Continuous‐Flow Synthesis of Nanostructured Na₄Fe₃(PO₄)₂P₂O₇ Cathode With Superior Rate Capability for Fast‐Charging Sodium‐Ion Batteries

Current synthetic methods for nanostructured Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 (NFPP) with favorable fast‐charging ability mainly rely on batch reactors that still suffer from limitations such as small‐scale production, manual operating requirements, and challenges in batch‐to‐batch reproducibility. Herein, two editions of continuous‐flow millifluidic synthetic devices are rationally designed for scalable and controllable production of NFPP nanostructures in high‐boiling solvents. Merely 8 min of reaction time in the first‐edition helical coil reactor achieves the optimal balance between yield and electrochemical performance of the resulting NFPP cathode. The as‐synthesized NFPP/C‐8 cathode delivers an initial capacity of 89.6 mAh g −1 that maintains 88.5% over 2000 cycles at a high rate of 20 C. An optimized multi‐turn pancake coil reactor that accommodates up to 389.5 mL of solution is further designed, resulting in 116.8 g h −1 of throughput that reaches a 46‐fold increase compared to that of a conventional batch reactor, finally producing ≈120 g of NFPP‐LS in this work. Impressively, the full cell matching NFPP‐LS cathode and hard carbon anode offers a reversible capacity of 70.7 mAh g −1 with 77.5% of retention after 200 cycles, even at 20 C, ranking the leading state among the current polyanion‐based full batteries.