Phase Purification and Crystallology Engineering Enable Fast‐Charging Na ₅ Fe _2.9 Ni _0.1 (PO ₄ ) ₂ (P ₂ O ₇ ) Cathode for Wide‐Temperature Sodium‐Ion Batteries

Abstract Na ₄ Fe ₃ (PO ₄ ) ₂ (P ₂ O ₇ ) (NFPP) holds considerable promise among sodium‐ion batteries (SIBs) cathodes benefit from non‐toxicity and structural stability. However, the concomitant inactive NaFePO ₄ impurities (NFP) and low intrinsic electronic conductivity hinder the practical application, especially for fast‐charging and wide‐temperature utilization. Herein, a novel NFP absent phase‐purified Na ₅ Fe _2.9 Ni _0.1 (PO ₄ ) ₂ (P ₂ O ₇ ) (N ₅ FNPP) with high electronic conductivity and low Na ⁺ diffusion barrier is successfully developed through Na enrichment and Ni introducing. The incorporated strategy aiming at hybrid orbital diversification (Ni─O) and spin‐state transition (Fe 3d) is predicted by DFT calculation to narrow the band gap, as well as the structural framework stabilizing and Na ⁺ diffusion accelerating, induced by lattice tuning and electronic delocalization. Benefiting from the original coupling designs, the N ₅ FNPP cathode exhibits an excellent discharging capacity (112.9 mAh g⁻¹ at 0.1 C), and outstanding fast‐charging performance (87.1 mAh g⁻¹ at 10 C, 95% for 2000 cycles). Particularly, it exhibits excellent applicability in a wide temperature range of −30–60 °C. This work sheds light on the comprehensive consideration of electron tuning, lattice adjustment, and phase purification on advanced polyanion phosphate cathode construction, as well as provides a guideline for fabricating other advanced cathodes and fast‐charging, wide‐temperature SIBs.