Modulating oxygen anion microenvironment of P2-type cathodes enables long-term cycling stability for high-voltage sodium-ion batteries

NiMn-based P2-type layered oxides are promising high-voltage cathodes for power-type sodium-ion batteries, but the instability of oxygen anionic redox under high-voltage operation severely limits their cycling stability. Herein, we design and synthesize a durable P2-type Na 0.67 Ca 0.02 Ni 0.27 Zn 0.01 Mn 0.55 Ti 0.12 Mg 0.05 O 1.99 F 0.01 cathode via a synergistic lattice-oxygen microenvironment regulation strategy that markedly enhances anionic-redox reversibility. The incorporation of Ni-O-Zn configurations, enabled by lower electronegativity of Zn 2+ , together with highly electronegative F - in O-TM-F bonding, weakens Ni 3d -O 2p hybridization and increases the electron density of lattice oxygen, thereby suppressing oxygen charge compensation at high states of charge. Meanwhile, Ca-O-Ni configurations partially replaces unstable nil (Na + vacancies)-O-Ni upon deep Na + extraction, restricting O 2p hole formation to prevent irreversible oxygen dimerization and O 2 release. These merits collectively alleviate structural degradation and interfacial parasitic reactions during long-term cycling. Consequently, the optimized cathode delivers a high reversible capacity of 135.1 mAh g -1 and a volumetric energy density of 1660 Wh L -1 cathode within 2.0-4.4 V, approximately 1.3 times that of commercial LiFePO 4 . Moreover, it retains 94.5% of its initial capacity after 100 cycles at 1C, outperforming previously reported high-voltage P2 type cathodes.