer primary particles, and having a degree of small particle size according to Formula 1 below of 4.5 to 6.0. The lithium composite transition metal oxide may have a layered structure.

[Equation 1]

Small particle magnetization = A/B

When the above positive active material was analyzed using a PSA (particle size analyzer),

The above A is the ratio (%) of the number of particles with a diameter of 1㎛ to 2㎛ to the total number of particles, and

The above B is the ratio (%) of the number of particles with a diameter of 3㎛ to 4㎛ to the total number of particles.

The inventors have discovered that when the positive electrode active material comprises the above-mentioned single-particle form lithium composite transition metal oxide and the degree of small particle size according to Formula 1 described in this specification is 4.5 to 6.0, the rolling density increases, thereby improving the capacity characteristics, initial efficiency, and lifespan characteristics of the lithium secondary battery, and have completed the present invention.

Meanwhile, when the degree of particle size according to the above Equation 1 is less than 4.5, there is a problem of low rolling density because the proportion of particles with a particle size of 3㎛ to 4㎛ is relatively high, and when it exceeds 6.0, the proportion of particles with a particle size of 1㎛ to 2㎛ increases excessively, so when applied to a lithium secondary battery, there is a problem of excessive gas generation and poor battery life characteristics.

According to the present invention, the positive active material may specifically have a small particle magnetization degree according to Formula 1 of 4.5 or higher, 4.6 or higher, or 4.7 or higher, and may be 5.9 or lower, or 6.0 or lower.

According to the present invention, the lithium composite transition metal oxide may be doped with Zr, Y, or a combination thereof. Meanwhile, when doped with Zr, it is stably doped into the transition metal layer, so that a stable structure can be maintained even if the insertion and extraction of lithium are repeated during repeated charging and discharging. In addition, when doped with Y, it acts as a flux material during sintering, and since an optimal primary particle size can be achieved even at a relatively low temperature, it is advantageous for resistance or rate capability characteristics.

According to the present invention, the lithium composite transition metal oxide may be doped with Zr at a concentration of 1,000 ppm to 4,000 ppm and Y at a concentration of 800 ppm to 4,000 ppm in order to have a desired primary particle size while having optimal performance in terms of lifespan and resistance. When the Zr content is within the above range, a high capacity can be achieved while maintaining a structure during charging and discharging, and when the Y content is within the above range, an optimal primary particle size can be achieved even at relatively low temperatures, so a high capacity can be achieved while being advantageous for resistance or rate capability characteristics.

According to the present invention, the lithium complex transition metal oxide may have a composition represented by the following chemical formula 1.

[Chemical Formula 1]

Li _1+x Ni _a1 Co _b1 M ¹ _c1 M ² _d1 M ³ _e1 O _2-y A _y

In the above chemical formula 1,

M ¹ is Mn, Al, or a combination thereof, and

M ² is Zr, Y, or a combination thereof, and

^M3 is one or more selected from the group consisting of W, Cu, Sr, Ti, Mg, Mo, B, Sn, Fe, Zn, and Si, and

A is one or more selected from F, Cl, Br, I, and S, and

-0.1≤x≤0.1, 0.6≤a1<1, 0<b1<0.4, 0<c1<0.4, 0<d1<0.01, 0≤e1<0.1, 0≤y≤0.2, a1+b1+c1+d1+e1=1.

According to the present invention, the lithium composite transition metal oxide may contain 60 mol% or more of nickel relative to the total molar amount of metals excluding lithium. That is, the lithium composite transition metal oxide may be a high-nickel (High Ni) lithium composite transition metal oxide. In this case, the energy density of the lithium secondary battery can be improved.

According to the present invention, in the above formula 1, x may be -0.1 or more, -0.09 or more, -0.08 or more, -0.07 or more, -0.06 or more, -0.05 or more, -0.04 or more, -0.03 or more, -0.02 or more, -0.01 or more, or 0 or more, and may be 0.06 or less, 0.07 or less, 0.08 or less, 0.09 or less, or 0.1 or less. When x satisfies the above range, high capacity characteristics and high energy density per unit volume can be realized.

According to the present invention, in Formula 1, a1 represents the atomic fraction of nickel among the metal elements in the lithium composite transition metal oxide, and may be 0.6 or more, 0.61 or more, or 0.62 or more, and 0.7 or less, 0.71 or less, 0.72 or less, 0.73 or less, 0.74 or less, 0.75 or less, 0.76 or less, 0.77 or less, 0.78 or less, 0.79 or less, 0.8 or less, 0.81 or less, 0.82 or less, 0.83 or less, 0.84 or less, 0.85 or less, 0.86 or less, 0.87 or less, 0.88 or less, 0.89 or less, 0.9 or less, 0.91 or less, 0.92 or less, 0.93 or less, 0.94 or less, 0.95 or less, 0.96 or less, It may be 0.97 or less, 0.98 or less, 0.99 or less, or less than 1. When a1 satisfies the above range, high capacitance characteristics can be realized, and in particular, when a1 is 0.6 to 0.75, high energy density is exhibited when driving at high voltage, thereby enabling high capacitance characteristics.

According to the present invention, in Formula 1, b1 represents the atomic fraction of cobalt among the metal elements in the lithium composite transition metal oxide, and may be greater than 0, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, or 0.05 or more, and 0.10 or less, 0.11 or less, 0.12 or less, 0.13 or less, 0.14 or less, 0.15 or less, 0.16 or less, 0.17 or less, 0.18 or less, 0.19 or less, 0.20 or less, 0.21 or less, 0.22 or less, 0.23 or less, 0.24 or less, 0.25 or less, 0.26 or less, 0.27 or less, 0.28 or less, 0.29 or less, 0.30 or less, 0.31 or less, 0.32 or less, 0.33 or less. It may be 0.34 or less, 0.35 or less, 0.36 or less, 0.37 or less, 0.38 or less, 0.39 or less, or less than 0.4. When b1 satisfies the above range, stability can be improved during the charge/discharge process and rate characteristics can be improved.

According to the present invention, in Formula 1, c1 represents the atomic fraction of ^M1 among the metal elements in the lithium composite transition metal oxide, and is greater than 0, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, 0.1 or more, 0.11 or more, 0.12 or more, 0.13 or more, 0.14 or more, 0.15 or more, 0.16 or more, 0.17 or more, 0.18 or more, 0.19 or more, 0.2 or more, 0.21 or more, 0.22 or more, 0.23 or more, 0.24 or more, 0.25 or more, 0.26 or more, 0.27 or more, 0.28 or more, 0.29 or more, or It may be 0.30 or higher, 0.32 or lower, 0.33 or lower, 0.34 or lower, 0.35 or lower, 0.36 or lower, 0.37 or lower, 0.38 or lower, 0.39 or lower, or less than 0.4. When c1 satisfies the above range, high capacity characteristics can be achieved. In addition, high temperature stability can be increased, and side reactions with the electrolyte can be relatively reduced.

According to the present invention, in the above formula 1, d1 represents the atomic fraction of ^M2 among the metal elements in the lithium composite transition metal oxide, and may be greater than 0 or greater than 0.0005, and may be less than 0.002, less than 0.003, less than 0.004, less than 0.005, less than 0.006, less than 0.007, less than 0.008, less than 0.009, or less than 0.01. When d1 satisfies the above range, the stability of the crystal structure of the positive active material is improved, and the resistance and lifespan of the battery may be improved due to the increase in structural stability.

According to the present invention, in the above formula 1, e1 represents the atomic fraction of ^M3 among the metal elements in the lithium composite transition metal oxide, and may be 0 or greater, 0.01 or less, 0.02 or less, 0.03 or less, 0.04 or less, 0.05 or less, 0.06 or less, 0.07 or less, 0.08 or less, 0.09 or less, or 0.10 or less. When e1 satisfies the above range, the stability of the crystal structure of the positive active material can be improved and the particle shape can be improved.

According to the present invention, the positive electrode active material may have a D ₅₀ measured by a PSA (particle size analyzer) of 3.0㎛ to 5.0㎛. Specifically, the positive electrode active material may have a D ₅₀ measured by a PSA (particle size analyzer) of 3.0㎛ or more, 3.1㎛ or more, 3.2㎛ or more, 3.3㎛ or more, 3.4㎛ or more, 3.5㎛ or more, 3.6㎛ or more, 3.7㎛ or more, or 3.8㎛ or more, and may have a D 50 of 4.0㎛ or less, 4.1㎛ or less, 4.2㎛ or less, 4.3㎛ or less, 4.4㎛ or less, 4.5㎛ or less, 4.6㎛ or less, 4.7㎛ or less, 4.8㎛ or less, 4.9㎛ or less, or 5.0㎛ or less. When D ₅₀ measured by a PSA (particle size analyzer) of the positive electrode active material is within the above range, the lifespan and capacity characteristics of the battery containing it are both improved, and the electrochemical performance can be optimized.

According to the present invention, the positive electrode active material further comprises a coating portion formed on the lithium composite transition metal oxide, and the coating portion may comprise Al, W, or a combination thereof. In this case, the capacity and lifespan of the battery comprising the positive electrode active material may have optimal performance.

According to the present invention, the content of Al included in the coating portion may be 1,000 ppm to 2,000 ppm relative to the total weight of the positive active material. Specifically, the content of Al may be 1,000 ppm or more, 1,100 ppm or more, 1,200 ppm or more, 1,300 ppm or more, or 1,400 ppm or more relative to the total weight of the positive active material, and may be 1,500 ppm or less, 1,600 ppm or less, 1,700 ppm or less, 1,800 ppm or less, 1,900 ppm or less, or 2,000 ppm or less. In this case, the electrical conductivity of the positive active material is improved, and the formation of by-products formed by side reactions with the electrolyte in the battery is suppressed, thereby improving the capacity characteristics, resistance characteristics, and lifespan characteristics of the positive active material.

According to the present invention, the content of W included in the coating portion may be 2,000 ppm to 4,000 ppm relative to the total weight of the positive active material. Specifically, the content of W may be 2,000 ppm or more, 2,100 ppm or more, 2,200 ppm or more, 2,300 ppm or more, 2,400 ppm or more, 2,500 ppm or more, 2,600 ppm or more, 2,700 ppm or more, 2,800 ppm or more, or 2,900 ppm or more relative to the total weight of the cathode active material, and may be 3,000 ppm or less, 3,100 ppm or less, 3,200 ppm or less, 3,300 ppm or less, 3,400 ppm or less, 3,500 ppm or less, 3,600 ppm or less, 3,700 ppm or less, 3,800 ppm or less, 3,900 ppm or less, or 4,000 ppm or less. In this case, the electrical conductivity of the positive electrode active material is improved, and the formation of by-products resulting from side reactions with the electrolyte in the battery is suppressed, thereby improving the capacity characteristics, resistance characteristics, and lifespan characteristics of the positive electrode active material.

Preferably, the coating portion may contain Al in an amount of 1,000 ppm to 2,000 ppm relative to the total weight of the positive active material, and W in an amount of 2,000 ppm to 4,000 ppm relative to the total weight of the positive active material.

According to the present invention, the positive active material may have a press density of 2.8 g/cc or more and 3.0 g/cc or less. Specifically, the positive active material may have a press density of 2.80 g/cc or more, 2.81 g/cc or more, 2.82 g/cc or more, 2.83 g/cc or more, 2.84 g/cc or more, or 2.85 g/cc or more, and may have a press density of 2.89 g/cc or less, 2.90 g/cc or less, 2.91 g/cc or less, 2.92 g/cc or less, 2.93 g/cc or less, 2.94 g/cc or less, 2.95 g/cc or less, 2.96 g/cc or less, 2.97 g/cc or less, 2.98 g/cc or less, 2.99 g/cc or less, or 3.00 g/cc or less. In this case, energy density can be increased by reducing internal voids during electrode manufacturing.

Method for manufacturing positive electrode active material

The present invention provides a method for manufacturing the above-described positive electrode active material. That is, the positive electrode active material according to the present invention is manufactured by the following method for manufacturing a positive electrode active material.

A method for manufacturing a single-particle cathode active material according to the present invention comprises: (A) a step of preparing a mixture by mixing a cathode active material precursor, a zirconium-containing raw material, a yttrium-containing raw material, and a lithium-containing raw material; and (B) a step of preparing a first-stage sintered product by first sintering the mixture at 750°C to 850°C and second sintering at 900°C to 1,000°C under an atmospheric atmosphere. At this time, the first-stage sintering is performed for 1 to 3 hours.

The inventors have completed the present invention by discovering that when a positive electrode active material is manufactured as described above, a positive electrode active material having a degree of small particle size according to Formula 1 described in this specification of 4.5 to 6.0 is produced and has a high rolling density.

(A) Step

The above step (A) is a step of preparing a mixture by mixing a positive electrode active material precursor, a zirconium-containing raw material, a yttrium-containing raw material, and a lithium-containing raw material.

According to the present invention, the positive electrode active material precursor may be a composite transition metal hydroxide containing 60 mol% or more of nickel (Ni) relative to the total molar amount of transition metals included in the positive electrode active material precursor. In this case, the energy density of the lithium secondary battery can be improved.

According to the present invention, the lithium-containing raw material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it is soluble in water. Specifically, the lithium-containing raw material may _{be Li₂CO₃} , _LiNO₃ , _LiNO₂ , _LiOH , LiOH·H₂O, LiH, _LiF , LiCl, _LiBr , _LiI , _CH₃COOLi , Li₂O, _Li₂SO₄ , _{CH₃COOLi ,} or _{Li₃C₆H₅O₇ ,} and any one or a mixture of two or more of these may be used.

According to the present invention, the positive active material precursor and the lithium-containing raw material can be mixed such that the ratio (M:Li) of the total number of moles of transition metal (M) included in the positive active material precursor and the number of moles of lithium (Li) included in the lithium-containing raw material is 1:1.03 to 1.07. In this case, the positive active material produced as a result can have a desired primary particle size, and the battery life and resistance characteristics can be improved.

According to the present invention, the zirconium (Zr)-containing raw material may be one _or more selected from Zr(OH) _₄ , _ZrO₂ , Zr( _NO₃ ) _₄ , _ZrCl₄ , _ZrS₂ , Zr( _SO₄ ) _₂, and _{C₅H₁₂O₅Zr ,} and specifically, one or more selected from _ZrO₂ , Zr(OH) _₄ , and Zr( _NO₃ ) _₄ , and more specifically, _ZrO₂ .

According to the present invention, the zirconium-containing raw material may be added in an amount such that the zirconium is 1,000 ppm to 4,000 ppm relative to the total weight of the positive electrode active material precursor. Specifically, the zirconium-containing raw material comprises zirconium at a concentration of 1,000 ppm or more, 1,100 ppm or more, 1,200 ppm or more, 1,300 ppm or more, or 1,400 ppm or more relative to the total weight of the complex transition metal hydroxide, and 1,500 ppm or less, 1,600 ppm or less, 1,700 ppm or less, 1,800 ppm or less, 1,900 ppm or less, 2,000 ppm or less, 2,100 ppm or less, 2,200 ppm or less, 2,300 ppm or less, 2,400 ppm or less, 2,500 or less, 2,600 or less, 2,700 or less, 2,800 or less, 2,900 or less, 3,000 ppm or less, 3,100 ppm or less, or 3,200 ppm It can be added in an amount such that it is less than 3,300 ppm, less than 3,400 ppm, less than 3,500 ppm, less than 3,600 ppm, less than 3,700 ppm, less than 3,800 ppm, less than 3,900 ppm, or less than 4,000 ppm. In this case, Zr is stably doped into the transition metal layer, so that a stable structure can be maintained even if the insertion and extraction of lithium are repeated as charging and discharging are repeated.

According to the present invention, the yttrium (Y)-containing raw material may be _one or more selected from _YCl3 , _Y2O3 , Y( _NO3 ) ₃ , Y(OH) ₃ , YSZ, _Y2 ( _SO4 ) ₃ , and _Y2S3 , specifically _one or more selected from _Y2O3 , Y(OH) ₃ , and YSZ, and more specifically _{, Y2O3} .

According to the present invention, the yttrium-containing raw material may be added in an amount such that the yttrium is 1,000 ppm to 4,000 ppm relative to the total weight of the positive electrode active material precursor. Specifically, the yttrium-containing raw material contains yttrium at a concentration of 1,000 ppm or more, 1,100 ppm or more, 1,200 ppm or more, 1,300 ppm or more, 1,400 ppm or more, 1,500 ppm or more, 1,600 ppm or more, 1,700 ppm or more, 1,800 ppm or more, 1,900 ppm or more, 2,000 ppm or more, 2,100 ppm or more, 2,200 ppm or more, 2,300 ppm or more, 2,400 ppm or more, 2,500 ppm or more, 2,600 ppm or more, 2,700 ppm or more, 2,800 ppm or more, or 2,900 ppm or more, and, 3,000 ppm or less, 3,100 ppm, based on the total weight of the complex transition metal hydroxide. It can be added in an amount such that it is less than 3,200 ppm, less than 3,300 ppm, less than 3,400 ppm, less than 3,500 ppm, less than 3,600 ppm, less than 3,700 ppm, less than 3,800 ppm, less than 3,900 ppm, or less than 4,000 ppm. In this case, Y acts as a flux material during firing, and since the optimal primary particle size can be achieved even at a relatively low temperature, it is advantageous for resistance or rate capability characteristics.

(B) Step

Step (B) above is a step of producing a first-stage fired product by first firing the mixture at 750°C to 850°C and second firing at 900°C to 1,000°C under an atmospheric environment.

According to the present invention, the first stage of sintering is performed for 1 to 3 hours. In this case, the lithium-containing raw material can be melted and sufficiently uniformly distributed on the surface of the precursor. Meanwhile, if the time for performing the first stage of sintering exceeds 3 hours, there is a problem in that the uniformity of the positive electrode active material particles after sintering is excessively improved, which actually lowers the rolling density. Furthermore, if the second stage of sintering is performed without performing the first stage of sintering, there is a problem in that the proportion of particles with a particle size of 1 μm to 2 μm increases excessively, thereby degrading the lifespan characteristics of the battery.

According to the present invention, when the mixture is calcined in a first stage at 750°C to 850°C, the lithium-containing raw material melts and is sufficiently uniformly distributed on the surface of the precursor, thereby allowing the lithium and the precursor to react effectively to produce an active material having a uniform primary particle shape. When the first stage calcination temperature is within the above range, the lithium-containing raw material can melt and be sufficiently uniformly distributed on the surface of the precursor. On the other hand, if the first stage calcination temperature is below 750°C, there is a problem that the lithium-containing raw material does not melt sufficiently, and if it exceeds 850°C, the lithium-containing raw material may be intercalated into the precursor before melting and being sufficiently uniformly distributed, thereby producing an active material having a relatively non-uniform shape.

According to the present invention, the first stage of calcination is performed under an atmospheric atmosphere in terms of uniform distribution of the lithium-containing raw material.

Immediately after the first stage of firing is completed, the temperature is continuously raised to 900°C to 1,000°C, and a second stage of firing is performed at 900°C to 1,000°C. This causes lithium to intercalate into the precursor to form a layered structure, and the interfaces of the primary particles merge to grow the primary particles. When the second stage of firing temperature is within the above range, the optimal primary particle size can be achieved, and thus, optimal performance can be exhibited in terms of particle breakage, rolling density, as well as the capacity, resistance, and lifespan of the battery. On the other hand, if the second stage of firing temperature is below 900°C, the primary particle size becomes smaller, resulting in inferior performance in terms of particle breakage and rolling density; if it exceeds 1,000°C, the primary particle size becomes larger, resulting in inferior performance in terms of efficiency and resistance.

The above two-stage firing is performed under an atmospheric environment in terms of proper growth of primary particles.

According to the present invention, the two-stage calcination may be performed for 1 to 10 hours. In this case, lithium is sufficiently intercalated into the precursor, and the growth of primary particles can also be appropriately achieved.

A method for manufacturing a positive electrode active material according to the present invention may further include (C) a step of finely grinding the primary calcined product in order to effectively fabricate an electrode and efficiently react at the active material-electrolyte interface. The fine grinding may be performed such that the D ₅₀ measured by a PSA (particle size analyzer) of the positive electrode active material is 3.0 μm to 5.0 μm.

According to the present invention, the fine grinding may be performed by air-flow grinding. In this case, compared to conventional physical grinding, not only is the grinding efficiency good, but heat is not generated, thereby suppressing the degradation of the surface of the active material.

According to the present invention, the air-flow grinding may be performed under a pressure of 2 bar to 5 bar. In this case, the target particle size can be effectively reached.

The method for manufacturing a positive electrode active material according to the present invention may further include the step of (D) manufacturing a secondary calcined product by calcining a finely ground primary calcined product at 500°C to 700°C. The calcination in step (D) increases the surface stabilization of the positive electrode active material, thereby improving the efficiency during charging and discharging of a battery containing the finally manufactured positive electrode active material.

The calcination of step (D) above can be performed under an atmospheric environment to stabilize the surface of the anode active material.

In addition, the firing of step (D) above may be performed for 5 to 10 hours, specifically 6 to 7 hours. In this case, efficiency may be increased.

The method for manufacturing a positive electrode active material according to the present invention may further include (E) a step of grinding the secondary calcined product. This is a process to resolve clumping between particles resulting from the calcination in step (D). The grinding may be performed using an Air Classifying Mill (ACM).

The method for manufacturing a positive electrode active material according to the present invention may further include the step of mixing the primary or secondary sintered product with one or more materials selected from aluminum raw materials and tungsten raw materials, and then heat-treating the mixture to form a coating portion comprising one or more materials selected from Al and W on the primary or secondary sintered product. In this case, a coating portion comprising one or more materials selected from Al and W is formed on the primary or secondary sintered product (a lithium composite transition metal oxide in the form of a single particle).

According to the present invention, the aluminum raw material may be one or more selected from _Al₂O₃ , Al(OH) _₃ , _AlCl₃ , _{AlF₃ ,} and _Al₂ ( _SO₄ ) _₃ , specifically one or more selected from _Al₂O₃ , Al(OH) _{₃ ,} and _AlF₃ , and more specifically _{Al₂O₃ .}

According to the present invention, the aluminum raw material may be added in an amount such that the aluminum content is 1,000 ppm to 2,000 ppm relative to the total weight of the primary or secondary fired product. Specifically, the aluminum raw material may be added in an amount such that the aluminum content is 1,000 ppm or more, 1,100 ppm or more, 1,200 ppm or more, 1,300 ppm or more, or 1,400 ppm or more, and 1,500 ppm or less, 1,600 ppm or less, 1,700 ppm or less, 1,800 ppm or less, 1,900 ppm or less, or 2,000 ppm or less relative to the total weight of the primary or secondary fired product.

In this case, the capacity retention rate due to charging and discharging can be improved.

According to the present invention, the tungsten raw material may be one or more selected from _WO3 , WC, and _H2WO4 , and more specifically _, may be _WO3 .

According to the present invention, the tungsten raw material may be added in an amount such that the tungsten content is 2,000 ppm to 4,000 ppm relative to the total weight of the primary or secondary fired product. Specifically, the tungsten raw material is such that the tungsten content is 2,000 ppm or more, 2,100 ppm or more, 2,200 ppm or more, 2,300 ppm or more, 2,400 ppm or more, 2,500 ppm or more, 2,600 ppm or more, 2,700 ppm or more, 2,800 ppm or more, or 2,900 ppm or more, and 3,000 ppm or less, 3,100 ppm or less, 3,200 ppm or less, 3,300 ppm or less, 3,400 ppm or less, 3,500 ppm or less, 3,600 ppm or less, 3,700 ppm or less, 3,800 ppm or less, 3,900 ppm or less, or 4,000 ppm or less, based on the total weight of the primary or secondary fired product. It can be added in the specified amount. In this case, output performance can be improved during battery operation.

According to the present invention, the heat treatment can be performed at 400°C to 600°C. In this case, the lifespan performance of the positive electrode active material can be further improved.

According to the present invention, the heat treatment can be performed under an atmospheric environment for surface stabilization.

According to the present invention, the heat treatment may be performed for 4 to 8 hours. In this case, side reactions between the positive active material and the electrolyte are suppressed as charging and discharging are repeated through surface stabilization of the positive active material, thereby improving the lifespan performance of the battery.

anode

The present invention provides a positive electrode comprising the above positive electrode active material.

The above positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer may include the positive electrode active material.

The above positive current collector may include a highly conductive metal, and is not particularly limited as long as it facilitates the adhesion of the positive active material layer and is non-reactive within the voltage range of the battery. The above positive current collector may be, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. Additionally, the above positive current collector may typically have a thickness of 3 μm to 500 μm, and may form fine irregularities on the surface of the current collector to increase the adhesion of the positive active material. It may be used in various forms, such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

The positive active material layer may include, together with the positive active material, a conductive material and a binder as needed. In this case, the positive active material may be included in an amount of 80% to 99% by weight, more specifically 85% to 98.5% by weight, based on the total weight of the positive active material layer, and may exhibit excellent capacity performance within this range.

The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powder or metal fibers such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The above conductive material may be included in an amount of 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

The above binder serves to improve the adhesion between positive active material particles and the adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogens thereof are substituted with Li, Na, or Ca, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The above binder may be included in an amount of 0.1% to 15% by weight relative to the total weight of the positive active material layer.

The above-described anode may be manufactured according to a conventional anode manufacturing method, except for using the above-described anode active material. Specifically, the above-described anode may be manufactured by applying a composition for forming an anode active material layer, prepared by dissolving or dispersing the above-described anode active material and, optionally, a binder, a conductive material, and a dispersant in a solvent, onto an anode current collector, followed by drying and rolling, or by casting the composition for forming an anode active material layer onto a separate support and then laminating the film obtained by peeling from the support onto an anode current collector.

The above solvent may be a solvent generally used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it is sufficient to dissolve or disperse the anode active material, conductive material, binder, and dispersant, taking into account the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that can exhibit excellent thickness uniformity when coated for anode manufacturing thereafter.

lithium secondary battery

The present invention provides a lithium secondary battery comprising: the anode; the cathode; a separator and an electrolyte interposed between the anode and the cathode.

The above lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

The above cathode may include a cathode current collector and a cathode active material layer located on the cathode current collector.

The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

The above-mentioned cathode active material layer may optionally include a binder and a conductive material together with the cathode active material.

As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and dedoping lithium, such as _SiO₂β (0<β<2), _SnO₂ , vanadium oxide, and lithium vanadium oxide; or composites comprising the above-mentioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. Furthermore, both low-crystallinity carbon and high-crystallinity carbon may be used as the carbon material. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes. The above-mentioned cathode active material may be included in an amount of 80% to 99% by weight based on the total weight of the cathode active material layer.

The binder of the above-mentioned negative electrode active material layer is a component that assists in the bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

The conductive material of the above-mentioned negative electrode active material layer is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less, based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

The above cathode may be manufactured by applying and drying a composition for forming a cathode active material layer, prepared by dissolving or dispersing a cathode active material and optionally a binder and a conductive material in a solvent, onto a cathode current collector, or by casting the composition for forming a cathode active material layer onto a separate support and then laminating the film obtained by peeling from the support onto a cathode current collector.

The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It can be used without special restrictions as long as it is commonly used as a separator in a lithium secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

Examples of the above electrolytes include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used in the manufacture of lithium secondary batteries, but are not limited to these. As a specific example, the above electrolyte may include an organic solvent and a lithium salt.

The above-mentioned organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above-mentioned organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; and carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC). Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond-directing ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge/discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion _of the lithium salt may be at least one _selected from _the group consisting of F- ^{, Cl-} , ^{Br- , I-} , _NO3- ^, N( ^CN ) _2- ^, _BF4- , _CF3CF2SO3- , ( _CF3SO2 ) _2N- , ( _FSO2 ) ^2N- _{, CF3CF2} ( _CF3 ) _2CO- ^, ( _CF3SO2 ) _2CH- , ( _{SF5 ) 3C-} ^{, (} _{CF3SO2 )} ^3C- _{, CF3 ( CF2 )} ^{7SO3- , CF3CO2-} , _CH3CO2- ^, _SCN- ^, and ( _{CF3CF2SO2 ) 2N- ,} and the _lithium salt may be ^LiPF6 _{, LiClO4 , LiAsF Li6} , _LiBF4 , _LiSbF6 , LiAlO4, _LiAlCl4 , _{LiCF3SO3 ,} LiC4F9SO3, _{LiN (C2F5SO3)2 , LiN ( C2F5SO2} ) ₂ , LiN( _CF3SO2 ) ₂ , LiCl, LiI, or LiB( _C2O4 ) ₂ may be used. It is preferable to use the lithium salt within the range of _0.1 M _{to 2.0 M.} When the concentration _of the lithium salt falls within _the above range, the electrolyte has appropriate conductivity and viscosity _, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving battery life, suppressing battery capacity reduction, and improving battery discharge capacity, such as, for example, haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1% to 5% by weight based on the total weight of the electrolyte.

Since the lithium secondary battery containing the positive electrode active material according to the present invention has excellent performance, it is useful in fields such as portable devices like mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEV) and electric vehicles (EV).

The external shape of the lithium secondary battery of the present invention is not particularly limited, but can be a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also preferably be used as a unit cell in a medium-to-large battery module comprising a plurality of battery cells.

Accordingly, a battery module including the above-mentioned lithium secondary battery as a unit cell and a battery pack including the same are provided.

The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

Examples and Comparative Examples

Example 1

A composite transition metal hydroxide in the form of secondary particles formed by the aggregation of tens to hundreds of primary particles (composition: Ni _0.605 Co _0.10 Mn _0.295 (OH) ₂ , D ₅₀ : 4.0㎛), ZrO ₂ (introduced in an amount such that Zr is 3000 ppm relative to the total weight of the composite transition metal hydroxide), and Y ₂ O ₃ (introduced in an amount such that Y is 1500 ppm relative to the total weight of the composite transition metal hydroxide) were added to an acoustic mixer, and mixed sequentially at 40 g (g: gravitational acceleration) for 2 minutes, at 80 g for 1 minute, and at 50 g for 2 minutes. Subsequently, _{Li₂CO₃ was} added to the acoustic mixer _such that the ratio of the total number of moles of transition metals (Ni+Co+Mn) contained in the complex transition metal hydroxide to the number of moles of lithium (Li) contained in _Li₂CO₃ ((Ni+Co+Mn):Li) was 1:1.05, and a mixture was prepared by sequentially mixing at 40g (g: gravitational acceleration) for 2 minutes, at 80g for 1 minute, and at 50g for 2 minutes.

After placing the above mixture into an alumina circular crucible (Φ75mm), the first stage of firing was performed at 800°C for 2 hours under an atmospheric conditions, and the second stage of firing was performed at 950°C for 4 hours to produce a first-stage fired product.

The above primary sintered product was finely ground using a jet mill under 2 to 4 bar. At this time, the feed rate was 50 to 100 g/min.

A finely ground primary sintered product was sintered at 600°C for 7 hours under an atmospheric environment to produce a secondary sintered product.

The above secondary calcined product was ground using an ACM (Air Classifying Mill).

A pulverized secondary calcined product was mixed with _Al₂O₃ (in an amount such that Al _is 1500 ppm relative to the total weight of the secondary calcined product) and _WO₃ (in an amount such that W is 3000 ppm relative to the total weight of the secondary calcined product), and then heat-treated at 500°C for 6 hours under an atmospheric environment to produce an anode active material containing a coating portion containing Al and W.

Example 2

A positive electrode active material was prepared in the same manner as in Example 1, except that the first stage of calcination was performed for 1 hour instead of 2 hours.

Comparative Example 1

A positive electrode active material was prepared in the same manner as in Example 1, except that the first stage of calcination was performed for 6 hours instead of 2 hours.

Comparative Example 2

A positive electrode active material was prepared in the same manner as in Example 1, except that the first stage of calcination was performed for 4 hours instead of 2 hours.

Comparative Example 3

A positive electrode active material was prepared in the same manner as in Example 1, except that the first stage of calcination was performed for 3 hours instead of 2 hours.

Comparative Example 4

A positive electrode active material was prepared in the same manner as in Example 1, except that a primary sintered product was prepared by performing only a second sintering step without performing a first sintering step.

Comparative Example 5

A positive electrode active material was prepared in the same manner as in Example 1, except that when finely grinding the primary calcined product, the process was performed using a jet mill at 0.5 to 1 bar instead of 2 to 4 bar.

Experimental Example

Experimental Example 1: ICP Analysis

0.1 g of each secondary calcined product (hereinafter referred to as lithium composite transition metal oxide) prepared in the examples and comparative examples was taken, 1 ml of hydrochloric acid was added, and the lithium composite transition metal oxide was dissolved by heating. Subsequently, a small amount of hydrogen peroxide was added to promote the reaction and the lithium composite transition metal oxide was completely dissolved to prepare a solution. Then, the solution was diluted with deionized water to a total volume of 10 ml to prepare an analytical sample. Using an ICP device (ICP-OES; Agilent 5110, Agilent Technologies), the weight ratio of constituent elements present in the analytical sample was measured, and the composition of the lithium composite transition metal oxide, the content of Zr (ppm), and the content of Y (ppm) present in the lithium composite transition metal oxide are shown in Table 1 below.

In addition, 0.1 g of each cathode active material prepared in the examples and comparative examples was taken, 1 ml of hydrochloric acid was added, and the cathode active material was dissolved by heating. Subsequently, a small amount of hydrogen peroxide was added to promote the reaction and completely dissolve the cathode active material to prepare a solution. Then, the solution was diluted with deionized water to a total volume of 10 ml to prepare an analytical sample. Using an ICP device (ICP-OES; Agilent 5110, Agilent Technologies), the weight ratio of constituent elements present in the analytical sample was measured, and the content of Al (ppm) and W (ppm) contained in the cathode active material is shown in Table 1 below.

division Lithium complex transition metal oxide composition Zr content
(ppm) Y content
(ppm) Al content
(ppm) W content
(ppm) Example 1 Li _1.033 [Ni _0.607 Co _0.099 Mn _0.294 ] _0.996 Zr _0.003 Y _0.001 O ₂ 2152 982 1120 2020 Example 2 Li _1.032 [Ni _0.606 Co _0.098 Mn _0.296 ] _0.996 Zr _0.003 Y _0.001 O ₂ 2120 1025 1140 2070 Comparative Example 1 Li _1.035 [Ni _0.604 Co _0.100 Mn _0.296 ] _0.996 Zr _0.003 Y _0.001 O ₂ 2057 1054 1200 2100 Comparative Example 2 Li _1.030 [Ni _0.605 Co _0.100 Mn _0.295 ] _0.996 Zr _0.003 Y _0.001 O ₂ 2145 1075 1180 2110 Comparative Example 3 Li _1.031 [Ni _0.605 Co _0.097 Mn _0.298 ] _0.996 Zr _0.003 Y _0.001 O ₂ 2204 972 1190 2020 Comparative Example 4 Li _1.034 [Ni _0.604 Co _0.101 Mn _0.295 ] _0.996 Zr _0.003 Y _0.001 O ₂ 2123 1015 1120 2150 Comparative Example 5 Li _1.034 [Ni _0.605 Co _0.099 Mn _0.296 ] _0.996 Zr _0.003 Y _0.001 O ₂ 2176 1048 1134 2084

Experimental Example 2: Analysis of Anode Active Material Shape

SEM images of each cathode active material prepared in the examples and comparative examples were obtained using an SEM (FEI, Inspect F), and are shown in FIG. 1 (Example 1), FIG. 2 (Example 2), FIG. 3 (Comparative Example 1), FIG. 4 (Comparative Example 2), FIG. 5 (Comparative Example 3), and FIG. 6 (Comparative Example 4).

Experimental Example 3: Analysis of Cathode Active Material Particle Size

0.01 g of each cathode active material (powder) prepared in the examples and comparative examples was placed in a vial containing 30 ml of ultrapure water and 500 µl of dispersant, and the cathode active material was dispersed with a sonicator for 1 minute. Then, it was placed in a PSA (Microtrac, S3500) and analyzed to confirm D ₅₀ , which is shown in Table 2 below.

At this time, D ₅₀ refers to the particle size at the 50% point of the volume cumulative distribution according to particle size.

In addition, the ratio (%) of the number of particles with a diameter of 1 μm to 2 μm to the total number of particles and the ratio (%) of the number of particles with a diameter of 3 μm to 4 μm to the total number of particles were determined, and the degree of fine particle formation was calculated according to Formula 1 described in this specification and shown in Table 2 below.

Experimental Example 4: Analysis of Coating Shape

SEM-EDS mapping data of the cathode active material prepared in Example 1 was obtained using SEM-EDS (FE-SEM (Jeol, JSM-IT800) & FlatQUAD (Bruker)) and is shown in Fig. 7.

Referring to Figures 1 and 7 above, it can be seen that a coating portion containing Al and W is formed on the surface of the positive active material.

Experimental Example 5: Measurement of Rolled Density

5g of each positive active material (powder) prepared in the examples and comparative examples was taken, placed into a mold with an inner diameter of 22mm, and pressed at 2 tons for 3 seconds. After pressing, the thickness of the pellet formed was measured. From the thickness, the volume of the pellet after applying pressure to 5g of positive active material was calculated, and the weight (g) of the active material per unit volume ( ^cm³ ) of the pellet after pressing, i.e., the rolling density, was determined and is shown in Table 2 below.

division Small particle size D ₅₀ (㎛) measured by PSA Rolled density
(g/cc) Example 1 4.71 3.87 2.850 Example 2 5.87 3.95 2.884 Comparative Example 1 2.50 3.92 2.790 Comparative Example 2 2.94 3.90 2.813 Comparative Example 3 3.73 3.88 2.801 Comparative Example 4 6.04 3.97 2.896 Comparative Example 5 3.82 5.32 2.782

Referring to Table 2 above, it can be seen that the positive active materials of Examples 1 and 2 satisfy a particle size range of 4.5 to 6.0, whereas the positive active materials of Comparative Examples 1 to 3 and 5 have a particle size less than 4.5, and the positive active material of Comparative Example 4 has a particle size greater than 6.0.

Experimental Example 6: Battery Performance Evaluation

A positive electrode slurry was prepared by mixing the positive electrode active materials prepared in the examples and comparative examples, FX35 conductive material, and polyvinylidene fluoride (PVDF) binder in a ratio of 95:3:2 in an N-methylpyrrolidone (NMP) solvent. The positive electrode slurry was applied to one side of an aluminum current collector, dried at 130°C for at least 10 minutes, and rolled to produce a positive electrode.

A lithium metal electrode was used as the negative electrode, and an electrode assembly was manufactured by interposing a porous polyethylene separator between the positive and negative electrodes. After placing the electrode assembly inside a battery case, an electrolyte was injected into the case to manufacture a half-cell. At this time, the electrolyte was prepared by dissolving 1.0 M LiPF6 in an organic solvent mixed with ethylene carbonate (EC):ethyl methyl carbonate (EMC):diethyl carbonate (DEC) in a volume ratio of ₃ :4:3.

For each half-cell manufactured as described above, the initial charge capacity and initial discharge capacity were measured and the initial efficiency was calculated and shown in Table 3 below while charging at 25°C in CC-CV mode at 0.1C until it reached 4.4V and discharging at a constant current of 0.1C until it reached 2.5V. For reference, the initial efficiency value is the percentage of the initial discharge capacity relative to the initial charge capacity.

division Initial charging capacity
(mAh/g) Initial discharge capacity
(mAh/g) Initial efficiency
(%) Example 1 215.7 195.9 90.8 Example 2 215.8 196.2 90.9 Comparative Example 1 214.2 194.3 90.7 Comparative Example 2 214.5 194.6 90.7 Comparative Example 3 214.8 194.8 90.7 Comparative Example 4 217.0 197.3 90.9 Comparative Example 5 214.7 193.6 90.2

In addition, for each half-cell manufactured as described above, charging at 0.33C in CC-CV mode at 45℃ until it reached 4.4V and discharging at a constant current of 0.33C until it reached 2.5V was repeated for a total of 100 cycles, and the discharge capacity in the first cycle and the 100th cycle was measured. Then, the percentage of the discharge capacity of the 100th cycle relative to the discharge capacity of the first cycle (capacity retention rate (%)) is shown in Table 4 below. Furthermore, after measuring the DC internal resistance (DCIR) of the first cycle and the DC internal resistance (DCIR) of the 100th cycle, the percentage of the DCIR value of the 100th cycle relative to the measured DCIR value of the first cycle (resistance increase rate (%)) was calculated and is shown in Table 4 below. The above DCIR value is calculated by dividing the difference between the initial voltage and the voltage at 60 seconds while discharging with a constant current of 0.33C in each cycle by the applied current.

division Capacity retention rate
(%) Resistance growth rate
(%) Example 1 95.5 15.8 Example 2 95.4 16.3 Comparative Example 1 95.8 15.2 Comparative Example 2 95.6 15.6 Comparative Example 3 95.5 15.6 Comparative Example 4 94.8 19.2 Comparative Example 5 94.2 13.8

Referring to Tables 3 and 4 above, it can be confirmed that the battery containing the positive electrode active material of Examples 1 and 2 has optimal lifespan performance, as it has a high capacity retention rate of 95.4% or higher and a low resistance increase rate of 16.3% or lower, and that it has high initial charge/discharge capacity. On the other hand, it can be confirmed that the battery containing the positive electrode active material of Comparative Examples 1 to 3 has optimal lifespan performance, but has low initial charge/discharge capacity, and it can be confirmed that the battery containing the positive electrode active material of Comparative Example 4 has poor lifespan performance. Furthermore, it can be confirmed that the battery containing the positive electrode active material of Comparative Example 5 has poor lifespan performance, as it has low initial charge/discharge capacity and initial efficiency, and a low capacity retention rate.

Accordingly, it can be seen that the positive electrode active material according to the present invention comprises a lithium composite transition metal oxide in the form of a single particle, and satisfies a degree of small particle size of 4.5 to 6.0, thereby enabling the realization of a battery with excellent capacity while having optimal lifespan performance.

Claims (10)

It comprises a lithium complex transition metal oxide in the form of a single particle composed of 10 or fewer primary particles, and A positive active material having a degree of small particle magnetization of 4.5 to 6.0 according to Formula 1 below: [Equation 1] Small particle magnetization = A/B When the above positive active material was analyzed using a PSA (particle size analyzer), The above A is the ratio (%) of the number of particles with a diameter of 1㎛ to 2㎛ to the total number of particles, and The above B is the ratio (%) of the number of particles with a diameter of 3㎛ to 4㎛ to the total number of particles. In claim 1, The above positive active material is a positive active material having a D ₅₀ of 3.0㎛ to 5.0㎛ as measured by a PSA (particle size analyzer). In claim 1, The above lithium composite transition metal oxide is a positive active material doped with Zr, Y, or a combination thereof. In claim 1, The above lithium complex transition metal oxide is a positive electrode active material having a composition represented by the following chemical formula 1: [Chemical Formula 1] Li _1+x Ni _a1 Co _b1 M ¹ _c1 M ² _d1 M ³ _e1 O _2-y A _y In the above chemical formula 1, M ¹ is Mn, Al, or a combination thereof, and M ² is Zr, Y, or a combination thereof, and ^M3 is one or more selected from the group consisting of W, Cu, Sr, Ti, Mg, Mo, B, Sn, Fe, Zn, and Si, and A is one or more selected from F, Cl, Br, I, and S, and -0.1≤x≤0.1, 0.6≤a1<1, 0<b1<0.4, 0<c1<0.4, 0<d1<0.01, 0≤e1<0.1, 0≤y≤0.2, a1+b1+c1+d1+e1=1. In claim 1, The above lithium composite transition metal oxide is a positive active material doped with Zr at 1,000 ppm to 4,000 ppm and Y at 800 ppm to 4,000 ppm. In claim 1, The above positive active material further comprises a coating portion formed on the lithium composite transition metal oxide, and The above coating portion is a positive active material comprising Al, W, or a combination thereof. In claim 6, The above coating portion comprises Al in an amount of 1,000 ppm to 2,000 ppm relative to the total weight of the positive active material and W in an amount of 2,000 ppm to 4,000 ppm relative to the total weight of the positive active material. In claim 1, The above positive active material is a positive active material having a press density of 2.8 g/cc or more and 3.0 g/cc or less. A positive electrode comprising a positive electrode active material according to any one of claims 1 to 8. A lithium secondary battery comprising a positive electrode according to claim 9.