Optimizing Na plating/stripping by a liquid sodiophilic Ga-Sn-In alloy towards dendrite-poor sodium metal anodes

Benefited by the abundant Na resources and high theoretical capacity of Na, rechargeable sodium metal batteries exhibit great potentials for next-generation energy storage systems. However, there are several key puzzles of Na anodes restricting the wide application, including high activity of Na metal, uncontrollable dendrite growth and unstable solid-electrolyte interface (SEI). In this work, a liquid alloy comprised of Ga, Sn and In was uniformly coated on commercial Cu foil in order to regulate the Na plating/stripping behaviors and thereupon enable stable sodium metal battery. The liquid sodiophilic Ga-Sn-In alloy on Cu foil (GSIC) can enhance the wettability of electrolyte and melted Na and decrease the Na nucleation overpotential. Based on the results of ex situ SEM and in situ optical microscopy, the Ga-Sn-In alloy coating layer can induce the uniform Na plating and decrease the volume expansion, enabling dendrite-poor capability. By taking NVP as cathode and optimal Na-GSIC as Na anode, the sodium metal full battery manifests a high reversible capacity of 108.7 mAh g−1 at the 1st cycles and offers 87.4 mAh g−1 (80.4% retention) at 5 C after 250 cycles. Such sodiophilic liquid alloy current collector would pave new pathway on designing feasible and highly stable Na metal anodes for sodium metal batteries.