US Patent 9954252 Electrical device

To provide a means capable of further improving cycle durability in an electrical device such as a lithium ion secondary battery containing a positive electrode using a solid solution positive electrode active material. An electrical device has a power generating element containing a positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a surface of a positive electrode current collector, a negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on a surface of a negative electrode current collector, and a separator impregnated with an electrolytic solution. The negative electrode active material layer contains a negative electrode active material represented by formula (1). The positive electrode active material layer contains a positive electrode active material (solid solution positive electrode active material) represented by formula (2). As the solid solution positive electrode active material contained in the positive electrode active material layer, a material having a composition represented by formula (3) as a basic structure is used. The electrolytic solution contains a predetermined additive.