The electrochemical performance of a Na2FeP2O7 positive electrode has been evaluated in an inorganic ionic liquid NaFSA-KFSA (FSA = bis(fluorosulfonyl)amide) at 363 K. The electrode delivers a reversible capacity of 91 mAh g(-1) with excellent rate capability (59 mAh g(-1) at 2000 mA g(-1)) and a capacity retention of 91% over 1000 cycles, which facilitates the development of low-cost and high-safety sodium secondary batteries for large-scale energy storage applications. The average oxidation state of iron increases upon sodium extraction, as evidenced by the edge shift of an X-ray absorption spectroscopy analysis. According to an extended X-ray absorption fine structure analysis, the sodium extraction is accompanied by a shortening of Fe-O bonds. (C) 2013 Elsevier B.V. All rights reserved.