Harnessing Capillary Effects to Unlock Application Potential of the Porous Na₄Fe_1.55(PO₄)P₂O₇ Cathode for Sodium-Ion Batteries

Iron-based phosphate cathode materials exhibit excellent cost-effectiveness and performance advantages, making them promising for large-scale applications in sodium-ion batteries. However, industrial efforts to enhance the energy density of battery packs by coating high-loading electrodes often lead to poor wettability and low conductivity, significantly impacting the performance. Herein, this work successfully fabricated an in situ carbon-coated porous Na₄Fe_1.55(PO₄)P₂O₇ (NFP/600) cathode, which exhibits a unique capillary effect when in contact with the electrolyte, enhancing the wettability of the NFP/600 electrode. While the porous structure and carbon coating improve ion and electron transport capabilities, significantly improving the kinetic performance. Consequently, the initial discharge capacity of the NFP/600 cathode reaches 97.6 mAh g^-1 at a rate of 5 C, with a capacity retention of 84.9 mAh g^-1 after 2500 cycles. Even with a loading exceeding 10 mg cm^-2, the NFP/600 electrode achieves a discharge specific capacity of 100.83 mAh g^-1 at 1 C, retaining 98.4% of its capacity after 460 cycles. Furthermore, the full cell pairing NFP/600 with hard carbon demonstrated a discharge specific capacity of 93.9 mAh g^-1 at 1 C, maintaining stable cycling over 200 cycles. These findings provide a promising pathway for the design of low-cost, high-performance phosphate cathode materials.