Positive electrode active material and lithium secondary battery including the same

Abstract

Disclosed herein are a positive electrode active material including at least one selected from among compounds represented by Formula 1 below and a lithium secondary battery including the same that is capable of improving lifetime characteristics and rate characteristics while exhibiting excellent safety: xLi.sub.2M.sub.yMn.sub.(1-y)O.sub.3-zA.sub.z*(1x)LiMO.sub.2-zA.sub.z (1), where M is at least one element selected from a group consisting of Ru, Mo, Nb, Te, Re, Ir, Pt, Cr, S, W, Os, and Po, M is at least one element selected from a group consisting of Ni, Ti, Co, Al, Mn, Fe, Mg, B, Cr, Zr, Zn, and second row transition metals, A and A are each independently a negative monovalent or divalent anion, and 0<x<1, 0.3<y<1, 0z<0.5, and 0z<0.5.

Claims

1. A positive electrode active material comprising at least one selected from among compounds represented by Formula 1 below:
xLi.sub.2M.sub.yMn.sub.(1-y)O.sub.3-zA.sub.z*(1x)LiMO.sub.2-zA.sub.z(1), where M is at least one element selected from a group consisting of Ru, Mo, Nb, Te, Re, Ir, Pt, Cr, S, W, Os, and Po, M is at least one element selected from a group consisting of Ni, Ti, Co, Al, Mn, Fe, Mg, B, Cr, Zr, Zn, and second row transition metals, A and A are each independently a negative monovalent or divalent anion, wherein A and A are each at least one element selected from a group consisting of halogen elements, sulfur, and nitrogen, and 0<x<1, 0.3<y<1, 0<z0.5, and 0z0.5.

2. The positive electrode active material according to claim 1, wherein M is at least one element selected from a group consisting of Ru, Mo, S, W, Os, and Po.

3. The positive electrode active material according to claim 1, wherein M is Ru.

4. The positive electrode active material according to claim 1, wherein M is Mn.sub.aM.sub.1-a (where M is at least one element selected from a group consisting of Ni, Ti, Co, Al, Fe, Mg, B, Cr, Zr, Zn, and second row transition metals, and 0<a<1).

5. The positive electrode active material according to claim 4, wherein M is at least two elements selected from a group consisting of Ni, Ti, Co, Al, Fe, Mg, B, Cr, Zr, and Zn.

6. The positive electrode active material according to claim 1, wherein M is Mn.sub.aNi.sub.bCo.sub.c (where 0<a<1, 0<b<1, 0<c<1, and a+b+c=1).

7. The positive electrode active material according to claim 4, wherein 0<a<0.5.

8. The positive electrode active material according to claim 1, wherein 0<x0.7.

9. The positive electrode active material according to claim 1, wherein 0.4<y<1.

10. The positive electrode active material according to claim 1, wherein 0<z0.2 and 0z0.2.

11. The positive electrode active material according to claim 1, wherein the compounds represented by Formula 1 above are layered composites or solid solutions.

12. A positive electrode formed by applying a positive electrode active material according to claim 1 to a current collector.

13. A lithium secondary battery comprising a positive electrode according to claim 12.

14. A battery module comprising a lithium secondary battery according to claim 13 as a unit battery.

15. A battery pack comprising a battery module according to claim 14.

16. A device using a battery pack according to claim 15 as a power source.

17. The device according to claim 15, wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage apparatus.

18. The positive electrode active material according to claim 6, wherein 0<a<0.5.

Description

BRIEF DESCRIPTION OF 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 drawings, in which:

(2) FIG. 1 is a graph showing the results of charge and discharge in second cycles of batteries according to Experimental Example 1; and

(3) FIG. 2 is capacity differentiation curves in second to seventh cycles of batteries according to Experimental Example 2.

BEST MODE

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

Example 1

(5) Transition metal precursors, NiCO.sub.3, MnCO.sub.3, RuO.sub.2, and Li.sub.2CO.sub.3, were placed in a planetary mill in the state in which the molar ratio of the transition metal precursors was 1:1.8:1.2:3 based on a stoichiometric ratio, and were mixed at a speed of 400 rpm for about 5 hours to obtain a mixture. The mixture was plasticized at an air atmosphere of 900 C. for 8 hours to manufacture a positive electrode active material doped with Ru, 0.5Li.sub.2Ru.sub.0.6Mn.sub.0.4O.sub.3*0.5LiNi.sub.0.5Mn.sub.0.5O.sub.2.

Comparative Example 1

(6) 0.5Li.sub.2Ru.sub.0.3Mn.sub.0.7O.sub.3*0.5LiNi.sub.0.5Mn.sub.0.5O.sub.2 was manufactured in the same manner as in Example 1 except that transition metal precursors, NiCO.sub.3, MnCO.sub.3, RuO.sub.2, and Li.sub.2CO.sub.3, were mixed in the state in which the molar ratio of the transition metal precursors was 1:2.4:0.6:3 based on a stoichiometric ratio.

Comparative Example 2

(7) 0.5Li.sub.2MnO.sub.3*0.5LiNi.sub.0.5Mn.sub.0.5O.sub.2 was manufactured in the same manner as in Example 1 except that Ru salt was not used.

Experimental Example 1

(8) 7 weight % of denka black, as a conductive agent, and 6 weight % of PVDF, as a binder, were added to 87 weight % of the positive electrode active materials manufactured according to Example 1 and Comparative Examples 1 and 2 to manufacture positive electrode active mixtures. NMP was added to the manufactured positive electrode active mixtures to manufacture slurries. The manufactured slurries were applied to positive electrode current collectors, and were then pressed and dried to manufacture positive electrodes for secondary batteries. Porous polyethylene separators were interposed between the positive electrodes and negative electrodes based on lithium metal, and then lithium electrolytic solutions were injected to manufacture coin type lithium half-cell batteries.

(9) The results of charge and discharge in second cycles of the coin type lithium half-cell batteries are shown in FIG. 1.

(10) Referring to this figure, it can be seen that the battery according to Example 1 exhibits high capacity at a lower voltage than the batteries according to Comparative Examples 1 and 2 and that a voltage sagging phenomenon is reduced.

Experimental Example 2

(11) The lithium half-cell batteries manufactured according to Experimental Example 1 using the positive electrode active materials manufactured according to Example 1 and Comparative Examples 1 and 2 were charged and discharged up to seventh cycles. Capacity differentiation curves in second to seventh electrochemical cycles of the batteries are shown in FIG. 2.

(12) Referring to this figure, it can be seen that the battery according to Example 1 has a lower activation level in a colored portion in a dotted-line box than the batteries according to Comparative Examples 1 and 2, whereby a voltage sagging phenomenon is reduced even when a plurality of charge and discharge cycles is performed.

INDUSTRIAL APPLICABILITY

(13) As is apparent from the above description, a positive electrode active material according to the present invention contains excessive lithium and a predetermined content of specific elements. Even at the time of high-voltage activation to utilize excess lithium, therefore, escape of oxygen may be prevented, whereby it is possible to secure structural stability. Consequently, it is possible to restrain voltage sagging due to the structural change of the positive electrode active material during cycles, thereby improving lifetime characteristics.

(14) In addition, the irreversible capacity of the positive electrode active material may be reduced through sufficient utilization of excess lithium, thereby improving rate characteristics while exhibiting excellent charge and discharge efficiency.

(15) Furthermore, voltage necessary for high-voltage activation may be lowered, with the result that it is possible to prevent the generation of oxygen radicals due to the restraint of the decomposition of an electrolytic solution, whereby the safety of a battery may be improved.

(16) Although the exemplary 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.