Using elemental selenium as an electrode, the redox-active Cu²⁺/Cu⁺ ion is reversibly hosted via the sequential conversion reactions of Se → CuSe → Cu₃Se₂ → Cu₂Se. The four-electron redox process from Se to Cu₂Se produces a high initial specific capacity of 1233 mA h g⁻¹ based on the mass of selenium alone or 472 mA h g⁻¹ based on the mass of Cu₂Se, the fully discharged product.