Non-aqueous liquid electrolyte and non-aqueous liquid electrolyte secondary battery

1. A non-aqueous liquid electrolyte secondary battery, comprising:

a negative electrode comprising graphite and a negative-electrode active material containing Si atoms,

a positive electrode capable of intercalating and deintercalating lithium ions, and

a non-aqueous liquid electrolyte comprising

a carbonate having a halogen atom selected from the group consisting of fluoroethylene carbonate, difluoroethylene carbonate and mixtures thereof, and

(A) at least one first lithium salt selected from the group consisting of LiPF 6 and LiBF 4 and at least one second lithium salt, which is different from the first lithium salt, and is represented by the formula (A-1):

Li l (α m X a n )  (A-1)

wherein

l represents an integer of 1 or larger and 10 or smaller,

m represents an integer of 1 or larger and 100 or smaller,

and n represents an integer of 1 or larger and 200 or smaller,

α represents any atom selected from the group consisting of boron atom, carbon atom, nitrogen atom, oxygen atom and phosphorus atom; when m is 2 or larger, the two or more of α may be the same as or different from each other,

X a represents a functional group having at least one kind of atom selected from 14 group to 17 group of the periodic table at its binding position to the α, when n is 2 or larger, the two or more of X a may be the same or different from each other, in addition, two or more X a may be connected to each other to form a ring structure,

except such a compound in which α is boron atom and X a is represented by

(C i H 2(i-2) O 4 )(C j H 2(j-2) O 4 )

wherein, i and j each represent, independently of each other, an integer of 2 or larger, and

wherein

the concentration of the first lithium salt in the non-aqueous liquid electrolyte is 0.5 mol/liter to 2.5 mol/liter,

the concentration of the second lithium salt in the non-aqueous liquid electrolyte is 0.001 mol/liter to 1 mol/liter, and

the molar ratio of the second lithium salt relative to the first lithium salt is 1 or smaller.

2. The non-aqueous liquid electrolyte secondary battery according to claim 1 , wherein a is boron atom or phosphorus atom, and X a is a substituent selected from the group consisting of fluorine atom, hydrocarbon group, substituted carbonyloxy group, alkoxy group, substituted sulfinyloxy group and substituted sulfonyloxy group, wherein when X a is a hydrocarbon group, substituted carbonyloxy group, alkoxy group, substituted sulfinyloxy group or substituted sulfonyloxy group, a part or all of the hydrogen atoms may be substituted with a fluorine atom, and when X a exists plurally, they may be different from or the same as each other and may be connected to each other to form a ring structure.

3. The non-aqueous liquid electrolyte secondary battery according to claim 1 , wherein a is carbon atom, nitrogen atom or oxygen atom, and Xa is a group represented by —SO 2 R a0 , wherein R a0 represents fluorine atom or a hydrocarbon group; when Rao is a hydrocarbon group, a part or all of the hydrogen atoms may be substituted with a fluorine atom, and, when the number of X a is two or more, the two or more of R a0 may be the same or different from each other and further, the two or more of Rao may be connected to each other to form a ring structure.

4. The non-aqueous liquid electrolyte secondary battery according to claim 1 , wherein the concentration of the carbonate having a halogen atom in the non-aqueous liquid electrolyte is 0.01 weight % to 70 weight %.

5. The non-aqueous liquid electrolyte secondary battery according to claim 1 , wherein the carbonate having a halogen atom is fluoroethylene carbonate.

6. The non-aqueous liquid electrolyte secondary battery according to claim 1 , wherein the non-aqueous liquid electrolyte further comprises ethylene carbonate and/or propylene carbonate.

7. The non-aqueous liquid electrolyte secondary battery according to claim 1 , wherein the non-aqueous liquid electrolyte further comprises at least one carbonate selected from the group consisting of dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate and di-n-propyl carbonate.

8. The non-aqueous liquid electrolyte secondary battery according to claim 1 , wherein the first lithium salt is LiPF 6 .

9. The non-aqueous liquid electrolyte secondary battery according to claim 1 , wherein the first lithium salt is LiBF 4 .

10. The non-aqueous liquid electrolyte secondary battery according to claim 1 , wherein a represents a boron atom.

11. The A non-aqueous liquid electrolyte secondary battery according to claim 1 , wherein a represents a carbon atom.

12. The non-aqueous liquid electrolyte secondary battery according to claim 1 , wherein a represents a nitrogen atom.

13. The non-aqueous liquid electrolyte secondary battery according to claim 1 , wherein a represents an oxygen atom.

14. The non-aqueous liquid electrolyte secondary battery according to claim 1 , wherein a represents a phosphorus atom.