Na₄Fe₃(PO₄)₂(P₂O₇)/C composite with porous structure enabling all-climate and long-life sodium-ion batteries

Na₄Fe₃(PO₄)₂(P₂O₇) (NFPP) with the advantages of low cost and stable crystal structure has been considered a highly promising cathode candidate for sodium-ion batteries. However, limited by its undesirable intrinsic conductivity, it still suffers from unsatisfactory electrochemical performance. Herein, we synthesized NFPP/C composites with porous structure (p-NFPP) by a facile self-assembly strategy. Its well-developed pore structure can effectively reduce the ion diffusion path, accelerate electrolyte infiltration and accommodate volume expansion during the charge/discharge process. In addition, in-situ X-ray diffraction revealed the superior structural stability of p-NFPP. They enable a high reversible capacity (104.8 mAh g⁻¹), and good rate performance (75.0 mAh g⁻¹ at 10 A g⁻¹), and excellent cycling stability (a reversible capacity of 85.1 mAh g⁻¹ after 2000 cycles). More importantly, the p-NFPP realizes a stable operation in a wide temperature range of 55°C to −10°C. This work highlights morphology engineering as a powerful strategy to boost the all-climate sodium storage performance of electrode materials.