Synergistic Strain and Charge Regulation via Zr Doping in NaTi2(PO4)3 Electrode Toward Efficient Na-Storage

Abstract

Sodium titanium phosphate (NaTi2(PO4)3, NTP) is regarded as a promising anode material for sodium-ion batteries (SIBs) owing to its structural stability. However, its practical application is hindered by intrinsically low electronic conductivity and sluggish Na + diffusion kinetics, which impair the rate capability and cycling stability. In this work, zirconium (Zr) with a larger ionic radius and higher electron density is introduced into the NTP lattice alongside in-situ carbon coating. Combined theoretical and experimental analyses reveal that Zr doping expands lattice spacing and contracts charge centers, thereby broadening Na + diffusion channels and facilitating ionic and electronic transport. Additionally, Zr doping induces grain refinement, which enhances the electrochemically active surface area, shortens ion diffusion paths, and thus substantially improves electronic conductivity and Na + diffusivity. In-situ and ex-situ analyses confirm the dominant Ti 4+ /Ti 3+ redox mechanism and structural integrity are maintained. Consequently, the modified electrode delivers significantly improved rate performance and remarkable long-term cyclability in SIBs, retaining 88.9% capacity over 2000 cycles at 2 A g -1 and 87.5% after 6000 cycles at 5 A g -1 . This study provides insights for developing high-power, long-life SIB anodes via lattice strain and charge regulation.