Lithium manganese-based oxide and cathode active material including the same

Abstract

Disclosed is a lithium manganese (Mn)-based oxide including Mn as an essential transition metal and having a layered crystal structure, in which the amount of Mn is greater than that of other transition metal(s), the lithium manganese-based oxide exhibits flat level section characteristics in which release of oxygen occurs together with lithium deintercalation during first charging in a high voltage range of 4.4 V or higher, and at least one of a transition metal layer including Mn and an oxygen layer is substituted or doped with a pillar element.

Claims

1. A lithium manganese (Mn)-based oxide comprising Mn as an essential transition metal and having a layered crystal structure, wherein an amount of Mn is greater than that of other transition metal(s), the lithium manganese-based oxide exhibits flat level section characteristics in which release of oxygen occurs together with lithium deintercalation during first charging in a high voltage range of 4.4 V or higher, wherein the lithium manganese-based oxide has a layered structure comprising at least one transition metal layer including Mn and at least one oxygen layer and is represented by Formula 1 below:
xLi.sub.2MnO.sub.3.(1−x)LiMO.sub.2  (1) wherein 0<x<1; and M is at least one element selected from the group consisting of nickel (Ni), cobalt (Co), and Mn wherein the at least one transition metal layer including Mn and/or the at least one oxygen layer is substituted or doped with a pillar element; and the pillar element is at least one selected from the group consisting of vanadium (V), sodium (Na), iron (Fe), barium (Ba), strontium (Sr), zirconium (Zr), and calcium (Ca).

2. The lithium manganese-based oxide according to claim 1, wherein an amount of the pillar element is 0.02 mol % to 0.1 mol % based on a total amount of the lithium manganese-based oxide.

3. The lithium manganese-based oxide according to claim 1, wherein an amount of Mn is 50 mol % or more based on a total amount of the transition metals.

4. The lithium manganese-based oxide according to claim 1, wherein the lithium manganese-based oxide is prepared by dry-mixing a compound comprising the pillar element with a transition metal precursor and a lithium precursor and heat-treating the mixture.

5. The lithium manganese-based oxide according to claim 4, wherein the heat-treating is performed at a temperature of 800° C. to 1000° C.

6. The lithium manganese-based oxide according to claim 4, wherein the heat-treating is performed in air.

7. A cathode active material for secondary batteries, comprising the lithium manganese-based oxide according to claim 1.

8. A cathode mixture for secondary batteries, comprising the cathode active material according to claim 7.

9. A cathode for secondary batteries, in which the cathode mixture according to claim 8 is coated on a current collector.

10. A lithium secondary battery comprising the cathode according to claim 9.

11. A battery module comprising the lithium secondary battery according to claim 10 as a unit cell.

12. A battery pack comprising the battery module according to claim 11.

13. A device using the battery pack according to claim 12 as a power source.

14. A cathode active material for secondary batteries, comprising the lithium manganese-based oxide according to claim 2.

15. A cathode active material for secondary batteries, comprising the lithium manganese-based oxide according to claim 3.

16. A cathode active material for secondary batteries, comprising the lithium manganese-based oxide according to claim 4.

17. A cathode active material for secondary batteries, comprising the lithium manganese-based oxide according to claim 5.

18. A cathode active material for secondary batteries, comprising the lithium manganese-based oxide according to claim 6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawing, in which:

(2) FIG. 1 is a graph showing initial discharge capacities according to Experimental Example 1;

(3) FIG. 2 is a graph showing lifespan characteristics according to Experimental Example 2;

(4) FIG. 3 is a graph showing initial discharge capacities according to Experimental Example 3; and

(5) FIG. 4 is a graph showing lifespan characteristics according to Experimental Example 4.

BEST MODE

(6) Now, the present invention will be described in more detail with reference to the following examples. These examples are provided only for illustration of the present invention and should not be construed as limiting the scope and spirit of the present invention.

Example 1

(7) In a process of preparing 0.25Li.sub.2MnO.sub.3.0.75(Mn.sub.0.47Ni.sub.0.53)O.sub.2 as a lithium manganese (Mn)-based oxide including Mn as an essential transition metal and having a layered crystal structure, 0.05 mol % of NaCO.sub.3 was added as a pillar material in the form of an oxide and the resulting mixture was sintered in air at a temperature of 800° C. for 5 hours, thereby completing preparation of a cathode active material in which at least one of a transition metal layer and an oxygen layer was substituted or doped with Na as a pillar element.

(8) The cathode active material, a conductive agent, and a binder were used in a ratio of 88:6.5:5.5 to prepare a slurry and the slurry was coated onto an Al-foil having a thickness of 20 μm to manufacture a cathode. The cathode, Li-metal as an anode, and an electrolyte containing 1M LiPF.sub.6 in a mixed solvent of EC:EMC (1:2) to which 2 wt % of LiBF.sub.4 was added were used to manufacture a coin cell.

Example 2

(9) A cathode and a coin cell were manufactured in the same manner as in Example 1, except that the sintering process was performed at 950° C.

Example 3

(10) In a process of preparing 0.15Li.sub.2MnO.sub.3.0.85(Mn.sub.0.47Ni.sub.0.47Co.sub.0.12)O.sub.2 as a lithium manganese (Mn)-based oxide including Mn as an essential transition metal and having a layered crystal structure, 0.02 mol % of ZrO.sub.2 was added as a pillar material in the form of an oxide and the resulting mixture was sintered in air at 950° C. for 5 hours, thereby completing preparation of a cathode active material in which at least one of a transition metal layer and an oxygen layer was substituted or doped with Zr as a pillar element.

(11) The cathode active material, a conductive agent, and a binder were used in a ratio of 88:6.5:5.5 to prepare a slurry and the slurry was coated onto an Al-foil having a thickness of 20 μm to manufacture a cathode. The cathode, Li-metal as an anode, and an electrolyte containing 1M LiPF.sub.6 in a mixed solvent of EC:(DMC+EMC) (1:2) to which 2 wt % of LiBF.sub.4 was added were used to manufacture a coin cell.

Comparative Example 1

(12) A cathode and a coin cell were manufactured in the same manner as in Example 2, except that the pillar material was not added in the process of preparing the lithium manganese composite oxide of Example 2.

Comparative Example 2

(13) A cathode and a coin cell were manufactured in the same manner as in Example 3, except that the pillar material was not added in the process of preparing the lithium manganese composite oxide of Example 3.

Experimental Example 1

(14) Discharge capacities of the cells manufactured according to Examples 1 and 2 and Comparative Example 1 were measured by performing an initial cycle under the following conditions: voltage of 2.5 V to 4.65 V and current of 0.1 C rate and results are shown in Table 1 below and FIG. 1.

(15) TABLE-US-00001 TABLE 1 Comparative Example 1 Example 2 Example 1 1.sup.st discharge capacity 198 mAh/g 204 mAh/g 213 mAh/g

Experimental Example 2

(16) An experiment for lifespan characteristics of the cells of Examples 1 and 2 and Comparative Example 1 was implemented under the following conditions: voltage of 3.0 V to 4.4. V and current of 0.5 C rate. In this regard, the lifespan characteristics were evaluated as retention rate with respect to initial capacity after 30 cycles and results are shown in Table 2 below and FIG. 2.

(17) TABLE-US-00002 TABLE 2 Comparative Example 1 Example 2 Example 1 Lifespan characteristics 101% 93% 91%

Experimental Example 3

(18) Discharge capacities of the cells of Example 3 and Comparative Example 2 were measured by performing an initial cycle under the following conditions: voltage of 3.0 V to 4.4 V and current of 0.1 C rate. Results are shown in Table 3 below and FIG. 4.

(19) TABLE-US-00003 TABLE 3 Comparative Example 3 Example 2 1.sup.st discharge capacity 165 mAh/g 167 mAh/g

Experimental Example 4

(20) An experiment for lifespan characteristics of the cells of Example 3 and Comparative Example 2 was implemented under the following conditions: voltage of 3.0 V to 4.4. V and current of 0.5 C rate. In this regard, the lifespan characteristics were evaluated as retention rate with respect to initial capacity after 30 cycles and results are shown in Table 4 below and FIG. 4.

(21) TABLE-US-00004 TABLE 4 Comparative Example 3 Example 2 Lifespan characteristics 95% 96%

(22) According to the results shown in Tables 1 to 4 and FIGS. 1 to 4, it can be confirmed that, although the cells of Examples 1 to 3 exhibit a reduction in initial capacity due to the pillar material added in the process of preparing the cathode active material, the cells of Examples 1 to 3 exhibit superior lifespan and capacity characteristics to the cells of Comparative Examples 1 and 2.

(23) Although the 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.