An MXene-Based Metal Anode with Stepped Sodiophilic Gradient Structure Enables a Large Current Density for Rechargeable Na-O 2 Batteries.

The metal anode is the pivotal component for advanced sodium-metal batteries such as Na-O 2 batteries. Designing a 3D confinement scaffold is a promising strategy for constructing dendrite-free sodium-metal anodes; however, cycling stability at a large current density (>10 mA cm -2 ) is still difficult to realize. Herein, the design of new lightweight and fibrous hydroxylated Ti 3 C 2 (h-Ti 3 C 2 ) MXene based scaffolds with stepped sodiophilic gradient structure (h-M-SSG) is reported, and its thickness can be controlled (80-250 µm). The sodiophilic gradient structure (adjusted by h-Ti 3 C 2 ) can effectively induce sodium ions to preferentially deposit at the bottom of the scaffold, thus inhibiting dendrite growth. h-M-SSG/Na-based symmetrical batteries exhibit a low polarization voltage and long cycling life at a high current density (40 mA cm -2 ) and a high cut-off capacity (40 mAh cm -2 ). Moreover, a Na-O 2 battery with an h-M-SSG/Na anode exhibits a low potential gap of 0.137 V after 45 cycles at 1000 mA g -1 and 1000 mAh g -1 . This deposition-regulation strategy would inspire the design of 3D scaffolds for high-performance sodium-metal-anode-based batteries.