Provided is a power storage device whose charging and discharging characteristics are unlikely to be degraded by heat treatment or a power storage device that is highly safe against heat treatment. The power storage device includes a positive electrode, a negative electrode, a separator, an electrolyte, and an exterior body. The separator is positioned between the positive electrode and the negative electrode and includes polyphenylene sulfide or cellulosic fiber. The electrolyte includes propylene carbonate, ethylene carbonate, and vinylene carbonate, lithium hexafluorophosphate, and lithium bis(pentafluoroethanesulfonyl)amide. A concentration of lithium hexafluorophosphate with respect to the electrolyte is more than or equal to 0.01 wt % and less than or equal to 1.9 wt % in a weight ratio.