Electrolyte for lithium secondary batteries and lithium secondary battery including the same

1. An electrolyte for lithium secondary batteries comprising a lithium salt and a non-aqueous solvent, wherein the non-aqueous solvent comprises an ester based solvent, a carbonate based solvent, and an ether based solvent

wherein the ester based solvent is present in an amount ranging from 20 wt % to 30 wt %-, the carbonate based solvent is present in an amount ranging from 20 wt % to 30 wt %-, and the ether based solvent is present in an amount ranging from 40 wt % to 60 wt % with respect to a total weight of the non-aqueous solvent, and

wherein the ester based solvent is at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate (EP), γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, and ε-caprolactone, and

wherein the lithium salt consists of at least one selected from the group consisting of LiCl, LiBr, LiI, LiClO 4 , LiBF 4 , LiB 10 Cl 10 , LiPF 6 , LiCF 3 SO 3 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiPF 6 , LiAlCl 4 , CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2 ) 2 NLi, chloroborane lithium, lithium tetraphenyl borate, and imides.

2. The electrolyte according to claim 1 , wherein the ester based solvent comprises at least one of methyl propionate (MP) or ethyl propionate (EP).

3. The electrolyte according to claim 2 , wherein a mixing ratio of the methyl propionate (MP) to ethyl propionate (EP) is 10:90 to 90:10 based on the total weight of the ester based solvent.

4. The electrolyte for lithium secondary batteries according to claim 1 , wherein the carbonate based solvent comprises a cyclic carbonate, and the cyclic carbonate is at least one of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, or 2,3-pentylene carbonate.

5. The electrolyte for lithium secondary batteries according to claim 4 , wherein the carbonate based solvent comprises the cyclic carbonate and a linear carbonate, and the linear carbonate is at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), or ethyl propyl carbonate (EPC), and the cyclic carbonate and the linear carbonate are mixed in a weight ratio of 1:4 to 4:1.

6. The electrolyte for lithium secondary batteries according to claim 1 , wherein a concentration of the lithium salt in the electrolyte is 0.5 to 3 M.

7. A lithium secondary battery comprising the electrolyte for lithium secondary batteries according to claim 1 .

8. The lithium secondary battery according to claim 7 , wherein the lithium secondary battery comprises:

a cathode comprising a lithium metal phosphate according to Formula 1 below, as a cathode active material; and

an anode comprising amorphous carbon, as an anode active material,

Li 1+a M(PO 4−b )X b   (1)

wherein M is at least one selected from metals of Groups II to XII, X is at least one selected from F, S and N, −0.5≦a≦+0.5, and 0≦b≦0.1.

9. The lithium secondary battery according to claim 8 , wherein the lithium metal phosphate is a lithium iron phosphate having an olivine crystal structure according to Formula 2 below:

Li 1+a Fe 1−x M′ x (PO 4−b )X b   (2)

wherein M′ is at least one selected from Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y,

X is at least one selected from F, S, and N, and

−0.5≦a≦+0.5, 0≦x≦0.5, and 0≦b≦0.1.

10. The lithium secondary battery according to claim 9 , wherein the lithium metal phosphate having the olivine crystal structure is LiFePO 4 .

11. The lithium secondary battery according to claim 10 , wherein the lithium iron phosphate having the olivine crystal structure is coated with conductive carbon.

12. The lithium secondary battery according to claim 8 , wherein the amorphous carbon is hard carbon and/or soft carbon.

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

14. A battery pack comprising the battery module according to claim 13 .

15. A device comprising the battery pack according to claim 14 .

16. The device according to claim 15 , wherein the device is a hybrid electric vehicle, a plug-in hybrid electric vehicle, or an energy storage system.