On the Electrochemical Properties of New Materials in the Li2o-Fe2O3-V2O5 Ternary System

Abstract

In order to discover innovative electrode and electrolyte battery materials responding to specific needs in terms of capacity, working voltage, polarisation, alkali insertion mechanisms, it appears interesting to explore various insertion chemistries. With this in mind, our study was dedicated on the structural properties and electrochemical performances of iron vanadates positive electrode for Li batteries. More specifically, our groups focussed on the search for new stable phases in the Li2O - Fe2O3 - V2O5 ternary system with respect to several vanadates (FeVO4, NaCuFe2(VO4)3, β-Cu3Fe4(VO4)6, …), which structural and electrochemical properties upon Li insertion have been highlighted in previous work [1]. 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). Figure 1