Improving long-cycle capability of O3 type NaNi1/3Fe1/3Mn1/3O2 via Ti replacing Fe for stable sodium-ion batteries

O3-type NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM) is recognized as a highly promising cathode material for sodium-ion batteries owing to its cost-effectiveness, substantial theoretical capacity, and facile synthesis. Nevertheless, this material suffers from rapid capacity decay caused by structural degradation and irreversible phase transitions at high voltages (> 4.0 V vs. Na + /Na). Herein, partial substitution of Fe 3+ sites with Ti 4+ in the transition metal layer was implemented. Systematic investigations via X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) reveal that Ti substitution effectively stabilizes the layered framework by suppressing detrimental phase transitions through enhanced structural pillar effects. The optimized NaNi 1/3 Fe 0.23 Mn 1/3 Ti 0.1 O 2 delivers a specific capacity of 144.1 mAh g −1 within 2.0–4.2 V at 0.1 C, demonstrating 71.3% capacity retention after 100 cycles at 1 C (130 mA g −1 ). This work establishes a viable strategy for enhancing structural stability in O3-type cathodes through selective cation substitution. Graphical