Bonding Engineering by Al/Ti Codoping for High-Rate Capability and Cycling Stability of NaNi _1/3 Fe _1/3 Mn _1/3 O ₂

The O3-type NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM) is a promising cathode material for sodium-ion batteries (SIBs) due to its high specific capacity and cost-effectiveness. However, its practical application is hindered by irreversible phase transitions and sluggish Na + transport kinetics. To address these challenges, this work proposes a bonding engineering strategy via Al/Ti codoping to synergistically enhance the high-rate capability and cycling stability of cathodes. Specifically, Al doping effectively alleviates the Jahn–Teller effect, while Ti doping mitigates the phase transition stress through the spring effect. The incorporation of stronger Al–O and Ti–O bonds can stabilize the transition metal framework, mitigate oxygen release during deep desodiation, and expand the interlayer spacing, thereby facilitating Na + diffusion. The synergistic effect enables prepared Na(Ni 1/3 Fe 1/3 Mn 1/3 ) 0.94 Al 0.03 Ti 0.03 O 2 to deliver a high-rate capacity of 102.42 mAh g –1 at 10 C and significantly improved cycling stability. This work highlights the importance of targeted bond strengthening in the development of layered oxide cathodes for high-performance SIBs.