To provide a means, in an electrical device such as a lithium ion secondary battery, whereby reduction in battery capacity as a charge/discharge cycle progresses can be suppressed (i.e., cycle durability can be improved), even if an electrolyte includes a cyclic sulfonic acid ester as an additive. An electrical device having a power-generating element including: a positive electrode comprising a positive electrode active substance layer that includes a positive electrode active substance and is formed on the surface of a positive electrode collector; a negative electrode comprising a negative electrode active substance layer that includes a negative electrode active substance and is formed on the surface of a negative electrode collector; and a separator including an electrolyte. The electrical device has, as the positive electrode active substance, a composition indicated by general formula [Li alpha Ni beta]3a [NixMny-rMrCoz]3bO2 and includes: a lithium nickel-based composite oxide having a layered crystal structure into/from which lithium ions can be inserted and removed; and a cyclic sulfonic acid ester as the electrolyte.