POSITIVE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY

Abstract

Disclosed is a cathode active material for lithium secondary batteries containing lithium transition metal composite oxide in the form of primary particles having a one-body structure, the cathode active material having a ratio (R/L) of a right area (R) to a left area (L) in a particle size distribution (PSD) graph of less than 1.1, based on a maximum point of a main peak in the particle size distribution (PSD) graph, in which an X-axis represents a particle size (μm) and a Y-axis represents a relative particle amount (%).

Claims

1. A cathode active material for lithium secondary batteries comprising lithium transition metal composite oxide in the form of primary particles having a one-body structure, the cathode active material having a ratio (R/L) of a right area (R) to a left area (L) in a particle size distribution (PSD) graph of less than 1.1, based on a maximum point of a main peak in the particle size distribution (PSD) graph, in which an X-axis represents a particle size (μm) and a Y-axis represents a relative particle amount (%).

2. The cathode active material according to claim 1, wherein the particle size distribution (PSD) graph is obtained under the following PSD measurement conditions: <Measurement conditions> Measuring equipment: Microtrac S3500 Extended Cycle rate: 45%/sec Refraction index ratio: 1.55 Solvent fed to equipment: distilled water Sample of cell: 0665 Calculation Logic: X100 Sample amount: 0.0025 g Dispersant fed to sample: 1 ml of 10% sodium hexametaphosphate Solvent fed to sample: 40 ml of distilled water Sample ultrasonic dispersion: 40 kHz, 1 min

3. The cathode active material according to claim 1, wherein the cathode active material has the ratio (R/L) of the right area (R) to the left area (L) in the particle size distribution (PSD) graph, based on the maximum point of the main peak in the graph, of not less than 0.8 and less than 1.1.

4. The cathode active material according to claim 1, wherein the cathode active material has a ratio (FWHM/maximum height) of a full width at half maximum (FWHM) to a maximum height of the main peak in the particle size distribution (PSD) graph of 1.0 or less.

5. The cathode active material according to claim 1, wherein the cathode active material has a particle size distribution, represented by (D90-D10)/D50, of 1.2 or less.

6. The cathode active material according to claim 1, wherein the primary particles have an average particle diameter of 3 to 10 μm.

7. The cathode active material according to claim 1, wherein the lithium transition metal composite oxide comprises at least one of Ni, Co, and Mn.

8. A lithium secondary battery comprising the cathode active material according to claim 1.

Description

DESCRIPTION OF THE DRAWINGS

[0051] FIG. 1 is a graph showing the particle size distribution of cathode active materials according to Comparative Examples 1, 2, and 3 and Examples 1, 2, and 3;

[0052] FIG. 2A is an SEM image showing a cathode active material according to Example 1, FIG. 2B is an SEM image showing the cathode active material according to Example 2, FIG. 2C is an SEM image showing the cathode active material according to Example 3, FIG. 2D is an SEM image showing the cathode active material according to Comparative Example 1, FIG. 2E is an SEM image showing the cathode active material according to Comparative Example 2, and FIG. 2F is an SEM image showing the cathode active material according to Comparative Example 3;

[0053] FIG. 3 is a charge/discharge cycling graph of cathode active materials according to Comparative Examples 1, 2 and 3 and Examples 1, 2 and 3; and

[0054] FIG. 4 is a graph illustrating changes in DCIR (resistance) during charge/discharge cycling of cathode active materials according to Comparative Examples 1, 2, and 3 and Examples 1, 2 and 3.

BEST MODE

[0055] Now, the present invention will be described in more detail with reference to the following examples. These examples should not be construed as limiting the scope of the present invention.

Example 1

[0056] NiSO.sub.4 as a nickel precursor, CoSO.sub.4 as a cobalt precursor, and MnSO.sub.4 as a manganese precursor were added to water at a molar ratio of 0.83:0.11:0.6 to prepare an aqueous solution of a nickel-cobalt-manganese hydroxide precursor. An aqueous solution of sodium hydroxide was slowly added dropwise while the aqueous solution was stirred for 5 hours to neutralize the aqueous precursor solution to thereby precipitate Ni.sub.0.83Co.sub.0.11Mn.sub.0.06(OH).sub.2 as nickel-cobalt-manganese hydroxide.

[0057] The precursor (nickel-cobalt-manganese hydroxide) thus obtained was mixed with LiOH, followed by heat treatment at 870° C. for 11 hours to prepare LiNi.sub.0.83Co.sub.0.11Mn.sub.0.06O.sub.2.

[0058] Subsequently, the prepared LiNi.sub.0.83Co.sub.0.11Mn.sub.0.06O.sub.2 was subjected to post-treatment by applying a pressure of about 3 MPa using an AutoPellet 3887.NE.L from Carver to produce a cathode active material for a lithium secondary battery.

Example 2

[0059] A cathode active material for a lithium secondary battery was produced under the same conditions as in Example 1, except that post-treatment was performed by applying shear force using ZM200 from Retsch (at 12,000 RPM, 0.4 millimeter mesh).

Example 3

[0060] A cathode active material for a lithium secondary battery was produced under the same conditions as in Example 1, except that post-treatment was performed by applying a pressure of about 2 MPa.

Comparative Example 1

[0061] A cathode active material for a lithium secondary battery was produced under the same conditions as in Example 1, except that post-treatment was not performed.

Comparative Example 2

[0062] A cathode active material for a lithium secondary battery was produced under the same conditions as in Comparative Example 1, except that heat treatment was performed at 850° C.

Comparative Example 3

[0063] A cathode active material for a lithium secondary battery was produced under the same conditions as in Example 1, except that post-treatment was performed by applying a pressure of about 1 MPa.

Experimental Example 1

[0064] The PSDs of the cathode active materials for lithium secondary batteries produced in Examples 1, 2, and 3, and Comparative Examples 1, 2, and 3 were measured, and the particle size distribution graph obtained from the measurement of PSD and the results of particle size distribution are shown in FIG. 1 and Table 1.

TABLE-US-00001 TABLE 1 Maximum height Composition Calcination Post- of main of transition temperature treatment PSD (D90 − D10)/ peak metal (° C.) process D10 D50 D90 R/L D50 FWHM (h) FWHM/h Example 1 Ni.sub.0.83Co.sub.0.10Mn.sub.0.07 870 Pressure 2.2 3.6 6.2 0.8 1.11 3.6 8.49 0.4 (3 MPa) Example 2 Ni.sub.0.83Co.sub.0.10Mn.sub.0.07 870 Shear 2.6 4.4 7.3 0.8 1.07 4.6 8.51 0.5 force Example 3 Ni.sub.0.83Co.sub.0.10Mn.sub.0.07 870 Pressure 2.3 4.8 8.0 0.9 1.19 4.6 6.54 0.7 (2 MPa) Comparative Ni.sub.0.83Co.sub.0.10Mn.sub.0.07 870 X 3.1 8.3 29.5 1.5 3.18 22.3 3.93 5.7 Example 1 Comparative Ni.sub.0.83Co.sub.0.10Mn.sub.0.07 850 X 3.1 7.3 18.8 1.1 2.15 15.5 4.76 3.3 Example 2 Comparative Ni.sub.0.83Co.sub.0.10Mn.sub.0.07 870 Pressure 3.2 7.2 14.5 0.7 1.57 10.4 6.20 1.7 Example 3 (1 Mpa)

[0065] As can be seen from FIG. 1, the distribution of Examples 1, 2 and 3 is narrower and more uniform than the PSD distributions of Comparative Examples 1, 2 and 3, which can be confirmed based on the observation that both the ratios (FWHM/h) of the full width at half maximum (FWHM) to the maximum height (h) of the main peak and the values of (D90−D10)/D50, indicating a particle size distribution, are lower for Examples than for Comparative Examples.

[0066] In addition, it can be seen that the ratios (R/L) of the right area (R) to the left area (L) in the graph based on the maximum point of the main peak in the particle size distribution graph of Examples 1, 2, and 3 are smaller than those of Comparative Examples 1 and 2.

[0067] Here, it can be seen that Comparative Example 3 has a lower R/L value of 0.7, but a higher ratio (FWHM/h) of the full width at half maximum (FWHM) to the maximum height (h) of the main peak of 1.7, and a higher value of (D90−D10)/D50, indicating a particle size distribution, of 1.57, compared to Examples.

[0068] It is considered that the active material of Comparative Example 3 was prepared through post-treatment by applying a pressure of 1 MPa during the production process, but proper post-treatment was not performed due to the application of a relatively weak pressure, so the particle size was not uniformly distributed.

[0069] That is, the active materials of Comparative Examples 1 and 2 were prepared without a separate post-treatment process, so the goals of uniform particle size distribution and reduced aggregation between primary particles were not accomplished. The active material of Comparative Example 3 was prepared by post-treatment at a relatively weak pressure (1 MPa), so aggregation between primary particles was reduced to some extent, but a uniform particle size distribution was not achieved.

[0070] On the other hand, the active materials of Examples 1, 2, and 3 exhibited a uniform particle size distribution and reduced aggregation between primary particles through appropriate post-treatment (application of 3 MPa pressure, application of shear force, and application of 2 MPa pressure) during the production process.

Experimental Example 2

[0071] The cathode active materials for lithium secondary batteries prepared in Examples 1, 2 and 3, and Comparative Examples 1, 2 and 3, were observed through a scanning electron microscope, and the results are shown in FIG. 2.

[0072] Referring to FIG. 2, a number of aggregates are observed in the Comparative Examples shown in (d), (e), and (f). In contrast, although small amounts of aggregates were observed in the Examples shown in (a), (b) and (c), the proportion of aggregates was remarkably reduced compared to Comparative Examples.

Experimental Example 3

[0073] The cathode active material prepared in each of Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3, a conductive agent, and a binder were mixed at a ratio of 92:5:3 (active material:conductive agent:binder) and applied to a copper current collector, followed by drying to produce a cathode. A secondary battery was fabricated using lithium metal as an anode and adding EC:EMC=1:2 and LiPF.sub.6 1 M as an electrolyte, the electrochemical properties thereof were measured, and the results are shown in Tables 2 and 3 and FIGS. 3 and 4.

TABLE-US-00002 TABLE 2 0.1/0.1 FM Lifespan Charge Discharge Efficiency 50.sup.th/1.sup.st mAh/g % % Example 1 226.4 195.6 86.4 93.4 Example 2 226.7 195.5 86.2 93.6 Example 3 226.3 195.1 86.2 93.0 Comparative 223.4 192.5 86.2 86.2 Example 1 Comparative 224.2 190.5 85.0 90.2 Example 2 Comparative 225.1 193.8 86.1 90.5 Example 3

TABLE-US-00003 TABLE 3 DCIR [%] Δ 10.sup.th-1.sup.st Δ 20.sup.th-1.sup.st Δ 30.sup.th-1.sup.st Δ 40.sup.th-1.sup.st Δ50.sup.th-1.sup.st Example 1 4.7 8.7 16.2 24.8 33.2 Example 2 6.3 9.9 20.2 27.2 34.2 Example 3 6.4 9.0 19.2 28.2 38.5 Comparative 8.0 15.1 25.1 35.4 45.9 Example 1 Comparative 8.6 15.2 22.8 31.9 43.4 Example 2 Comparative 8.9 15.6 22.2 31.1 43.3 Example 3

[0074] First, as can be seen from Table 2 and FIG. 3, compared to Comparative Examples, the active materials of Examples 1, 2 and 3, in which both reduced aggregation between primary particles and a uniform particle size distribution are achieved, exhibit relatively high charging capacity and excellent lifespan characteristics.

[0075] In addition, Tables 3 and 4 show a change in DCIR (resistance) during cycling of the secondary batteries to which the active materials of Examples 1, 2, and 3 and Comparative Examples 1, 2 and 3 are applied. It can be seen therefrom that, compared to Comparative Examples, the batteries to which the active materials of Examples are applied exhibited relatively low resistance, based on which it can be expected that battery characteristics such as lifespan characteristics are improved.

[0076] Although preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible without departing from the scope and spirit of the invention as disclosed in the accompanying claims.