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_1/3Fe_1/3Mn_1/3O₂ (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_1/3Fe_1/3Mn_1/3)_0.94Al_0.03Ti_0.03O₂ 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.