Lithium secondary battery comprising disulfonate additive and method of preparing the same

1. A lithium secondary battery comprising:

a positive electrode comprising a positive active material represented by Formula 1;

a negative electrode; and

an electrolyte disposed between the positive electrode and the negative electrode, the electrolyte comprising a lithium salt, a nonaqueous solvent, and a cyclic compound represented by Formula 2, wherein an amount of the cyclic compound is less than about 2 percent by weight based on a total weight of the electrolyte,

wherein, in Formulae 1 and 2,

0.9≤x≤1.2, 0.7≤y≤0.95, 0≤z≤0.2,

M comprises Al, Mg, Mn, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Bi, or a combination thereof,

A comprises a monovalent anion, a divalent anion, a trivalent anion, or a combination thereof, and

R 1 and R 2 are each independently a substituted or unsubstituted C 1 -C 30 alkylene group,

wherein a substituent of the substituted C 1 -C 30 alkylene group comprises a halogen, a methyl group, an ethyl group, a propyl group, an iso-propyl group, a butyl group, a tert-butyl group, a trifluoromethyl group, a tetrafluoroethyl group, a vinyl group, a propenyl group, a butenyl group, or a combination thereof,

wherein the nonaqueous solvent comprises fluorinated ethylene carbonate, ethylene carbonate, and vinylene carbonate,

wherein, an amount of the fluorinated ethylene carbonate is about 7 volume percent or less, based on a total volume of the nonaqueous solvent,

wherein the vinylene carbonate is contained in an amount of less than 2 percent by volume, based on a total volume of the electrolyte.

2. The lithium secondary battery of claim 1 , wherein the amount of the cyclic compound is in a range of about 0.1 weight percent to about 1 weight percent, based on the total weight of the electrolyte.

3. The lithium secondary battery of claim 1 , wherein R 1 and R 2 are each independently a substituted or unsubstituted methylene group or a substituted or unsubstituted ethylene group.

4. The lithium secondary battery of claim 1 , wherein the lithium salt comprises lithium difluoro(oxalate)borate, LiBF 4 , LiPF 6 , LiCF 3 SO 3 , (CF 3 SO 2 ) 2 NLi, (FSO 2 ) 2 NLi, or a combination thereof.

5. The lithium secondary battery of claim 4 , wherein the lithium salt comprises lithium difluoro(oxalate)borate and LiPF 6 , and wherein an amount of lithium difluoro(oxalate)borate is about 2 weight percent or less, based on the total weight of the electrolyte.

6. The lithium secondary battery of claim 4 , wherein the lithium salt comprises (FSO 2 ) 2 NLi and LiPF 6 , and wherein an amount of (FSO 2 ) 2 NLi is about 10 weight percent or less, based on the total weight of the electrolyte.

7. The lithium secondary battery of claim 1 ,

wherein the electrolyte further comprises maleic anhydride, succinic anhydride, or a combination thereof, and

wherein the maleic anhydride, succinic anhydride, or combination thereof are contained in an amount of less than about 2 percent by volume, based on a total volume of the electrolyte.

8. The lithium secondary battery of claim 7 , wherein the electrolyte comprises maleic anhydride in an amount of less than about 2 volume percent, based on a total volume of the electrolyte.

9. The lithium secondary battery of claim 1 , wherein the electrolyte further comprises an additive comprising a phosphine compound, a phosphite compound, a phosphate compound, or a combination thereof.

10. The lithium secondary battery of claim 9 , wherein the electrolyte comprises the additive in an amount of less than about 3 weight percent, based on the total weight of the electrolyte.

11. The lithium secondary battery of claim 1 , wherein, in Formula 1, 0.8≤y≤0.95.

12. The lithium secondary battery of claim 1 , wherein the positive active material is represented by Formula 3 or Formula 4:

LiNi y′ Co 1y′−z′ Al z′ O 2 , or  Formula 3

LiNi y Co 1−y−z Mn z O 2 ,  Formula 4

wherein, in Formulae 3 and 4, 0.8≤y′≤0.95, 0<z′<0.1, and 0<1−y′−z′<0.2.

13. The lithium secondary battery of claim 1 , wherein the positive electrode comprises LiNi 0.8 Co 0.15 Al 0.05 O 2 , LiNi 0.88 Co 0.1 Al 0.02 O 2 , LiNi 0.85 Co 0.1 Al 0.05 O 2 , LiNi 0.8 Co 0.15 Mn 0.05 O 2 , LiNi 0.88 Co 0.1 Mn 0.02 O 2 , LiNi 0.85 Co 0.1 Mn 0.05 O 2 , or a combination thereof.

14. The lithium secondary battery of claim 1 , wherein the negative electrode comprises a negative active material comprising a metalloid which is alloyable with lithium, or a carbonaceous negative active material.

15. The lithium secondary battery of claim 14 , wherein the negative active material comprising the metalloid which alloyable with lithium comprises silicon, a silicon-carbon composite, SiO a′ , wherein 0<a′<2, or a combination thereof.

16. The lithium secondary battery of claim 1 , wherein the silicon-carbon composite comprises silicon particles having an average diameter of about 200 nanometers or less.

17. The lithium secondary battery of claim 1 , wherein, after 300 cycles of charging and discharging at a temperature of about 45° C., an increase in direct current internal resistance is less than about 150%.

18. The lithium secondary battery of claim 1 , wherein the lithium secondary battery has a cell energy density of about 500 watt hours per liter or greater.

19. The lithium secondary battery of claim 1 , wherein the positive active material is represented by Formula 3 or Formula 4:

LiNi y Co 1−y′−z′ Al z′ O 2 , or  Formula 3

LiNi y′ Co 1−y′−z′ Mn z′ O 2 ,  Formula 4

wherein, in Formulae 3 and 4, 0.8<y′≤0.95, 0<z′<0.1, and 0<1−y′−z′<0.2.

20. A method of preparing a lithium secondary battery, the method comprising:

providing a positive electrode comprising a positive active material represented by Formula 1;

providing a negative electrode; and

disposing an electrolyte between the positive electrode and the negative electrode, the electrolyte comprising a lithium salt, a nonaqueous solvent, and a cyclic compound represented by Formula 2, wherein an amount of the cyclic compound is less than about 2 percent by weight, based on a total weight of the electrolyte,

wherein, in Formulae 1 and 2,

0.9≤x≤1.2, 0.7≤y≤0.95, 0≤z<0.2,

M comprises Al, Mg, Mn, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Bi, or a combination thereof,

A comprises a monovalent anion, a divalent anion, a trivalent anion, or a combination thereof, and

R 1 and R 2 are each independently a substituted or unsubstituted C 1 -C 30 alkylene group,

wherein a substituent of the substituted C 1 -C 30 alkylene group comprises a halogen, a methyl group, an ethyl group, a propyl group, an iso-propyl group, a butyl group, a tert-butyl group, a trifluoromethyl group, a tetrafluoroethyl group, a vinyl group, a propenyl group, a butenyl group, or a combination thereof,

wherein the nonaqueous solvent comprises fluorinated ethylene carbonate, ethylene carbonate, and vinylene carbonate,

wherein, an amount of the fluorinated ethylene carbonate is about 7 volume percent or less, based on a total volume of the nonaqueous solvent,

wherein the vinylene carbonate is contained in an amount of less than 2 percent by volume, based on a total volume of the electrolyte.