Interface and Oxygen-Vacancy Dual-Engineering of 2D NiFe₂O₄/N-Doped Graphene Sheet Heterostructure Securing Superior...

Lithium-oxygen batteries (LOBs) are regarded as highly promising energy storage systems due to their ultrahigh theoretical energy density (~3500 Wh kg^-1), yet their practical application is severely hindered by sluggish oxygen reduction/evolution reaction (ORR/OER) kinetics. Herein, an efficient bifunctional oxygen catalyst is rationally designed by anchoring enriched-oxygen-vacancy NiFe₂O₄ nanoparticles onto 2D nitrogen-doped graphene nanosheets (NGS/Ov-NiFe₂O₄). The abundant oxygen vacancies from the acid etching and the generated heterostructures efficiently modulate the electronic structure, leading to optimized adsorption energies of oxygen intermediates to improve the intrinsic activity for OER/ORR. Besides, the highly conductive NGS prevents aggregation of NiFe₂O₄ nanoparticles, thereby exposing plentiful active sites, but also ensures rapid charge transfer to accelerate the OER/ORR kinetics. The NGS/Ov-NiFe₂O₄ heterostructure facilitates the highly reversible deposition and decomposition of thin-film-like Li₂O₂, thus guaranteeing an exceptionally prolonged cycle life for LOBs. Consequently, the NGS/Ov-NiFe₂O₄ cathode delivers an ultrahigh full discharge capacity (>12,000 mAh g^-1), a significantly reduced initial overpotential of 1.12 V, and exceptional long-term cycling stabilities (198 cycles at a curtailed capacity of 1000 mAh g^-1 and 60 cycles under a deep discharge of 4000 mAh g^-1). This work provides a novel interfacial and oxygen-vacancy dual-engineering strategy for developing high-performance cathode catalysts for LOBs.