Core-shell hexacyanoferrate for superior Na-ion batteries

Sodium iron hexacyanoferrate (Fe-HCF) is regarded as a potential cathode material for sodium-ion batteries (SIBs) due to its high specific capacity, low cost, facile synthesis and environmentally friendly. However, Fe-HCF always suffers from poor electronic conductivity, low crystallinity and side reactions with electrolyte, leading to poor rate performance, low coulombic efficiency and deterioration of cycling stability. Herein, we report a green and facile synthesis to encapsulate Fe-HCF microcubes with potassium nickel hexacyanoferrate (Ni-HCF). The core-shell Fe-HCF@Ni-HCF composite delivers a reversible capacity of 79.7 mAh g(-1) at 200 mA g(-1) after 800 cycles and a high coulombic efficiency of 99.3%. In addition, Fe-HCF@Ni-HCF exhibits excellent rate performance, retaining 60 mAh g(-1) at 2000 mA g(-1). The results show that Fe-HCF@Ni-HCF integrates the advantages of both Fe-HCF and Ni-HCF, making it electrochemically stable as cathode material for SIBs. (C) 2016 Elsevier B.V. All rights reserved.