Lithium secondary battery including phosphite additive
A lithium secondary battery includes a positive electrode; a negative electrode; and an electrolyte disposed between the positive electrode and the negative electrode, wherein the positive electrode includes a positive active material represented by Formula 1, and the electrolyte includes a lithium salt; a non-aqueous solvent; and a phosphite compound represented by Formula 2, wherein the phosphite compound is present in amount of about 0.1 wt % to about 5 wt % 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 independently an unsubstituted C 1 -C 30 alkyl group or an unsubstituted C 6 -C 60 aryl group.
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 active material represented by Formula 1, and
wherein the electrolyte comprises:
a lithium salt;
a non-aqueous solvent; and
a phosphite compound represented by Formula 2,
wherein the phosphite compound is present in an amount in a range of about 0.1 weight percent to about 5 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; and
wherein in Formula 2,
R1 to R3 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 the phosphite compound is present in an amount in a range of about 0.1 weight percent to about 3 weight percent based on the total weight of the electrolyte.
3. The lithium secondary battery of claim 1 , wherein the phosphite compound comprises tributyl phosphite, triphenyl phosphite, tris(o-tolyl)phosphite, or a combination thereof.
4. The lithium secondary battery of claim 1 , wherein the lithium salt comprises lithium difluoro(oxalate)borate, lithium bis(oxalate)borate, lithium difluorobis(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 1 , wherein the non-aqueous solvent comprises dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methylethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, tetraethyleneglycoldimethylether, 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 the fluoroethylene carbonate is present in an amount in a range of about 0.1 volume percent to about 10 volume percent based on a 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, vinylethylene carbonate, maleic anhydride, succinic anhydride, or a combination thereof.
10. The lithium secondary battery of claim 9 , wherein vinylene carbonate, maleic anhydride, or the combination thereof is present in an amount in a range of about 0.1 weight percent to about 2 weight percent based on the total weight of the electrolyte.
11. The lithium secondary battery of claim 1 , wherein the electrolyte further comprises a sulfone compound, a sulfonate compound, a disulfonate compound, or a combination thereof in an amount in a range of about 0.1 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 disulfonate compound is methylene methane disulfonate.
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 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 active material comprises 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 , or Li 1.02 Ni 0.88 Co 0.08 Al 0.04 O 2 .
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 (Si), a silicon-carbon composite material comprising a Si particle, 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 a direct current internal resistance (DCIR) increase ratio of the lithium secondary battery is 150% or less before and after 200 charge/discharge cycles at 45° C.
20. The lithium secondary battery of claim 1 , wherein a cell energy density of the lithium secondary battery is about 500 watt-hours per liter or greater.