Electrolyte for rechargeable lithium battery, and rechargeable lithium battery including the same

1. An electrolyte for a rechargeable lithium battery comprising:

a first lithium salt;

a second lithium salt comprising a compound selected from the group consisting of compounds represented by Chemical Formula 1, compounds represented by Chemical Formula 3-1, compounds represented by Chemical Formula 3-2, and combinations thereof;

wherein in Chemical Formula 1,

R 1 and R 2 are optionally linked by a moiety represented by Chemical Formula 2 to form a ring,

when R 1 and R 2 are not linked by the moiety represented by Chemical Formula 2, each of R 1 and R 2 is F, and

R 3 and R 4 are linked by a moiety represented by Chemical Formula 2 to form a ring,

wherein in Chemical Formula 2,

each of R 5 and R 6 is independently O or S,

each of X and Y is independently H or F,

each of l and n is 0 or 1, and

m is an integer ranging from 0 to 5,

wherein in Chemical Formula 3-1,

R 7 and R 8 are optionally linked by a moiety represented by Chemical Formula 2 to form a ring,

when R 7 and R 8 are not linked by the moiety represented by Chemical Formula 2, each of R 7 and R 8 is F,

R 9 and R 10 are linked by a moiety represented by Chemical Formula 2 to form a ring, and

each of R 11 and R 12 is F,

wherein in Chemical Formula 3-2,

each of R 17 and R 18 is independently selected from the group consisting of O, S and NR′, wherein R′ is selected from the group consisting of substituted C1 to C5 alkyl groups and unsubstituted C1 to C5 alkyl groups, and

each of R 19 and R 20 is F;

a non-aqueous organic solvent; and

an additive comprising a compound represented by Chemical Formula 9;

wherein in Chemical Formula 9,

A is selected from the group consisting of S, O, and NR″, where R″ is selected from the group consisting of H, substituted C1 to C20 alkyl groups, and unsubstituted C1 to C20 alkyl groups, and

each of R 13 to R 16 is independently selected from the group consisting of H, halogens, substituted C1 to C20 alkyl groups, unsubstituted C1 to C20 alkyl groups, substituted C1 to C20 alkoxy groups, and unsubstituted C1 to C20 alkoxy groups, wherein R 14 and R 15 may optionally be linked to each other to form a ring.

2. The electrolyte of claim 1 , wherein the second lithium salt comprises a compound selected from the group consisting of compounds represented by Chemical Formulae 4 and 5:

3. The electrolyte of claim 1 , wherein the second lithium salt comprises a compound selected from the group consisting of compounds represented by Chemical Formulae 6 to 8:

4. The electrolyte of claim 1 , wherein the additive comprises a compound selected from the group consisting of compounds represented by Chemical Formulae 10 to 13:

5. The electrolyte of claim 1 , wherein the second lithium salt is present in an amount of about 0.1 to about 10 wt % based on the total weight of the electrolyte.

6. The electrolyte of claim 5 , wherein the second lithium salt is present in an amount of about 0.5 to about 1.5 wt % based on the total weight of the electrolyte.

7. The electrolyte of claim 1 , wherein a weight ratio of the first lithium salt to the second lithium salt is about 1:9 to about 9:1.

8. The electrolyte of claim 1 , wherein the additive is present in amount of about 0.005 to about 3 wt % based on the total weight of the electrolyte.

9. The electrolyte of claim 8 , wherein the additive is present in an amount of about 0.03 to about 0.1 wt % based on the total weight of the electrolyte.

10. The electrolyte of claim 1 , wherein the first lithium salt comprises a material selected from the group consisting of LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiSO 3 CF 3 , LiN(CF 3 SO 2 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiClO 4 , LiAlO 2 , LiAlCl 4 , and combinations thereof.

11. The electrolyte of claim 1 , wherein a weight ratio of the additive to the second lithium salt is about 0.005:1 to about 1:1.

12. A rechargeable lithium battery comprising:

a positive electrode including a positive active material;

a negative electrode including a negative active material; and

the electrolyte of claim 1 .

13. The lithium rechargeable battery of claim 12 , wherein the positive active material comprises at least one lithium metal oxide selected from the group consisting of lithium metal oxides represented by Chemical Formulae 14 to 16:

Li x MO 2   Chemical Formula 14

wherein M is at least one transition element, and 0≦x≦1,

Li y M 2 O 4   Chemical Formula 15

wherein M is at least one transition element, and 0≦y≦2,

x (Li 2 MnO 3 ).(1 −x )(LiMn 2-y M y O 4 )  Chemical Formula 16

wherein M is at least one transition element, 0<x<1, and 0≦y<1.

14. The lithium rechargeable battery of claim 12 , wherein the negative active material comprises an active material selected from the group consisting of carbon-based active materials, Si-based active materials, and combinations thereof.

15. The lithium rechargeable battery of claim 12 , wherein the second lithium salt comprises a compound selected from the group consisting of compounds represented by Chemical Formulae 4 and 5:

16. The lithium rechargeable battery of claim 12 , wherein the second lithium salt comprises a compound selected from the group consisting of compounds represented by Chemical Formulae 6 to 8:

17. The lithium rechargeable battery of claim 12 , wherein the additive comprises a compound selected from the group consisting of compounds represented by Chemical Formulae 10 to 13:

18. The lithium rechargeable battery of claim 12 , wherein the second lithium salt is present in an amount of about 0.1 to about 10 wt % based on the total weight of the electrolyte.

19. The lithium rechargeable battery of claim 18 , wherein the second lithium salt is present in an amount of about 0.5 to 1.5 wt % based on the total weight of the electrolyte.

20. The lithium rechargeable battery of claim 12 , wherein the additive is present in an amount of about 0.005 to about 3 wt % based on the total weight of the electrolyte.