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 VO4 units and scattered dangling oxygen bonds, which facilitated O–O binding. Moreover, a-LVOF demonstrates a high capacity of 230 mAh g−1. Our findings reveal a low-voltage O–O formal redox mechanism in an amorphized cathode material. Cathode materials for lithium-ion batteries typically possess octahedral coordination, which may exclude other possible solutions to degradation during deep cycling. A series of tetrahedral-framework-based amorphous Li–V–O–F materials are investigated, and shown to demonstrate O–O formal redox at 4.1 V.