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

Abstract

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 K_0.95Ag_3.05Fe(CN)₆ (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, Fe³⁺/Fe²⁺ and Ag⁺/Ag⁰, to deliver a large capacity of 179.6 mAh g^-1 at 20 mA g^-1 with Coulomb efficiency of ~100 %. The Zn//AgHCF-3 cell delivers an estimated energy density of 200 Wh kg^-1, surpassing reported PBAs-based ZIBs. The formation of Ag⁰ in the cycling process merits favorable rate performance of AgHCF-3 (156.4 mAh g^-1 at 200 mA g^-1 with 80.3 % capacity retention after 100 cycles). This investigation paves new pathways for high-capacity PBA cathodes.

Keywords: Capacity; Mechanism; Prussian blue analogues; Silver hexacyanoferrate; Zinc-ion battery.