Regulating Chemomechanical Interactions in a High-Compaction Na4Fe3(PO4)2P2O7 Cathode for Durable Sodium Storage

Abstract The polyanionic Na4Fe3(PO4)2P2O7 (NFPP) cathode is recognized for its cost-effectiveness and three-dimensional framework structure. However, its anisotropic lattice evolution induces internal stress accumulation. Furthermore, the pursuit of high energy density necessitates high-compaction processing, which exacerbates localized stress buildup. Herein, this study explores and regulates the chemomechanical interactions of NFPP under high-compaction conditions. The formation of microcracks and new reaction interfaces constitutes a chemomechanical failure pathway. To suppress this, the introduction of large-sized La promotes grain refinement and close packing, thereby enhancing mechanical strength. Meanwhile, lattice substitution triggers local FeO6 structural rearrangement, strengthening the Fe–O bonds and mitigating lattice strain. The optimized NFPP-La exhibits a remarkable reversible capacity of 90.4 mAh g–1 at 10 C and retains 92.2% capacity after 5000 cycles under high compaction conditions. Moreover, pouch cell evaluation validated its outstanding temperature adaptability (−40 to 60 °C) and robust cycling stability.