A facile method to prepare bi-phase lithium vanadate as cathode materials for Li-ion batteries

Bi-crystal lithium vanadate is synthesized with starting materials of V₂O₅ and LiF by one-step solid-state reaction. Since fluorine reacts with crucible made of silica, Li_0.3V₂O₅-liked and LiV₃O₈-liked phases without F coexist in the produces. The stoichiometric proportion of two phases depends on the amount of dopant LiF. These are confirmed by X-ray diffraction (XRD), Fourier transform infrared (FTIR), and transmission electron microscopy (TEM). Charge and discharge curves of bi-crystal materials present better reversibility of voltage plateaus than that of pure V₂O₅. The initial discharge capacity of Li_0.3V₂O₅-liked phase dominated bi-crystal material is higher than pure V₂O₅. LiV₃O₈-liked phase dominated bi-crystal material has lower initial discharge capacity but delivers better cycling performance. Electrochemical impedance spectroscopy (EIS) measurements are performed to evaluate electrochemical kinetics of the bi-crystal materials. The results indicate that bi-crystal phase benefit the transfer resistance, interior diffusion resistance, and structure stability. Cathodes with different bi-phase structures have variable charge transfer resistance and lithium-ion diffusion speed due to this special structure.