Synthesis and electrode performance of carbon coated Na2FePO4F for rechargeable Na batteries

Carbon-coated Na2FePO4F is synthesized by a simple solid-state method with ascorbic acid as carbon source. Structural characterization of Na2FePO4F by synchrotron X-ray diffraction, scanning/transmission electron microscopy, and Raman spectroscopy reveals that ascorbic acid effectively suppresses the particle growth of Na2FePO4F, forming the nano-sized carbon coated materials. Electrode performance of Na2FePO4F for rechargeable sodium batteries is also examined. The carbon-coated Na2FePO4F sample (1.3 wt% carbon) delivers initial discharge capacity of 110 mAh g(-1) at a rate of 1/20 C (6.2 mA g(-1)) with well-defined voltage plateaus at 3.06 and 2.91 V vs. Na metal. The sample also shows acceptable capacity retention and rate capability as the positive electrode materials for rechargeable Na batteries, which is operable at room temperature. (C) 2011 Elsevier B.V. All rights reserved.