Lithium battery having higher performance

Abstract

Disclosed is a lithium secondary battery including an electrode assembly including a cathode, an anode, and a separator disposed between the cathode and the anode and an electrolyte, wherein the anode includes a lithium titanium oxide (LTO) as an anode active material, and the lithium secondary battery has a charge cut-off voltage of 3.3 to 4 V and, when the charge cut-off voltage is reached, the anode has a potential of 0.75 to 1.545 V within a range within which a potential of the cathode does not exceed 4.95 V.

Claims

1. A lithium secondary battery comprising: an electrode assembly comprising a cathode, an anode, and a separator disposed between the cathode and the anode; and an electrolyte, wherein the anode comprises a lithium titanium oxide as an anode active material, and the lithium secondary battery has a charge cut-off voltage of 3.3 to 4 V and, when the charge cut-off voltage is reached, the anode has a potential of 0.75 to 1.545 V within a range within which a potential of the cathode does not exceed 4.95 V, wherein the cathode is a high-voltage cathode, wherein the cathode comprises, as a cathode active material, a spinel-structure lithium nickel manganese composite oxide represented by Formula 3 below:
Li.sub.xNi.sub.yMn.sub.2−yO.sub.4  (3), wherein 0.9≦x≦1.2 and 0.4≦y≦0.5, and wherein the capacity of the anode is 80 to 100% the capacity of the cathode.

2. The lithium secondary battery according to claim 1, wherein the charge cut-off voltage of the lithium secondary battery is in a range of 3.3 to 3.5 V and, when the cut-off voltage is reached, the anode has a potential of 1.2 to 1.545 V within a range within which the potential of the cathode does not exceed 4.95 V.

3. The lithium secondary battery according to claim 1, wherein the lithium nickel manganese composite oxide is LiNi.sub.0.5Mn.sub.1.5O.sub.4 or LiNi.sub.0.4Mn.sub.1.6O.sub.4.

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

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

6. The lithium secondary battery according to claim 1, wherein the capacity of the anode is 90 to 100% the capacity of the cathode.

7. A battery module comprising the lithium secondary battery according to claim 1 as a unit battery.

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

9. A device comprising the battery pack according to claim 8.

10. The device according to claim 9, wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system 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 between lifespan characteristics according to Experimental Example 2; and

(3) FIG. 2 is a graph showing comparison between gas generation amounts according to Experimental Example 2.

MODE FOR INVENTION

(4) 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

(5) Li.sub.1.33Ti.sub.1.67O.sub.4 as an anode active material, Denka black as a conductive material, and PVdF as a binder were added in a weight ratio of 90:5:5 to NMP and mixed therein to prepare an anode mixture. Subsequently, the anode mixture was coated onto 20 μm Al foil and the coated Al foil was pressed and dried, thereby completing fabrication of an anode of 6.6 mg/cm.sup.2.

(6) In addition, LiNi.sub.0.5Mn.sub.1.5O.sub.4 as a cathode active material, Denka black as a conductive material, and PVdF as a binder were added in a weight ratio of 90:5:5 to NMP and mixed therein to prepare a cathode mixture. Subsequently, the cathode mixture was coated onto 20 μm Al foil and the coated Al foil was pressed and dried, thereby completing fabrication of a cathode of 8.6 mg/cm.sup.2.

(7) An electrode assembly was manufactured by interposing separators (thickness: 20 μm) between the prepared cathodes and anodes. After accommodating the electrode assembly in a pouch-type battery case, a lithium salt-containing non-aqueous electrolyte in which ethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed in a volume ratio of 1:1:1 and which contains 1M LiPF.sub.6 as a lithium salt was injected thereinto. The resulting battery case was sealed, thereby completing manufacture of a lithium secondary battery.

EXAMPLE 2

(8) A lithium secondary battery was manufactured in the same manner as in Example 1, except that an anode of 6.6 mg/cm.sup.2 and a cathode of 7.8 mg/cm.sup.2 were manufactured.

COMPARATIVE EXAMPLE 1

(9) A lithium secondary battery was manufactured in the same manner as in Example 1, except that an anode of 6.6 mg/cm.sup.2 and a cathode of 7.1 mg/cm.sup.2 were manufactured.

EXPERIMENTAL EXAMPLE 1

(10) Cut-off voltages of the secondary batteries manufactured according to Examples 1 and 2 and Comparative Example 1 were set to 3.5 V and anode and cathode potentials of each secondary battery were measured when the cut-off voltage was reached. Results are shown in Table 1 below.

(11) TABLE-US-00001 TABLE 1 Anode potential (V) Cathode potential (V) Example 1 1.3 4.8 Example 2 1.4 4.9 Comparative 1.55 5.05 Example 1

(12) Referring to Table 1, in the secondary batteries of Examples 1 and 2, the potentials of the anodes are 1.3 and 1.4 V when the cut-off voltage is reached and thus the potentials of the cathodes are 4.8 and 4.9 V and, accordingly, the potential of the cathode reaches the cut-off voltage before reaching an oxidation potential of an electrolyte. By contrast, in the secondary battery of Comparative Example 1, the potential of the anode is 1.55 V when the cut-off voltage is reached and thus the potential of the cathode is 5.05 V and thus reaches an oxidation potential of an electrolyte.

EXPERIMENTAL EXAMPLE 2

(13) Evaluation of Lifespan Characteristics of Secondary Battery

(14) The secondary batteries of Examples 1 and 2 and Comparative Example 1 were subjected to charging and discharging at 1 C and 600 mA in a range of 2 to 3.35 V. Changes in charge capacity of each battery were measured while 50 charging and discharging cycles were repeated at room temperature. Results are shown in FIG. 1.

(15) Referring to FIG. 1, the secondary batteries of Examples 1 and 2 according to the present invention exhibit less reduction in charge capacity, compared to the battery of Comparative Example 1 even when charging and discharging processes are repeated.

EXPERIMENTAL EXAMPLE 3

(16) Measurement of Gas Generation Amount of Secondary Battery

(17) The secondary batteries of Examples 1 and 2 and Comparative Example 1 were subjected to charging and discharging at 1 C and 600 mA in a range of 2 to 3.35 V and 50 charging and discharging cycles were repeated at room temperature. Gas generation amounts were measured during 50 cycles and measurement results are shown in FIG. 2.

(18) Referring to FIG. 2, it can be confirmed that the batteries of Examples 1 and 2 exhibit smaller gas generation amounts and particularly, when cut-off voltage is reached, the battery of Example 1, in which the potential of the anode is lower, exhibits much less gas generation than the battery of Comparative Example 1.

(19) Therefore, it can be confirmed that, when the secondary battery according to the present invention is used, generation of gases in the battery is suppressed and thus expansion of the battery is prevented and lifespan characteristics of the battery are enhanced.

(20) 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

(21) As described above, a lithium secondary battery according to the present invention prevents Li plating by using an LTO anode and has a particular range of charge cut-off voltage and an anode has a particular potential when the charge cut-off voltage is reached and thus, even when a high-voltage cathode is used, increase of the potential of a cathode to an oxidation potential or greater of an electrolyte is prevented and thus oxidation of the electrolyte is prevented, which results in enhancement of secondary battery performance.