Nonaqueous electrolyte for secondary battery and nonaqueous-electrolyte secondary battery employing the same
An object is to provide a nonaqueous electrolyte and a nonaqueous-electrolyte secondary battery which have excellent discharge load characteristics and are excellent in high-temperature storability, cycle characteristics, high capacity, continuous-charge characteristics, storability, gas evolution inhibition during continuous charge, high-current-density charge/discharge characteristics, discharge load characteristics, etc. The object has been accomplished with a nonaqueous electrolyte which comprises: a monofluorophosphate and/or a difluorophosphate; and further a compound having a specific chemical structure or specific properties.
1. A nonaqueous electrolyte solution, comprising:
an electrolyte; and
a nonaqueous solvent dissolving the electrolyte which comprises:
a compound (A) selected from the group consisting of optionally substituted acyclic alkyl nitriles and optionally substituted cyclic alkyl nitriles; and
from 0.001 to 5% by mass based on a total weight of the nonaqueous solvent of a salt of a monofluorophosphate ion and/or difluorophosphate ion with one or more cations selected from the group consisting of metals of Group 1, Group 2, and Group 13 of the periodic table and a quaternary onium ion of formula (1);
wherein R 1 to R 4 each independently represent a C1 to C20 alkyl group, a C3 to C20 cycloalkyl group, a C6 to C20 aryl group and a C7 to C20 aralkyl group;
wherein
the compound (A) does not comprise a carbonyl group,
the optional substituent of the compound (A) is at least one selected from the group consisting of halogen atoms and a saturated aliphatic hydrocarbon group optionally substituted with a halogen atom,
the compound (A) is a liquid at 25° C., has a permittivity of 5 or higher and a coefficient of viscosity of 0.6 cP or lower, and
wherein the permittivity (ε r ) of the compound (A) is determined according to the formula:
ε r =C/C 0
wherein C is a capacitance of a capacitor (condenser) filled with a sample liquid between electrode plates and C 0 represents a capacitance the case where the space between the electrode plates is in a vacuum state, and
the coefficient of viscosity of compound (A) is measured with an Ostwald viscometer.
2. The nonaqueous electrolyte solution of claim 1 , wherein the compound (A) comprises at least one substituent selected from the group consisting of a halogen and a saturated aliphatic hydrocarbon comprising no substituent other than halogen atoms.
3. A nonaqueous-electrolyte secondary battery, comprising:
a negative electrode and a positive electrode, which are capable of occluding/releasing lithium ions; and
the nonaqueous electrolyte solution according to claim 1 .
4. The nonaqueous-electrolyte secondary battery according to claim 3 , wherein the negative electrode comprises a carbonaceous material.