Lithium- and Proton-Driven Redox Reactions in BIMEVOX-Type Phases

Bi4V2O11 reduction was followed using two methods: high-temperature X-ray diffraction under H2 flow and oxygen removal with Zr acting as an oxygen acceptor. In both cases, the reversible domain of reduction of Bi4V2O11 appeared to be limited to one-third of VV and therefore to the formation of a Bi6V3O16 (Bi4V2O10.66) phase. Various BIMEVOX/electrolyte/Li cells were characterized evidencing the progressive reduction of the BIMEVOX materials. Pursuing the cell discharge down to 0.02 V resulted in a full amorphization of the material together with an uptake of 32 lithium ions per formula unit. From both electrochemical and in situ X-ray diffraction data extended to the BIMEVOX (ME = Bi, Ta), a two-step mechanism is proposed involving first an oxygen removal concomitant with the formation of Li2O and the Bi6V3O16 (Bi4V2O10.66) phase, followed by a Li-driven decomposition of the latter in an inert Li2O matrix, a Li-alloying Bi phase and a vanadate.