Crystal structure modulation enabling fast charging and stable layered sodium oxide cathodes†

Layered oxide cathodes show great promise for commercial applications due to their low cost, high specific capacity, and energy density. However, their rapid capacity decay and slow kinetics primarily caused by harmful phase transitions and a high energy barrier for Na⁺ diffusion result in inferior battery performance. Herein, we modulate the crystal structure of layered oxide cathodes by replacing the Fe³⁺ site with Al³⁺, which strengthens the transition metal layers and enlarges the Na translation layer owing to the smaller ion radius of Al³⁺ and the stronger bonding energy of Al–O. This restrains the Jahn–Teller effect owing to transition metal dissolution and improves the electrochemical kinetics. Consequently, the modified cathodes exhibited an excellent high-rate performance of 111 mA h g⁻¹ at a high rate of 5.0C and an unexpectedly long cycling life with a 73.88% capacity retention rate after 500 cycles at 5.0C, whereas the bare cathode exhibited a rate performance of 97.3 mA h g⁻¹ with a low capacity retention rate of 48.42% after 500 cycles at 5.0C. This study provides valuable insights into tuning the crystal structure for designing fast charging and highly stable O3-type cathodes.