Lithium- and proton-driven redox reactions in BIMEVOX-type phases

Bi4V2O11 reduction was followed using two methods: high-temperature X-ray diffraction under H-2 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.