Electrolyte for power storage devices and nonaqueous electrolyte solution

To provide an electrolyte for a storage device capable of lowering the electric resistance and maintaining a high capacity even after charging and discharging are repeatedly carried out, and a storage device.An electrolyte for a storage device, which comprises a lithium-containing complex compound represented by the following formula (1), (2), (3), (4) or (5):(Li)m(A)n(UFx)y (1)(Li)m(Si)n(O)q(UFx)y (2)wherein A is O, S, P or N; U is a boron atom or a phosphorus atom; m and n are each independently from 1 to 6; q is from 1 to 12; x is 3 or 5; and y is from 1 to 6;(Li)m(O)n(B)p(OWFq)x (3)wherein W is a boron atom or a phosphorus atom; m, p and x are each independently from 1 to 15; n is from 0 to 15; and q is 3 or 5;(Li)m(B)p(O)n(OR)y(OWFq)x (4)wherein W is a boron atom or a phosphorus atom; n is from 0 to 15; p, m, x and y are each independently from 1 to 12; q is 3 or 5; and R is hydrogen, an alkyl group, an alkenyl group, an aryl group, a carbonyl group, a sulfonyl group or a silyl group, and such a group may have a fluorine atom, an oxygen atom or other substituent;(Li)m(O)n(B)p(OOC-(A)z-COO)y(OWFq)x (5)wherein W is a boron atom or a phosphorus atom, A is a C1-6 allylene group, alkenylene group or alkynylene group, a phenylene group, or an alkylene group having an oxygen atom or a sulfur atom in its main chain; m, p, x and y are each independently from 1 to 20; n is from 0 to 15; z is 0 or 1; and q is 3 or 5.