Secondary battery and electrolyte liquid

1. A secondary battery, comprising: a positive electrode, a negative electrode comprising a negative electrode active material, and an electrolyte liquid;

wherein the negative electrode active material comprises a metal (a) that can be alloyed with lithium and wherein the metal (a) is silicon;

wherein the electrolyte liquid comprises a chain fluorinated sulfone compound represented by following formula (1):

wherein, in formula (1), R 1 and R 2 each independently denote a substituted or non-substituted alkyl group or a substituted or non-substituted aryl group, and at least one of R 1 and R 2 is CH 2 F—, CHF 2 —, CH 2 FCH 2 —, or CHF 2 CH 2 —, and

wherein the electrolyte liquid further comprises a chain fluorinated ether compound represented by following formula (2):

R a —O—R b   (2)

wherein, in formula (2), R a and R b each independently denote an alkyl group or a fluorine-substituted alkyl group, and at least one of R a and R b is a fluorine-substituted alkyl group.

2. The secondary battery according to claim 1 , wherein one of R 1 and R 2 is CH 2 F—, CHF 2 —, CH 2 FCH 2 —, or CHF 2 CH 2 —, and the other is a fluorine-substituted alkyl group.

3. The secondary battery according to claim 1 , wherein R 1 and R 2 are each independently CH 2 F—, CHF 2 —, CH 2 FCH 2 —, or CHF 2 CH 2 —.

4. The secondary battery according to claim 1 , wherein one of R 1 and R 2 is CH 2 F—, CHF 2 —, CH 2 FCH 2 —, or CHF 2 CH 2 —, and wherein the other is an alkyl group with a carbon number of 1 to 6 which may be substituted by an aryl group or is an aryl group with a carbon number of 6 to 10 which may be substituted by an alkyl group.

5. The secondary battery according to claim 1 , wherein the chain fluorinated ether compound is represented by following formula (3);

H—(CX 1 X 2 —CX 3 X 4 ) n —CH 2 O—CX 5 X 6 —CX 7 X 8 —H  (3)

wherein, in formula (3), n is 1, 2, 3, or 4, and X 1 to X 8 are each independently fluorine atom or hydrogen atom provided that at least one of X 1 to X 4 is fluorine atom and at least one of X 5 to X 8 is fluorine atom.

6. The secondary battery according to claim 1 , wherein the electrolyte liquid further comprises a carbonate compound.

7. The secondary battery according to claim 6 ,

wherein the content of the chain fluorinated sulfone compound is 1 to 15 vol % with respect to the total of the chain fluorinated sulfone compound, the chain fluorinated ether compound, and a solvent;

wherein the content of the chain fluorinated ether compound is 10 to 35 vol % with respect to the total of the chain fluorinated sulfone compound, the chain fluorinated ether compound, and the solvent; and

wherein the content of the carbonate compound is 30 to 89 vol % with respect to the total of the chain fluorinated sulfone compound, the chain fluorinated ether compound, and the solvent.

8. The secondary battery according to claim 1 , wherein the negative electrode active material further comprises a metal oxide (b) that can absorb and desorb lithium ion and a carbon material (c) that can absorb and desorb lithium ion.

9. The secondary battery according to claim 8 , wherein the metal oxide (b) is silicon oxide.

10. The secondary battery according to claim 9 , where at least a part of the silicon oxide has an amorphous structure, and at least a part of the silicon is dispersed in the silicon oxide.

11. The secondary battery according to claim 1 , wherein the negative electrode comprises a binder, and the binder is a polyimide or a polyamide-imide.

12. The secondary battery according to claim 1 , which has a stacked laminate structure.

13. The secondary battery according to claim 12 , comprising a package, wherein the package is an aluminum laminate film.

14. The secondary battery according to claim 1 , wherein the negative electrode active material comprises a silicon-lithium alloy.