Rechargeable lithium battery

1. A rechargeable lithium battery, comprising

an electrolyte comprising a lithium salt and a non-aqueous organic solvent;

a negative electrode, said negative electrode comprising:

i) a current collector; and

ii) a negative active material layer formed on the current collector, and including a binder and a negative active material, said negative active material consisting of:

a) a silicon-based negative active material in an amount of about 3 to about 20 wt % based on 100 wt % of the negative active material, and

b) a carbon-based negative active material, wherein the silicon-based negative active material is at least one component selected from the group consisting of silicon (Si), a silicon oxide, silicon coated with conductive carbon on the surface, and a silicon oxide coated with conductive carbon on the surface, and wherein the carbon-based negative active material is crystalline carbon, amorphous carbon, or a combination thereof; and

a positive electrode, said positive electrode comprising a positive active material having charge and discharge efficiency of less than or equal to about 95%, wherein the positive active material is a mixture of a first positive active material where the first positive active material is a lithium cobalt-based oxide and a second positive active material where the second positive active material is a lithium nickel cobalt manganese-based oxide having an average particle diameter of about 5 μm to about 15 μm, and the first and second positive active material are mixed in a weight ratio ranging from about 8:2 to about 6:4.

2. The rechargeable lithium battery of claim 1 , wherein the silicon-based negative active material is in an amount of about 3 to about 5 wt % based on 100 wt % of the negative active material.

3. The rechargeable lithium battery of claim 1 , wherein the silicon-based negative active material is silicon oxide powder (SiO x , x=0.95 to 1.1) and the carbon-based negative active material is graphite.

4. The rechargeable lithium battery of claim 1 , wherein the positive active material is a mixture of a first positive active material having charge and discharge efficiency of greater than about 90% and a second positive active material having charge and discharge efficiency of less than or equal to about 90%.

5. The rechargeable lithium battery of claim 4 , wherein the first and second positive active material are mixed in a weight ratio ranging from about 7:3 to about 6:4.

6. The rechargeable lithium battery of claim 1 , wherein the silicon-based negative active material is at least one component selected from the group consisting of a silicon oxide and a silicon oxide coated with conductive carbon on the surface.

7. The rechargeable lithium battery of claim 1 , wherein the first positive active material is LiCoO 2 .

8. The rechargeable lithium battery of claim 7 , wherein the second positive active material is LiNi 0.5 Co 0.2 Mn 0.3 O 2 .

9. The rechargeable lithium battery of claim 1 , wherein the second positive active material is LiNi 0.5 Co 0.2 Mn 0.3 O 2 .

10. The rechargeable lithium battery of claim 1 , wherein the lithium salt is at least one selected from the group consisting of LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiC 4 F 9 SO 3 , LiClO 4 , LiAlO 2 , LiAlCl 4 , LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 ) (where x and y are natural numbers of 1 to 20, respectively), LiCl, LiI, and LiB(C 2 O 4 ) 2 (lithium bis(oxalato) borate).

11. The rechargeable lithium battery of claim 1 , wherein the lithium salt is at least one selected from the group consisting of LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiC 4 F 9 SO 3 , LiClO 4 , LiCl, LiI, and LiB(C 2 O 4 ) 2 (lithium bis(oxalato) borate).

12. The rechargeable lithium battery of claim 1 , wherein the lithium salt is at least one selected from the group consisting of LiPF 6 , LiBF 4 , LiClO 4 , LiCl, LiI, and LiB(C 2 O 4 ) 2 (lithium bis(oxalato) borate).

13. The rechargeable lithium battery of claim 1 , wherein the lithium salt is at least one selected from the group consisting of LiPF 6 , LiBF 4 , and LiB(C 2 O 4 ) 2 (lithium bis(oxalato) borate).