Synergistic Regulation of Nucleation and Interfacial Chemistry for Energy-Dense and Durable Anode-Free Na Batteries

Anode-free Na batteries are promising for achieving ultimate high energy density yet experience unsatisfactory cycling stability largely stemming from inhomogeneous Na deposition and an unstable solid electrolyte interphase (SEI). Herein, we report a multifunctional interface layer composed of Sn nanodots and ZnF2 nanosheets on a lightweight Al current collector (Sn-ZnF2/Al) to homogenize Na growth and stabilize the SEI layer. The abundant sodiophilic Sn and ZnF2 sites reduce Na nucleation energy barriers and uniformize the electric field distribution, further guiding homogeneous Na growth. Moreover, the in situ formed NaF-rich SEI enhances interfacial stability and serves as a protective layer against side reactions. Consequently, synergistic performance improvement is realized with highly reversible Na plating and stripping of around 99.98% at 8.0 mA cm-2 and 1.0 mAh cm-2 over 4440 cycles. Remarkably, an energy-focused anode-free pouch cell (Sn-ZnF2/Al//Na3V2O2(PO4)2F) exhibits an energy density of 442.9 Wh kg-1 (calculated based on active materials of both electrodes) and 80.37% capacity retention after 220 cycles. Meanwhile, a lifetime-focused anode-free pouch cell (Sn-ZnF2/Al//Na4Fe3(PO4)2P2O7) achieves ultrastable cyclability with 80.59% capacity retention over 2600 cycles. This work offers a potentially universal strategy for the development of anode-free Na batteries.