An amorphous Li–V–O–F cathode with tetrahedral coordination and O–O formal redox at low voltage
Kun Zhang, Tonghuan Yang, Tao Chen, Yali Yang, Zewen Jiang, Chuan Gao, Yuxuan Zuo, Wukun Xiao, Dingguo Xia
Abstract
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.