An Encapsulation-Based Sodium Storage via Zn-Single-Atom Implanted Carbon Nanotubes

The properties of high theoretical capacity, low cost, and large potential of metallic sodium (Na) has strongly promoted the development of rechargeable sodium-based batteries. However, the issues of infinite volume variation, unstable solid electrolyte interphase (SEI), and dendritic sodium causes a rapid decline in performance and notorious safety hazards. Herein, a highly reversible encapsulation-based sodium storage by designing a functional hollow carbon nanotube with Zn single atom sites embedded in the carbon shell (Zn_SA -HCNT) is achieved. The appropriate tube space can encapsulate bulk sodium inside; the inner enriched Zn_SA sites provide abundant sodiophilic sites, which can evidently reduce the nucleation barrier of Na deposition. Moreover, the carbon shell derived from ZIF-8 provides geometric constraints and excellent ion/electron transport channels for the rapid transfer of Na⁺ due to its pore-rich shell, which can be revealed by in situ transmission electron microscopy (TEM). As expected, Na@Zn_SA -HCNT anodes present steady long-term performance in symmetrical battery (>900 h at 10 mA cm^-2 ). Moreover, superior electrochemical performance of Na@Zn_SA -HCNT||PB full cells can be delivered. This work develops a new strategy based on carbon nanotube encapsulation of metallic sodium, which improves the safety and cycling performance of sodium metal anode.