Thermodynamically stable quasi-liquid interface for dendrite-free sodium metal anodes

The dendrite-associated cell degradation is a key challenge to the practical application of sodium metal anodes. Here, we present that tiny amount of mercury incorporation into sodium generates a unique quasi-liquid interface that affords long-term stability cycling. This amalgam layer allows fast electron transfer as well as sodium migration at the electrolyte-electrode interphase, which significantly promotes the cycling performance over 5000 h with a practically desired capacity of 2 mAh cm-2 and current density of 8 mA cm-2. In-situ optical microscopy analyses confirm the dendrite nucleation and growth can be remarkably suppressed with the amalgam-protected anodes. The prototype full cells also demonstrate much improved rate and long-term cycling stability. These promising results provide new perspectives on the regulation of sodium electrodeposition by introducing low-melting metals and hence the elimination of the dendritic morphology for the practical development of sodium metal batteries.