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

The ever-increasing demand for lithium-ion batteries has necessitated the development of high-performance cathode materials. However, previous studies have predominantly focused on crystal cathodes comprising the octahedral coordination of metal atoms and a well-ordered layered topology. This omits other cathode materials with other structures or coordination that could potentially surpass conventional counterparts in terms of performance. Here, using X-ray diffraction, resonant inelastic X-ray scattering and X-ray absorption near-edge spectra experiments, we investigated an amorphous Li-V-O-F cathode (a-LVOF) with tetrahedral coordination and elucidated an O-O formal redox mechanism at a moderate voltage of 4.1 V, without a conventional octahedral Li-O-Li configuration. The electrochemically amorphized material fosters randomly distributed VO units and scattered dangling oxygen bonds, which facilitated O-O binding. Moreover, a-LVOF demonstrates a high capacity of 230 mAh g. Our findings reveal a low-voltage O-O formal redox mechanism in an amorphized cathode material.