KR102249562B1 - Cathode Active Material for Lithium Secondary Battery - Google Patents

Abstract

The present invention includes primary particles of a monolithic structure of a lithium transition metal composite oxide, and the main particle size distribution graph (X axis: particle size (㎛), Y axis: relative particle amount (%)) on PSD (Particle Size Distribution) It provides a positive electrode active material for a lithium secondary battery, characterized in that the ratio (R/L) of the right area (R) and the left area (L) in the graph is less than 1.1 based on the peak maximum point.

Description

Cathode Active Material for Lithium Secondary Battery

The present invention relates to a positive electrode active material for a lithium secondary battery, and more particularly, to a positive electrode active material capable of providing a lithium secondary battery having excellent resistance reduction and life characteristics by having a particle size distribution under specific conditions.

The demand for lithium secondary batteries is mainly digital devices such as laptops and mobile phones, and through cost reduction and performance stabilization through mass production and technology development, the future applications of lithium secondary batteries are from portable information and communication devices to electric vehicles and hybrids. Continued market growth is predicted by expanding to the automotive, space and aviation sectors, and energy storage systems (ESS) [lithium secondary battery material technology trends, S&T Market Report, Science and Technology Job Promotion Agency, 2018.9].

The core materials of lithium secondary batteries are cathode materials, anode materials, electrolytes, and separators. Of these, cathode materials are the most important materials for producing secondary batteries. Depending on the material, LCO (lithium cobalt oxide), NCM (Lithium Nickel Cobalt Manganese Oxide), NCA (Lithium Nickel Cobalt Aluminum Oxide), LMO (Lithium Manganese Oxide), LFP (Lithium Iron Phosphate).

Conventional positive electrode active materials are mainly used in the form of secondary particles in which primary particles are agglomerated, but the positive active material in the form of secondary particles increases the direct contact area with the electrolyte due to its high specific surface area, resulting in side reactions with the electrolyte. I can.

In addition, the presence of secondary particles in the positive electrode active material increases the internal impedance of the battery to deteriorate the initial discharge capacity, and stress is generated at the grain boundary due to the expansion and contraction of the crystal lattice due to charging and discharging, thereby destroying the particles. It may cause capacity deterioration.

Meanwhile, as one of the methods for suppressing side reactions with the surface of the active material and the electrolyte, there is a method of forming a coating layer on the surface of the active material. The presence of such a coating layer may provide an effect of suppressing side reactions by preventing direct contact between the surface of the electrolyte and the active material, and ultimately improving the life characteristics of the battery.

However, aggregation between a plurality of active materials may occur during the firing process, and coating treatment may be omitted for surfaces that are in contact with each other due to aggregation during coating. When such an active material is applied and used on a current collector, As the uncoated portion of which the coating treatment is omitted is exposed during charging and discharging, there may be a problem in that the performance of the battery is deteriorated.

Therefore, there is a high need for a technology capable of solving these problems.

An object of the present invention is to solve the problems of the prior art and technical problems that have been requested from the past.

The inventors of the present application developed a positive electrode active material for a lithium secondary battery having a specific particle size distribution condition after various experiments and studies, and such a positive electrode active material contains primary particles of a monolithic structure, and the degree of aggregation between the primary particles As a result, it was confirmed that battery characteristics such as a decrease in resistance were improved, and additional surface treatment was also easy, and the present invention was completed.

Therefore, the positive electrode active material for a lithium secondary battery according to the present invention contains primary particles of a monolithic structure, which is a lithium transition metal composite oxide, and a particle size distribution graph (X axis: particle size (㎛), on PSD (Particle Size Distribution), Y axis: The ratio (R/L) of the right area (R) and the left area (L) in the graph is less than 1.1 based on the maximum point of the main peak of the relative particle amount (%)).

Here, the particle size X value of the right portion with respect to the main peak maximum point is larger with respect to the particle size X value of the left portion. Therefore, in the cathode active material for a lithium secondary battery according to the present invention, particles with small particles have a larger relative particle amount compared to particles with a larger particle size (R/L<1), based on the particle size having the highest relative particle amount, or within a certain range. It has a similar (1≦R/L<1.1) relative particle weight within. Specifically, the PSD measurement of the active material is performed to determine the particle size distribution.As the area in the particle size distribution graph derived from the PSD becomes more skewed to the right, the aggregated ratio between the primary particles is higher, so that the active material has a relatively large particle size. It can be determined that there are a lot of these, and as the area in the graph is skewed to the left, the aggregated ratio between the primary particles is lower, so it can be determined that there are many active materials having relatively small particle sizes.

Therefore, the positive active material for a lithium secondary battery according to the present invention has a limited bias to the right of the area in the particle size distribution graph derived from the PSD, which is the degree of aggregation between the primary particles, that is, the degree of aggregation between the primary particles is relatively low. This means that the relative particle amount of particles having a small particle size is secured and the relative particle amount of particles having a relatively large particle size is limited.

A positive electrode active material having such a particle size distribution has a low degree of cohesion between primary particles, and its resistance is reduced compared to an active material having a high degree of cohesion between primary particles, thereby improving battery characteristics such as capacity increase. It can reduce the possibility of the occurrence of the coating area. In addition, the primary particles that may be included in such an active material are less likely to cause particle destruction, that is, cracks during repeated charging and discharging processes, thereby contributing to the improvement of the performance of the lithium secondary battery.

The particle size distribution graph can be obtained, for example, by the following PSD measurement conditions.

<Measurement conditions>

-Measuring equipment: Microtrac S3500 Extended

-Circulation rate: 45%/sec

-Refractive index ratio: 1.55

-Equipment input solvent: distilled water

-Sample of cell: 0665

-Calculation Logic: X100

-Sample amount: 0.0025 g

-Sample input dispersant: 10% Sodium Hexamethaphosphate 1 ml

-Sample input solvent: 40 ml of distilled water

-Sample ultrasonic dispersion: 40 KHz, 1 min

The positive active material for a lithium secondary battery according to the present invention may have reduced aggregation between primary particles by controlling process conditions such as firing temperature during the manufacturing process, or reduced aggregation through a separate post-treatment process after firing during the manufacturing process. It may have been. Here, a separate post-treatment process after firing may be a process of applying an appropriate pressure and shear force to the fired active material, but is not limited thereto.

The degree of aggregation between the primary particles can also be confirmed through a scanning electron microscope or the like, and this can be confirmed through the results of scanning electron microscopy for the examples described later.

In one specific example, the positive active material of the present invention may have a ratio between a full width at half-maximum (FWHM) and a maximum height (FWHM/maximum height) of 1.0 or less in the particle size distribution graph on the PSD.

One of the characteristics that can affect performance, such as improving the life and efficiency of a lithium secondary battery, is the uniform particle size distribution of the active material. The narrower the width of the main peak of the graph that can be obtained through PSD is, the smaller the particle size distribution of the active material. Can be determined to be uniform, which can be determined by measuring the half-width value of the main peak.

Accordingly, it can be determined that the positive electrode active material of the present invention exhibits a more uniform particle size distribution by satisfying the above range when the half width value of the main peak is divided by the maximum height in the PSD graph.

The lower limit of the FWHM/maximum height is not particularly limited, and may be, for example, 0.3 or more.

In addition to measuring the half-width value of the maximum peak on the particle size distribution graph, the uniformity of the particle size distribution can be determined by checking the particle size distribution represented by (D90-D10)/D50. The smaller this may indicate that the particle size distribution is uniform.

Accordingly, in another specific example, the positive electrode active material of the present invention may have a particle size distribution represented by (D90-D10)/D50 of 1.2 or less.

The lower limit of (D90-D10)/D50 is not particularly limited, and may be, for example, 0.8 or more.

As described above, the present invention can provide a positive electrode active material for a lithium secondary battery having low cohesion between primary particles and excellent uniformity of particle size distribution, according to various embodiments that can be provided.

In this case, in order to provide a positive electrode active material with excellent particle size distribution uniformity, the ratio of the particles having a relatively small particle size and a particle having a large particle size can be adjusted, based on the maximum point of the main peak of the PSD phase particle size distribution graph. , If the difference between the right area R and the left area L in the graph is too large, the particle size distribution graph may be formed broad, which cannot be regarded as having a uniform particle size distribution of the positive electrode active material.

Therefore, the positive active material for a lithium secondary battery according to an embodiment of the present invention is the ratio (R/L) of the right area (R) and the left area (L) in the graph based on the maximum point of the main peak of the PSD phase particle size distribution graph. Is preferably 0.8 or more to less than 1.1, more preferably 0.8 or more to 1.0 or less, and the positive electrode active material has a relatively sharp shape of the PSD measurement graph, so it can be determined that the particle size distribution is uniform.

The positive electrode active material for a lithium secondary battery according to the present invention may include primary particles of a monolithic structure of a lithium transition metal composite oxide containing at least one of Ni, Co, and Mn, and the average particle diameter of the primary particles is 3 to 10 μm. Can be

In one specific example, the lithium transition metal composite oxide may have a composition represented by Formula 1 below.

Li _a [M _1-b X _b ]O _cd Q _d (1)

In the above formula,

M is Ni _x Co _y Mn _z ,

X is selected from alkali metals excluding lithium, alkaline earth metals, transition metals from groups 3 to 12 excluding nickel, cobalt and manganese, post-transition metals and metalloids from groups 13 to 15, and nonmetal elements from groups 14 to 16 Is more than one,

Q is at least one of F, P and S,

0.8≤a≤1.2, 0≤b≤0.3, 1.8<c<2.2, 0≤d<0.2

0<x<1, 0<y<1, 0<z<1, 0<x+y+z≤1.

Specifically, X is an alkali metal other than lithium and may be, for example, Na, K, Rb, Cs, Fr, and the like, and as an alkaline earth metal, for example, Be, Mg, Ca, Sr, Ba, Ra, etc. may be used, and nickel And as a Group 3 to Group 12 transition metal excluding cobalt and manganese, for example, Sc, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd , Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, etc., as post-transition metals and metalloids of groups 13 to 15, for example Al, Ga, In, Sn, Tl, Pb, It may be Bi, Po, B, Si, Ge, As, Sb, Te, At, and the like, and as a non-metal element in groups 14 to 16, for example, C, P, S, Se, and the like. The transition metal element may include a lanthanum group element or an actinium group element. In one preferred example, X may be at least one selected from the group consisting of Zr, Ti, W, B, P, Al, Si, Mg, Zn, and V.

The present invention also provides a lithium secondary battery including the positive electrode active material. Since other configurations and manufacturing methods of the lithium secondary battery are known in the art, detailed descriptions thereof will be omitted in the present invention.

As described above, the positive active material for a lithium secondary battery according to the present invention has a low degree of aggregation between primary particles, and thus has an effect of reducing resistance and improving life characteristics of a lithium secondary battery to which it is applied.

1 is a graph showing particle size distribution of positive electrode active materials according to Comparative Examples 1, 2 and 3 and Examples 1, 2 and 3;
In FIG. 2, (a) is an SEM photograph of the positive active material according to Example 1, (b) is an SEM photograph of the positive active material according to Example 2, and (c) is an SEM photograph of the positive active material according to Example 3. , (d) is an SEM photograph of the positive electrode active material according to Comparative Example 1, (e) is an SEM photograph of the positive electrode active material according to Comparative Example 2, and (f) is an SEM photograph of the positive electrode active material according to Comparative Example 3;
3 is a charge/discharge cycling graph of positive electrode active materials according to Comparative Examples 1, 2 and 3 and Examples 1, 2 and 3;
4 is a graph showing the amount of change in DCIR (resistance) during charge/discharge cycling of positive electrode active materials according to Comparative Examples 1, 2 and 3 and Examples 1, 2, and 3;

Hereinafter, the present invention will be described in more detail with reference to the drawings according to an embodiment of the present invention, but the scope of the present invention is not limited thereto.

[Example 1]

Nickel precursor, NiSO _4, CoSO ₄ cobalt precursor and manganese precursor of the MnSO ₄ 0.83: 0.11: 0.6 in a molar ratio of the added water, the nickel-cobalt-manganese hydroxide precursor solution was prepared. While stirring the aqueous solution, an aqueous sodium hydroxide solution was slowly added dropwise, and the reaction mixture was stirred for 5 hours to neutralize the precursor aqueous solution to precipitate _{Ni 0.83} Co _0.11 Mn _0.06 (OH) _{2, which is a nickel-cobalt-manganese hydroxide.}

LiOH was mixed with the thus obtained precursor (nickel cobalt manganese hydroxide) and heat-treated at 870°C for 11 hours to obtain LiNi _{0 . 83} Co _{0 . 11} Mn _{0 . 06} O ₂ was prepared.

Then, the prepared LiNi _{0 . 83} Co _{0 . 11} Mn _{0 . As} a post-treatment process of 06 O ₂ , a pressure of about 3 MPa was applied using CARVER's AutoPellet 3887.NE.L, through which a positive active material for a lithium secondary battery was manufactured.

[Example 2]

A positive electrode active material for a lithium secondary battery was prepared under the same conditions as in Example 1, except that a shear force was applied using Retsch's ZM200 (12,000 RPM and 0.4 mm mesh) as a post-treatment process.

[Example 3]

A positive electrode active material for a lithium secondary battery was prepared under the same conditions as in Example 1, except that a pressure of about 2 MPa was applied as a post-treatment process.

[Comparative Example 1]

A cathode active material for a lithium secondary battery was prepared under the same conditions as in Example 1, except that the post-treatment process was not performed.

[Comparative Example 2]

A cathode active material for a lithium secondary battery was prepared under the same conditions as in Comparative Example 1, except that heat treatment was applied at 850°C.

[Comparative Example 3]

A positive electrode active material for a lithium secondary battery was prepared under the same conditions as in Example 1, except that a pressure of about 1 MPa was applied as a post-treatment process.

[Experimental Example 1]

The PSD of the positive electrode active material for lithium secondary batteries prepared in Examples 1, 2, 3 and Comparative Examples 1, 2, and 3 was measured, and the particle size distribution graph and particle size distribution results derived from the PSD measurement are shown in FIGS. 1 and 1 I got it.

Referring to FIG. 1, when compared with the PSD distribution values of Comparative Examples 1, 2 and 3, it can be seen that the distribution of Examples 1, 2 and 3 is narrow and the uniformity is high, which is a particle size distribution graph in the PSD shown in Table 1. In both the ratio of the half width value (FWHM) and the maximum height (h) of the main peak (FWHM/h) and the (D90-D10)/D50 values representing the particle size distribution, the examples show lower values compared to the comparative examples. It can also be understood through.

In addition, when the ratio (R/L) of the right area (R) and the left area (L) in the graph was confirmed based on the maximum point of the main peak of the particle size distribution graph, compared to Comparative Examples 1 and 2, Examples 1 and 2 and It was confirmed that the value of 3 was small.

Here, it can be seen that Comparative Example 3 exhibits a lower R/L value of 0.7 compared to the examples, but the ratio of the main peak half-width (FWHM) and the maximum height (h) of the PSD phase particle size distribution graph (FWHM/ h) represents 1.7 higher than the examples, and the (D90-D10)/D50 value representing the particle size distribution represents 1.57, which was also confirmed to be higher than the examples.

It is determined that the active material of Comparative Example 3 was manufactured by applying a pressure of 1 MPa as a post-treatment process during the manufacturing process, but the appropriate post-treatment was not performed due to the application of a relatively weak pressure, so that the particle size was not uniformly distributed.

That is, in the case of the active materials of Comparative Examples 1 and 2, since they were prepared without a separate post-treatment process, uniform particle size distribution and reduction of aggregation between primary particles were not resolved, and in the case of the active material of Comparative Example 3, relatively weak pressure ( As the post-treatment process proceeded to 1 MPa), the aggregation between primary particles decreased to some extent, but it was judged that a uniform particle size distribution was not achieved.

On the other hand, the active materials of Examples 1, 2 and 3 showed uniform particle size distribution and reduced aggregation between primary particles as appropriate post-treatment processes (3 MPa pressure application, shear force application, 2 MPa pressure application) were performed during the manufacturing process. It can be judged to have been achieved.

[Experimental Example 2]

The cathode active materials for lithium secondary batteries prepared in Examples 1, 2 and 3 and Comparative Examples 1, 2 and 3, respectively, were observed through a scanning electron microscope, and the results are shown in FIG. 2.

Referring to FIG. 2, in the comparative examples of (d), (e), and (f), a number of aggregates are observed. On the other hand, in the examples (a), (b), and (c), a small amount of aggregates was identified, but it can be seen that the ratio of aggregates was significantly reduced compared to the comparative examples.

[Experimental Example 3]

Examples 1, 2 and 3 and Comparative Examples 1, 2, and 3, respectively, a conductive agent and a binder in the positive electrode active material prepared in a ratio of 92: 5: 3 (active material: conductive agent: binder) was mixed and applied to a copper current collector And then dried to prepare a positive electrode. After manufacturing a secondary battery by using lithium metal as a negative electrode and adding electrolyte EC:EMC = 1:2, LiPF ₆ 1M, electrochemical properties were measured, and the results are shown in Tables 2 and 3 and FIGS. Indicated.

First, referring to Tables 2 and 3, compared to the comparative examples, the active materials of Examples 1, 2, and 3, in which the degree of aggregation between primary particles and uniform particle size distribution were both achieved, had relatively high charging capacity and excellent lifespan. It can be seen that the characteristics are shown.

In addition, Tables 3 and 4 show the results of the amount of change in DCIR (resistance) during cycling of the secondary battery to which the active materials of Examples 1, 2 and 3 and Comparative Examples 1, 2, and 3 are applied. It can be seen that the battery to which the active material of the embodiments is applied exhibits a relatively low resistance value, and it can be understood that battery characteristics such as life characteristics are improved through this.

Those of ordinary skill in the field to which the present invention belongs will be able to make various modifications and improvements based on the above contents, which should all be interpreted as belonging to the scope of the present invention.

Claims (8)

The maximum point of the main peak of the particle size distribution graph (X-axis: particle size (㎛), Y-axis: relative particle amount (%)) on PSD (Particle Size Distribution), including primary particles of a monolithic structure of lithium transition metal composite oxide On the basis of, a ratio (R/L) of a right area (R) and a left area (L) in the graph is less than 1.1. The cathode active material of claim 1, wherein the particle size distribution graph is obtained by the following PSD measurement conditions:
<Measurement conditions>
-Measuring equipment: Microtrac S3500 Extended
-Circulation rate: 45%/sec
-Refractive index ratio: 1.55
-Equipment input solvent: distilled water
-Sample of cell: 0665
-Calculation Logic: X100
-Sample amount: 0.0025 g
-Sample input dispersant: 10% Sodium Hexamethaphosphate 1 ml
-Sample input solvent: 40 ml of distilled water
-Sample ultrasonic dispersion: 40 KHz, 1 min. The method of claim 1, wherein the ratio (R/L) of the right area (R) and the left area (L) in the graph is 0.8 or more to less than 1.1 based on the maximum point of the main peak of the particle size distribution graph on the PSD. Positive active material for lithium secondary batteries. The cathode active material for a lithium secondary battery according to claim 1, wherein a ratio between a full width at half-maximum (FWHM) and a maximum height (FWHM/maximum height) of the particle size distribution graph in the PSD phase is 1.0 or less. . The cathode active material for a lithium secondary battery according to claim 1, wherein the particle size distribution represented by (D90-D10)/D50 is 1.2 or less. The cathode active material for a lithium secondary battery according to claim 1, wherein the primary particles have an average particle diameter of 3 to 10 µm. The cathode active material for a lithium secondary battery according to claim 1, wherein the transition metal composite oxide contains at least one element selected from Ni, Co, and Mn. A lithium secondary battery comprising the positive active material according to any one of claims 1 to 7.

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