In Situ XRD Study of Silicon, Lead and Bismuth Negative Electrodes in Nonaqueous Sodium Cells

The electrochemical alloying of sodium with silicon, lead and bismuth was studied by in-situ X-ray diffraction. No evidence was found for sodium insertion into silicon at temperatures up to 60 degrees C. Lead was found to catalytically decompose electrolyte, hindering sodiation. This could be avoided by applying a high current pulse to the cell to sodiate the lead surface. Once the surface was sodiated, further sodiation of lead could proceed at low currents. The sodiation of lead followed a path that differs from the equilibrium phase diagram and from that described in earlier reports. During sodiation, Na9Pb4 was formed with a previously unreported structure that was found to be isostructural with Na9Sn4. It was found that Na could be reversibly inserted into bismuth. The mechanism for bismuth sodiation follows equilibrium phase behavior. (C) 2014 The Electrochemical Society. All rights reserved.