The role of potassium ions in iron hexacyanoferrate as a cathode material for hybrid ion batteries

The synthesis of NaxKyFe[Fe(CN)(6)] througha simple co-precipitation method and the application of these nanoparticles in sodium-ion batteries are presented. K1.90Fe[Fe(CN)(6)] with a cubic structure shows low volumetric change during electrochemical cycling. It is clarified by ex-situ X-ray diffraction and cyclic voltammetry curves that K+ influences the intercalation sites of the neighboring Na+. More significantly, this hexacyanoferrate delivers a high capacity of 137.0 mAh g(-1) at a current density of 14 mA g(-1) and superior cyclability with 94% capacity retention after 120 cycles, showing great promise for sodium-ion battery applications. (C) 2016 Elsevier Ltd. All rights reserved.