Cathode active material for secondary battery with enhanced lifespan characteristics and method of preparing the same

Abstract

Disclosed is a cathode active material in which lithium cobalt oxide particles and manganese (Mn) or titanium (Ti)-containing lithium transition metal oxide particles co-exist and a method of preparing the same.

Claims

1. A cathode active material comprising coexisting (1) lithium cobalt oxide particles including particle boundaries and (2) manganese (Mn) -containing lithium transition metal oxide particles provided by a manganese-containing compound selected from MnO.sub.2, MnCO.sub.3, MnOOH, Mn(CH.sub.3COO).sub.3, Mn(CH.sub.3COO).sub.2, MnSO.sub.4, and Mn(NO.sub.3).sub.2, wherein said manganese-containing lithium transition metal oxide particles are present inside the particle boundaries of the lithium cobalt oxide particles, wherein the lithium cobalt oxide particles have a diameter of 5 m to 30 m, and include a lithium deficiency layer of Li.sub.xCoO.sub.2(x<1.0), wherein the Mn-containing lithium transition metal oxide particles have a diameter of 5 m or less, wherein the diameter of the Mn-containing lithium transition metal oxide particles is smaller than the diameter of the lithium cobalt oxide particles, wherein the Mn-containing lithium transition metal oxide particles are inserted into the particle boundaries of lithium cobalt oxide particles, and wherein the Mn-containing lithium transition metal oxide particles comprise Li.sub.2MnO.sub.3 having a layered crystal structure and Mn exists as a stable tetravalent cation, whereby phase transition does not occur during high-rate charge and discharge.

2. The cathode active material according to claim 1, wherein the cathode active material further comprises an electrochemically inert lithium compound on outer surfaces of the lithium cobalt oxide particles.

3. The cathode active material according to claim 2, wherein the lithium compound is LiOH.

4. The cathode active material according to claim 2, wherein the lithium compound is Li.sub.2CO.sub.3.

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

6. A battery module comprising the lithium secondary battery according to claim 5 as a unit battery.

7. A battery pack comprising the battery module according to claim 6.

8. A device using the battery pack according to claim 7 as a power source.

9. The device according to claim 8, wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a device for storing power.

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 drawings, in which:

(2) FIG. 1 is a graph showing comparison in initial charge and discharge efficiency between batteries according to Example 1 and Comparative Example;

(3) FIGS. 2 and 3 are graphs showing comparison between cycle characteristics of the batteries of Example 1 and Comparative Example; and

(4) FIG. 4 is a graph showing comparison between discharge capacities according to C-rate of the batteries of Example 1 and Comparative Example.

MODE FOR INVENTION

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

EXAMPLE 1

(6) Solid-phase LiCoO.sub.2 and solid-phase MnCO.sub.3 were mixed and calcined at a temperature of 890 C. to 930 C. to prepare LiCoO.sub.2 treated with the Mn source, the Mn-treated LiCoO.sub.2, a conductive material, and a binder were weighed so as to have a weight ratio of 95:2.5:2.5, added to NMP and mixed therein to prepare a cathode mixture, and the cathode mixture was coated on 20 m thick Al foil, and the coated Al foil was pressed and dried, thereby completing fabrication of an electrode. The electrode was subjected to blanking into a coin shape, and the coin-shaped electrode, Li metal as an anode, and a carbonate electrolyte containing 1M LiPF.sub.6 were used to manufacture a coin cell.

EXAMPLE 2

(7) Solid-phase LiCoO.sub.2 was immersed in an aqueous MnSO.sub.4 solution and calcined at a temperature of 890 C. to 930 C. for 10 hours to prepare LiCoO.sub.2 treated with the Mn source, the Mn-treated LiCoO.sub.2, a conductive material, and a binder were weighed so as to have a weight ratio of 95:2.5:2.5, added to NMP and mixed therein to prepare a cathode mixture, and the cathode mixture was coated on 20 m thick Al foil to a thickness of 200 m, and the coated Al foil was pressed and dried, thereby completing fabrication of an electrode. The electrode was subjected to blanking into a coin shape, and the coin-shaped electrode, Li metal as an anode, and a carbonate electrolyte containing 1M LiPF.sub.6 were used to manufacture a coin cell.

COMPARATIVE EXAMPLE

(8) A coin cell was manufactured in the same manner as in Example 1, except that LiCoO.sub.2 not treated with a Mn source (Bare LiCoO.sub.2) was used.

EXPERIMENTAL EXAMPLE 1

(9) The cells of Example 1 and Comparative Example were subjected to charging and discharging at 3.0 to 4.4 V under the following conditions: charging at 0.1 C and discharging at 0.1 C (1 C=150 mA/g) and initial charge and discharge efficiencies thereof were compared. Results are shown in Table 1 and FIG. 1 below.

(10) TABLE-US-00001 TABLE 1 Unit Comparative Example Example 1 1.sup.st charge mAh/g 181.0 177.7 1.sup.st discharge 175.4 175 Efficiency % 96.9 98.5

EXPERIMENTAL EXAMPLE 2

(11) The cells of Example 1 and Comparative Example were subjected to 30 charging and discharging cycles at 3.0 to 4.4 V under the following conditions: charging at 0.5 C and discharging at 0.5 C (1 C=150 mA/g) and cycle characteristics thereof were compared. Results are shown in Table 2 below and FIGS. 2 and 3. Referring to FIG. 3, it can be confirmed that the cell of Comparative Example 1 exhibits significantly decreased specific capacity as cycles are repeated unlike the cell of Example 1.

(12) TABLE-US-00002 TABLE 2 Unit Comparative Example Example 1 Cycle (30 times) % 84.6 98.4

EXPERIMENTAL EXAMPLE 3

(13) The cells of Example 1 and Comparative Example were subjected to charging and discharging at 3.0 to 4.4 V under the following conditions: charging at 0.5 C and discharging at 0.1 C, 0.2 C, 0.5 C, 1.0 C, and 2.0 C (1 C=150 mA/g) and rate-limiting characteristics thereof were compared. Results are shown in Table 3 below and FIG. 4.

(14) TABLE-US-00003 TABLE 3 Unit Comparative Example Example 1 0.1 C % 100.0 100.0 0.2 C 98.9 99.7 0.5 C 96.6 99.3 1.0 C 92.9 98.9 2.0 C 87.7 97.3

(15) 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.

INDUSTRIAL APPLICABILITY

(16) As described above, a cathode active material according to the present invention has a structure in which Mn or Ti-containing lithium transition metal oxide particles produced through reaction with lithium impurities coexist with lithium cobalt oxide particles in the cathode active material and thus exhibits enhanced high-voltage lifespan characteristics and power output characteristics.