Four-Electron Redox Reaction in Prussian Blue Analogue Cathode Material for High-Performance Sodium-Ion Batteries

Prussian blue analogues (PBAs) are considered promising cathode materials for sodium-ion batteries (SIBs). However, traditional PBAs have limitations, such as up to two-electron-transfer reactions, lattice vacancies, coordinated water, and poor intrinsic conductivity, leading to low capacity and poor rate performance. Herein, we have developed vacancy/water-free silver hexacyanoferrate nanoparticles interlinked with carbon nanotubes (AgHCF@CNTs) to improve the electrochemical performance. Benefiting from the four-electron redox capacity of Fe3+/Fe2+ and Ag+/Ag, the AgHCF@CNTs exhibit a reversible capacity of 168.4 mAh g–1 at 50 mA g–1, high rate capability (90.7 mAh g–1 at 2 A g–1), and long cycling stability over 500 cycles. The in-situ-generated Ag during the discharging/charging process, along with the large interstitial spaces of ferricyano-coordination groups, facilitate electron transfer and Na+ transportation, guaranteeing high electrochemical performance. This study provides insights into the design and synthesis strategy for advancing multiple-electron redox hexacyanoferrate as cathode materials for high-performance SIBs.