Dual Redox Reactions of Silver Hexacyanoferrate Prussian Blue Analogue Enable Superior Electrochemical Performance for Zinc-ion Storage.

Prussian blue analogues (PBAs) have been employed as host materials of aqueous zinc-ion batteries (ZIBs), however, they suffer from low capacity and poor cycling stability due to limited electron transfer and the presence of interstitial water in PBAs. Herein, a vacancy and water-free silver hexacyanoferrate KAgFe(CN) (AgHCF-3) was synthesized by adjusting the ratio of K and Ag in the framework. It offers nearly four electrons involving two sequential redox reactions, namely, Fe/Fe and Ag/Ag, to deliver a large capacity of 179.6 mAh g at 20 mA g with Coulomb efficiency of ~100 %. The Zn//AgHCF-3 cell delivers an estimated energy density of 200 Wh kg, surpassing reported PBAs-based ZIBs. The formation of Ag in the cycling process merits favorable rate performance of AgHCF-3 (156.4 mAh g at 200 mA g with 80.3 % capacity retention after 100 cycles). This investigation paves new pathways for high-capacity PBA cathodes.