3D Sodiophilic Ti 3 C 2 MXene@g-C 3 N 4 Hetero-Interphase Raises the Stability of Sodium Metal Anodes.

Owing to several advantages of metallic sodium (Na), such as a relatively high theoretical capacity, low redox potential, wide availability, and low cost, Na metal batteries are being extensively studied, which are expected to play a major role in the fields of electric vehicles and grid-scale energy storage. Although considerable efforts have been devoted to utilizing MXene-based materials for suppressing Na dendrites, achieving a stable cycling of Na metal anodes remains extremely challenging due to, for example, the low Coulombic efficiency (CE) caused by the severe side reactions. Herein, a g-C 3 N 4 layer was attached in situ on the Ti 3 C 2 MXene surface, inducing a surface state reconstruction and thus forming a stable hetero-interphase with excellent sodiophilicity between the MXene and g-C 3 N 4 to inhibit side reactions and guide uniform Na ion flux. The 3D construction can not only lower the local current density to facilitate uniform Na plating/stripping but also mitigate volume change to stabilize the electrolyte/electrode interphase. Thus, the 3D Ti 3 C 2 MXene@g-C 3 N 4 nanocomposite enables much enhanced average CEs (99.9% at 1 mA h cm -2 , 0.5 mA cm -2 ) in asymmetric half cells, long-term stability (up to 700 h) for symmetric cells, and stable cycling (up to 800 cycles at 2 C), together with outstanding rate capability (up to 20 C), of full cells. The present study demonstrates an approach in developing practically high performance for Na metal anodes.