Improving Oxygen‐Redox‐Active Layered Oxide Cathodes for Sodium‐Ion Batteries Through Crystal Facet Modulation and Fluorinated Interfacial Engineering

Layered oxides with active oxygen redox are attractive cathode materials for sodium-ion batteries (SIBs) due to high capacity but suffer from rapid capacity/voltage deterioration and sluggish reaction kinetics stemming from lattice oxygen release, interfacial side reactions, and structural reconstruction. Herein, a synergistic strategy of crystal-facet modulation and fluorinated interfacial engineering is proposed to achieve high capacity, superior rate capability, and long cycle stability in Na_0.67Li_0.24Mn_0.76O₂. The synthesized single-crystal Na_0.67Li_0.24Mn_0.76O₂ (NLMO{010}) featuring increased {010} active facet exposure exhibits faster anionic redox kinetics and delivers a high capacity (272.4 mAh g^-1 at 10 mA g^-1) with superior energy density (713.9 Wh kg^-1) and rate performance (116.4 mAh g^-1 at 1 A g^-1). Moreover, by incorporating N-Fluorobenzenesulfonimide (NFBS) as electrolyte additive, the NLMO{010} cathode retains 84.6% capacity after 400 cycles at 500 mA g^-1 with alleviated voltage fade (0.27 mV per cycle). Combined in situ analysis and theoretical calculations unveil dual functionality of NFBS, which results in thin yet durable fluorinated interfaces on the NLMO{010} cathode and hard carbon anode and scavenges highly reactive oxygen species. The results indicate the importance of fast-ion-transfer facet engineering and fluorinated electrolyte formulation to enhance oxygen redox-active cathode materials for high-energy-density SIBs.