LITHIUM-TITANIUM COMPLEX OXIDE, PREPARATION METHOD THEREOF, AND LITHIUM SECONDARY BATTERY COMPRISING SAME

Abstract

The present invention relates to a lithium-titanium complex oxide, a preparation method thereof, and a lithium secondary battery comprising the same and, more specifically, to a lithium-titanium complex oxide which maintains appropriate pores within particles, and which is prepared by adding a pore inducing material in the wet-milling step to adjust sizes of primary particles of the lithium-titanium complex oxide, a preparation method thereof, and a lithium secondary battery comprising the same.

Claims

1. A lithium-titanium complex oxide characterized by having a molar ratio of lithium to titanium (Li/Ti ratio) of 0.80 to 0.85.

2. The lithium-titanium complex oxide of claim 1, comprising 5 wt % or less of a rutile-type titanium oxide.

3. The lithium-titanium complex oxide of claim 1, comprising 0.05 mol/L or less of Zr.

4. The lithium-titanium complex oxide of claim 1, having a Brunauer-Emmett-Teller (BET) surface areas of 4.3 m.sup.2/g or more.

5. The lithium-titanium complex oxide of claim 1, having a tap density of 1.0 g/cm.sup.3 or more and a pellet density of 1.75 g/cm.sup.3 or more.

6. A preparation method of the lithium-titanium complex oxide according to claim 1, the preparation method comprising: of solid phase-mixing a pore inducing compound, a titanium compound, and a dissimilar metal-containing compound at a stoichiometric ratio to obtain a solid phase mixture; of preparing a slurry in which primary particles are dispersed by dispersing the solid phase mixture in a solvent and wet-milling the solid phase mixture dispersed in the solvent; of forming secondary particles by spray drying the slurry; of mixing the secondary particles with a lithium-containing compound to obtain lithium compound-mixed particles; calcining the lithium compound-mixed particles to obtain calcined particles; and classifying the calcined particles.

7. The preparation method of claim 6, wherein the pore inducing compound is one or more selected from lithium carbonate (Li.sub.2CO.sub.3), sodium bicarbonate (NaHCO.sub.3), and potassium carbonate (K.sub.2CO.sub.3).

8. The preparation method of claim 6, wherein the titanium compound is one or more selected from the group consisting of titanium dioxide (TiO.sub.2), titanium chloride, titanium sulfide, and titanium hydroxide.

9. The preparation method of claim 6, wherein the dissilimar metal is one or more selected from the group consisting of Na, Zr, K, B, Mg, Al, and Zn.

10. The preparation method of claim 6, wherein the wet-milling comprises wet-milling the solid phase mixture dispersed in the solvent by using water as the solvent and using zirconia beads having a rotational speed of 2,000 to 5,000 rpm.

11. The preparation method of claim 10 claim 6, wherein the primary particles have an average particle diameter D.sub.50 of 0.05 to 0.4 μm.

12. The preparation method of claim 6, wherein the third step of performing the spray drying process comprises spray drying the slurry at a hot air input temperature of 200 to 300° C. and a hot air exhaust temperature of 100 to 150° C.

13. The preparation method of claim 6, wherein the second particles obtained by spray drying the slurry have an average particle diameter D.sub.50 of 5 to 20 μm.

14. The preparation method of claim 6, wherein the lithium-containing compound is lithium hydroxide (LiOH) or lithium carbonate (Li.sub.3CO.sub.2).

15. The preparation method of claim 6, wherein the calcining is performed at a temperature of 700 to 800° C. in an air atmosphere for 10 to 20 hours.

16. The preparation method of claim 6, wherein classifying the calcined particles comprises classifying the calcined particles to a particle size corresponding to a sieve size of 200 to 400 meshes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG. 1 is a schematic diagram illustrating a preparation method according to the present invention.

[0036] FIG. 2A to FIG. 2G show SEM (Scanning Electron Microscope) results of lithium-titanium complex oxides prepared in Comparative Example 1 and Examples 1 to 6 of the present invention.

[0037] FIG. 3A to FIG. 3F show SEM results of cross-sections of the lithium-titanium complex oxides prepared in Comparative Example 1 and Examples 1 to 6 of the present invention.

[0038] FIG. 4A to FIG. 4G show SEM results of active materials after analyzing pellet densities of active materials prepared in Comparative Example 1 and Examples 1 to 6 of the present invention.

[0039] FIG. 5A to FIG. 5J show SEM results of secondary particles of lithium-titanium complex oxides which are prepared in particle size-controlled primary particles by Comparative Examples 2 to 6 according to the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0040] Hereinafter, the present invention is described more in detail by Examples. However, the present invention is not limited by the following Examples.

EXAMPLES 1 TO 18

Preparation of Pore Induced In Compound-Added Lithium-Titanium Complex Oxides

[0041] After obtaining solid phase mixtures by solid phase-mixing titanium oxide as a starting material, lithium carbonate as a pore inducing compound, and zirconium oxide as a dissimilar metal, the solid phase mixtures were stirred and dissolved in water to obtain mixtures. The mixtures were designed such that molar ratios of lithium contents to titanium contents (Li/Ti ratios) became 0.81 by adjusting equivalent weights of lithium carbonates compared to lithium hydroxides.

[0042] After wet-milling particles of the mixtures into primary particles having an average particle diameter of 0.12 μm at a milling speed of 4,200 rpm using zirconia beads to prepare slurries, spray drying the slurries at a hot air input temperature of 250° C. and a hot air exhaust temperature of 110° C., and adding lithium hydroxide to the spray dried slurries to mix lithium hydroxide with the spray dried slurries at a rotational speed 700 rpm for 10 minutes using a Herschel mixer, active materials were prepared by calcining the mixtures at 750 to 780° C. to obtain calcined products and classifying the calcined products using a sieve having a sieve size corresponding to 325 meshes.

TABLE-US-00001 TABLE 1 Classification LiOH:Li.sub.2CO.sub.3 Calcination temperature Example 1 90:10 750° C. Example 2 70:30 750° C. Example 3 50:50 750° C. Example 4 30:70 750° C. Example 5 10:90 750° C. Example 6  0:100 750° C. Example 7 95:5  760° C. Example 8 90:10 760° C. Example 9 85:15 760° C. Example 10 80:20 760° C. Example 11 95:5  770° C. Example 12 90:10 770° C. Example 13 85:15 770° C. Example 14 80:20 770° C. Example 15 95:5  780° C. Example 16 90:10 780° C. Example 17 85:15 780° C. Example 18 80:20 780° C.

COMPARATIVE EXAMPLE 1

Preparation of a Lithium-Titanium Complex Oxide

[0043] After obtaining a solid phase mixture by solid phase-mixing 0.01 mol of titanium oxide and zirconium hydroxide as starting materials without adding a pore inducing compound, a mixture was obtained by stirring the solid phase mixture in water, thereby dissolving the solid phase mixture in water.

[0044] After wet-milling particles of the mixture into primary particles having an average particle diameter of 0.12 μm at a milling speed of 4,200 rpm using zirconia beads having a particle diameter of 0.1 mm to prepare a slurry, spray drying the slurry at a hot air input temperature of 250° C. and a hot air exhaust temperature of 110° C., and adding lithium hydroxide to the spray dried slurry to mix lithium hydroxide with the spray dried slurry at a rotational speed 700 rpm for 10 minutes using a Herschel mixer, an active material was prepared by calcining the mixture at 750° C. to obtain a calcined product and classifying the calcined product using a sieve having a sieve size corresponding to 325 meshes.

COMPARATIVE EXAMPLES 2 TO 6

Preparation of Lithium-Titanium Complexes of Which Primary Particles are Particle Size-Controlled by Wet-Milling

[0045] After obtaining solid phase mixtures by solid phase-mixing 0.01 mol of titanium oxide and zirconium hydroxide as starting materials without adding a pore inducing compound, mixtures were obtained by stirring the solid phase mixtures in water, thereby dissolving the solid phase mixtures in water.

[0046] After wet-milling particles of the mixtures into primary particles having average particle diameters of 0.40 μm, 0.30 μm, 0.20 μm, 0.15 μm and 0.10 μm using zirconia beads having a particle diameter of 0.1 mm to prepare slurries, spray drying the slurries at a hot air input temperature of 250° C. and a hot air exhaust temperature of 110° C., and adding lithium hydroxide to the spray dried slurries to mix lithium hydroxide with the spray dried slurries at a rotational speed 700 rpm for 10 minutes using a Herschel mixer, active materials were prepared by calcining the mixtures at 750° C. to obtain calcined products and classifying the calcined products.

TABLE-US-00002 TABLE 2 Classification Primary particle size Comparative Example 2 SPL-1 0.40 μm Comparative Example 3 SPL-2 0.30 μm Comparative Example 4 SPL-3 0.20 μm Comparative Example 5 SPL-4 0.15 μm Comparative Example 6 SPL-5 0.10 μm

EXPERIMENTAL EXAMPLE

Measurement of SEM Photographs

[0047] After measuring SEM photographs of the active materials prepared in Examples 1 to 6 and Comparative Example 1, measurement results are shown in FIG. 2A to FIG. 2G and FIG. 3A to FIG. 3F.

[0048] In FIG. 2A to FIG. 2G, it can be seen that the more contents of Li.sub.2CO.sub.3 added as a pore inducting material are increased, the more pores are formed within the particles, and it can be seen that formation ratios of doughnut shaped particles of the lithium-titanium complex oxides are low in secondary particles of lithium-titanium complex oxides of Examples 2 to 6 formed of primary particles having an average particle diameter of 0.12 μm. The doughnut shaped particles are formed in such a form that the electrode is easily crushed in the rolling process after manufacturing an electrode from the active material. Therefore, it has been known that the doughnut shaped particles can cause deterioration of battery capacity.

[0049] After preparing particles by varying addition amounts of Li.sub.2CO.sub.3 added as the pore inducing material, SEM photographs of cross-sections of the respective prepared particles are shown in FIG. 3A to FIG. 3F. It can be seen in FIG. 3A to FIG. 3F that the more the addition amounts of Li.sub.2CO.sub.3 added as the pore inducing material are increased, the more uniformly pores are formed in the particles.

[0050] SEM results of the lithium-titanium complex oxides of Comparative Examples 2 to 6 of which primary particles have controlled particle sizes are shown in FIG. 3A to FIG. 3F. As shown in FIG. 3A to FIG. 3F, it can be seen that the smaller particles of the slurries become, the smaller primary particles of the active materials also become, and it can be seen that large amounts of doughnut shaped particles are generated when the primary particles of the slurries of Comparative Examples 2 to 6 to which the pore inducing compound is not added have a particle diameter D.sub.50 of 0.2 μm or less.

EXPERIMENTAL EXAMPLE

Measurement of the Surface Area

[0051] After measuring surface areas of the active materials prepared in Examples and Comparative Example 1 using BET equipment, measurement results are shown in Table 3.

[0052] In Table 3, since the more contents of Li.sub.2CO.sub.3 added as the pore inducting material are increased, the smaller and the more uniformly the pores are dispersed and formed to be, it can be seen that BET surface area values of 4.3 m.sup.3/g or more of Examples are increased than that of Comparative Example, and this, as a decarboxylation reaction due to Li.sub.2CO.sub.3 added as the pore inducting material, results from the formation of internal pores.

TABLE-US-00003 TABLE 3 Active material Tap density Pellet density BET surface area Classification [g/ml] [g/cm.sup.3] [m.sup.2/g] Comparative 0.81 1.76 3.4 Example Example 1 1.18 1.72 5.3 Example 2 0.98 1.67 5.8 Example 3 0.87 1.71 5.9 Example 4 0.77 1.72 6.0 Example 5 0.70 1.71 6.8 Example 6 0.75 1.71 7.7 Example 7 1.15 1.76 4.7 Example 8 1.13 1.74 5.0 Example 9 1.10 1.73 5.1 Example 10 1.08 1.71 5.5 Example 11 1.15 1.77 4.4 Example 12 1.15 1.75 4.6 Example 13 1.13 1.75 4.6 Example 14 1.11 1.74 4.7 Example 15 1.16 1.78 4.3 Example 16 1.15 1.76 4.5 Example 17 1.16 1.76 4.5 Example 18 1.15 1.75 4.6

EXPERIMENTAL EXAMPLE

Measurement of Tap Densities and Pellet Densities

[0053] After measuring tap densities and pellet densities of the active materials prepared in Examples and Comparative Example 1, measurement results are shown in Table 1 and FIG. 4A to FIG. 4G.

[0054] Table 1 shows that the more the contents of Li.sub.2CO.sub.3 added as the pore inducting material are increased, the more the tap densities are decreased.

[0055] After preparing particles by varying addition amounts of Li.sub.2CO.sub.3 added as the pore inducing material, SEM photographs of the prepared particles are shown in FIG. 4A to FIG. 4G. It can be seen in FIG. 4A to FIG. 4G that the more the addition amounts of Li.sub.2CO.sub.3 added as the pore inducing material are increased, the more pellet densities are increased. This can be seen from a reason that, when the pore inducing material is added in an excessive amount, the pellet densities are rather increased while the particles are being cracked.

EXPERIMENTAL EXAMPLE

Measurement of Weight Ratios of Anatase Phase TiO.SUB.2 .To Rutile Phase

TiO.SUB.2

[0056] After measuring pore volumes and pore sizes of the active materials prepared in Examples and Comparative Example 1, measurement results are shown in the following Table 4.

TABLE-US-00004 TABLE 4 LiOH:Li.sub.2CO.sub.3 Items Unit 100:0 90:10 70:30 50:50 30:70 10:90 0:100 Pore cm.sup.3/g 0.0239 0.0231 0.0227 0.0223 0.0191 0.0190 0.0186 volume Pore nm 24.6575 17.9271 15.7095 15.2178 12.3167 11.5216 10.0913 size

[0057] It can be seen that the pore volumes and the pore sizes are decreased since the more addition amounts of Li.sub.2CO.sub.3 that is the pore inducing material are increased, the smaller and the more uniformly the pores are dispersed and formed to be.

EXPERIMENTAL EXAMPLE

Measurement of Pore Volumes and Pore Sizes

[0058] After measuring weight ratios of anatase phase TiO.sub.2 to rutile phase TiO.sub.2 from the active materials prepared in Examples and Comparative Example 1, measurement results are shown in the following Table 5.

[0059] It can be confirmed in the following Table 5 that the active materials prepared by the present invention comprise 3.0 wt % or less of the rutile phase TiO.sub.2.

TABLE-US-00005 TABLE 5 Ratio of Anatase phase TiO.sub.2 to LiOH:Li.sub.2CO.sub.3 Rutile phase TiO.sub.2 100:0 90:10 70:30 50:50 30:70 10:90 0: 100 A-TiO.sub.2 % 0.0 0.0 0.0 0.0 0.0 0.0 0.0 R-TiO.sub.2 2.0 1.8 2.6 2.0 1.2 0.9 0.8

MANUFACTURING EXAMPLE

Manufacturing of Coin Cells

[0060] Coin cells were manufactured from the active materials prepared in Examples and Comparative Example 1 according to a commonly known manufacturing process by using lithium metal as a counter electrode and a porous polyethylene film as a separator, and using a liquid electrolyte which is dissolved at 1 mol concentration in a solvent having ethylene carbonate and dimethyl carbonate mixed therein at a volume ratio of 1:2.

EXPERIMENTAL EXAMPLE

Evaluation of Initial Charge and Discharge Characteristics

[0061] After measuring initial charge and discharge characteristics at 0.1 C using an electrochemical analyzer in order to evaluate test cells comprising the active materials prepared in Examples and Comparative Example 1, measurement results are shown in Table 6.

EXPERIMENTAL EXAMPLE

Evaluation of Rate Properties

[0062] After evaluating rate properties of the test cells by charging the test cells at 0.1 C and discharging the test cells at 0.1 C and 10 C using the electrochemical analyzer in order to evaluate test cells comprising the active materials prepared in Examples and Comparative Example 1, evaluation results are shown in Table 6.

TABLE-US-00006 TABLE 6 Charge and discharge characteristics Rate properties 0.1 C Discharge 0.1 C Efficiency 10 C/0.1 C Classification [mAh/g] [%] [%] Comparative 170.1 98.5 83 Example Example 1 165.7 98.5 92 Example 2 168.0 98.1 93 Example 3 166.4 97.9 90 Example 4 167.1 97.3 88 Example 5 167.2 97.5 83 Example 6 170.2 97.5 90 Example 7 165.0 98.3 91 Example 8 164.0 98.0 92 Example 9 165.8 98.1 91 Example 10 165.9 97.6 93 Example 11 168.0 98.3 90 Example 12 166.1 98.0 92 Example 13 166.9 98.5 90 Example 14 167.0 97.7 90 Example 15 167.4 98.5 87 Example 16 166.0 98.3 90 Example 17 170.0 98.7 90 Example 18 168.6 98.3 90

[0063] It can be confirmed in the above Table 6 that cells comprising active materials prepared by adding the pore inducing material by the present invention have greatly improved charge and discharge characteristics and rate properties.

[0064] A preparation method according to the present invention can prepare a lithium-titanium complex oxide which is prepared from a particle size-controlled slurry having sizes of primary particles reduced by adding a pore inducing material in the wet-milling step such that appropriate pores are contained within the particles.

[0065] Since a lithium-titanium complex oxide having sizes of the primary particles reduced, the lithium-titanium complex oxide prepared according to the preparation method according to the present invention shortens a moving distance of lithium ions by adding the pore inducing material, diffusion rate of the lithium ions is increased. Thereby, a battery comprising the lithium-titanium complex oxide according to the preparation invention exhibits excellent output characteristics as the lithium-titanium complex oxide becomes favorable to electron transport.