Electrochemical Sodium Ion Intercalation Properties of Na2.7Ru4O9 in Nonaqueous and Aqueous Electrolytes

Abstract

This paper represents the first description of the electrochemical sodium ion intercalation properties of Na2.7Ru4O9 in both nonaqueous and aqueous electrolytes. Na2.7Ru4O9 was synthesized at 700-850 degrees C by solid-state reaction under Ar flow. It has single, double and triple chains of edge-sharing RuO6 octahedra and one-dimensional tunnels between them parallel to the b-axis, accommodating three different sites of Na1, Na2 and Na3. In an organic electrolyte (1 M NaClO4 in PC), Na2.7Ru4O9 shows three redox peaks in its cyclic voltammogram between 2.8 and 3.9 V vs. Na. In an aqueous (1 M Na2SO4) electrolyte, Na2.7Ru4O9 exhibits three anodic peaks during the first charge, similar to the behavior observed in the organic electrolyte. However, the three peaks become a single broad peak over the following cycles. Electrochemical data and ex-situ XRD results indicate that once Na ions are removed from the Na2.7Ru4O9 structure containing the maximum amount of sodium, only a portion (<60%) can be re-intercalated and that the aqueous electrolyte allows a lower reversible capacity than the nonaqueous electrolyte. (C) 2013 The Electrochemical Society. All rights reserved.