Electrolyte for power storage device, reinforcing agent, electrolyte solution, and power storage device using same

An electrolyte for power storage device, comprising a complex compound (A),

• wherein the complex compound (A) comprises one or more compounds represented by Formula (1) below:
• wherein X1 is a P(═O) group or a P(═S) group,
• R1 to R3 are each independently a group selected from the group consisting of a hydrogen atom, an alkyl group, an alkenyl group, a halogen atom, an alkoxy group, a siloxy group, a thiosilane group, and a group represented by Formula (2) below;
• or one of two groups selected from the group consisting of R1 to R3 is an oxygen atom and is linked to the other group to form a ring structure, and
• at least one of R1 to R3 is a group containing a structure represented by Formula (2) below:
• wherein the Formula (2) represents an oligomer having a molecular structure that includes a structure in which respective repeating units represented in brackets are linked to each other, and a linkage order of the repeating units is arbitrary,
• m represents a repeating number of the repeating unit put in [ ]m, and is a number of 1 to 10,
• n represents a repeating number of the repeating unit put in [ ]n, and is a number of 0 to 10,
• M+ is an alkali metal cation or a quaternary ammonium cation,
• Y1 and Y2 are each independently an oxygen atom or a sulfur atom,
• B is a boron atom,
• G is a halogen atom,
• X2 is a P(═O) group or a P(═S) group, and
• R4 is each independently a group selected from the group consisting of a hydrogen atom, an alkyl group, an alkenyl group, a halogen atom, an alkoxy group, a siloxy group, a thiosilane group, and the group put in [ ]m.