Synergistic Conductive Network of Polypyrrole and Carbon for High-Performance NFPP Cathode

Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 (NFPP) has emerged as a promising cathode material for sodium-ion batteries, but intrinsically low electronic conductivity and sluggish Na + ion diffusion severely limit performance. Conventional strategies involving in situ carbon incorporation during synthesis fail to establish a continuous conductive network because the resulting carbon is unevenly distributed. In this study, a uniform polypyrrole (PPy) coating layer was introduced onto the surface of NFPP particles through a mild oxidative polymerization process. The intrinsic carbon layer serves as a homogeneous anchoring platform for pyrrole adsorption. This enables surface-directed polymerization to form a continuous and thickness-controlled PPy shell without disturbing the NFPP crystal structure. This carbon–polymer integrated network increases interfacial charge-transfer and accelerates Na + ion diffusion, enabling NFPP@PPy-II to deliver high reversible capacity and superior rate capability. Notably, the composite retains over 90% of its capacity after 1000 cycles at a high rate of 10 °C, highlighting its exceptional cycling durability.