Cathode active material and lithium secondary battery comprising the same

Abstract

Disclosed is a cathode active material comprising a lithium manganese composite oxide with a spinel structure represented by the following Formula 1, wherein the lithium manganese composite oxide is surface-coated with a conductive polymer in an area of 30 to 100%, based on the surface area of the lithium manganese composite oxide:
Li.sub.xM.sub.yMn.sub.2-yO.sub.4-zA.sub.z  (1) wherein 0.9≦x≦1.2, 0<y<2, and 0≦z<0.2; M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti and Bi; and A is at least one monovalent or bivalent anion. Disclosed is also a secondary battery comprising the cathode active material.

Claims

1. A secondary battery, comprising: (i) a cathode, which comprises a cathode active material, the cathode active material comprising a lithium manganese composite oxide with a spinel structure represented by the following Formula 1, and a conductive polymer coated directly on the surface of the lithium manganese composite oxide, wherein the lithium manganese composite oxide is surface-coated with the conductive polymer in an area of 30 to 100%, based on the surface area of the lithium manganese composite oxide:
Li.sub.xM.sub.yMn.sub.2-yO.sub.4-zA.sub.z  (1) wherein 0.9≦x≦1.2, 0<y<2, and 0≦z<0.2, M is at least one element selected from the group consisting of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti and Bi, and A is at least one monovalent or bivalent anion, wherein the conductive polymer is at least one selected from the group consisting of polyaminopyridine, polypyrrole, and polyaniline, and a content of nitrogen of the conductive polymer is 0.05 to 10% by weight, with respect to the total weight of the cathode active material; and (ii) an anode, which comprises an anode active material, the anode active material comprising a lithium metal oxide represented by the following Formula 3:
Li.sub.aM′.sub.bO.sub.4-cA.sub.c  (3) wherein M′ is at least one element selected from the group consisting of Ti, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr, a and b are determined according to an oxidation number of M′ within ranges of 0.1≦a≦4 and 0.2≦b≦4, c is determined according to an oxidation number of A within a range of 0≦c≦0.2; and A is at least one monovalent or bivalent anion.

2. The secondary battery according to claim 1, wherein the oxide of Formula 1 is represented by the following Formula 2:
Li.sub.xNi.sub.yMn.sub.2-yO.sub.4  (2) wherein 0.9≦x≦1.2, and 0.4≦y≦0.5.

3. The secondary battery according to claim 2, wherein the oxide of Formula 2 is LiNi.sub.0.5Mn.sub.1.5O.sub.4 or LiNi.sub.0.4Mn.sub.1.6O.sub.4.

4. The secondary battery according to claim 1, wherein secondary particles of the oxide of Formula 1 have a mean particle diameter (D50) of 5 to 30 μm.

5. The secondary battery according to claim 1, wherein the conductive polymer is coated to a thickness of 0.1 nm to 1,000 nm.

6. The secondary battery according to claim 1, wherein the lithium metal oxide is represented by the following Formula 4:
Li.sub.aTi.sub.bO.sub.4  (4) wherein 0.5≦a≦3 and 1≦b≦2.5.

7. The secondary battery according to claim 6, wherein the lithium metal oxide is Li.sub.1.33Ti.sub.1.67O.sub.4 or LiTi.sub.2O.sub.4.

8. The secondary battery according to claim 7, wherein the secondary battery is a lithium secondary battery.

9. A battery module comprising the secondary battery according to claim 8 as a unit battery.

10. A battery pack comprising the battery module according to claim 9.

11. A device comprising the battery pack according to claim 10.

12. The device according to claim 11, wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle or a power storage system.

Description

DETAILED DESCRIPTION OF THE INVENTION

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

Example 1

(2) A cathode active material was prepared by coating polyaniline on the surface of LiNi.sub.0.5Mn.sub.1.5O.sub.4 having a particle diameter of 14 μm and a surface area of 0.6 m.sup.2/g such that a content of nitrogen present on the surface of LiNi.sub.0.5Mn.sub.1.5O.sub.4 was 0.05% by weight with respect to the total weight of the cathode active material.

Example 2

(3) A cathode active material was prepared in the same manner as in Example 1, except that polyaniline was coated on the surface of LiNi.sub.0.5Mn.sub.1.5O.sub.4 such that a content of nitrogen present on the surface thereof was 10% by weight with respect to the total weight of the cathode active material.

Comparative Example 1

(4) A cathode active material was prepared in the same manner as in Example 1, except that the cathode active material was prepared using LiNi.sub.0.5Mn.sub.1.5O.sub.4 not coated with polyaniline.

Experimental Example 1

(5) 90% by weight of each of the cathode active materials prepared in Examples 1 and 2, and Comparative Example 1, 5% by weight of Super-C (conductive material) and 5% by weight of PVdF (binder) were added to NMP to prepare a cathode mix and the cathode mix was applied to an aluminum current collector, followed by drying and pressing, to produce a cathode for secondary batteries. 90% by weight of Li.sub.1.33Ti.sub.1.67O.sub.4, 5% by weight of Super-C (conductive material) and 5% by weight of PVdF (binder) were added to NMP to prepare an anode mix and the anode mix was applied to an aluminum current collector, followed by drying and pressing, to produce an anode. An electrode assembly was produced by inserting a porous separator made of polypropylene between the cathode and the anode. Then, the electrode assembly was inserted into a pouch, a lead line was connected thereto, a solution of 1M LiPF.sub.6 in a mixed solvent consisting of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) at a volume ratio of 1:1:1 was injected as an electrolyte and sealed to assemble a 9 bicell-type lithium secondary battery. The battery was discharged at a SOC of 50% and at 10 C for 10 seconds and a resistance thereof was measured. Results are shown in Table 1 below.

(6) TABLE-US-00001 TABLE 1 Resistance [Ω] Ex. 1 0.153 Ex. 2 0.145 Comp. Ex. 1 0.207

(7) As can be seen from Table 1 above, the batteries of Examples 1 and 2 exhibited improved electrical conductivity due to the conductive polymer coated on the surface thereof and thus exhibited low internal resistance, as compared to the battery of Comparative Example 1.

(8) 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.