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°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, Na 9 Pb 4 was formed with a previously unreported structure that was found to be isostructural with Na 9 Sn 4 . It was found that Na could be reversibly inserted into bismuth. The mechanism for bismuth sodiation follows equilibrium phase behavior.