An amorphous Li-V-O-F cathode with tetrahedral coordination and O-O formal redox at low voltage

Area of Science:

• Materials Science
• Electrochemistry
• Inorganic Chemistry

Background:

• Growing demand for high-performance lithium-ion batteries requires novel cathode materials beyond conventional crystal structures.
• Existing research predominantly focuses on octahedral coordination and layered topologies, potentially overlooking alternative material designs.
• Exploring non-conventional coordination and structures is crucial for surpassing current battery performance limitations.

Purpose of the Study:

• To investigate an amorphous lithium-vanadium-oxygen-fluoride (a-LVOF) cathode material.
• To elucidate the redox mechanism and structural properties of a-LVOF, particularly its tetrahedral coordination.
• To assess the electrochemical performance and potential of a-LVOF as a next-generation cathode.

Main Methods:

• Utilized X-ray diffraction (XRD) for structural analysis.
• Employed resonant inelastic X-ray scattering (RIXS) to probe electronic structure.
• Conducted X-ray absorption near-edge structure (XANES) spectroscopy to determine coordination and oxidation states.

Main Results:

• Identified tetrahedral coordination of vanadium within the amorphous Li-V-O-F structure.
• Elucidated a low-voltage oxygen-oxygen (O-O) formal redox mechanism occurring at 4.1 V, distinct from conventional Li-O-Li configurations.
• Demonstrated a high specific capacity of 230 mAh g⁻¹ for the a-LVOF cathode.

Conclusions:

• The amorphous structure with randomly distributed VO₄ units and dangling oxygen bonds facilitates the O-O redox mechanism.
• This study reveals a novel low-voltage O-O formal redox pathway in an amorphized cathode material.
• Amorphous cathode materials with non-conventional coordination offer a promising avenue for developing advanced lithium-ion batteries.