Ni-induced Structural Spring Effect in High-performance Mn-Rich P2-Type Sodium Cathodes

Anionic redox chemistry offers a promising pathway toward high capacity in P2-type Mn-rich layered cathodes. However, the practical application is hindered by sluggish redox kinetics, severe oxygen loss, and structural deterioration, leading to poor cycling performance and particularly inadequate activity under high-current conditions. Herein, we propose a Ni-induced structural spring effect in P2-Na_5/6Li_1/4Mn_3/4O₂ (NLM) by partially substituting Li with Ni. This Ni-induced covalent strengthening acts as a structural "spring" that dynamically buffers mechanical stress during Na⁺ extraction/insertion, effectively suppressing phase transitions at deep desodiation states and preserving structural integrity. Meanwhile, Ni incorporation effectively mitigates the Jahn–Teller distortion of Mn³⁺ by modulating the local coordination environment, thereby alleviating anisotropic lattice strain. Concurrently, the Ni–O octahedral spring effect bonding accelerates oxygen redox kinetics, mitigates voltage hysteresis, and suppresses irreversible oxygen release, thereby stabilizing the anionic redox activity at high rates. The resulting material, P2-Na_0.73Li_0.15Ni_0.1Mn_0.75O₂ (NLNM), exhibits nearly twofold reduction in overpotential during oxygen redox, delivers a specific capacity of ~150 mAh/g at the average voltage of 3.4 V, and retains 82% capacity after 200 cycles at 600 mA/g. This work demonstrates the strategy of Ni-induced spring effect for stable anionic activation and structural robustness, consequently achieving long-term cycling stability in high-performance oxide cathodes.