Two‐Alloys‐Layer Modified Current Collector toward the Efficient Plating/Stripping of Sodium in Ester‐Based Electrolyte

Abstract Sodium metal anode is considered the most promising alternative to lithium due to its cost‐effectiveness and widespread availability. To realize its practical applications, numerous strategies have been devised in metallic Na and electrolyte to enhance the cycle life. However, the improvements in 2D current collector in ester‐based electrolyte remain limited. Herein, a two‐alloys‐layer modified current collector (Na 15 Sn 4 /Cu 6 Sn 5 /Cu) has been constructed through electrodeposition and sodiation processes. The Na 15 Sn 4 /Cu 6 Sn 5 alloys‐layer guarantees the dense plating of Na and establishes a credible connection between Na and substrate. The failure of sodium anode is attributed to the depletion of ester‐based electrolyte resulting from their side reactions, which could be mitigated on Na 15 Sn 4 surface. Thus, the asymmetric cell, containing merely 100 µL electrolyte, achieves efficient Na plating/stripping for 110 times with an average Coulombic efficiency of 94.9%, which is superior than those reported using excessive fluorine‐rich electrolytes. The full cell consisting of an anode with 3 mAh cm −2 of Na on Na 15 Sn 4 /Cu 6 Sn 5 /Cu and a Na 3 V 2 (PO 4 ) 3 cathode demonstrates a capacity retention rate of 96% after 200 cycles at 1.0 C. By improving the Coulombic efficiency solely through the modified copper foil, this work provides a new route for the practical application of Na anode in ester‐based electrolytes.