Nickel-Doping Strategy on P2-Type Na0.6Mg0.23Mn0.67Ni0.1O2 for High-Performance Sodium-ion Batteries

The activation of oxygen redox reactions ORR in P2-type layered oxide cathodes has drawn significant attention as a promising approach to overcome energy density limitations. However, challenges persist due to irreversible lattice oxygen loss and associated structural distortions during ORR processes, leading to rapid capacity degradation and sluggish kinetics. In this work, we propose a Ni-substitution strategy for the P2-type Na0.6Mg0.23Mn0.67Ni0.1O2 cathode, which effectively alleviates Mn3+ Jahn-Teller distortion, mitigates oxygen loss-induced structural collapse, and expands Na–O interlayer spacing to enhance Na+ diffusion. The engineered NMMNO cathode achieves a discharge specific capacity of 164.8 mA h g-1 at 0.2 C and demonstrates superior cycling stability (capacity retention of 91.3%) within the 1.5–4.4 V voltage range. These metrics notably outperform the pristine Na0.67Mg0.33Mn0.67O2 (capacity retention of 47 % after 50 cycles). This study elucidates the dual functionality of Ni doping in suppressing Mn/O redox-induced phase transitions while stabilizing the host structure, thereby providing an effective pathway for developing high-energy-density sodium-ion battery cathodes with prolonged cycle life.