Universal architecture and defect engineering dual strategy for hierarchical antimony phosphate composite toward fast and durable sodium storage

Antimony (Sb)-based anode materials are feasible candidates for sodium-ion batteries (SIBs) due to their high theoretical specific capacity and excellent electrical conductivity. However, they still suffer from volume distortion, structural collapse, and ionic conduction interruption upon cycling. Herein, a hierarchical array-like nanofiber structure was designed to address these limitations by combining architecture engineering and anion tuning strategy, in which SbPO4−x with oxygen vacancy nanosheet arrays are anchored on the surface of interwoven carbon nanofibers (SbPO4−x@CNFs). In particular, bulky PO43− anions mitigate the large volume distortion and generate Na3PO4 with high ionic conductivity, collectively improving cyclic stability and ionic transport efficiency. The abundant oxygen vacancies substantially boost the intrinsic electronic conductivity of SbPO4, further accelerating the reaction dynamics. In addition, hierarchical fibrous structures provide abundant active sites, construct efficient conducting networks, and enhance the electron/ion transport capacity. Benefiting from the advanced structural design, the SbPO4−x@CNFs electrodes exhibit outstanding cycling stability (1000 cycles at 1.0 A g−1 with capacity decay of 0.05% per cycle) and rapid sodium storage performance (293.8 mA h g−1 at 5.0 A g−1). Importantly, systematic in-/ex-situ techniques have revealed the "multi-step conversion-alloying" reaction process and the "battery-capacitor dual-mode" sodium-storage mechanism. This work provides valuable insights into the design of anode materials for advanced SIBs with elevated stability and superior rate performance.