Unveiling electrode compression impact on vanadium flow battery from polarization perspective via a symmetric cell configuration

Full commercialization of vanadium flow batteries requires a high current density operation. However, this can be only realized when associated large polarizations of the cell are properly reduced. Of all the cell components, the porous electrode plays a critical role in determining cell polarizations since it directly relates to each of the polarizations. Despite that, an in-depth understanding of electrode compression impact on polarizations of a flow cell is still limited in literature. In this work, a quantitatively experimental study to unveil the electrode compression impact on each of the polarizations as well as the performance of a vanadium flow cell is conducted by employing a symmetric cell configuration. Four different compression ratios are investigated by both ex-situ characterizations and in-situ symmetric cell tests, which successfully reveal its influence on activation, ohmic and concentration polarizations at varied operating current densities. Charge-discharge cycling tests further prove the significance of electrode compression to both efficiency and discharge capacity, while also delivering an optimal compression ratio for the investigated flow cell. Such a quantitative analysis not only promotes a deep understanding of the importance of electrode compression to cell performance, but is also of vital importance for stack design and optimization in practice. [Display omitted] •Electrode compression impact on polarizations is revealed for vanadium flow battery.•Ex-situ characterizations show the morphology variations with electrode compressions.•In-situ symmetric cells deliver activation polarizations for V2+/V3+ and VO2+/VO2+.•Polarization analysis and full cell tests demonstrate an optimal compression ratio.