Facile Method To Synthesize Na-Enriched Na_1+xFeFe(CN)₆ Frameworks as Cathode with Superior Electrochemical Performance for Sodium-Ion Batteries

Different Na-enriched Na 1+ x FeFe(CN) 6 samples can be synthesized by a facile one-step method, utilizing Na 4 Fe(CN) 6 as the precursor in a different concentration of NaCl solution. As-prepared samples were characterized by a combination of synchrotron X-ray powder diffraction (S-XRD), Mössbauer spectroscopy, Raman spectroscopy, magnetic measurements, thermogravimetric analysis, X-ray photoelectron spectroscopy, and inductively coupled plasma analysis. The electrochemical results show that the Na 1.56 Fe[Fe(CN) 6 ]·3.1H 2 O (PB-5) sample shows a high specific capacity of more than 100 mAh g –1 and excellent capacity retention of 97% over 400 cycles. The details structural evolution during Na-ion insertion/extraction processes were also investigated via in situ synchrotron XRD. Phase transition can be observed during the initial charge and discharge process. The simple synthesis method, superior cycling stability, and cost-effectiveness make the Na-enriched Na 1+ x Fe[Fe(CN) 6 ] a promising cathode for sodium-ion batteries.