Carbon coated Na7Fe7(PO4)6F3: A novel intercalation cathode for sodium-ion batteries

Electrode materials are being developed to realise sodium-ion batteries that can provide energy storage solutions. Here, we develop amorphous carbon coated Na7Fe7(PO4)(6)F-3, prepared by combining hydrothermal and solid state reaction methods, as an insertion electrode for sodium-ion batteries applications. Na7Fe7(PO4)(6)F-3 particles are surrounded by a thin layer (similar to 1.5-2 nm) of amorphous carbon. The Na7Fe7(PO4)(6)F-3/C composite cathode undergoes reversible sodium intercalation/de-intercalation with an average operational potential of 3.0 V (vs Na+/Na). This cathode has a capacity of 65 mA h g(-1) at 100 mA g(-1) current after 60 cycles and features twice higher capacity than that of an uncoated Na7Fe7(PO4)(6)F-3 sample. Therefore, the carbon-coated Na7Fe7(PO4)(6)F-3 composite presents feasible sodium intercalation/de-intercalation capacity, offering possibilities for developing a low cost, high performance sodium-ion battery positive electrode. (C) 2014 Elsevier B.V. All rights reserved.