A secondary battery which exhibits less deterioration of capacity, can maintain high energy densities in high temperature atmospheres, and has high practicality, and an electrolyte used therefor, are provided. The electrolyte contains an anion expressed by (PF.sub.aQ.sub.bR.sub.c).sup.-, so degradation of the electrolyte can be prevented. In the formula, Q expresses at least one of CF.sub.3, C.sub.2F.sub.5, and C.sub.3F.sub.7, and R expresses SO.sub.2CF.sub.3 and/or SO.sub.2C.sub.2F.sub.5. a, b and c satisfy 1.ltoreq.a.ltoreq.5, 0.ltoreq.b.ltoreq.5, and, 0.ltoreq.c.ltoreq.5, respectively. Furthermore, an anion expressed by N(C.sub.nF.sub.2n+1SO.sub.2).sub.2.sup.- is contained, which can further prevent the degradation of the electrolyte. In the formula, n satisfies 1.ltoreq.n.ltoreq.2. Therefore, the capacity recovery rate after storage and heavy load discharge maintenance rate are high even in high temperature atmospheres, and high reliability can be obtained.