Abstract: A power storage device with reduced initial irreversible capacity is provided. The power storage device includes a positive electrode including a positive electrode current collector and a positive electrode active material layer, a negative electrode including a negative electrode current collector and a negative electrode active material layer, and an electrolyte solution. In the negative electrode active material layer, the content percentage of a carbon material with an R value of 1.1 or more is less than 2 wt %. The R value refers to a ratio of a peak intensity I1360 to a peak intensity I1580 (I1360/I1580). The peak intensity I1360 and the peak intensity I1580 are observed by Raman spectrometry at a Raman shift of 1360 cm?1 and a Raman shift of 1580 cm?1, respectively. The electrolyte solution contains a lithium ion and an ionic liquid composed of an organic cation and an anion.

Abstract: A power storage device with a higher degree of safety is provided. Further, a power storage device with improved cycle life is provided. In the power storage device, an ionic liquid as a solvent of an electrolyte solution, and an exterior body is covered with a conductive component so as to prevent direct contact between a positive electrode current collector and the exterior body. This suppresses elution of the positive electrode current collector due to contact between different kinds of metals and accordingly prevents a phenomenon in which the eluted metal of the positive electrode current collector is deposited on a negative electrode and the deposited metal comes in contact with a positive electrode. Thus, an internal short-circuit caused by the contact can be prevented.

Abstract: To provide an ionic liquid which has at least one of properties such as high ionic conductivity, a small reduction in ionic conductivity at a low temperature, a low melting point, and a low viscosity. To provide a power storage device having higher initial charge and discharge efficiency than a power storage device containing a conventional ionic liquid. A cyclic quaternary ammonium salt is liquid at room temperature and contains a quaternary spiro ammonium cation having an asymmetrical structure including two aliphatic rings and one or more substituents bonded to one or both of the two aliphatic rings and an anion corresponding to the quaternary spiro ammonium cation. The power storage device includes a positive electrode, a negative electrode, and a nonaqueous electrolyte containing the cyclic quaternary ammonium salt as a nonaqueous solvent.

Abstract: A mixture of amorphous PAHs and at least one of a carrier ion storage metal, a Sn compound, a carrier ion storage alloy, a metal compound, Si, Sb, and SiO2 is used as the negative electrode active material. The theoretical capacity of amorphous PAHs greatly exceeds that of a graphite-based carbon material. Thus, the use of amorphous PAHs enables the negative electrode active material to have a higher capacity than in the case of using the graphite-based carbon material. Further, addition of at least one of the carrier ion storage metal, the Sn compound, the carrier ion storage alloy, the metal compound, Si, Sb, and SiO2 to the amorphous PAHs enables the negative electrode active material to have a higher capacity than the case of only using the amorphous PAHs.