Characterizing Degradation in Non-aqueous Vanadium(III) Acetylacetonate Redox Flow Batteries.

A detailed study characterizing the degradation of non-aqueous vanadium flow batteries under moisture-free conditions is presented. Despite assembly and operation in an inert glovebox, rapid cell failure is still observed. The capacity loss is attributed to a combination of electrolyte degradation and increased cell impedance. Cyclic voltammetry verifies the formation of VO(acac)2 within the positive electrolyte, while Raman spectroscopy reveals the formation of additional degradation products in the negative electrolyte. Scanning electron micrographs and X-ray photoelectron spectroscopy reveal the growth of a surface film on cycled electrodes harvested post-mortem, particularly in the negative half-cell. The appearance of the surface film is correlated with electrochemical impedance measurements, which indicate a dramatic increase in charge-transfer resistance post-cycling. The individual electrode contributions to the total cell impedance are resolved post-mortem. It is determined that even when great care is taken to exclude water from the system, the stability of the non-aqueous vanadium flow battery is limited by degradation processes occurring at the negative electrode. Furthermore, the lifetime is not noticeably enhanced, compared to earlier studies where moisture was present. [ABSTRACT FROM AUTHOR]