Vacancy and Low-Energy 3p-Orbital Endow Na₄Fe₃(PO₄)₂(P₂O₇) Cathode with Superior Sodium Storage Kinetics

Iron-based phosphate Na₄Fe₃(PO₄)₂(P₂O₇) (NFPP) has been regarded as the most promising cathode for sodium-ion batteries (SIBs) thanks to its cost-effectiveness and eco-friendliness. However, it is in a predicament from the intrinsic low ionic/electronic conductivity, becoming a great challenge for its practical application. Herein, the significant roles of the low-energy 3p-orbital and transition metal vacancies are emphasized in facilitating charge rearrangement and reconstructing ion-diffusion channels, from the perspectives of crystallography and electron interaction for the first time, and the modification mechanism is fully explored by various characterizations and theoretical calculations. As proof of this concept, the designed Na₄Fe_2.85Al_0.1(PO₄)₂(P₂O₇) (NF_2.85A_0.1PP) delivers prominent electrochemical performance, achieving high energy density (≈350 Wh kg⁻¹), superior kinetics (62 mAh g⁻¹ at 10 A g⁻¹), excellent power density (23 kW kg⁻¹, 143 Wh kg⁻¹), and extraordinary cycling stability (with negligible attenuation after 10 000 cycles). This work provides a brand-new perspective for designing ultra-endurable high-rate polyanion cathodes.