KR20220061035A - 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, provided is a positive electrode active material including secondary particles with improved surface resistance compared to a case of applying existing single particles. According to one embodiment of the present invention, provided is a nickel-based positive electrode active material with increased rolling strength and increased energy density of the positive electrode active material.

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 intercalated/deintercalated from the positive electrode and the negative electrode. The conversion of electrical energy and chemical energy occurs by a reduction reaction with

As a cathode 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. were 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.

Meanwhile, in most cases, two types of positive electrode active materials having different sizes are used to increase output and rolling density. In this case, the positive electrode active material may be secondary particles formed by gathering primary particles. However, in the case of configuring the positive electrode using secondary particles formed by collecting existing primary fine particles, the particles are broken during rolling or internal voids are generated to reduce the density or increase the rolling density due to surface roughness. There were limits. Accordingly, in order to improve the energy density of the anode, it is necessary to develop a cathode material having a higher density under the same pressure condition.

An object of the present invention is to solve the above problems, and to provide a positive electrode active material capable of minimizing particle breakage during rolling by controlling particle size and shape.

Accordingly, the rolling strength of the positive electrode active material is increased, and as a result, a nickel-based positive electrode active material having an increased energy density is provided.

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

It is a positive electrode active material for a lithium secondary battery comprising a first positive electrode active material of large particles and a second positive electrode active material of small particles,

The first positive active material includes at least one secondary large particle including an aggregate of primary micro particles,

The second positive active material includes at least one secondary small particle including an aggregate of primary macro particles,

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

The weight ratio of the first positive active material to the second positive active material is 75: 25 to 90: 10,

It relates to a positive active material for a lithium secondary battery, characterized in that the particle strength of the second positive active material is smaller than the particle strength of the first positive active material.

In the second embodiment, according to the first embodiment,

It relates to a positive active material for a lithium secondary battery, characterized in that the second positive active material is broken before the first positive active material during rolling.

A third embodiment, according to any one of the preceding embodiments,

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

The ratio of the average particle diameter (D50) of the primary large particles to the average crystal size of the primary large particles is 3 or more.

A fourth embodiment, according to any one of the preceding embodiments,

The first positive electrode active material has an average particle diameter (D50) of 10 μm to 20 μm.

A fifth embodiment, according to any one of the preceding embodiments,

The second positive electrode active material has an average particle diameter (D50) of 3 μm to 6 μm.

A sixth embodiment, according to any one of the preceding embodiments,

The average particle diameter (D50) of the primary fine particles of the first positive electrode active material relates to a positive electrode active material for a lithium secondary battery, characterized in that 0.1 μm to 0.5 μm.

A seventh embodiment, according to any one of the preceding embodiments,

The second positive electrode active material relates to a positive electrode active material for a lithium secondary battery, characterized in that the primary large particles fall off when the secondary small particles are rolled, and the primary large particles themselves are not broken.

An eighth embodiment, according to any one of the preceding embodiments,

The rolling relates to a positive electrode active material for a lithium secondary battery, characterized in that the porosity of the positive electrode including the positive electrode active material is 15 to 30%.

A ninth embodiment, according to any one of the preceding 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 tenth embodiment, according to any one of the preceding embodiments,

The ratio of the average particle diameter (D50) of the secondary small particles to the average particle diameter (D50) of the primary large particles is 2 to 4 times.

An eleventh embodiment, according to any one of the preceding embodiments,

The first and second positive electrode active materials relate to a positive electrode active material for a lithium secondary battery, characterized in that it includes a nickel-based lithium transition metal oxide.

The twelfth embodiment, according to the eleventh embodiment,

The nickel-based lithium transition metal oxide is, Li _(1+a) Ni _{(1-(a+x+y+w))} Co _x M1 _y M2 _w O ₂ (0≤a≤0.5, 0≤x≤0.35, 0≤y≤0.35, 0≤w≤0.1, 0≤a+x+y+w≤0.7, M1 is at least one selected from the group consisting of Mn and Al, and M2 is Ba, Ca, Zr, Ti, Mg , Ta, Nb, and at least one selected from the group consisting of Mo) relates to a positive electrode active material for a rechargeable lithium battery, characterized in that it contains.

A thirteenth embodiment, according to any one of the preceding embodiments,

The positive active material relates to a positive active material for a lithium secondary battery, characterized in that the angle of repose is less than 50 °.

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

A fourteenth embodiment provides a positive electrode for a lithium secondary battery comprising 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 fifteenth embodiment provides a lithium secondary battery including the positive electrode active material according to any one of the above embodiments.

According to an embodiment of the present invention, as compared to the case of using secondary particles having a large particle diameter and secondary particles having a small diameter in a bimodal manner, the amount of particle breakage or fine powder generation during rolling can be significantly suppressed. can

According to an embodiment of the present invention, it is possible to provide a positive electrode active material having an increased energy density.

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.
1 is a SEM image of a cross-section of an electrode to which a positive active material according to Comparative Example 1 is applied.
FIG. 2 is an SEM image of a cross-section of an electrode to which a positive active material according to Example 1 of the present invention is applied.

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 their ordinary 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. Accordingly, the configuration described in the embodiments described in the present specification is only the most preferred embodiment of the present invention and does not represent all the technical spirit 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. 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.

For example, it can be analyzed as follows.

First, for sampling, place a sample in a groove in the middle of a general powder holder, use a slide glass to make the surface even, and prepare the height equal to the edge of the holder. Using a Bruker D8 Endeavor (Cu Kα, λ= 1.54 Å) equipped with LynxEye XE-T position sensitive detector, FDS 0.5°, 2-theta 15° to 90° step size 0.02°, total scan time is ~20 Measure the sample in minutes. For the measured data, Rietveld refinement is performed considering charge (+3 for metals at transition metal site, +2 for Ni at Li site) and cation mixing at each site. When analyzing crystallite size, instrumental broadening is considered using the Fundamental Parameter Approach (FPA) implemented in the Bruker TOPAS program, and the entire peaks of the measurement range are used during fitting. The peak shape was fitted using only Lorenzian contribution as FP (First Principle) among the peak types available in TOPAS, and strain was not considered at this time. Structural analysis was performed through the above method, and the average crystal size of grains can be quantitatively analyzed.

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, secondary particles may be classified into secondary large particles and secondary small particles according to an average particle diameter (D50).

Meanwhile, the secondary large particle may be referred to as a secondary large particle. Here, the secondary particle large particle is a particle formed by aggregation of tens to hundreds of primary micro particles. Secondary particles Small particles exist as a concept in contrast to large particles. Here, the secondary particle small particle is a particle formed by aggregation of several tens to hundreds of primary micro particles. The average particle diameter (D50) of the large secondary particles is larger than the average particle diameter (D50) of the small secondary particles.

On the other hand, the secondary small particle referred to in the present invention is different from the above-described large secondary particle and/or secondary particle small particle. That is, the secondary small particles in one aspect of the present invention are particles formed by agglomeration of preferably about 10 primary micro particles.

Secondary particles formed by agglomeration of primary fine particles Large secondary particles/ When comparing small secondary particles and secondary small particles formed by agglomeration of primary large particles, secondary particles formed by aggregation of primary large particles are more have a smooth surface.

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

A cathode active material used in a lithium secondary battery is mostly used by mixing two types of particles having different particle size distributions in order to improve energy density per volume. For example, when a large particle positive active material and a small particle positive active material are used in an appropriate ratio, the bimodal effect causes a higher density than the value calculated arithmetically from the density values of large and small particles under the same pressure condition. do.

This bimodal effect appears as a density increase as small particles fill the space between large particles and large particles. For this, the particles must be able to move smoothly in the state of contact between the particles so that the empty space can be filled when pressure is applied to the mixture of large and small particles. When secondary particles formed by aggregation of primary fine particles are compared with secondary particles formed by agglomeration of primary large particles, secondary particles formed by agglomeration of primary large particles have a smoother surface. In the case of a large-particle/small-particle mixed bimodal positive electrode active material composed only of secondary particles formed by aggregation of primary fine particles, the frictional force between particles is high due to the roughness of the particle surface during rolling. This will cause particle breakage. When particle breakage occurs, particle movement may occur at the same time, but the frictional force between the particles is still high. On the other hand, when the primary large particles are replaced by small particles with agglomerated secondary particles, the surface of the secondary large particles is rough, but the friction force with the surface in contact with the small particles is relatively low, so that the pressure applied during rolling is reduced. It facilitates particle movement, reduces particle breakage, and makes it possible to exhibit high rolling densities. Even if the rolling is continuously increased and small particles are broken due to this, the broken surface is still smooth and the subsequent additional pressure causes particle movement, preventing additional particle breakage and improving the density.

In one aspect of the present invention, there is provided a positive electrode active material including a secondary particle shape different from the conventional one.

Specifically,

It is a positive electrode active material for a lithium secondary battery comprising a first positive electrode active material of large particles and a second positive electrode active material of small particles,

The first positive active material includes at least one secondary large particle including an aggregate of primary micro particles,

The second positive active material includes at least one secondary small particle including an aggregate of primary macro particles,

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

The weight ratio of the first positive active material to the second positive active material is 75: 25 to 90: 10,

It is a positive electrode active material for a lithium secondary battery, characterized in that the particle strength of the second positive electrode active material is smaller than the particle strength of the first positive electrode active material.

The positive active material may provide a nickel-based positive active material having improved rolling density and increased energy density by having the above characteristics. In addition, it is possible to provide a positive electrode active material having a reduced rate of generation of fine powder during rolling.

Hereinafter, the characteristics of the first and second particles will be described in detail.

Secondary small particles in which the primary large particles are aggregated and small particles comprising the secondary small particles Second positive active material

In one aspect of the present invention, in order to solve the above-described problem, the primary large particles include secondary particles agglomerated. In the existing secondary particles, tens to hundreds of primary fine particles are aggregated to form secondary particles. On the other hand, in one aspect of the present invention, the primary large particles having an average particle diameter (D50) of 1 μm or more are preferably aggregated within 1 to 10 to constitute secondary small particles.

The present inventors have discovered that, in the case of mixing the existing large secondary particles and small secondary particles, cracking of the secondary particles occurs during the rolling process and there is a problem in that the electrochemical properties are inferior. At this time, the existing large secondary particles and small secondary particles are secondary particles formed by aggregation of tens to hundreds of primary fine particles, but with a large average diameter (D50), “large secondary particles” , the case where the average diameter (D50) is small is referred to as “small secondary particles”.

On the other hand, in one aspect of the present invention, by mixing the “secondary small particles in which the primary large particles are aggregated” with the existing “large secondary particles” in an appropriate ratio, cracking in the rolling process can be suppressed. This is because, when the secondary small particles according to the present invention are mixed with the existing secondary large particles, the press density of the secondary small particles is relatively high, so that the secondary large particles at the same rolling density for the entire mixed positive electrode active material. This appears to be due to the reduced stress on the particles. In addition, the surface of the secondary small particle according to the present invention is smoother than the conventional secondary particle small particle, and thus it seems to effectively exhibit a bimodal effect when mixed with the secondary large particle.

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 a ratio of average particle diameter (D50)/average crystal size of 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 that grain boundaries exist and do not exist, but have a large average particle diameter like the conventional single particles. However, when the existing single particles are mixed with the existing secondary particle type particles and used, there may be a problem in that the secondary particle type cathode active material is broken first during rolling. In addition, in order to make a shape with a large average particle diameter without apparent grain boundaries, the calcination temperature is higher than that of the existing secondary particle type. found To solve these two problems, a cathode active material in the form of secondary particles in which primary large particles are agglomerated by firing at a temperature slightly lower than the conventional single particle firing conditions was developed. That is, in the present invention, the primary large particles refer to particles having a larger average crystal size as well as an average particle diameter as compared to a positive electrode active material in the form of a conventional secondary particle, and having no apparent grain boundaries.

As such, in the case of producing a cathode active material in the form of secondary particles in which primary large particles are aggregated by sintering at a temperature slightly lower than the existing single-particle sintering conditions, rock salt is formed on the surface due to sintering at high temperature, resulting in a large increase in resistance. Compared to the conventional single particles, the surface resistance is lowered and it is advantageous in terms of long life.

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. For example, it can be analyzed by the method described above.

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.

Meanwhile, in the present invention, the secondary small particles are preferably 1 to 10 aggregated primary large particles described above. The secondary small particles are different from the conventional method for obtaining single particles in the following points.

As for the existing single particles, single particles were formed by increasing only the primary firing temperature by using the existing precursor for secondary particles as it is. On the other hand, in the secondary small particles according to an aspect of the present invention, a precursor having a high porosity is used separately. Accordingly, the primary large particles having a large particle size may be grown without raising the firing temperature, while the average diameter of the secondary small particles may be relatively small compared to the conventional ones.

Accordingly, the secondary small particles according to an aspect of the present invention have a large average diameter (D50) of the primary particles while having the same or similar average particle diameter (D50) as before. 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.

In a specific embodiment of the present invention, the secondary small particles may be agglomerated 1 to 10 or less of the primary large particles. More specifically, the secondary small particles may be one or more, two or more, three or more, or four or more aggregates of the primary large particles, and within the numerical range, the primary large particles are 10 It may be an aggregate of no more than 9 pieces, no more than 8 pieces, or no more than 7 pieces.

In the present invention, the secondary small particles have a large average diameter (D50) of the primary large particles while having the same or similar average particle diameter (D50) as before. In other words, unlike the conventional positive electrode active material, in which primary fine particles with small average particle diameters gather to form secondary particles, the secondary particle form in which primary large particles of increased primary particle size are aggregated to provide.

The secondary small particles according to an aspect of the present invention have an average diameter (D50) of 3 μm to 6 μm. More specifically, it is 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 small 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 sintering temperature higher than in the prior art, whereas the secondary small particles can grow relatively less than before.

Accordingly, the secondary small particles according to one aspect of the present invention have the same or similar average diameter (D50) to the conventional secondary particles, and have larger average diameter and average crystal size than the conventional primary fine particles. consists of

In a specific embodiment of the present invention, the ratio of the average particle diameter (D50) of the secondary small particles to the average particle diameter (D50) of the primary large particles may be 2 to 4 times.

In the present invention, the second positive electrode active material of small particles means including the above-described secondary small particles. In this case, the second positive active material may be one in which the primary large particles fall off when the secondary small particles are rolled, and the primary large particles themselves are not broken. The rolling condition may be a condition in which the cathode active material is manufactured as an electrode and rolled to a level of 15 to 30% porosity. For example, the rolling condition may be to apply a pressure of 9 tons or more. More specifically, it may be to press 9 ton

Secondary large particles in which primary fine particles are aggregated and large-particle first positive electrode active material comprising the secondary large particles

In one aspect of the present invention, it further includes a secondary large particle in addition to the secondary small particle described above.

In this case, the secondary large particles are in the form of agglomerated primary fine particles. For example, the primary fine particles may be in the form of agglomerated tens to hundreds. In other words, in the present invention, the “secondary large particle” is the same concept as the aforementioned “secondary large particle”.

In a specific embodiment of the present invention, the average diameter (D50) of the secondary large particles is 10 μm to 20 μm. When the average diameter (D50) of the secondary large particles is less than 10 μm, the particle breakage of the secondary large particles may be increased. More specifically, it is 10 μm or more, 12 μm or more, or 14 μm or more, and is 20 μm or less, 18 μm or less, or 16 μm or less.

In a specific embodiment of the present invention, the average particle diameter (D50) of the primary fine particles is 0.1 μm to 0.5 μm. More specifically, it may be 0.1 μm or more, 0.2 μm or more, or 0.3 μm or more, and may be 0.5 μm or less, or 0.4 μm or less.

On the other hand, the particle strength of the second positive active material is smaller than the particle strength of the first positive electrode active material.

The inventors of the present invention found that compared to the case of mixing the existing large secondary particles (secondary large particles) and the existing small secondary particles, the existing large secondary particles (secondary large particles) and the 2 It was found that when small tea grains were mixed, grain breakage during rolling was reduced.

In the case of the conventional large-particle/small-particle mixed bimodal positive electrode active material composed only of secondary particles formed by agglomeration of primary fine particles, there was a problem in that the surface roughness of the particles during rolling was large, so that the friction force between the particles was high. Due to this, the pressure applied during rolling was caused by particle cracking, not particle packing due to particle movement. Although particle movement may occur even when particle breakage occurs, particle breakage with additional pressure being applied frequently occurs due to still high frictional force between particles. Accordingly, there is a limit in increasing the packing of the electrode.

On the other hand, as in one aspect of the present invention, when the secondary large particles (secondary large particles) and the secondary small particles are mixed, the surface of the secondary large particles is rough as before, but with the secondary small particles The frictional force of the contacting surfaces is relatively reduced. Accordingly, the pressure applied during electrode rolling facilitates particle movement, thereby reducing particle breakage and exhibiting high rolling density. Even if the rolling is continuously increased and additional pressure is generated, only the secondary small particles themselves are broken, and the primary large particles separated from the secondary small particles are not broken. In addition, since the broken side of the secondary small particles is still smooth, the subsequent additional pressure only causes particle movement and particle breakage is reduced. Accordingly, the rolling density may be increased.

In addition, looking at the aspect of the primary particles, in the case of the primary fine particles constituting the existing secondary particles small particles, further breakage may occur. On the other hand, after the secondary small particles referred to in the present invention are separated into primary large particles, additional fine powder formation does not appear. That is, the formation of fine powder of the positive electrode is suppressed as a whole. In order to exhibit this effect, the secondary small particles of the present invention should be aggregates composed of less than 10 primary large particles, and should not be simply single particles composed of one mass.

content and proportion

In the positive active material according to an aspect of the present invention, the ratio of the average particle diameter (D50) of the first positive active material / the average particle diameter (D50) of the second positive active material is 2 or more, and the first positive active material and the first positive active material 2 The weight ratio of the positive active material is 75:25 to 90:10. More specifically, the weight ratio of the first positive active material to the second positive active material may be 75:25 to 90:10, for example, 80:20 or 85:15, or 90:10.

Furtherance

The secondary large particles and/or secondary small particles include nickel-based lithium transition metal oxide.

At this time, the nickel-based lithium transition metal oxide is, Li _(1+a) Ni _{(1-(a+x+y+w))} Co _x M1 _y M2 _w O ₂ (here, 0≤a≤0.5, 0≤x≤0.35, 0≤y≤0.35, 0≤w≤0.1, 0≤a+x+y+w≤0.7, M1 is at least one selected from the group consisting of Mn and Al, M2 is Ba, Ca , Zr, Ti, Mg, Ta, at least one selected from the group consisting of Nb and Mo) may include.

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

At this time, the doped metals M1 and M2 in the crystal lattice of the secondary particles may be located only on a part of the surface of the particle according to the position preference of the element M1 and/or the element M2, and the concentration decreases from the particle surface to the particle center It may be positioned with a gradient, or it may be uniformly present throughout the particle.

When the secondary particles are doped or coated and doped with metals M1 and M2, in particular, the long life characteristics of the active material may be further improved by stabilizing the surface structure.

Method for manufacturing cathode active material

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, it may be formed by preparing the first positive active material and the second positive active material, respectively, and then mixing.

For example, the first positive active material and the second positive active material may be manufactured by the following method.

Specifically, the method comprising: mixing a cathode active material precursor including nickel (Ni), cobalt (Co) and manganese (Mn) and a lithium raw material and performing primary firing; and mixing the lithium raw material after the primary firing and performing secondary firing.

Through the primary and secondary firing, secondary particles including primary particles may be manufactured.

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.

At this time, the precursor for preparing the first positive electrode active material of large particles 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 is prepared by mixing 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 can be uniformly mixed 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 11 to 13.

Meanwhile, the co-precipitation reaction may be performed at a temperature of 40° C. to 70° C. under an inert atmosphere such as nitrogen or argon.

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, it is possible to prepare a precursor having a nickel (Ni) content of 60 mol% or more in the total content of the metal. 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.

Additionally, in the case of the second positive electrode active material of small particles including secondary small particles including primary large particles having both grown in average particle size and crystal size, porous particles may be used as the positive electrode active material precursor.

In this case, the pH concentration may be controlled to prepare the second cathode active material precursor. Specifically, it may be added in an amount such that the pH is 7 to 9.

After that, the above-described precursor and lithium raw material are mixed, and primary firing is performed.

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 is soluble in water. Specifically, the lithium raw material is Li ₂ CO ₃ , LiNO ₃ , LiNO ₂ , LiOH, LiOH·H ₂ O, 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 800 to 1,000° C., more preferably from 830 to 1,000° 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 sintered at 980°C, more preferably at 850 to 950°C. In the case of a low-content nickel (Low-Ni) NCM-based lithium composite transition metal oxide having a nickel (Ni) content of less than 60 mol%, the primary firing may be performed at 900 to 1,100° C., more preferably from 930 to 1,070° C. , more preferably at 950 to 1,050 °C.

The primary firing may be carried out in an air or oxygen atmosphere, and may be performed for 15 to 35 hours.

Next, an additional secondary firing may be performed after the first firing.

The secondary sintering may be performed at 600 to 950° C., more preferably 650 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 can be calcined at 930°C, more preferably 700 to 900°C. In the case of a low-content nickel (Low-Ni) NCM-based lithium composite transition metal oxide having a nickel (Ni) content of less than 60 mol%, the secondary firing may be performed at 700 to 1,050° C., more preferably at 750 to 1,000° C. , more preferably at 800 to 950 °C.

The secondary sintering may be performed under an air or oxygen atmosphere, and may be performed for 10 to 24 hours.

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, hydroxypropylcellulose, 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 concavities and convexities 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, amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite (Kish) 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's not going to be

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

The organic solvent may be used without any 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; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, carbonate-based solvents such as PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 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 may be used. Among them, a carbonate-based solvent is preferable, and a cyclic carbonate (eg, ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of increasing the charge/discharge performance of the battery, and a low-viscosity linear carbonate-based compound ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) 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(CF3SO 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.

The lithium secondary battery including the positive electrode active material according to the present invention is useful in the field of portable devices such as mobile phones, notebook computers, digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

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.

Example 1.

In Example 1, the first positive active material including large secondary particles having an average diameter (D50) of 15 μm and the second positive active material including small secondary particles having an average diameter (D50) of 4 μm were mixed at 80:20. (weight ratio) was mixed and used as a positive electrode active material. In this case, the secondary small particles are secondary particles in which 10 or less primary large particles having a diameter of 1 μm or more are aggregated.

(Preparation of first positive electrode active material of large particles)

Specifically, a positive electrode active material was prepared as follows:

After putting 4 liters of distilled water into the coprecipitation reactor (capacity 20L), maintaining the temperature at 50 ° C., and adding 100 mL of 28 wt% ammonia aqueous solution, NiSO ₄ , CoSO ₄ , MnSO ₄ Molar ratio of nickel: cobalt: manganese is 0.8 : A 3.2 mol/L concentration of a transition metal solution mixed to be 0.1:0.1 was continuously added to the reactor at 300 mL/hr, and an aqueous ammonia solution of 28% by weight was added to the reactor at 42 mL/hr. The speed of the impeller was stirred at 400 rpm, and 40% by weight of sodium hydroxide solution was used to maintain the pH so that the pH was maintained at 11.0. The precursor particles were formed by co-precipitation reaction for 24 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 800 ° C. in an oxygen atmosphere for 10 hours to form LiNi _0.8 Co _0.1 Mn _0.1 O ₂ A lithium composite transition metal oxide first positive active material was prepared.

(Preparation of second positive electrode active material of small particles)

The second cathode in the same manner as in the manufacture of the first cathode active material of large particles, except that the pH was controlled to 9 during the coprecipitation reaction in the preparation of the precursor, the coprecipitation reaction time was changed to 10 hours, and the heat treatment conditions were changed to 850 ° C. The active material was synthesized.

The results according to Example 1 are shown in FIG. 2 and Tables 1 to 5.

Example 2.

By changing the co-precipitation reaction time to 8 hours in the preparation of the second positive electrode active material of small particles, primary large particles with a diameter of 1 μm or more are aggregated within 10 and secondary small particles with an average diameter (D50) of 3 μm It was carried out in the same manner as in Example 1, except that it was prepared and used.

Comparative Example 1 .

In Comparative Example 1, the first positive electrode active material including large secondary particles having an average diameter (D50) of 15 μm and the second positive active material including secondary small particles having an average diameter (D50) of 4 μm were mixed at 80:20. (weight ratio) was mixed and used as a positive electrode active material. In this case, the secondary small particles are secondary particles in which primary fine particles having a diameter of 0.5 μm or less are aggregated.

Specifically, a positive electrode active material was prepared as follows:

The first positive active material was prepared in the same manner as in the preparation of the first positive active material of large particles in Example 1. The second cathode active material was synthesized in the same manner as in Example 1, except that in the preparation of the second cathode active material of small particles, the pH was controlled to 11 when the precursor was synthesized and the heat treatment was changed to 800° C.

Results according to Comparative Example 1 are shown in FIG. 1 and Tables 1 to 5.

division D50 Example 1 Example 2 Comparative Example 1 Secondary large particle (=secondary large particle) 15㎛ 80 80 80 Secondary particle Small particle (primary fine particle agglomeration) 4㎛ - - 20 Secondary Small Particles (1st Large Particle Aggregation) 4㎛ 20 - Secondary Small Particles (1st Large Particle Aggregation) 3㎛ - 20 -

[Experimental Example 1: Comparison of small particle cracking due to electrode rolling] The positive active material prepared in Example 1 and Comparative Example 1 was mixed with each of the positive active material, carbon black conductive material, and PVdF binder in a N-methylpyrrolidone solvent in a weight ratio A positive electrode slurry was prepared by mixing in a ratio of 96:2:2, coated on one side of an aluminum current collector, dried at 100 °C, and rolled to a porosity of 25% to prepare a positive electrode. This electrode was cross-sectioned and the shape was compared by SEM, and the results are shown in FIGS. 1 to 2 .

Referring to FIG. 1 , in the case of Comparative Example 1, the secondary particles are broken during rolling, lose the shape of the aggregate, and are divided into primary fine particles to generate fine particles. On the other hand, as can be seen in FIG. 2 , in the case of Example 1 in which secondary small particles, which are aggregates of primary large particles, are used, the primary large particles are not broken after rolling and their shape is maintained in units of primary particles. From this, it can be confirmed that it has a high rolling density.

[Experimental Example 2: Comparison of rolling density according to pressure]

The positive active materials prepared in Examples 1-2 and Comparative Example 1 were rolled under 9 ton conditions, and then the rolling density was measured, and the results are shown in Table 2 below.

Rolling density was measured using HPRM-1000. Specifically, 5 g of the positive active material of Examples 1-2 and Comparative Example 1 was put into a cylindrical mold, respectively, and then the mold containing the positive active material was pressed by 9 tons. Then, the height of the pressed mold was measured with a vernier caliper and the rolling density was obtained.

Large particle/small particle 8:2 mixture Comparative Example 1 Example 1 Example 2 Rolling density [g/cc] 9 ton press 3.33 3.7 3.6

In Table 2, Comparative Example 1 is a case in which the conventional large secondary particles and small secondary particles are applied in a bimodal manner. On the other hand, Example 1-2 is a case in which secondary small particles are used instead of conventional secondary particles. Here, the secondary particle large particle is a particle formed by aggregation of tens to hundreds of primary micro particles. Here, the secondary particle small particle is a particle formed by aggregation of several tens to hundreds of primary micro particles. The average particle diameter (D50) of the large secondary particles is larger than the average particle diameter (D50) of the small secondary particles.

On the other hand, the secondary small particle referred to in the present invention is different from the above-described large secondary particle and/or secondary particle small particle. That is, the secondary small particles in one aspect of the present invention are particles formed by aggregating about 10 primary micro particles.

When secondary particles formed by aggregation of primary fine particles are compared with secondary particles formed by agglomeration of primary large particles, secondary particles formed by agglomeration of primary large particles have a smoother surface.

As can be seen from Table 2, in the case of Example 1-2, the rolling density is higher than that of Comparative Example 1.

[Experimental Example 3: Comparison of angle of repose]

The angles of repose of Comparative Example 1 and Example 1 were measured in the following way.

, 80mm

)를 분체물성측정장치에 안착시킨 후, 천방식 시료 공급방식의 hopper에 시료를 투입한다. hopper의 분말 원료를 상하로 진동시켜 시료가 균일한 속도로 원판 위에 낙하하게 하여 쌓여있는 시료의 쌓임각 을 측정한다.The angle of repose was measured using a powder physical property measuring device (Model PT-R, Hosokawa Midron Co.). Sample plate for angle of repose measurement (60mm)

, 80mm

) is seated in the powder physical property measuring device, and then put the sample into the cloth sample supply type hopper. Measure the stacking angle of the stacked samples by vibrating the powder raw material of the hopper up and down to make the sample fall on the disk at a uniform speed.

The results are shown in Table 3.

Large particle/small particle 8:2 mixture Comparative Example 1 Example 1 angle of repose degree 56 47

As can be seen from Table 3, Example 1 exhibited a lower angle of repose compared to Comparative Example 1. From this, it can be confirmed that the flowability of the positive electrode active material according to Example 1 is better.

[Experimental Example 4: Energy Density Comparison]

Energy density was measured using the positive active materials prepared in Examples 1-2 and Comparative Example 1, and the results are shown in Table 4.

Large particle/small particle 8:2 mixture Comparative Example 1 Example 1 Example 2 energy density Wh/L 2600 2860 2780

From Table 4, it was confirmed that Example 1-2 had an improved energy density compared to Comparative Example 1.

[Experimental Example 5: Comparison of rolling density according to content of positive electrode active material]

The rolling density was measured in the same manner as in Experimental Example 1 using the positive active materials prepared in Example 1 and Comparative Examples 2 to 4, and the results are shown in Table 5.

Comparative Examples 2 to 5

A positive active material was prepared in the same manner as in Example 1, except that the weight ratio of the first positive active material and the second positive active material was controlled as shown in Table 5 below. In this case, the secondary small particles are secondary particles in which 10 or less primary large particles having a diameter of 1 μm or more are aggregated.

Comparative Example 2 Comparative Example 3 Example 1 Comparative Example 4 Comparative Example 5 100:0 90:10 80:20 70:30 0 : 100 9ton press rolling density [g/cc] 3.3 3.5 3.7 3.45 3.40

In the case of Comparative Example 2 composed only of the large secondary particles and Comparative Example 5 composed only of the secondary small particles, it can be seen that the rolling density exhibited under the same pressure is slightly increased. This is a phenomenon that occurs because the density inside the particles increases as the primary particles become larger. When the secondary particles were used while changing the mixing ratio of the large particles and the secondary small particles, the rolling density of Comparative Example 3 was 3.5 g/cc, and the rolling density of Example 1 was 3.7 g/cc, and the ratio of the secondary small particles was As it increases, the eye lead density also tends to increase. On the other hand, as in Comparative Example 4, when the weight ratio of the large secondary particles to the secondary small particles was 70:30, it could be confirmed that 3.45 g/cc, which was similar to that of Comparative Example 5, was exhibited. From this, it was confirmed that the weight ratio for maximizing the rolling density was 75:25 to 90:10.

Claims (15)

It is a positive electrode active material for a lithium secondary battery comprising a first positive active material of large particles and a second positive active material of small particles,
The first positive active material includes at least one secondary large particle including an aggregate of primary micro particles,
The second positive active material includes at least one secondary small particle including an aggregate of primary macro particles,
The average particle diameter (D50) of the primary large particles is 1 μm or more,
The weight ratio of the first positive active material to the second positive active material is 75: 25 to 90: 10,
A positive active material for a lithium secondary battery, characterized in that the particle strength of the second positive active material is smaller than the particle strength of the first positive active material. According to claim 1,
The positive active material for a lithium secondary battery, characterized in that during rolling, the second positive active material is broken before the first positive active material. According to claim 1,
The average diameter (D50) of the primary large particles is 2 μm or more,
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 3 or more. According to claim 1,
The positive electrode active material for a lithium secondary battery, characterized in that the average particle diameter (D50) of the first positive active material is 10 μm to 20 μm. According to claim 1,
The second positive electrode active material has an average particle diameter (D50) of 3 μm to 6 μm. According to claim 1,
The positive electrode active material for a lithium secondary battery, characterized in that the average particle diameter (D50) of the primary fine particles of the first positive electrode active material is 0.1 μm to 0.5 μm. According to claim 1,
The second positive active material is a positive electrode active material for a lithium secondary battery, characterized in that the primary large particles fall off when the secondary small particles are rolled, and the primary large particles themselves are not broken. 8. The method of claim 2 or 7,
The rolling is a positive electrode active material for a lithium secondary battery, characterized in that it is performed so that the porosity of the positive electrode including the positive electrode active material is 15 to 30%. According to 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. According to claim 1,
A cathode active material for a lithium secondary battery, characterized in that the ratio of the average particle diameter (D50) of the secondary small particles to the average particle diameter (D50) of the primary large particles is 2 to 4 times. According to claim 1,
The first and second positive electrode active materials are a positive electrode 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 nickel-based lithium transition metal oxide is, Li _(1+a) Ni _{(1-(a+x+y+w))} Co _x M1 _y M2 _w O ₂ (0≤a≤0.5, 0≤x≤0.35, 0≤y≤0.35, 0≤w≤0.1, 0≤a+x+y+w≤0.7, M1 is at least one selected from the group consisting of Mn and Al, and M2 is Ba, Ca, Zr, Ti, Mg , Ta, at least one selected from the group consisting of Nb and Mo) a cathode active material for a lithium secondary battery comprising: According to claim 1,
The positive active material is a positive active material for a lithium secondary battery, characterized in that the angle of repose is less than 50 °. 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 .

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