Enhanced electrochemical performance of Na ₂ FeP ₂ O ₇ cathode material for sodium-ion batteries through composite with Cu ₃ (PO ₄ ) ₂

Abstract Among the various polyanionic cathode materials for sodium-ion batteries, phosphate-based materials have demonstrated excellent electrochemical and thermal properties, thereby attracting considerable attention. Na 2 FeP 2 O 7 stands out as one of the most stable cathode materials, distinguished by its well-defined pore structure and excellent cycling stability, and exceptional air stability. Nonetheless, due to the electron-blocking effect of the metal atoms, Na 2 FeP 2 O 7 exhibits poor electronic conductivity. To address this, an appropriate amount of Cu 3 (PO 4 ) 2 is integrating with Na 2 FeP 2 O 7 to synthesize the Na 2 FeP 2 O 7 @Cu 3 (PO 4 ) 2 (NFPO@CPH) composite material. Benefiting from the excellent electronic properties of Cu 3 (PO 4 ) 2 , the composite enhances both electronic conductivity and Na + ion diffusion capabilities of the material. Consequently, the NFPO@3%CPH electrode material exhibits a high specific capacity (88.1 mAh g −1 ) and excellent cycling stability, retaining 94% its capacity after 250 cycles at 0.1 C. Furthermore, it maintains excellent electrochemical performance under extreme conditions, such as a high temperature of 60 °C and a high mass loading of 11 mg cm −2 . The full battery, when paired with hard carbon, achieves a discharge capacity of 82.2 mAh g −1 at 0.1 C, demonstrating its promise for practical application.