Electrolyte for lithium secondary battery and lithium secondary battery comprising the same
The present disclosure relates to an electrolyte for a lithium secondary battery capable of improving safety and reliability of the lithium secondary battery and a lithium secondary battery comprising the electrolyte. The electrolyte for a lithium secondary battery of the present embodiments comprises a non-aqueous organic solvent, a lithium salt, flame retarding materials of fluoroalkyl ether and phosphazene, and a solvent comprising at least one ester.
1. An electrolyte for a lithium secondary battery comprising a mixture of:
a non-aqueous organic solvent comprising one or more of a cyclic carbonate-based solvent, a halogen substituted ethylene carbonate-based solvent, a lactone-based solvent, an ether-based solvent, a ketone-based solvent, a linear carbonate solvent and a fluorine-based solvent represented by the following chemical formula 4:
Rf 1 —O—C(═O)—O—R
wherein Rf 1 is a fluoroalkyl group with 2 to 4 carbon atoms, and R is CH 3 or C 2 H 5 ;
a lithium salt;
a fluoroalkyl ether in an amount of from 10% to 40% by volume and represented by the following chemical formula:
Rf 1 -O—Rf 2
wherein Rf 1 and Rf 2 are each independently a fluoroalkyl group having 2 to 6 carbon atoms and a fluorination ratio of 50% to 100%,
a phosphazene in an amount of from 3% to 10% by volume represented by chemical formula 2:
wherein R 1 to R 6 are independently F or O—R 7 , wherein R 7 has 1 to 6 carbon atoms and is an alkyl group, a fluoroalkyl group or an aromatic group;
and a solvent comprising at least one ester in an amount of from 20% to 70% by volume;
wherein the at least one ester is represented by the following chemical formula 3:
wherein R 1 ′ is an aliphatic hydrocarbon group with 1 to 4 carbon atoms, and R 2 ′ is an aliphatic hydrocarbon group with 1 to 5 carbon atoms,
wherein the ratio of the fluoroalkyl ether to the sum of the phosphazene compound and the solvent comprising at least one ester is from about 0.15:1 to about 1.5:1.
2. The electrolyte of claim 1 , wherein R 7 is an alkyl group.
3. The electrolyte of claim 1 , wherein R 1 ′ and R 2 ′ are each independently selected from the group consisting of an alkyl group, an alkenyl group and an alkynyl group.
4. The electrolyte of claim 1 , wherein the at least one ester comprises methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, methyl valerate, or a mixture thereof.
5. A secondary lithium battery comprising:
a container;
an electrode assembly;
a cap assembly; and
an electrolyte comprising a mixture of:
a non-aqueous organic solvent comprising one or more of a cyclic carbonate-based solvent, a halogen substituted ethylene carbonate-based solvent, a lactone-based solvent, an ether-based solvent, a ketone-based solvent, a linear carbonate solvent and a fluorine-based solvent represented by the following chemical formula 4:
Rf 1 —O—C(═O)—O—R
wherein Rf 1 is a fluoroalkyl group with 2 to 4 carbon atoms, and R is CH 3 or a lithium salt;
a fluoroalkyl ether in an amount of from 10% to 40% by volume and represented by the following chemical formula:
Rf 1 —O—Rf 2
wherein Rf 1 and Rf 2 are each independently a fluoroalkyl group having 2 to 6 carbon atoms and a fluorination ratio of 50% to 100%,
a phosphazene in an amount of from 3% to 10% by volume represented by chemical formula 2:
wherein R 1 to R 6 are independently F or O—R 7 , wherein R 7 has 1 to 6 carbon atoms and is an alkyl group, a fluoroalkyl group or an aromatic group;
and a solvent comprising at least one ester in an amount of from 20% to 70% by volume;
wherein the at least one ester is represented by the following chemical formula 3:
wherein R 1 ′ is an aliphatic hydrocarbon group with 1 to 4 carbon atoms, and R 2 ′ is an aliphatic hydrocarbon group with 1 to 5 carbon atoms, and
wherein the ratio of the fluoroalkyl ether to the sum of the phosphazene compound and the solvent comprising at least one ester is from about 0.15:1 to about 1.5:1.
6. The secondary lithium battery of claim 5 , wherein R 7 is an alkyl group.
7. The secondary lithium battery of claim 5 , wherein R 1 ′ and R 2 ′ are each independently selected from the group consisting of an alkyl group, an alkenyl group and an alkynyl group.
8. The secondary lithium battery of claim 5 , wherein the at least one ester comprises methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, methyl valerate, or a mixture thereof.