Synergistic Ti doping and carbon-coating to modulate Na+ migration channels in Na2FeP2O7 cathode for fast sodium storage

Abstract

Phosphate salt Na2FeP2O7 has emerged as a potential candidate material for sodium-ion batteries due to its high stability in the triclinic structure and low cost. However, its practical implementation is hindered by intrinsic limitations such as poor electronic conductivity and sluggish Na+ diffusion kinetics. In this study, Ti-doped Na2FeP2O7 composite coated with an in situ formed amorphous carbon layer (0.1Ti-NFO@C) was synthesized via a sol-gel method followed by high-temperature calcination. The introduced Fe/Ti–O bonding network and carbon coating synergistically enhance the electronic conductivity and Na+ transport kinetics, which significantly improve the rate performance and specific capacity. The resulting 0.1Ti-NFO@C delivers a reversible capacity of 109.67 mAh g−1 at 0.2C, and retains a capacity of 77.90 mAh g−1 even at a high current density of 10C. Furthermore, when assembled into a full cell with hard carbon, it exhibits an initial discharge capacity of 110.04 mAh g−1 at 0.5C and retains a capacity of 54.88 mAh g−1 after 200 cycles at 2.0C, with a Coulombic efficiency exceeding 99%. These structural modifications significantly enhance the material's performance, providing valuable insights toward the practical implementation of polyanion cathodes.