Fluffy-Like Cation-Exchanged Prussian Blue Analogues for Sodium- Ion Battery Cathodes

Prussian blue (PB) and its analogues are considered as promising cathode materials for sodium-ion batteries (SIBs) owing to their low cost and high capacity. However, it is still a huge challenge to avoid obvious capacity decay during cycling due to the structural collapse. Herein, we design a method to replace parts of Fe ion sites in PB with Ni ions to prepare fluffy-like nickel PB (PB-Ni) by cationic solution immersion, which improves cycling stability for sodium storage. The content of Ni in PB-Ni is explored by regulating the soaking time in the Ni-containing solution, which results in different effects on the electrochemical performance as cathodes of SIBs. Especially, PB-Ni-1d (soaking in NiCl2 solution for 1 day) exhibits an initial capacity of 114.2 mA h g(-1 ) at 50 mA g(-1) and a stable cycling performance of 800 cycles at 300 mA g(-1). Furthermore, the reversible phase transformation and small volume variation for PB-Ni-1d are revealed by in situ X-ray diffraction characterization. The nickel hexacyanoferrate in outer layer maintains the cubic phase to stabilize the crystal structure. The cation-exchange strategy provides a facile idea to fabricate high-quality PB cathodes with superior stability for high-performance SIBs.

Automated summary

In this study, fluffy-like nickel PB (PB-Ni) was prepared by replacing parts of Fe ion sites in PB with Ni ions, resulting in improved cycling stability for sodium-ion batteries. PB-Ni exhibited an initial capacity of 114.2 mA h g(-1) and a stable cycling performance of 800 cycles at 50mA g(-1). In situ X-ray diffraction characterization revealed reversible phase transformation and small volume variation for PB-Ni.