KR20220059931A - Positive electrode material for lithium secondary battery, method for preparing same and lithium secondary battery comprising same - Google Patents

Abstract

The present invention relates to a positive electrode active material including at least one secondary particle including an aggregate of primary macro particles, a manufacturing method thereof, and a lithium secondary battery including the same. According to one embodiment of the present invention, electrochemical properties can be improved by coating the surface of the secondary particle with a lithium phosphate compound. Accordingly, the present invention can provide a nickel-based positive electrode active material having excellent energy density and safety.

Description

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

The present invention relates to a cathode active material for a lithium secondary battery comprising primary large particles and a method for manufacturing the same.

Recently, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for small, lightweight and relatively high-capacity secondary batteries is rapidly increasing. In particular, a lithium secondary battery has been in the spotlight as a driving power source for a portable device because it is lightweight and has a high energy density. Accordingly, research and development efforts for improving the performance of lithium secondary batteries are being actively conducted.

In a lithium secondary battery, an organic electrolyte or a polymer electrolyte is charged between a positive electrode and a negative electrode made of an active material capable of intercalation and deintercalation of lithium ions, and lithium ions are inserted/deintercalated from the positive electrode and the negative electrode. Electric energy is produced by a reduction reaction with

As a positive active material of a lithium secondary battery, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMnO ₂ or LiMn ₂ O ₄ , etc.), lithium iron phosphate compound (LiFePO ₄ ), etc. are used. . Among them, lithium cobalt oxide (LiCoO ₂ ) has advantages of high operating voltage and excellent capacity characteristics, and is widely used, and is applied as a positive electrode active material for high voltage. However, there is a limit to mass use as a power source in fields such as electric vehicles due to an increase in the price of cobalt (Co) and unstable supply, and the need to develop a cathode active material that can replace it has emerged. Accordingly, a nickel-cobalt-manganese-based lithium composite transition metal oxide (hereinafter simply referred to as 'NCM-based lithium composite transition metal oxide') in which a part of cobalt (Co) is substituted with nickel (Ni) and manganese (Mn) has been developed.

On the other hand, the conventionally developed NCM-based lithium composite transition metal oxide was in the form of secondary particles in which primary micro particles were aggregated, and had a large specific surface area and low particle strength. In addition, when an electrode is manufactured with a positive electrode active material including secondary particles in which the primary fine particles are aggregated and then rolled, there is a problem of severe particle breakage, a large amount of gas generated during cell operation, and poor stability. In particular, in the case of an NCM-based lithium composite transition metal oxide of high nickel (Ni) with an increased nickel (Ni) content to secure a high capacity, primary fine particles anisotropically contract during charging and discharging, and the particles The expansion width is large. Accordingly, due to a side reaction with the electrolyte penetrating along the microc-rack between the primary fine particles, the crystal structure of the surface of the primary fine particles is changed, which reduces the lifespan of the battery and generates gas in the battery Therefore, there is a problem of poor stability. For this reason, the structural and chemical stability of the high-Ni NCM-based lithium composite transition metal oxide is further deteriorated, and there is a problem in that it is more difficult to secure thermal stability.

To solve this problem, researched monoliths have been developed. A single particle means a particle which exists independently from the said secondary particle, and does not exist a grain boundary in appearance. When the cathode active material has a single particle shape, it is possible to improve cracks or particle breakage in the active material that occur during electrode rolling. In addition, since micro-cracks do not occur during charging and discharging, side reactions with the electrolyte are reduced, thereby improving lifespan and reducing gas generation.

However, compared with the secondary particles including the primary fine particles, these single particles increase resistance in the charging and discharging process and output characteristics as the movement path of lithium ions from the inside of the positive electrode active material to the surface becomes longer. has a low problem.

The problem to be solved by the present invention is to solve the above problems, and to provide a positive electrode active material of a new concept.

The problem to be solved by the present invention is to improve the electrochemical stability of the particle surface by coating a lithium phosphate compound on the surface of the secondary particle in which the large primary particle is aggregated.

Accordingly, it is an object to provide a nickel-based positive electrode active material having excellent energy density and output characteristics and securing stability.

One aspect of the present invention provides a cathode active material for a lithium secondary battery according to the following embodiments.

A first embodiment is

A cathode active material for a lithium secondary battery comprising at least one secondary particle including an aggregate of primary macro particles,

The average particle diameter (D50) of the primary large particles is 1 μm or more,

Part or all of the secondary particle surface is coated with a lithium phosphate compound,

The secondary particles have an average particle diameter (D50) of 2.5 to 6 μm,

The positive active material relates to a positive active material for a lithium secondary battery, characterized in that it includes a nickel-based lithium transition metal oxide.

In the second embodiment, according to the first embodiment,

The lithium phosphate compound relates to a positive active material for a lithium secondary battery, characterized in that it includes a compound represented by the following formula (1):

[Formula 1]

LiAPO ₄

In this case, A is any one selected from the group consisting of Ni, Co, Mn and Fe, or two or more of these elements.

A third embodiment, according to the first or second embodiment,

The nickel-based lithium transition metal oxide is, Li (Ni _x Co _y M _1-xy )O ₂ (M = Mn, Al, Y, Ti and Zr any one or two or more of these elements selected from the group consisting of) It relates to a cathode active material for a lithium secondary battery, characterized in that it comprises a.

A fourth embodiment, according to any one of the first to third embodiments,

The ratio of the average particle diameter (D50) of the primary large particles to the average crystal size of the primary large particles is 2 or more.

A fifth embodiment, according to any one of the first to fourth embodiments,

The coating amount of the lithium phosphate compound relates to a cathode active material for a lithium secondary battery, characterized in that less than 10,000 ppm.

A sixth embodiment, according to any one of the first to fifth embodiments,

The average crystal size of the primary large particles relates to a cathode active material for a lithium secondary battery, characterized in that 150 nm or more.

A seventh embodiment, according to any one of the first to sixth embodiments,

The ratio of the average particle diameter (D50) of the secondary particles to the average particle diameter (D50) of the primary large particles is 2 to 5 times.

The eighth embodiment, according to any one of the first to seventh embodiments,

The positive active material relates to a positive active material for a lithium secondary battery, wherein the primary large particle is separated from the secondary particle during rolling, and the primary large particle itself is not broken.

One aspect of the present invention provides a positive electrode for a lithium secondary battery according to the following embodiments.

The ninth embodiment relates to a positive electrode for a lithium secondary battery including the positive electrode active material according to any one of the above-described embodiments.

One aspect of the present invention provides a lithium secondary battery according to the following embodiments.

A tenth embodiment provides a lithium secondary battery according to any one of the above embodiments.

One aspect of the present invention provides a method of manufacturing a cathode active material for a lithium secondary battery according to the following embodiments.

The eleventh embodiment is

(S1) preparing a nickel-based lithium transition metal hydroxide precursor by mixing a transition metal-containing solution containing nickel, cobalt and manganese, an ammonia-containing solution, and a basic aqueous solution;

(S2) mixing and heat-treating the nickel-based lithium transition metal hydroxide precursor and the lithium raw material to prepare secondary particles;

(S3) mixing the secondary particles with the raw material of the lithium phosphate compound and then heat-treating;

The positive active material is a positive active material for a lithium secondary battery comprising at least one secondary particle including an aggregate of primary macro particles,

The average particle diameter (D50) of the primary large particles is 1 μm or more,

Part or all of the secondary particle surface is coated with a lithium phosphate compound,

The secondary particles have an average particle diameter (D50) of 2.5 to 6 μm,

The cathode active material relates to a method of manufacturing a cathode active material for a lithium secondary battery, characterized in that it comprises a nickel-based lithium transition metal oxide.

The twelfth embodiment, according to the eleventh embodiment,

The step (S1) is carried out at 25 to 60 ℃,

The step (S2) is carried out at 700 to 950 ℃,

The step (S3) relates to a method of manufacturing a positive electrode active material, characterized in that it is carried out at 600 to 800 ℃.

The thirteenth embodiment, according to the eleventh or twelfth embodiment,

The raw material of the lithium phosphate compound relates to a method of manufacturing a cathode active material for a lithium secondary battery, characterized in that it includes a compound represented by the following formula (1):

[Formula 1]

LiAPO ₄

In this case, A is any one selected from the group consisting of Ni, Co, Mn and Fe, or two or more of these elements.

The fourteenth embodiment, according to any one of the eleventh to thirteenth embodiments,

The step (S1) relates to a method of manufacturing a positive electrode active material, characterized in that it is carried out at a pH of 9 to 12 conditions.

A fifteenth embodiment, according to any one of the eleventh to fourteenth embodiments,

In the step (S3), the raw material of the lithium phosphate compound,

C ₂ H ₃ LiO ₂ 2H ₂ O, C ₄ H ₆ CoO ₄ 4H ₂ O, NH ₄ H ₂ PO ₄ While stirring an aqueous solution, C ₆ H ₈ O ₇ H ₂ O is added and gelled, characterized in that It relates to a method of manufacturing a positive electrode active material.

According to an embodiment of the present invention, it is possible to provide a high-stability high-Ni-based positive electrode active material with improved resistance and output characteristics by using secondary particles having the shape of secondary particles in which large primary particles are aggregated. .

According to an embodiment of the present invention, the surface of the secondary particles may be coated with a lithium phosphate compound to improve electrochemical stability.

Accordingly, it is possible to provide a nickel-based positive electrode active material having excellent energy density and securing stability.

The drawings accompanying the present specification illustrate preferred embodiments of the present invention, and serve to better understand the technical spirit of the present invention together with the above-described content of the present invention, so the present invention is limited only to the matters described in such drawings is not interpreted as On the other hand, the shape, size, scale, or ratio of elements in the drawings included in this specification may be exaggerated to emphasize a clearer description.
1A and 1B are SEM photographs and enlarged views of the positive active material according to Comparative Example 1, respectively.
2A and 2B are SEM photographs and enlarged views of the positive active material according to Example 1, respectively.

Hereinafter, embodiments of the present invention will be described in detail. Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor should properly understand the concept of the term in order to best describe his invention. Based on the principle that it can be defined, it should be interpreted as meaning and concept consistent with the technical idea of the present invention. Therefore, the configuration described in the embodiment described in this specification is only the most preferred embodiment of the present invention and does not represent all of the technical idea of the present invention, so various equivalents and It should be understood that there may be variations.

Throughout this specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

In the present specification and claims, "including a plurality of crystal grains" means a crystal formed by gathering two or more crystal grains having an average crystal size in a specific range. In this case, the crystal size of the crystal grains may be quantitatively analyzed using X-ray diffraction analysis (XRD) by Cu Kα X-rays (Xrα). Specifically, the average crystal size of the crystal grains can be quantitatively analyzed by putting the prepared particles in a holder and analyzing the diffraction grating that irradiates X-rays to the particles.

In the specification and claims, D50 may be defined as a particle size based on 50% of a particle size distribution, and may be measured using a laser diffraction method. For example, in the method of measuring the average particle diameter (D50) of the positive active material, the particles of the positive active material are dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (eg, Microtrac MT 3000) to about 28 kHz After irradiating the ultrasonic waves with an output of 60 W, the average particle diameter D50 corresponding to 50% of the volume accumulation amount in the measuring device can be calculated.

In the present invention, the term 'primary particles' refers to particles having no apparent grain boundaries when observed in a field of view of 5000 times to 20000 times using a scanning electron microscope. In the present invention, the primary particles may be classified into primary micro particles and primary macro particles according to an average particle diameter (D50).

In the present invention, 'secondary particles' are particles formed by agglomeration of the primary particles.

In the present invention, 'single particle' is a particle that exists independently of the secondary particles and does not have a grain boundary in appearance, for example, a particle having a particle diameter of 0.5 µm or more.

In the present invention, when 'particle' is described, it may mean that any one or all of single particles, secondary particles, and primary particles are included.

cathode active material

In one aspect of the present invention, there is provided a positive electrode active material in the form of secondary particles different from the conventional ones.

Specifically,

1) A cathode active material for a lithium secondary battery comprising at least one secondary particle including an aggregate of primary macro particles,

2) The average particle diameter (D50) of the primary large particles is 1 μm or more,

3) a part or all of the secondary particle surface is coated with a lithium phosphate compound,

4) The average particle diameter (D50) of the secondary particles is 2.5 to 6 ㎛,

5) The positive electrode active material for a lithium secondary battery, characterized in that it contains a nickel-based lithium transition metal oxide

The secondary particles may provide a nickel-based positive electrode active material having high energy density and improved battery life by having the characteristics of 1) to 5) above.

Hereinafter, the characteristics 1) to 5) of the secondary particles will be described in detail.

Particle morphology and primary macroparticles

In general, the nickel-based lithium transition metal oxide is a secondary particle. These secondary particles may be in the form of agglomerated primary particles.

Specifically, the high-density nickel-based lithium transition metal hydroxide secondary particles prepared by the co-precipitation method are used as a precursor, and when this precursor is mixed with a lithium precursor and calcined at a temperature of less than 960° C., the primary fine particles Nickel-based lithium transition metal oxide secondary particles comprising a can be obtained. However, when rolling after coating the positive electrode active material including the conventional secondary particles on the current collector, the particles themselves are broken and the specific surface area is widened. When the specific surface area is widened, the change from a layered structure to a rock salt structure is accelerated by a side reaction with the electrolyte, which increases the intercalation/desorption resistance of lithium ions on the surface of the active material and causes electrochemical inactivation of some primary fine particles a problem arises

In order to solve this problem, conventionally, single-particle positive electrode active materials have been additionally developed. Specifically, unlike the conventional method using the aforementioned dense nickel-based lithium transition metal hydroxide secondary particles as a precursor, it can be synthesized at a high calcination temperature compared to the same nickel content by using a porous precursor compared to the existing precursor And, it no longer has the form of secondary particles, and a single-particulated nickel-based lithium transition metal oxide can be obtained. However, compared with the secondary particles including the primary fine particles, these single particles increase resistance in the charging and discharging process and output characteristics as the movement path of lithium ions from the inside of the positive electrode active material to the surface becomes longer. has a low problem.

One aspect of the present invention is to solve this problem.

In the case of sintering by increasing only the sintering temperature with a precursor having the same high density as before, the average particle diameter (D50) of the primary particles and the average particle diameter (D50) of the secondary particles inevitably increase at the same time.

On the other hand, the secondary particle according to an aspect of the present invention is different from the conventional method for obtaining single particles in the following points.

As for the conventional single particles, as described above, single particles were formed by increasing only the primary firing temperature by using the existing precursor for secondary particles as they are. On the other hand, the secondary particles according to an aspect of the present invention, a precursor having a high porosity is used separately. Accordingly, primary large particles having a large particle size may be grown without increasing the firing temperature, whereas secondary particles may be grown relatively less than before.

Accordingly, the secondary particles according to an aspect of the present invention have the same or similar average particle diameter (D50) as before, and have a large average diameter (D50) of the primary particles. In other words, unlike the conventional positive electrode active material, in which primary particles with small average particle diameters gather to form secondary particles, the primary large particles with increased primary particle size are aggregated to, for example, less than 30. Provides secondary particle morphology.

In the present invention, 'primary large particles' means those having an average diameter (D50) of 1 µm or more.

In a specific embodiment of the present invention, the average particle diameter of the primary large particles may be 1 μm or more, 1.5 μm or more, 2 μm or more, 2.5 μm or more, 3 μm or more, or 3.5 μm or more, and 5 μm or less; It may be 4.5 μm or less, or 4 μm or less. When the average particle diameter of the primary large particles is less than 1 μm, the agglomerated secondary particles correspond to conventional secondary small particles, and thus there may be a problem in that particles are broken during rolling.

In the present invention, 'primary large particles' means that the ratio of average particle diameter (D50)/average crystal size is 2 or more, and more preferably 3 or more. That is, the primary large particles have an average particle diameter and an average crystal size of the primary particles grown at the same time as compared to the primary micro particles constituting the conventional secondary particles.

From the point of view of cracks, it is advantageous to have a large average particle diameter while apparently not having grain boundaries like conventional single particles. Accordingly, the present inventors focused on growing the average particle diameter (D50) of the primary particles. In the meantime, it was discovered that, when only the average particle diameter (D50) of the primary particles is increased due to under-plasticity, rock salt is formed on the surface of the primary particles and the resistance increases. To solve this, in one aspect of the present invention, primary large particles were used. Also, the average crystal size of the primary particles seems to be related to lowering the resistance.

That is, the primary large particles in the present invention mean particles having a large average crystal size as well as an average particle size and no apparent grain boundaries.

As such, when the average particle size and average crystal size of primary particles grow at the same time, rock salt is formed on the surface due to sintering at high temperature, which lowers resistance and is advantageous in terms of long life compared to conventional single particles with a large increase in resistance. .

As such, in the case of “secondary particles composed of agglomerates of secondary large particles” used in one aspect of the present invention, compared to conventional single particles, the size of the primary particles itself increases and the formation of rock salt is reduced, resulting in resistance It is advantageous in that it is lowered.

In this case, the average crystal size of the primary large particles may be quantitatively analyzed using X-ray diffraction analysis (XRD) by Cu Kα X-rays. Specifically, the average crystal size of the primary large particles can be quantitatively analyzed by putting the prepared particles in a holder and analyzing the diffraction grating that irradiates the particles with X-rays.

In a specific embodiment of the present invention, the ratio of the average particle size (D50) / average crystal size (crystal size) may be 2 or more, 2.5 or more, 3 or more, and 50 or less, 40 or less, 35 or less.

In addition, the average crystal size of the primary large particles may be 150 nm or more, 170 nm or more, 200 nm or more, and 300 nm or less, 270 nm or less, or 250 nm or less.

secondary particles

The secondary particles according to one aspect of the present invention have the same or similar average particle diameter (D50) as before, but have a large average diameter (D50) of the primary particles. In other words, unlike the conventional positive electrode active material, in which primary particles with small average particle diameters gather to form secondary particles, it provides a secondary particle form in which primary large particles with increased primary particle size are aggregated. do.

Specifically, the secondary particles according to one aspect of the present invention are aggregates of primary macro particles. In a specific embodiment of the present invention, the secondary particles may be aggregates of 1 to 30 primary large particles. More specifically, the secondary particles may be one or more, two or more, three or more, or four or more aggregates of the primary large particles within the numerical range, and within the numerical range, the primary particles may be agglomerated. The large particles may be agglomerated into 30 or less, 25 or less, 20 or less, 15 or less, or 10 or less.

The secondary particles according to an aspect of the present invention have an average diameter (D50) of 2.5 μm to 6 μm. More specifically, it is 2.5 µm or more, 3 µm or more, 3.5 µm or more, 4 µm or more, or 4.5 µm or more, and is 6 µm or less, 5.5 µm or less, or 5 µm or less.

In general, regardless of particle shape, when the composition is the same, the size of the particles and the average crystal size within the particles increase as the firing temperature increases. On the other hand, in the secondary particles according to an aspect of the present invention, by using a porous precursor, primary large particles having a large particle size can be grown without raising the calcination temperature higher than in the prior art, whereas the secondary particles are can grow relatively little compared to

Accordingly, the secondary particles according to one aspect of the present invention are primary macro particles having the same or similar average diameter (D50) as the conventional secondary particles, and having larger average diameter and average crystal size than the conventional primary fine particles. consist of.

In a specific embodiment of the present invention, the ratio of the average particle diameter (D50) of the secondary particles to the average particle diameter (D50) of the primary large particles may be 2 to 5 times.

In this case, when the secondary particles are rolled, the primary large particles may come off, and the primary large particles themselves may not be broken. At this time, the rolling condition may be 9 tons.

The secondary particles include a nickel-based lithium transition metal oxide.

Specifically, the nickel-based lithium transition metal oxide is Li(Ni _x Co _y M _1-xy )O ₂ (M = any one or two or more elements selected from Mn, Al, Y, Ti, Zr, etc.) will include

In the above formula, x and y represent the molar ratio of each element in the nickel-based lithium transition metal oxide.

In this case, 0 < x < 1, 0 < y ≤ 0.35, 0 < x+y ≤ 1 may be.

For example, x = 0.8, y = 0.1.

For example, the nickel-based lithium transition metal oxide may include LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , and LiNi _0.5 Co _0.3 Mn _0.2 O ₂ . It can be selected from the group consisting of.

Nickel (Ni) is an element contributing to high potential and high capacity of the secondary battery, and an amount corresponding to x may be included in an amount of 0<x<1. When the value of x is 0, there is a fear that the charge/discharge capacity characteristics may be deteriorated, and if the value of x is greater than 1, there is a risk of deterioration of the structure and thermal stability of the active material, and consequent deterioration of the lifespan characteristics. Considering the effect of high potential and high capacity according to the control of the nickel content, the nickel may be more specifically included in an amount of 0.5≤x<1, and more specifically, 0.5≤x≤0.8.

Cobalt (Co) is an element contributing to improvement of charge/discharge cycle characteristics of the active material, and an amount corresponding to y may be included in an amount of 0 < y ≤ 0.35. When y = 0, there is a risk of a decrease in charge and discharge capacity due to a decrease in structural stability and a decrease in lithium ion conductivity. Considering the effect of improving the cycle characteristics of the active material according to the control of the cobalt content, the cobalt may be included in an amount of 0.1≤y<0.35, more specifically 0.1≤y≤0.3.

The positive electrode active material according to an embodiment of the present invention optionally further includes any one or two or more of these elements selected from Mn, Al, Y, Ti, Zr, etc., in order to improve battery characteristics through improvement of thermal/structural stability of the active material can do.

When the element M is further included, it may be included in the lithium composite metal oxide in an amount corresponding to 1-x-y, specifically, in an amount of 0<1-x-y≦0.2. When 1-x-y is more than 0.2, there is a fear that the charge/discharge capacity may be lowered due to the reduction of metal elements contributing to the redox reaction. In addition, in consideration of the significant improvement effect of the control of the substitution amount of element M included in the lithium composite metal oxide, 0<1-x-y≤0.05 or 0.01≤1-x-y≤0.05.

Manganese (Mn) is an element contributing to improving thermal stability of the active material, and may be included in an amount corresponding to 1-x-y.

Meanwhile, in the present invention, a part or all of the surface of the secondary particles is coated with a lithium phosphate compound.

The present inventors have invented secondary particles in which primary macro particles are aggregated, as described above. Through these secondary particles, high resistance and low output characteristics, which were problems in conventional single particles, were improved.

However, while continuing the research, the present inventors applied High-Ni NCM-based lithium composite transition metal oxide to secondary particles including primary large particles as in the case of secondary particles containing primary fine particles. In this case, it was found that there is a problem in that structural and chemical stability is lowered on the particle surface.

Specifically, the lithium phosphate compound on the surface of the positive electrode active material by mixing the NCM-containing precursor for forming lithium transition metal oxide and the lithium raw material and then under-calcining the cathode active material prepared by mixing with the raw material of the lithium phosphate compound and then heat-treating it. A coating layer may be formed.

In this case, the lithium phosphate compound may include a compound represented by Formula 1 below.

[Formula 1]

LiAPO ₄

In this case, A is any one selected from Ni, Co, Mn, Fe, and the like, or two or more of these elements.

Specifically, when the secondary particles are coated with a lithium phosphate compound, the secondary particles may include a coating layer including the lithium phosphate compound formed in whole or in part on the surface thereof.

The content of the elemental lithium phosphate compound included in the finally prepared positive active material, specifically, is determined within the range of 500 ppm to 10,000 ppm.

In one aspect of the present invention, the lithium phosphate compound has an operating voltage of 4.6V or more. That is, at an operating voltage of 4.3V or less of the secondary particles in one aspect of the present invention, it does not contribute to the electrochemical reaction. In other words, the lithium phosphate compound is in a deactivated state at an operating voltage of 4.3 V or less. Accordingly, by coating the lithium phosphate compound on the surface of the secondary particles as described above, high energy density and excellent stability may be satisfied. Specifically, it is applied to the surface of the secondary particles can reduce the interfacial side reaction with the electrolyte. In addition, it is possible to improve lithium ion conductivity and improve coulombic efficiency.

When the content of the lithium phosphate compound is less than 500 ppm, the structural stabilization effect due to the inclusion of element A is insignificant, and when the content of the lithium phosphate compound exceeds 10,000 ppm, there is a risk of a decrease in charge/discharge capacity and an increase in resistance due to an excess of element A. Considering the superiority of the improvement effect according to the element A content control, the element A may be coated in an amount of 1,000 to 2,000 ppm. When doping and surface coating are made within the above content range, the implementation effect according to the optimization of the position of element A can be further improved.

Meanwhile, in the present invention, the content of A in the lithium phosphate compound in the cathode active material may be measured using an inductively coupled plasma spectrometer (ICP).

Manufacturing method

The positive active material according to an aspect of the present invention may be manufactured by the following method. However, the present invention is not limited thereto.

Specifically, (S1) preparing a nickel-based lithium transition metal hydroxide precursor by mixing a transition metal-containing solution, ammonia-containing solution, and a basic aqueous solution containing nickel, cobalt and manganese;

(S2) mixing and heat-treating the nickel-based lithium transition metal hydroxide precursor and the lithium raw material to prepare secondary particles;

(S3) mixing the secondary particles with the raw material of the lithium phosphate compound and then heat-treating;

The positive active material is a positive active material for a lithium secondary battery comprising at least one secondary particle including an aggregate of primary macro particles,

The average particle diameter (D50) of the primary large particles is 1 μm or more,

Part or all of the secondary particle surface is coated with a lithium phosphate compound,

The secondary particles have an average particle diameter (D50) of 2.5 to 6 μm,

The cathode active material relates to a method of manufacturing a cathode active material for a lithium secondary battery, characterized in that it comprises a nickel-based lithium transition metal oxide.

A method of manufacturing the positive active material will be further described step by step.

First, a cathode active material precursor including nickel (Ni), cobalt (Co), and manganese (Mn) is prepared.

In this case, the precursor for preparing the positive electrode active material may be prepared by purchasing a commercially available positive electrode active material precursor or according to a method for preparing a positive electrode active material precursor well known in the art.

For example, the precursor may be prepared by adding an ammonium cation-containing complexing agent and a basic compound to a transition metal solution including a nickel-containing raw material, a cobalt-containing raw material, and a manganese-containing raw material, followed by a co-precipitation reaction.

The nickel-containing raw material may be, for example, nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, specifically, Ni(OH) ₂ , NiO, NiOOH, NiCO ₃ ㆍ 2Ni(OH) ₂ ㆍ4H ₂ O, NiC ₂ O ₂ ㆍ2H ₂ O, Ni(NO ₃ ) ₂ ㆍ6H ₂ O, NiSO ₄ , NiSO ₄ ㆍ6H ₂ O, fatty acid nickel salt, nickel halide or these It may be a combination, but is not limited thereto.

The cobalt-containing raw material may be cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and specifically, Co(OH) ₂ , CoOOH, Co(OCOCH ₃ ) ₂ ∙ 4H ₂ O , Co(NO ₃ ) ₂ ㆍ6H ₂ O, CoSO ₄ , Co(SO ₄ ) ₂ ㆍ7H ₂ O, or a combination thereof, but is not limited thereto.

The manganese-containing raw material may be, for example, manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof, specifically Mn ₂ O ₃ , MnO ₂ , Mn ₃ manganese oxides such as O ₄ ; manganese salts such as MnCO ₃ , Mn(NO ₃ ) ₂ , MnSO ₄ , manganese acetate, dicarboxylic acid manganese salt, manganese citrate, fatty acid manganese salt; It may be manganese oxyhydroxide, manganese chloride, or a combination thereof, but is not limited thereto.

The transition metal solution includes a nickel-containing raw material, a cobalt-containing raw material, and a manganese-containing raw material in a solvent, specifically water, or a mixed solvent of an organic solvent that can be uniformly mixed with water (eg, alcohol). It may be prepared by adding, or may be prepared by mixing an aqueous solution of a nickel-containing raw material, an aqueous solution of a cobalt-containing raw material, and a manganese-containing raw material.

The ammonium cation-containing complexing agent may be, for example, NH ₄ OH, (NH ₄ ) ₂ SO ₄ , NH ₄ NO ₃ , NH ₄ Cl, CH ₃ COONH ₄ , NH ₄ CO ₃ or a combination thereof, However, the present invention is not limited thereto. On the other hand, the ammonium cation-containing complexing agent may be used in the form of an aqueous solution, and as the solvent, water or a mixture of water and an organic solvent that is uniformly miscible with water (specifically, alcohol, etc.) and water may be used.

The basic compound may be a hydroxide of an alkali metal or alkaline earth metal such as NaOH, KOH or Ca(OH) ₂ , a hydrate thereof, or a combination thereof. The basic compound may also be used in the form of an aqueous solution, and as the solvent, water or a mixture of water and an organic solvent that is uniformly miscible with water (specifically, alcohol, etc.) and water may be used.

The basic compound is added to adjust the pH of the reaction solution, and may be added in an amount such that the pH of the metal solution is 9 to 12.

Thereafter, a porous nickel-based lithium transition metal hydroxide precursor may be prepared by mixing a precursor containing nickel, cobalt, and manganese and a hydroxide.

At this time, the co-precipitation reaction may be carried out at a temperature of 25 °C to 60 °C under an inert atmosphere such as nitrogen or argon.

Accordingly, a porous nickel-based lithium transition metal hydroxide precursor may be prepared by mixing a hydroxide and a precursor containing nickel, cobalt and manganese (S1).

By the above process, particles of nickel-cobalt-manganese hydroxide are generated and precipitated in the reaction solution. By controlling the concentrations of the nickel-containing raw material, the cobalt-containing raw material, and the manganese-containing raw material, a precursor having a nickel (Ni) content of 60 mol% or more among the total metal content can be prepared. The precipitated nickel-cobalt-manganese hydroxide particles may be separated according to a conventional method and dried to obtain a nickel-cobalt-manganese precursor. The precursor may be secondary particles formed by agglomeration of primary particles.

Thereafter, the precursor and the lithium raw material are mixed and heat-treated (primary firing) (S2).

The lithium raw material may include lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide, and is not particularly limited as long as it can be dissolved in water. Specifically, the lithium raw material is Li ₂ CO ₃ , LiNO ₃ , LiNO ₂ , LiOH, LiOH•H2O, LiH, LiF, LiCl, LiBr, LiI, CH ₃ COOLi, Li ₂ O, Li ₂ SO ₄ , CH ₃ COOLi , or Li ₃ C ₆ H ₅ O ₇ and the like, and any one or a mixture of two or more thereof may be used.

The primary sintering may be sintered at 700 to 950° C., more preferably 780 to 950° C. in the case of a high-Ni NCM-based lithium composite transition metal oxide having a nickel (Ni) content of 60 mol% or more. It may be calcined at 930°C, more preferably at 780 to 900°C. The primary firing may be carried out in an air or oxygen atmosphere, and may be performed for 15 to 35 hours.

Next, after the primary sintering, an additional heat treatment (second sintering) may be performed after mixing the raw materials of the lithium phosphate compound (S3).

The secondary sintering may be performed at 600 to 800° C., more preferably from 630 to 800° C., in the case of a high-Ni NCM-based lithium composite transition metal oxide having a nickel (Ni) content of 60 mol% or more. It can be fired at 730°C and more preferably at 600 to 700°C. The secondary sintering may be performed under an air or oxygen atmosphere, and may be performed for 10 to 24 hours.

On the other hand, it is characterized in that a separate washing process is not included between the step (S2) and the step (S3). In this case, the total amount of lithium remaining on the particle surface after the first firing may be 0.5 to 1.5 wt% based on the total weight of the positive active material. In the past, it went through a process of washing lithium by-products existing on the surface of the positive electrode active material. This is because, when lithium by-products are present, there are problems such as a side reaction with an electrolyte when applied to a battery and an increase in the amount of gas generated when stored at a high temperature. On the other hand, in the manufacturing method according to an aspect of the present invention, a separate washing process is not performed. Accordingly, lithium by-product is present on the particle surface, and when the lithium by-product is 0.5 to 1.5 wt % based on the total weight of the positive active material, the secondary particle aggregate including the primary large particle according to an aspect of the present invention is provided One positive electrode active material can be manufactured.

Positive electrode and lithium secondary battery

According to another embodiment of the present invention, there is provided a positive electrode for a lithium secondary battery and a lithium secondary battery including the positive electrode active material.

Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

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

The positive active material layer may include a conductive material and a binder together with the above-described positive active material.

In this case, the conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it has electronic conductivity without causing chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one or a mixture of two or more thereof may be used. The conductive material may be included in an amount of 1 to 30% by weight based on the total weight of the positive active material layer.

In addition, the binder serves to improve adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC) ), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used. The binder may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the above positive electrode active material. Specifically, it may be prepared by applying the above-described positive electrode active material and, optionally, a composition for forming a positive electrode active material layer including a binder and a conductive material on a positive electrode current collector, followed by drying and rolling. In this case, the types and contents of the positive electrode active material, the binder, and the conductive material are as described above.

The solvent may be a solvent generally used in the art, dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropyl alcohol), N-methylpyrrolidone (NMP), acetone (acetone) or water, and the like, and any one of them or a mixture of two or more thereof may be used. The amount of the solvent used is enough to dissolve or disperse the positive electrode active material, the conductive material and the binder in consideration of the application thickness of the slurry and the production yield, and to have a viscosity capable of exhibiting excellent thickness uniformity when applied for the production of the positive electrode thereafter. Do.

Alternatively, the positive electrode may be manufactured by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating a film obtained by peeling it from the support on the positive electrode current collector.

According to another embodiment of the present invention, an electrochemical device including the positive electrode is provided. The electrochemical device may specifically be a battery or a capacitor, and more specifically, may be a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned to face the positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the positive electrode is as described above. In addition, the lithium secondary battery may optionally further include a battery container for accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

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

The anode active material layer optionally includes a binder and a conductive material together with the anode active material. The anode active material layer may be formed by applying a composition for forming an anode including an anode active material and, optionally, a binder and a conductive material on an anode current collector and drying, or casting the composition for forming a cathode on a separate support, and then , may be produced by laminating a film obtained by peeling from this support onto a negative electrode current collector.

As the anode 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; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; Alternatively, a composite including the metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite may be used, and any one or a mixture of two or more thereof may be used. In addition, a metal lithium thin film may be used as the negative electrode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. As low crystalline carbon, soft carbon and hard carbon are representative, and as high crystalline carbon, natural or artificial graphite of amorphous, plate-like, scale-like, spherical or fibrous shape, and Kish graphite graphite), pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitches (Mesophase pitches), and petroleum and coal tar pitch (petroleum or coal tar pitch) High-temperature calcined carbon such as derived cokes) is a representative example.

In addition, the binder and the conductive material may be the same as those described above for the positive electrode.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for the movement of lithium ions, and can be used without particular limitation as long as it is usually used as a separator in a lithium secondary battery, especially for the movement of ions in the electrolyte It is preferable to have a low resistance to respect and an excellent electrolyte moisture content. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer and ethylene/methacrylate copolymer, or these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, and the like, which can be used in the manufacture of lithium secondary batteries, and are limited to these. it is not going to be

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C ₂ to C ₂₀ linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Or sulfolane (sulfolane) may be used. Among them, a carbonate-based solvent is preferable, and a cyclic carbonate (eg, ethylene carbonate or propylene carbonate, etc.) having a high dielectric constant capable of increasing the charge/discharge performance of the battery and a low-viscosity linear carbonate-based compound (eg, ethyl A mixture of methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ )2 , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ , etc. may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has appropriate conductivity and viscosity, excellent electrolyte performance may be exhibited, and lithium ions may move effectively.

In the electrolyte, in addition to the electrolyte components, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, tri Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as jolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included. 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.

As described above, the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and capacity retention rate, so portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful in the field of electric vehicles such as hybrid electric vehicle and HEV).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or battery pack is a power tool (Power Tool); electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for any one or more medium-to-large devices in a system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein.

Comparative Example 1.

After adding 4 liters of distilled water to the coprecipitation reactor (capacity 20L), maintaining the temperature at 50° C., NiSO ₄ , CoSO ₄ , MnSO ₄ 3.2 mol/ The L-concentration transition metal solution was continuously introduced into the reactor at 300 mL/hr and 28 wt% of an aqueous ammonia solution at 42 mL/hr. The speed of the impeller was stirred at 400 rpm, and a 40 wt% sodium hydroxide solution was used to maintain pH 9 to maintain pH. The precursor particles were formed by co-precipitation reaction for 10 hours. The precursor particles were separated, washed, and dried in an oven at 130° C. to prepare a precursor.

The Ni _0.8 Co _0.1 Mn _0.1 (OH) ₂ precursor synthesized by the coprecipitation reaction was mixed with Li ₂ CO ₃ and Li/Me (Ni, Co, Mn) so that the molar ratio was 1.05, followed by heat treatment at 850° C. in an oxygen atmosphere for 10 hours to form LiNi _0.8 Co _0.1 Mn _0.1 O ₂ A positive electrode active material including secondary nickel-based lithium transition metal oxide particles was prepared.

Example 1.

LiCoPO ₄ was coated on the secondary particles prepared in Comparative Example 1 using a sol-gel method. Specifically, it was prepared in the following way.

C ₂ H ₃ LiO _2· 2H ₂ O, C ₄ H ₆ CoO _4· 4H ₂ O, and NH ₄ H ₂ PO ₄ were dissolved in distilled water at a quantitative ratio to prepare a solution. To the stirring solution, C ₆ H ₈ O _7· H ₂ O was slowly added dropwise in an appropriate amount. The solution was stirred at 80°C until it turned into a gel. The LiNi0.8Co0.1Mn0.1O2 positive electrode active material was weighed so that the LiCoPO ₄ /LiNi _0.8 Co _0.1 Mn _0.1 O ₂ weight ratio was 0.05 wt%, and then added to a stirring gel, and further stirred for a certain time to prepare a mixture. The mixture was dried in an oven at 130° C. and then heat treated at 650° C. in an air atmosphere for 10 hours to prepare a LiNi _0.8 Co _0.1 Mn _0.1 O ₂ positive electrode active material coated with LiCoPO ₄ , a lithium phosphate compound, in 0.05 wt%. The average crystal size of the primary particles was 250 nm.

Example 2.

A cathode active material was prepared in the same manner as in Example 1, except that the coating amount of LiCoPO ₄ was 0.10 wt%.

Example 3.

A cathode active material was prepared in the same manner as in Example 1, except that the coating amount of LiCoPO ₄ was 0.30 wt%.

division Comparative Example 1 Example 1 Example 2 Example 3 45 °C;
100 cycle unit Bare LiCoPO ₄ 500 ppm 1000 ppm 3000 ppm Average particle diameter of primary particles (D50) μm 2.62 2.74 2.74 2.74 Average particle diameter of secondary particles (D50) μm 3.7 3.7 3.7 3.8 Capacity retention rate % 92.5 93.2 94.1 93.9 DCIR 120 113 95 101

[Experimental Example 1: Comparison of Residual Capacity of 100 Charge/Discharge Battery According to Composition]

Using the positive active material according to Examples 1 to 3 and Comparative Example 1, capacity retention was measured in the following manner.

Each of the positive electrode active material, carbon black conductive material, and PVdF binder prepared in Examples and Comparative Examples was mixed in an N-methylpyrrolidone solvent in a weight ratio of 96:2:2 to prepare a positive electrode mixture, which was then used as an aluminum current collector. After coating on one surface of the, dried at 100 ℃, and rolled to prepare a positive electrode.

Graphite was used for the negative electrode.

An electrode assembly was prepared by interposing a separator of porous polyethylene between the positive electrode and the negative electrode prepared as described above, the electrode assembly was placed inside the case, and the electrolyte was injected into the case to prepare a lithium secondary battery. At this time, the electrolyte solution is obtained by dissolving lithium hexafluorophosphate (LiPF6) at a concentration of 1.0M in an organic solvent consisting of ethylene carbonate/ethylmethyl carbonate/diethyl carbonate/(mixed volume ratio of EC/EMC/DEC=3/4/3). prepared.

The prepared lithium secondary battery full cell was charged at 45° C. in CC-CV mode at 0.5 C until 4.2 V, and discharged to 2.5 V at a constant current of 1 C to conduct 100 charge/discharge experiments. When the capacity retention rate was measured, the lifespan characteristics were evaluated. The results are shown in Table 1 above.

[Experimental Example 2: Observation of positive electrode active material]

The positive active materials prepared in Comparative Example 1 and Examples 1 to 3 were magnified and observed with a scanning electron microscope (SEM). A photograph according to Comparative Example 1 is shown in FIGS. 1 (a) and 1 (b).

[Experimental Example 3: Average particle size]

D50 is a volume accumulation amount in a measuring device after dispersing particles of a positive active material in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (eg, Microtrac MT 3000), irradiating an ultrasonic wave of about 28 kHz with an output of 60 W The average particle diameter (D50) corresponding to 50% of the was calculated.

[Experimental Example 4: Resistance Measurement Method]

The lithium secondary battery prepared as in Experimental Example 1 using the positive electrode active material of Examples 1 to 3 and Comparative Example 1 was subjected to constant current discharge for 10 seconds at 25° C. and 100% SOC at 1.0 C using the measured voltage drop. The resistance was calculated and compared, and the results are shown in Table 1 above.

[Experimental Example 5: Crystal Size of Primary Particles]

Using a Bruker Endeavor (Cu Kα, λ=1.54 Å) equipped with LynxEye XE-T potision sensitive detector, FDS 0.5°, 2-theta 15° to 90° step size 0.02° for total scan time (total scan time) time) was measured so that the sample was 20 minutes.

For the measured data, Rietveld refinement was performed considering the charge (+3 for metals at the transition metal site, +2 for Ni at the Li site) and cation mixing at each site. When analyzing crystallite size, instrumental bradening was considered using the Fundemental Parameter Approach (FPA) implemented in the Bruker TOPAS program, and the entire peak of the measurement range was used for fitting. The peak shape is used in TOPAS. Among the possible peak types, only Lorenzian contribution was used as the FP (First Principle) for fitting, and strain was not considered at this time.

Claims (15)

A cathode active material for a lithium secondary battery comprising at least one secondary particle including an aggregate of primary macro particles,
The average particle diameter (D50) of the primary large particles is 1 μm or more,
Part or all of the secondary particle surface is coated with a lithium phosphate compound,
The secondary particles have an average particle diameter (D50) of 2.5 to 6 μm,
The positive active material is a positive active material for a lithium secondary battery, characterized in that it comprises a nickel-based lithium transition metal oxide.
According to claim 1,
The lithium phosphate compound is a positive active material for a lithium secondary battery, characterized in that it comprises a compound represented by the following formula (1):
[Formula 1]
LiAPO ₄
In this case, A is any one selected from the group consisting of Ni, Co, Mn and Fe, or two or more of these elements.
The method of claim 1,
The nickel-based lithium transition metal oxide is Li (Ni _x Co _y M _1-xy )O ₂ (M = Mn, Al, Y, Ti and Zr any one selected from the group consisting of, or two or more of these elements ) A cathode active material for a lithium secondary battery, characterized in that it comprises a.
The method of claim 1,
The positive active material for a lithium secondary battery, characterized in that the ratio of the average particle diameter (D50) of the primary large particles to the average crystal size of the primary large particles is 2 or more.
The method of claim 1,
The cathode active material for a lithium secondary battery, characterized in that the coating amount of the lithium phosphate compound is 10,000 ppm or less.
The method of claim 1,
The positive active material for a lithium secondary battery, characterized in that the average crystal size of the primary large particles is 150 nm or more.
The method of claim 1,
A positive active material for a lithium secondary battery, characterized in that the ratio of the average particle diameter (D50) of the secondary particles to the average particle diameter (D50) of the primary large particles is 2 to 5 times.
The method of claim 1,
The cathode active material is a cathode active material for a lithium secondary battery, characterized in that the primary large particles are separated from the secondary particles during rolling, and the primary large particles themselves are not broken.
A positive electrode for a lithium secondary battery comprising the positive active material according to claim 1 .
A lithium secondary battery comprising the positive active material according to claim 1 .
(S1) preparing a nickel-based lithium transition metal hydroxide precursor by mixing a transition metal-containing solution containing nickel, cobalt and manganese, an ammonia-containing solution, and a basic aqueous solution;
(S2) mixing and heat-treating the nickel-based lithium transition metal hydroxide precursor and the lithium raw material to prepare secondary particles;
(S3) mixing the secondary particles with the raw material of the lithium phosphate compound and then heat-treating;
The positive active material is a positive active material for a lithium secondary battery comprising at least one secondary particle including an aggregate of primary macro particles,
The average particle diameter (D50) of the primary large particles is 1 μm or more,
Part or all of the secondary particle surface is coated with a lithium phosphate compound,
The secondary particles have an average particle diameter (D50) of 2.5 to 6 μm,
The cathode active material is a method of manufacturing a cathode active material for a lithium secondary battery, characterized in that it comprises a nickel-based lithium transition metal oxide.
12. The method of claim 11,
The step (S1) is carried out at 25 to 60 ℃,
The step (S2) is carried out at 700 to 950 ℃,
The (S3) step is a method for producing a cathode active material, characterized in that it is carried out at 600 to 800 ℃.
12. The method of claim 11,
The raw material of the lithium phosphate compound is a method for producing a cathode active material for a lithium secondary battery, characterized in that it comprises a compound represented by the following formula (1):
[Formula 1]
LiAPO4
In this case, A is any one selected from the group consisting of Ni, Co, Mn and Fe, or two or more of these elements.
12. The method of claim 11,
The step (S1) is a method for producing a cathode active material, characterized in that it is carried out at a pH of 9 to 12 conditions.
12. The method of claim 11,
In the step (S3), the raw material of the lithium phosphate compound,
C ₂ H ₃ LiO _2· 2H ₂ O, C ₄ H ₆ CoO _4· 4H ₂ O, NH ₄ H ₂ PO ₄ Addition and gelation of C ₆ H ₈ O _7· H ₂ O while stirring the aqueous solution A method of manufacturing a positive electrode active material, characterized in that.

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