Abstract: A secondary battery includes: a solid electrolyte layer which contains a tantalum oxide as a solid electrolyte; a positive-electrode active material layer which is disposed on an upper surface of the solid electrolyte layer and contains a nickel hydroxide (Ni(OH)2) as a positive-electrode active material; and a negative-electrode active material layer disposed on a lower surface of the solid electrolyte layer so as to be opposite to the positive-electrode active material layer and containing a titanium oxide (TiOx) or a titanium oxide (TiOx) and a silicon oxide (SiOx) as a negative-electrode active material. There is provided a secondary battery capable of improving electricity storage performance by improving a self-discharge.