2D Sn/C freestanding frameworks as a robust nucleation layer for highly stable sodium metal anodes with a high utilization

Sodium metal anodes (SMAs) are regarded as a good candidate for next-generation alkali metal batteries owing to the higher natural reserves and lower cost of sodium. Nevertheless, the challenging issues associated with SMAs, including the dendritic formation and the high reactivity of sodium metal, have significantly impeded the utilization of SMAs in the practical deployment of sodium metal batteries. Herein, we report that 2D graphitic carbon frameworks embedded with highly dispersive Sn nanoparticles (denoted as Sn/C) serve as a robust nucleation buffer layer to spatially guide the sodium deposition. The embedded Sn nanoparticles (NPs) are able to lower the nucleation barrier through in situ formed “sodiophilic” Na-Sn alloy. Meanwhile, the supporting carbon frameworks can effectively keep the functionality of nucleation sites for long-term cycling. As a result, the synergistic effects of these two components endow the cell with outstanding cyclability even at high areal capacities. The symmetric cells using the 2D Sn/C nucleation buffer layer can deliver a continuous plating/stripping cycles for nearly 3900 h with an average Coulombic efficiency (CE) of 99.63% at 4 mA h cm−2. Additionally, an ultrahigh sodium utilization can also be realized, as is evidenced by the stable cycling (up to 1272 h), large reversible capacity (4 mA h cm−2) and high depth of discharge (66.67%) of the symmetric cells with the nucleation buffer layer. It is found that the current density plays a greater influence than the reversible areal capacity on the SMA stability. This study provides a new insight on the role of nucleation buffer layer in the stabilization of SMAs.