Electrochemical Performance of NaFeFe(CN)6 Prepared by Solid Reaction for Sodium Ion Batteries

Commercially available Na4Fe(CN)(6) and Fe-4[Fe(CN)(6)](3) are two cheap compounds that have ever been investigated as positive electrode materials for sodium-ion batteries. However, poor electronic conductivity of Na4Fe(CN)(6) and sodium deficiency of Fe-4[Fe(CN)(6)](3) prevent these two materials from being used in practical rechargeable sodium-ion batteries. In this paper, a NaFeFe(CN)(6) cathode material was synthesized by ball milling the Fe-4[Fe(CN)(6)](3)/Na4Fe(CN)(6) mixture. The obtained NaFeFe(CN)(6) demonstrated a single cubic phase indexed to Fm3m space group similar to Fe-4[Fe(CN)(6)](3) but with larger lattice parameter due to the existence of Na+ in the lattice framework. The NaFeFe(CN)(6) electrode delivered first desodiation capacity of 119.4 mAh g(-1) and first sodiation capacity of 153.6 mAh g(-1) at 0.05C rate. The NaFeFe(CN)(6) showed excellent cycling stability with reversible capacities of 118.2 mAh g(-1) and 96.8 mAh g(-1) at 0.1C and 1C rate, respectively. In-situ XRD analyses demonstrated a single cubic phase process during charge-discharge of NaFeFe(CN)(6) electrode. Low water content benefited from the solid reaction method and the homogenous single phase process during charge/discharge assured the stable long term cycling performance of the NaFeFe(CN)(6) product. (C) The Author(s) 2018. Published by ECS.