Building Fast Ion-Conducting Pathways on 3D Metallic Scaffolds for High-Performance Sodium Metal Anodes.

Building 3D electron-conducting scaffolds has been proven to be an effective way to alleviate severe dendritic growth and infinite volume change of sodium (Na) metal anodes. However, the electroplated Na metal cannot completely fill these scaffolds, especially at high current densities. Herein, we revealed that the uniform Na plating on 3D scaffolds is strongly related with the surface Na conductivity. As a proof of concept, we synthesized NiF hollow nanobowls grown on nickel foam (NiF@NF) to realize homogeneous Na plating on the 3D scaffold. The NiF can be electrochemically converted to a NaF-enriched SEI layer, which significantly reduces the diffusion barrier for Na ions. The NaF-enriched SEI layer generated along the Ni backbones creates 3D interconnected ion-conducting pathways and allows for the rapid Na transfer throughout the entire 3D scaffold to enable densely filled and dendrite-free Na metal anodes. As a result, symmetric cells composed of identical Na/NiF@NF electrodes show durable cycle life with an exceedingly stable voltage profile and small hysteresis, particularly at a high current density of 10 mA cm or a large areal capacity of 10 mAh cm. Moreover, the full cell assembled with a NaV(PO) cathode exhibits a superior capacity retention of 97.8% at a high current of 5C after 300 cycles.