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

Bi4V2O11 reduction was followed using two methods: high-temperature X-ray d iffraction under H-2 flow and oxygen removal with Zr acting as an oxygen ac ceptor. In both cases, the reversible domain of reduction of Bi4V2O11 appea red to be limited to one-third of VV and therefore to the formation of a Bi 6V3O16 (Bi4V2O10.66) phase. Various BIMEVOX/electrolyte/Li cells were chara cterized evidencing the progressive reduction of the BIMEVOX materials. Pur suing 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 th e BIMEVOX (ME = Bi, Ta), a two-step mechanism is proposed involving first a n oxygen removal concomitant with the formation of Li2O and the Bi6V3O16 (B i4V2O10.66) phase, followed by a Li-driven decomposition of the latter in a n inert Li2O matrix, a Li-alloying Bi phase and a vanadate.