Disclosed are nonaqueous electrolyte additives, which can improve the safety of a battery upon overcharge of the battery without reducing the performance of the battery, as well as a nonaqueous electrolyte comprising the additives, and a lithium secondary battery comprising the nonaqueous electrolyte. More particularly, disclosed are a nonaqueous electrolyte comprising both fluorobiphenyl and fluorotoluene as additives, and a lithium secondary battery comprising the nonaqueous electrolyte.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the structure of one example of a secondary battery, which is generally used.
Claims
1. A nonaqueous electrolyte for lithium secondary batteries, which comprises a lithium salt and an electrolyte compound, the nonaqueous electrolyte comprising fluorobiphenyl and fluorotoluene as additives.
2. The nonaqueous electrolyte according to claim 1, wherein the fluorobiphenyl is contained in an amount of 0.1-3 wt % based on the total weight of the nonaqueous electrolyte, and the fluorotoluene is contained in an amount of 3-10 w %, based on the total weight of the nonaqueous electrolyte.
3. The nonaqueous electrolyte according to claim 1, wherein the fluorobiphenyl is any one selected from among compounds represented by Formula 1a or 1b below:
4. The nonaqueous electrolyte according to claim 1, wherein the fluorotoluene is any one selected from among compounds represented by Formula 2 below:
5. The nonaqueous electrolyte according to claim 1, wherein the lithium salt is at least one selected from the group consisting of LiClO4, LiCF3SO3, LiPF6, LiBF4, LiAsF6 and LiN(CF3SO2)2.
6. The nonaqueous electrolyte according to claim 1, wherein the electrolyte compound comprises at least one cyclic carbonate selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC) and gamma-butyrolactone (GBL); and at least one linear carbonate selected from the group consisting of diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and methyl propyl carbonate.
7. The nonaqueous electrolyte according to claim 1, wherein the fluorobiphenyl forms a passivation layer by oxidation at a voltage higher than 4.2V, and the fluorotoluene undergoes an exothermic reaction at a voltage higher than 4.2V.
8. A lithium secondary battery comprising: a cathode capable of intercalating lithium salts; an anode capable of intercalating lithium ions; a porous separator; and a nonaqueous electrolyte containing a lithium salt and an electrolyte compound,
wherein the nonaqueous electrolyte comprises fluorobiphenyl and fluorotoluene as additives.
9. The lithium secondary battery according to claim 8, wherein the cathode comprises at least one cathode material selected from the group consisting of LiCoO2, LiNiO2, LiMn2O4 LiNi1-xCoxO2 (where 0<X<1) and MnO2.
10. The lithium secondary battery according to claim 8, wherein the anode comprises, as an anode material, carbon, lithium, a lithium metal, a lithium metal alloy, TiO2 or SnO2.
11. The lithium secondary battery according to claim 8, wherein the fluorobiphenyl is contained in an amount of 0.1-3 wt % based on the total weight of the nonaqueous electrolyte, and the fluorotoluene is contained in an amount of 3-10 w % based on the total weight of the nonaqueous electrolyte.
12. The lithium secondary battery according to claim 8, wherein the fluorobiphenyl is any one selected from among compounds represented by Formula 1a or 1b below:
13. The lithium secondary battery according to claim 8, wherein the fluorotoluene is any one selected from among compounds represented by Formula 2 below:
14. The lithium secondary battery according to claim 8, wherein the lithium salt is one or more selected from the group consisting of LiClO4, LiCF3SO3, LiPF6, LiBF4, LiAsF6 and LiN(CF3SO2)2.
15. The lithium secondary battery according to claim 8, wherein the electrolyte compound comprises at least one cyclic carbonate selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC) and gamma-butyrolactone (GBL); and at least one linear carbonate selected from the group consisting of diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and methyl propyl carbonate.
16. The lithium secondary battery according to claim 8, wherein the fluorobiphenyl forms a passivation layer by oxidation at a voltage higher than 4.2V, and the fluorotoluene undergoes an exothermic reaction at a voltage higher than 4.2V.
Patent Application
20070172729
