Achieving Long-Term Cyclability in Sodium-Ion Batteries: Site-Selective Doping to Inhibit Irreversible Phase Transitions in P2-Na<sub>2/3</sub>Ni<sub>1/3</sub>Mn<sub>2/3</sub>O<sub>2</sub> Cathode
Xiaoqian Xu, Youqi Chu, Yongbiao Mu, Xianbin Wei, Qing Zhang, H. Suresh Rao, Huicun Gu, Lyuming Pan, Meisheng Han, Yichun Wang, Lin Zeng, Lei Wei
Abstract
The typical P2-type Na 2/3 Ni 1/3 Mn 2/3 O 2 exhibits a high theoretical capacity for sodium-ion batteries (SIBs). However, its P2–O2 phase transition during deep charging causes severe structural degradation and capacity decay. In this work, we propose a site-selective doping strategy based on multielement synergy to suppress irreversible phase transitions. The alkali metal site doping by Sr doping as an interlayer pillar prevents cracks along the a b -plane and restrains interlaminar slip during deep desodiation. Y 3+ and Mo 6+ doping in transition metal layers stabilizes the transition metal bond and effectively prevents Na–O plate collapse during sodium deintercalation, dissipating strain accumulation and thereby inhibiting intergranular cracking. Additionally, Y 3+ /Mo 6+ doping activates additional Mn redox, effectively limits electron delocalization and charge order in transition metal layers, and creates a disordered sodium vacancy configuration, thus reducing the migration barrier of Na + . Benefiting from this, the site-selectively doped P2-Na 0.65 Sr 0.02 Ni 0.30 Mn 0.67 Y 0.01 Mo 0.02 O 2 cathode exhibits excellent electrochemical performance, delivering a high reversible capacity of 90 mAh g –1 at 200 C and maintaining 85.8% capacity retention after 2500 cycles at 20 C, significantly surpassing the pristine P2-NaNM cathode material. This work demonstrates the rational design of ultrastable layered cathode materials for sodium-ion batteries, contributing to the development of high-performance and long-life energy storage systems.