Electrochemical behavior of LiV3O8 positive electrode in hybrid Li,Na–ion batteries

Abstract Vanadium(V)-containing oxides show superior intercalation properties for alkaline ions, although the performance of the material strongly depends on its surface morphology. In this work, intercalation activity of LiV 3 O 8 , prepared by a conventional solid state synthesis, is demonstrated for the first time in non-aqueous Li,Na-ion hybrid batteries with Na as negative electrode, and different Na/Li ratios in the electrolyte. In the pure Na-ion cell, one Na per formula unit of LiV 3 O 8 can be reversibly inserted at room temperature via a two-step process, while further intercalation leads to gradual amorphisation of the material, with a specific capacity of 190 mAhg −1 after 10 cycles in the potential window of 0.8–3.4 V. Hybrid Li,Na-ion batteries feature simultaneous intercalation of Li + and Na + cations into LiV 3 O 8 , resulting in the formation of a second phase. Depending on the electrolyte composition, this second phase bears structural similarities either to Li 0.7 Na 0.7 V 3 O 8 in Na-rich electrolytes, or to Li 4 V 3 O 8 in Li-rich electrolytes. The chemical diffusion coefficients of Na + and Li + in crystalline LiV 3 O 8 are very close, hence explaining the co-intercalation of these cations. As DFT calculations show, once formed, the Li 0.7 Na 0.7 V 3 O 8 -type structure favors intercalation of Na + , whereas the LiV 3 O 8 -type prefers to accommodate Li + cations.