Non-aqueous electrolyte and lithium secondary battery using the same

1. A non-aqueous electrolyte solution for a lithium secondary battery, comprising

an electrolyte salt,

an organic solvent,

a cyclic carbonate, and

an ester-based compound having a branched-chain alkyl group, represented by the following formula (I), wherein the amount of the ester-based compound is in the range of 50 to 80 vol % based on the total volume of the organic solvent and the ester-based compound:

wherein,

R 1 is a substituted or unsubstituted alkyl group having 2 and 10 carbon atoms and

R 2 is a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms,

where at least one of R 1 and R 2 is a substituted or unsubstituted branched-chain alkyl group having 3 to 10 carbon atoms,

wherein the ester-based compound having a branched-chain alkyl group is at least one selected from the group consisting of isobutyl propionate, isoamyl propionate, isobutyl butylate, ethyl 2-methyl butylate, ethyl isobutylate, methyl 2-methyl butyrate, methyl isovalerate, propyl-2-methyl butylate, propyl isovalerate and propyl isobutylate, and

wherein the ester-based compound inhibits the decomposition of the cyclic carbonate.

2. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1 , wherein

R 1 is a substituted or unsubstituted alkyl group having 2 to 8 carbon atoms and

R 2 is a substituted or unsubstituted alkyl group having 1 to 8 carbon atoms,

where at least one of R 1 and R 2 is a substituted or unsubstituted branched-chain alkyl group having 3 to 8 carbon atoms.

3. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1 , wherein

R 1 is a substituted or unsubstituted alkyl group having 2 to 6 carbon atoms and

R 2 is a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms,

where at least one of R 1 and R 2 is a substituted or unsubstituted isoalkyl group having 3 to 6 carbon atoms, substituted or unsubstituted sec-alkyl group having 4 to 6 carbon atoms, or substituted or unsubstituted tert-alkyl group having 4 to 6 carbon atoms.

4. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1 , wherein

R 1 is ethyl or propyl, and

R 2 is isopropyl, isobutyl, isopentyl, isohexyl, sec-butyl, sec-pentyl, tert-butyl or tert-pentyl.

5. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1 , wherein

R 1 is isopropyl, isobutyl, isopentyl, isohexyl, sec-butyl, sec-pentyl, tert-butyl or tert-pentyl, and

R 2 is methyl, ethyl or propyl.

6. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1 , wherein the electrolyte salt is a lithium salt.

7. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 6 , wherein the lithium salt has an anion selected from the group consisting of F − , Cl − , Br − , I − , NO 3 − , N(CN) 2 − , BF 4 − , ClO 4 − , PF 6 − , (CF 3 ) 2 PF 4 − , (CF 3 ) 3 PF 3 − , (CF 3 ) 4 PF 2 − , (CF 3 ) 5 PF − , (CF 3 ) 6 P − , CF 3 SO 3 − , CF 3 CF 2 SO 3 − , (CF 3 SO 2 ) 2 N − , (FSO 2 ) 2 N − , CF 3 CF 2 (CF 3 ) 2 CO − , (CF 3 SO 2 ) 2 CH − , (SF 5 ) 3 C − , (CF 3 SO 2 ) 3 C − , CF 3 (CF 2 ) 7 SO 3 − , CF 3 CO 2 − , CH 3 CO 2 − , SCN − and (CF 3 CF 2 SO 2 ) 2 N − .

8. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1 , wherein the organic solvent is selected from the group consisting of a linear carbonate, an ether, an ester, an amide and a mixture thereof.

9. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 8 , wherein the linear carbonate is selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate and a mixture thereof.

10. The non-aqueous electrolyte solution for a lithium secondary battery according to claim l, wherein the cyclic carbonate compound is selected from the group consisting of ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinyl ethylene carbonate, a halide thereof and a mixture thereof.

11. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 10 , wherein the halide of the cyclic carbonate is a compound having the following formula (II):

wherein,

R 3 to R 6 are each independently hydrogen, or substituted or unsubstituted C 1-10 alkyl, where hydrogen contained in at least one of R 3 to R 6 is substituted with halogen.

12. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 11 , wherein the halide of the cyclic carbonate is fluoroethylene carbonate.

13. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 8 , wherein the ether is selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether and a mixture thereof.

14. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1 , which further comprises any one selected from the group consisting of a cyclic sulfite, a saturated sultone, an unsaturated sultone, a non-cyclic sulfone and a mixture thereof.

15. A lithium secondary battery comprising an electrode assembly consisting of a cathode, an anode and a separator interposed therebetween, and a non-aqueous electrolyte solution introduced in the electrode assembly, wherein the non-aqueous electrolyte solution is the non-aqueous electrolyte solution for a lithium secondary battery according to claim 1 .

16. The lithium secondary battery according to claim 15 , wherein the anode has an anode active material layer comprising lithium metal, a carbon-based material, a metal compound or a mixture thereof.

17. The lithium secondary battery according to claim 15 , wherein the metal compound is a compound containing at least one metal selected from the group consisting of Si, Ge, Sn, Pb, P, Sb, Bi, Al, Ga, In, Ti, Mn, Fe, Co, Ni, Cu, Zn, Ag, Mg, Sr, and Ba, or a mixture thereof.

18. The lithium secondary battery according to claim 15 , wherein the cathode has a cathode layer comprising a lithium-containing oxide.

19. The lithium secondary battery according to claim 16 , wherein the lithium-containing oxide is selected from the group consisting of LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , Li(Ni a Co b Mn c )O 2 (0<a<1, 0<b<1, 0<c<1, a+b+c=1), LiNi 1-y Co y O 2 , LiCo 1-y Mn y O 2 , LiNi 1-y Mn y O 2 (O≦y<1), Li(Ni a Co b Mn c )O 4 (0<a<2, 0<b<2, 0<c<2, a+b+c=2), LiMn 2-z Ni z O 4 , LiMn 2-z Co z O 4 (0<z<2), LiCoPO 4 , LiFePO 4 and a mixture thereof.

20. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1 , wherein the ester-based compound having a branched-chain alkyl group is at least one selected from the group consisting of isobutyl propionate, isoamyl propionate, isobutyl butylate, ethyl 2-methyl butylate, methyl 2-methyl butyrate, methyl isovalerate, propyl-2-methyl butylate, propyl isovalerate and propyl isobutylate.