Shape Engineering: Morphological Size Optimization for High-Pressure Solid Density Na₃Fe₂(PO₄)P₂O₇ Cathode Material Preparation and Performance Investigation

Iron-based mixed sodium phosphate ion batteries have been widely studied due to their low cost, environmental friendliness, and excellent cycle stability. However, insufficient energy density greatly hinders their practical application, especially because of the positive electrode. Herein, we adopt a kilogram-scale method to synthesize Na 3 Fe 2 (PO 4 )P 2 O 7 (NFPP-C) with high powder (2.031 g cm –3 ) and pole piece (2.0 g cm –3 ) compaction density. NFPP-C has an outstanding rate capability (57.02 mAh g –1 at 20 C). Even after 1800 cycles at 5 C, the capacity retention rate remains as high as 94.19%. In addition, we assembled and tested 13 Ah HC||NFPP-C pouch cells, which have excellent rate performance, extraordinary low-temperature performance (78.02% for −40 °C), and unprecedentedly high cyclic stability (96.88% capacity retention after 1000 cycles). The energy density of the assembled NFPP-C-integrated pouch cell reaches 91.731 Wh kg –1 (based on overall battery quality), which is 1.127 times that of the original material (NFPP-A). In summary, these results will contribute to the further development of sodium-ion batteries, reveal the feasibility of sodium-ion batteries in practical applications, and provide a forward-looking idea for the industrialization of sodium-ion batteries.