A New Rutile‐Type NaFe ₂ F ₆ Cathode for Sodium‐Ion Batteries

ABSTRACT The development of low‐cost and sustainable cathode materials is crucial for advancing sodium‐ion battery technology. This work proposes a new rutile‐type NaFe ₂ F ₆ cathode synthesized through an energy‐efficient mechanochemical method without high‐temperature processing. The rutile‐type NaFe ₂ F ₆ possess a unique crystal structure of edge‐sharing MF ₆ octahedra, forming a 1D Na ⁺ diffusion channels with an ultralow migration barrier of 0.299 eV. In situ X‐ray diffraction analysis demonstrates its exceptional structural stability during cycling, with only a 1.94% volume variation and a single‐phase reaction mechanism without phase transitions. The NaFe ₂ F ₆ cathode can deliver a high reversible capacity of 181 mAh g ⁻¹ via a Fe ²⁺ /Fe ³⁺ redox couple. Comprehensive kinetic analyses confirm superior Na ⁺ transport properties compared to conventional FeF ₃ . Given the earth's crust abundance of Na and Fe elements, this work establishes NaFe ₂ F ₆ as an environmentally sustainable and economically viable cathode material, paving the way for large‐scale energy storage applications.