Ultra-stable Cu-ion-exchanged cobalt hexacyanoferrate(ii) in aqueous copper-ion storage

Abstract

Since Prussian blue analogues possess large vacant sites and available diffusion channels, they can accommodate and release a variety of cations. In this work, CuCoFe(CN)₆ as a member of the Prussian blue analogues is used as an electrode material in aqueous copper-ion batteries. It is prepared by coprecipitation and ion-exchange and is composed of small flaky particles with sizes varying from 30 to 800 nm. The CuCoFe(CN)₆ electrode exhibits high initial discharge capacity (61.0 mA h g⁻¹ at 0.5 C), long-term cycling life (a capacity retention of 97.2% after 200 cycles at 0.5 C and a capacity retention of 86.5% after 1000 cycles at 15 C), and excellent rate performance. The Cu-storage mechanism is systematically investigated. The results reveal that CuCoFe(CN)₆ exhibits a stable structure and possesses good reversibility during the extraction/insertion of Cu²⁺ from/into its lattice. Furthermore, a full cell with a Zn anode and a CuCoFe(CN)₆ cathode exhibits stable cycling performance and a high operating voltage of 1.85 V, showing its practicability. Overall, this work reports an applicable electrode material for high-performance aqueous copper-ion batteries, which greatly promises the evolution of aqueous metal-ion batteries.