Nonaqueous electrolytic solution and nonaqueous-electrolyte secondary battery

1. A nonaqueous electrolytic solution for nonaqueous-electrolyte secondary battery which comprises:

a nonaqueous solvent; LiPF 6 ; and a fluorosulfonic acid salt represented by formula (1):

M(FSO 3 ) x

wherein

M is a metal atom, N(R) 4 , or P(R) 4 wherein R is either an organic group having 1-12 carbon atoms or a hydrogen atom wherein not all of the four R's are hydrogen atoms, the R's may be the same or different, and a part or all of the four R's may form a ring in cooperation with the nitrogen atom or phosphorus atom to which the R's have been bonded;

when M is a metal atom, x indicates the valence of the metal atom M and is an integer of 1 or larger; and when M is N(R) 4 or P(R) 4 , x is 1,

wherein the nonaqueous electrolytic solution further comprises at least one selected from the group consisting of a cyclic carbonate having a fluorine atom, a cyclic carbonate having carbon-carbon unsaturated bond, a cyclic sulfonic acid ester compound, a compound having cyano group, a diisocyanate compound, a fluorophosphoric acid lithium salt other than LiPF 6 , a lithium imide salt, and a lithium salt having an oxalic acid group, and

wherein the ratio of the molar content of FSO 3 in the nonaqueous electrolytic solution to the molar content of PF 6 in the nonaqueous electrolytic solution is 0.0005-0.5.

2. The nonaqueous electrolytic solution for nonaqueous-electrolyte secondary battery according to claim 1 , wherein the fluorosulfonic acid salt represented by formula (1) is lithium fluorosulfonate.

3. The nonaqueous electrolytic solution for nonaqueous-electrolyte secondary battery according to claim 1 , which comprises the cyclic carbonate having a fluorine atom in the nonaqueous electrolytic solution in an amount of 0.001-85% by mass.

4. The nonaqueous electrolytic solution for nonaqueous-electrolyte secondary battery according to claim 1 , which comprises the cyclic carbonate having a carbon-carbon unsaturated bond in the nonaqueous electrolytic solution in an amount of 0.001-10% by mass.

5. The nonaqueous electrolytic solution for nonaqueous-electrolyte secondary battery according to claim 1 , which comprises the cyclic sulfonic acid ester in the nonaqueous electrolytic solution in an amount of 0.001-10% by mass.

6. The nonaqueous electrolytic solution for nonaqueous-electrolyte secondary battery according to claim 1 , which comprises the compound having a cyano group in the nonaqueous electrolytic solution in an amount of 0.001-10% by mass.

7. The nonaqueous electrolytic solution for nonaqueous-electrolyte secondary battery according to claim 1 , which comprises the diisocyanate compound in the nonaqueous electrolytic solution in an amount of 0.001-5% by mass.

8. The nonaqueous electrolytic solution for nonaqueous-electrolyte secondary battery according to claim 1 , wherein the concentration of the at least one salt selected from fluorophosphoric acid lithium salt other than LiPF 6 and lithium imide salt, and the lithium salt having an oxalic acid group in the nonaqueous electrolytic solution is 0.0005-0.5 mol/L.

9. A nonaqueous-electrolyte secondary battery which comprises:

a negative electrode and a positive electrode that are capable of occluding and releasing lithium ions; and the nonaqueous electrolytic solution for nonaqueous-electrolyte secondary battery according to claim 1 .

10. The nonaqueous-electrolyte secondary battery according to claim 9 , wherein the negative electrode comprises a current collector and a negative-electrode active-material layer disposed on the current collector, the negative-electrode active-material layer containing a negative-electrode active material which comprises at least one member selected from an elemental metal, alloys and compounds of silicon, and an elemental metal, alloys and compounds of tin.

11. The nonaqueous-electrolyte secondary battery according to claim 9 , wherein the negative electrode comprises a current collector and a negative-electrode active-material layer disposed on the current collector, the negative-electrode active-material layer containing a negative-electrode active material which comprises a carbonaceous material.

12. The nonaqueous-electrolyte secondary battery according to claim 9 , wherein the negative electrode comprises a current collector and a negative-electrode active-material layer disposed on the current collector, the negative-electrode active-material layer containing a negative-electrode active material which comprises a lithium-titanium composite oxide.

13. The nonaqueous-electrolyte secondary battery according to claim 9 , wherein the positive electrode comprises a current collector and a positive-electrode active-material layer disposed on the current collector, the positive-electrode active-material layer containing one member selected from the group consisting of lithium-cobalt composite oxides, lithium-manganese composite oxides, lithium-cobalt-manganese composite oxides, lithium-nickel composite oxides, lithium-cobalt-nickel composite oxides, lithium-nickel-manganese composite oxides, and lithium-nickel-cobalt-manganese composite oxides.

14. The nonaqueous-electrolyte secondary battery according to claim 9 , wherein the positive electrode comprises a current collector and a positive-electrode active-material layer disposed on the current collector, the positive-electrode active-material layer containing Li x MPO 4 wherein M is one element selected from the group consisting of the Group-4 to Group-11 transition metals belonging to the fourth period of the periodic table, and x satisfies 0<x<1.2.

15. The nonaqueous electrolytic solution for nonaqueous-electrolyte secondary battery according to claim 1 , wherein the ratio of a molar content of FSO 3 to a molar content of PF 6 in the nonaqueous electrolytic solution is 0.01-0.5.

16. The nonaqueous electrolytic solution for nonaqueous-electrolyte secondary battery according to claim 1 , wherein the ratio of the molar content of FSO 3 in the nonaqueous electrolytic solution to the molar content of PF 6 in the nonaqueous electrolytic solution is 0.001-0.5.