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 and an organic solvent, wherein the non-aqueous electrolyte solution further comprises a first ester-based compound having the following formula (I) and a second ester-based compound having the following formula (II), and the amount of the first and the second ester-based compounds is in the range of 50 to 90 vol % based on the total volume of the organic solvent, the first ester-based compound and the second ester-based compound; and

wherein a radical-transfer reaction occurs between the first ester-based compound and the second ester-based compound:

wherein,

R 1 is substituted or unsubstituted straight- or branched-chain alkyl group having 1 to 10 carbon atoms,

R 2 is substituted or unsubstituted branched-chain alkyl group having 3 to 10 carbon atoms, and

R 3 and R 4 are substituted or unsubstituted straight-chain alkyl group having 1 to 10 carbon atoms.

2. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1 , wherein the volume mixing ratio (a:b) of the first ester-based compound (a) and the second ester-based compound (b) is 80:20 to 20:80.

3. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1 , wherein R 1 is substituted or unsubstituted straight- or branched-chain alkyl group having 1 to 8 carbon atoms, R 2 is substituted or unsubstituted branched-chain alkyl group having 3 to 8 carbon atoms, and R 3 and R 4 are substituted or unsubstituted straight-chain alkyl group having 1 to 8 carbon atoms.

4. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1 , wherein R 1 is substituted or unsubstituted straight- or branched-chain alkyl group having 1 to 6 carbon atoms; R 2 is substituted or unsubstituted isoalkyl group having 3 to 8 carbon atoms, substituted or unsubstituted sec-alkyl group having 4 to 8 carbon atoms or substituted or unsubstituted tert-alkyl group having 4 to 8 carbon atoms; and R 3 and R 4 are substituted or unsubstituted straight-chain alkyl group having 1 to 6 carbon atoms.

5. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1 , wherein R 1 , R 3 and R 4 are methyl, ethyl, propyl or butyl, and R 2 is isopropyl, isobutyl, isopentyl, isohexyl, sec-butyl, sec-pentyl, tert-butyl or tert-pentyl.

6. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 1 , wherein the first ester-based compound is at least one selected from the group consisting of isobutyl propionate, isoamyl propionate, isobutyl butylate, and isopropyl propionate, and the second ester-based compound is at least one selected from the group consisting of methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl butylate, ethyl butylate, propyl butylate and butyl butylate.

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

8. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 7 , 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 − .

9. 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, a cyclic carbonate, an ether, an ester, an amide and a mixture thereof.

10. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 9 , 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.

11. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 9 , wherein the cyclic carbonate compound is any one 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 or a halide thereof or a mixture thereof.

12. The non-aqueous electrolyte solution for a lithium secondary battery according to claim 9 , 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.

13. 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.

14. 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 .

15. The lithium secondary battery according to claim 14 , wherein the anode has an anode active material layer comprising a carbon-based material, lithium metal, a metal compound or a mixture thereof.

16. 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.

17. The lithium secondary battery according to claim 14 , wherein the cathode has a cathode layer comprising a lithium-containing oxide.

18. The lithium secondary battery according to claim 17 , wherein the lithium-containing oxide is a lithium-containing transition metal oxide.

19. The lithium secondary battery according to claim 18 , wherein the lithium-containing transition metal 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.