A 2-volt Aqueous Battery Enabled by Synergistic Effect of Cu2+/Cu+ Redox and Intercalation/Deintercalation in Copper Hexacyanoferrate Cathodes

Abstract

Aqueous copper-ion batteries represent a promising direction for developing high-safety, multivalent ion battery technologies. However, their advancement is hindered by significant challenges due to the large ionic radius and high redox potential of the Cu²⁺/Cu redox couple. In this study, copper hexacyanoferrate (CuHCF), a Prussian blue analogue, was demonstrated as a promising copper-ion storage material, which activates higher reaction potentials during cycling and boosts the storage capability based on the redox reaction of Cu²⁺/Cu⁺. CuHCF exhibited an initial capacity of 281 mAh g⁻¹ and maintained a stable capacity of 141 mAh g⁻¹. First-principle study, in-situ X-ray diffraction (XRD), in-situ Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS) studies reveal a synergistic effect of Cu²⁺/Cu⁺ redox and intercalation/deintercalation in CuHCF. A decoupled Zn//CuHCF aqueous battery was fabricated with a CuHCF cathode and a Zn anode, achieving a working voltage of up to 2 V. This study provides an effective strategy for improving the voltage and capacity of aqueous batteries.