Investigation of the Prussian Blue Analog Co₃[Co(CN)₆]₂ as an Anode Material for Nonaqueous Potassium‐Ion Batteries

Nonaqueous potassium-ion batteries (KIBs) are attracting increasing attention as a potential low-cost energy-storage system due to the abundance of potassium resources. Here, cobalt hexacyanocobaltate (Co₃ [Co(CN)₆ ]₂ ), a typical Prussian blue analog (PBA), is reported as an anode material for nonaqueous KIBs. The as-prepared Co₃ [Co(CN)₆ ]₂ exhibits a highly reversible capacity of 324.5 mAh g⁻¹ at a current density of 0.1 A g⁻¹ , a superior rate capability (221 mAh g⁻¹ at 1 A g⁻¹ ), and a favorable long-term cycling stability (200 cycles with 82% capacity retention). Based on a series of characterizations, it is found that potassiation/depotassiation in Co₃ [Co(CN)₆ ]₂ proceeds via solid-state diffusion-limited K-ion insertion/extraction process, in which both carbon- and nitrogen-coordinated cobalt are electrochemically active toward K-ion storage. Finally, the reaction pathway between potassium and Co₃ [Co(CN)₆ ]₂ is proposed. The present study provides new insights on further exploration of PBAs as high-performance electrode materials for KIBs.