Electrosprayed hierarchical mesoporous Na₄Fe₃(PO₄)₂(P₂O₇)@C microspheres exhibit outstanding sodium-storage performance

The mixed phosphate Na₄Fe₃(PO₄)₂(P₂O₇) (NFPP) via synergistic coordination of mixed [PO₄]/[P₂O₇] anion groups achieves a flat voltage plateau at 3.2 V (vs. Na + /Na) and a theoretical specific capacity of 129 mAh g −1 , but its practical application is still limited by its inherent low electronic conductivity. Through structural integration of polyanion-type cathode materials, this study innovatively designed and constructed hierarchical Na₄Fe₃(PO₄)₂(P₂O₇)@C mesoporous microspheres (NFPP@CMMS). The NFPP nanocrystals uniformly embedded in a three-dimensional interconnected meso porous carbon matrix (pore size distribution: 2–5 nm). Such hierarchical meso/micro-nano architectures provided expansive ion-exchange interfaces, accelerating Na + de/intercalation kinetics while enhancing electronic conductivity and mitigating structural collapse during cycling. Consequently, the NFPP@CMMS delivers exceptional reversible discharge capacity (121 mAh g −1 at 0.1C), outstanding rate capability (72 mAh g −1 at 50C), and superior cycling stability (90.70 % capacity retention after 3500 cycles at 5C). This triple-synergy strategy—combining nano-confinement effects, interconnected mesoporous channels, and carbon-encapsulated network—provides a novel pathway for developing practical sodium-ion battery cathodes.