Ti-Doped Na4Fe3(PO4)2P2O7/C Cathode Synthesized via a Low-Cost Solid-State Method for High-Performance Sodium-Ion Batteries

Na4Fe3(PO4)2P2O7 (NFPP) is regarded as a highly promising cathode material for sodium-ion batteries (SIBs) in energy storage systems. In particular, the low cost and environmental friendliness of NFPP render it especially suitable for large-scale commercialization. Nevertheless, the inherently low ionic/electronic conductivity of NFPP severely impedes its practical deployment in SIBs. Herein, employing a bulk-phase regulation strategy through elemental doping, we prepared Ti-doped Na4Fe3–xTix(PO4)2P2O7/C cathode materials using iron phosphate as both the iron and phosphorus source via a low-cost solid-state method, aiming to further reduce cost and enhance overall material performance. The results demonstrate that moderate Ti4+ doping shortens the average Fe–O bond length, reinforces the structural stability of the crystalline framework, and effectively improves Na+ diffusion kinetics. Among the compositions investigated, the optimized Na4Fe2.94Ti0.06(PO4)2P2O7/C (denoted NFPP-Ti0.06) exhibits the best comprehensive electrochemical properties, delivering outstanding rate capability from 0.2 to 20 C (with a specific capacity of 96.11 mAh g–1 at 20 C, retaining 83.51% of the 0.2 C capacity) and exceptional cycling stability (capacity retention of 99.18% after 400 cycles at 2 C and 82.59% after 3000 cycles at 20 C). Furthermore, a full cell assembled with NFPP-Ti0.06 as the cathode and hard carbon as the anode also exhibited favorable electrochemical performance.