Among the Li2O - Fe2O3 - V2O5 system, this presentation is dedicated to two new compounds, which were not known from the literature. Both materials were obtained through solid synthesis routes, after optimising the annealing parameters to reach pure phases. After determination of the structure using single crystal X-Ray Diffraction, their physical and electrochemical properties were thoroughly characterized using SEM, Mossbauer spectroscopy, galvanostatic and potentiostatic cycling. Electrochemical characterizations in half cells resulted in finding the optimal voltage window to enhance the capacity retention of the material as compared to previously studied vanadates. The galvanostatic curves indicated complex mechanisms for both materials involving several monophasic and biphasic steps upon Li insertion (see figure for the structure of LiFeV2O7 viewed along the [-101] direction and its electrochemical curve in half cell). Mossbauer spectroscopy allows assessing the oxidation state of iron atoms in the structures before and upon the electrochemical processes.
[1] Patoux, S., Richardson, T.J. “Lithium insertion chemistry of some iron vanadates”, Electrochemistry Communications, 9 (3), pp. 485-491 (2007).
[2] Benabed, Y., Castro, L., Penin, N., Darriet, J., Dollé, M. “Synthesis, Structure, and Electrochemical Properties of LiFeV2O7”, Chemistry of Materials, 29 (21), pp. 9292-9299 (2017).