Electronic structure regulation inducing robust solid electrolyte interphase for stable anode-free sodium metal batteries

Anode-free sodium metal batteries (AFSMBs) have gained attention as next-generation storage systems with high energy density and cost-effectiveness. However, non-uniform sodium (Na) deposition and an unsteady solid electrolyte interphase (SEI) lead to dendrite-related issues and severe irreversible Na + plating/stripping, greatly aggravating their cycle deterioration. In this study, we effectively modified the 3D current collector’s electronic structure by introducing Zn-N x active sites (Zn-CNF), which enhances lateral Na + diffusion and the Na planar growth, enabling uniform deep Na deposition at an exceptionally high capacity of 10 mA h cm −2 . Furthermore, the Zn-N x bonds enhance the adsorption capacity of PF 6 − and contribute to forming a stable inorganic-rich SEI layer. Consequently, Zn-CNF with the electronic structure regulation endows an ultra-low nucleation overpotential (8 mV) and ultra-high Coulombic efficiency of 99.94% over 1600 cycles. Symmetric cells demonstrate stable Na + plating/stripping behavior for more than 4400 h at 1 mA cm −2 . Moreover, under high cathode loading (7.97 mg cm −2 ), the AFSMBs achieve a high energy density of 374 Wh kg −1 and retain a high discharge capacity of 82.49 mA h g −1 with a capacity retention of 80.4% after 120 cycles. This work proposes a viable strategy to achieving high-energy-density AFSMBs. The introduction of Zn-N x active sites significantly regulates the electronic structure of the 3D current collector, thereby facilitating the formation of a robust inorganic-rich SEI, enhancing lateral Na + diffusion, and promoting planar Na deposition. This enables high cathode loading (7.97 mg cm −2 ) in anode-free sodium metal batteries with a high energy density of 374 Wh kg −1 and 80.4% capacity retention over 120 cycles. • Zn-N x active sites effectively tune the electronic structure of the 3D current collector, facilitating the formation of an anion-derived robust solid electrolyte interphase (SEI) to suppress electrolyte decomposition and interfacial side reactions. • Enhanced lateral Na + diffusion promotes planar Na growth, enabling highly reversible plating/stripping and uniform Na deposition at a high areal capacity of 10 mA h cm −2 . • This strategy effectively regulates Na plating and interphase-depleted Na + ratios during plating/stripping, maintaining a high Na plating proportion (∼80%) over long-term cycling and ensuring superior Na + utilization. • Anode-free sodium metal batteries (N/P = 0) with a high-loading cathode (7.97 mg cm −2 ) achieve a high discharge capacity of 82.49 mA h g −1 with a capacity retention of 80.4% after 120 cycles.