Tuning Electronegativity‐Difference Configuration to Construct Non‐Bonded O 2p Orbitals for Reversible Anionic Redox in O3‐Type Cathode

Abstract

How to tune the activity and reversibility of oxygen anion redox (OAR) is a critical issue for O3‐type sodium‐ion battery (SIB) cathodes. Herein, the key role of electronegativity‐difference configuration on the activation of OAR is find out, and further tune electronegativity‐difference configuration with La incorporation to construct non‐bonded O 2p orbitals and achieve the reversible anionic redox in O3‐type NaMn1/3Fe1/3Ni1/3O2. Owing to the special extranuclear electronic structure of La3+ [Xe], the La electron cloud is difficult to be disturbed by the O electron cloud, and some O electrons do not participate in the formation of ionic bonds, thus retaining the non‐bonded electrons of O 2p and activating OAR. Moreover, La3+ doping also decreases the Coulomb force between Na+ and O2− favoring Na+ migration as well as strengthening the La─O bonds inhibiting the irreversible phase transition. La2O3 coating layer also plays a role on inhibiting the reaction between molecular oxygen and the electrolyte, and making OAR reversible. After modification, the cycling stability is significantly improved (86.9% vs 27.3%@2C@200cycles; 90.8% vs 52.9%@5C@300 cycles). This study presents some insights on OAR activation mechanism and offers a facile strategy to improve the activity and reversibility of OAR for designing high performance SIBs cathodes.