Honeycomb-like Superstructure of 3D Sodiophilic Host for Anode-Free Sodium Batteries

Sodium metal batteries (SMBs) have emerged as a promising candidate for large-scale energy storage systems due to their abundance and cost-effectiveness. However, the high reactivity of sodium (Na) inevitably leads to side reactions and it's infinite volume expansion would definitely limit the applications. The anode-free Na batteries (AFNB) significantly enhance energy density by eliminating excess sodium, but bring a few challenges in terms of cycling stability. In this study, we report that honeycomb-like Bi-nanosheets arrays vertically grown on a Cu mesh, this unique 3D superstructure accommodate the volumetric changes and provides abundant sodiophilic nucleation sites. The Na||Cu half-cell battery demonstrates high reversibility of Na plating/stripping with an average coulombic efficiency (CE) of 99.8% at high current density. The Na||Na symmetrical cell exhibits a stable cycle lifespan of over 1000 hours at a significant discharge depth (DOD) of 75%. The NaTi₂(PO₄)₃ (NTP) cathode in AFNB cell with an N/P ratio of 1 displays an initial capacity of 95.18 mA h g^-1 for 267 cycles at 1 C, with an outstanding capacity retention of 93.22%. Our work proposes a potential path toward establishing a highly sodiophilic 3D sodium host, thereby promoting its application in high-stability AFNBs.