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Pure-phase iron-based phosphate Na 3.4 Fe 2.4 (PO 4 ) 1.4 P 2 O 7 (NFPP) is anticipated to emerge as a competitive candidate material for sodium-ion batteries (SIBs). Nevertheless, the low electronic conductivity and sluggish sodium ion diffusion kinetics during sodium storage present significant challenges to its electrochemical performance. Consequently, a sodium-rich fluorine-doping strategy has been proposed, and we elucidate the mechanism through which F doping influences the crystal structure and electronic conductivity of NFPP. Both experimental and theoretical calculations demonstrate that F doping expands the diffusion channels for Na +, reduces the band gap and Na + migration energy barrier, and enhances the intrinsic electronic conductivity of NFPP. Owing to the enhanced charge transport capability, the electrochemical performance of Na 3.475 Fe 2.4 (PO 4 ) 1.4 (P 2 O 7 )F 0.075 (NFPPF-0.075) significantly surpasses that of the undoped sample. NFPPF-0.075 demonstrates a discharge specific capacity of 113.7 mAh g –1 at 0.1 C; even at a current density of 30 C, the discharge specific capacity is sustained at 84.1 mAh g –1 . NFPPF-0.075 also exhibits remarkable cycle stability, achieving a capacity retention of 88.7% over 2000 cycles at 10 C. Furthermore, the NFPPF-0.075||HC full cell demonstrates remarkable rate performance and cycle performance. Therefore, Na 3.475 Fe 2.4 (PO 4 ) 1.4 (P 2 O 7 )F 0.075 has the potential to serve as a highly promising cathode material for large-scale applications in SIBs.
Ding et al. (Mon,) studied this question.