Secondary battery having improved safety

1. A secondary battery comprising an electrode assembly including a cathode, an anode, a separator interposed between the cathode and the anode and an electrolyte, the secondary battery comprising a HF scavenger in the electrolyte,

wherein the cathode comprises lithium manganese composite oxide with a spinel structure represented by the following Formula 2 as a cathode active material:

Li x Ni y Mn 2-y O 4   (2)

wherein 0.9≦x≦1.2 and 0.4≦y≦0.5;

wherein the anode comprises lithium titanium oxide (LTO) represented by Formula 4:

Li a Ti b O 4   (4)

wherein 0.5≦a≦3 and 1≦b≦2.5; and

wherein the HF scavenger is contained in the electrolyte in an amount of 0.1% to 10%, based on the total weight of the electrolyte.

2. The secondary battery according to claim 1 , wherein the lithium nickel manganese oxide of Formula 2 is LiNi 0.5 Mn 1.5 O 4 or LiNi 0.4 Mn 1.6 O 4 .

3. The secondary battery according to claim 1 , wherein the lithium titanium oxide of Formula 4 is Li 1.33 Ti 1.67 O 4 or LiTi 2 O 4 .

4. The secondary battery according to claim 1 , wherein the HF scavenger is a silane compound.

5. The secondary battery according to claim 4 , wherein the HF scavenger is silazane.

6. The secondary battery according to claim 1 , wherein the HF scavenger is present in an amount of 0.1% to 3%, based on the total weight of the electrolyte.

7. The secondary battery according to claim 1 , wherein the secondary battery is a lithium secondary battery.

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

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

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

11. The device according to claim 10 , wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle or a power storage system.