LITHIUM SECONDARY BATTERY INCLUDING PHOSPHATE-BASED ADDITIVE

1 . A lithium secondary battery, comprising:

a positive electrode;

a negative electrode; and

an electrolyte disposed between the positive electrode and the negative electrode,

wherein the positive electrode comprises a positive electrode active material represented by Formula 1,

the electrolyte comprises a lithium salt, a non-aqueous solvent, and a phosphate compound represented by Formula 2, and

an amount of the phosphate compound is less than 3 weight percent based on a total weight of the electrolyte,

Li x Ni y M 1-y O 2-z A z ,  Formula 1

wherein, in Formula 1,

0.9≤x≤1.2, 0.7≤y≤0.98, and 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, and

A is an element having an oxidation number of −1 or −2,

wherein, in Formula 2, R 1 to R 3 are each independently an unsubstituted linear or branched C 1 -C 30 alkyl group or an unsubstituted C 6 -C 60 aryl group.

2 . The lithium secondary battery of claim 1 , wherein an amount of the phosphate compound is about 0.1 weight percent or more to less than about 3 weight percent, based on the total weight of the electrolyte.

3 . The lithium secondary battery of claim 1 , wherein the phosphate compound comprises trimethyl phosphate, triethyl phosphate, tri(2,2,2-trifluoroethyl)phosphate, tri(3,3,3,2,2-pentafluoropropyl)phosphate, triphenyl phosphate, or a combination thereof.

4 . The lithium secondary battery of claim 1 , wherein the lithium salt comprises lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)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 1 , wherein the non-aqueous solvent comprises dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, or a combination thereof.

6 . The lithium secondary battery of claim 1 , wherein the non-aqueous solvent comprises fluoroethylene carbonate.

7 . The lithium secondary battery of claim 6 , wherein an amount of the fluoroethylene carbonate is about 0.1 volume percent to about 10 volume percent, based on the total volume of the non-aqueous solvent.

8 . The lithium secondary battery of claim 1 , wherein the electrolyte comprises a cyclic carbonate comprising a carbon-carbon double bond, a cyclic carboxylic acid anhydride comprising a carbon-carbon double bond, or a combination thereof.

9 . The lithium secondary battery of claim 1 , wherein the electrolyte further comprises vinylene carbonate vinyl ethylene carbonate, maleic anhydride, succinic anhydride, or a combination thereof.

10 . The lithium secondary battery of claim 9 , wherein an amount of the vinylene carbonate, the maleic anhydride, or the combination thereof is about 0.1 weight percent to about 3 weight percent, based on the total weight of the electrolyte.

11 . The lithium secondary battery of claim 1 , wherein the electrolyte further comprises a phosphorus-containing compound, a sulfur-containing compound, or a combination thereof in an amount of about 0.5 weight percent to about 2 weight percent, based on the total weight of the electrolyte.

12 . The lithium secondary battery of claim 11 , wherein the sulfur-containing compound is methylene methane disulfonate, busulfan, tosyloxydisulfonate, methylene bis methansulfonate, or a combination thereof.

13 . The lithium secondary battery of claim 1 , wherein, in Formula 1, 0.8≤y≤0.98.

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

Li x′ Ni y′ Co 1-y′-z′ Al z′ O 2 , or  Formula 3

Li x′ Ni y′ Co 1-y′-z′ Mn z′ O 2 ,  Formula 4

wherein, in Formula 3 and Formula 4, 0.9≤x′≤1.2, 0.8≤y′≤0.98, 0≤z′<0.1, and 0<1−y′−z′<0.2.

15 . The lithium secondary battery of claim 1 , wherein the positive electrode comprises LiNi 0.8 Co 0.15 Mn 0.05 O 2 , LiNi 0.85 Co 0.1 Mn 0.05 O 2 , LiNi 0.88 Co 0.08 Mn 0.04 O 2 , LiNi 0.88 Co 0.08 Al 0.04 O 2 , Li 1.02 Ni 0.80 Co 0.15 Mn 0.05 O 2 , Li 1.02 Ni 0.85 Co 0.10 Mn 0.05 O 2 , Li 1.02 Ni 0.88 Co 0.08 Mn 0.04 O 2 , Li 1.02 Ni 0.88 Co 0.08 Al 0.04 O 2 , or a combination thereof.

16 . The lithium secondary battery of claim 1 , wherein the negative electrode comprises a negative active material comprising a metal alloyable with lithium, a carbonaceous negative active material, or a combination thereof.

17 . The lithium secondary battery of claim 16 , wherein the negative active material comprising a metal alloyable with lithium comprises silicon, a silicon-carbon composite material comprising, SiO a′ (0<a′<2), or a combination thereof.

18 . The lithium secondary battery of claim 16 , wherein the carbonaceous negative active material comprises graphite.

19 . The lithium secondary battery of claim 1 , wherein the lithium secondary battery has a direct current internal resistance increase rate of 150% or less after 300 charge/discharge cycles at a temperature of 45° C.

20 . The lithium secondary battery of claim 1 , wherein a cell energy density is about 500 Watt hours per liter or greater.