In situ Synthesis of a Bismuth Layer on a Sodium Metal Anode for Fast Interfacial Transport in Sodium-Oxygen Batteries

Na metal has shown great promise as anode material for Na-based batteries due to its high theoretical capacity, low potential, high abundance, and low cost. However, the uneven solid electrolyte interphase layer formed on the Na anode surface caused by side reactions with the electrolyte and serious corrosion will lead to dendrite formation and safety issues. Here we report a stable Na anode by coating a Bi layer, which is formed in situ through simple ion-exchange. The compact Bi layer can effectively prevent Na reacting with the electrolyte and suppress the formation of dendrites. The Na/Bi anode exhibits high exchange current densities and fast charge-transfer kinetics. As a result, the overpotential of the symmetric cells using this Na/Bi electrode does not increase obviously after cycling for 1000 h at a current density of 0.5 mA cm(-2). Moreover, the Na-O-2 batteries with Na/Bi anode can run for 50 cycles. The presented surface coating approach provides a new strategy to protect Na anodes in Na-based batteries.