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.