In-Situ Investigation of Vanadium Ions Transport in Redox Flow Battery

In-Situ Investigation of Vanadium Ions Transport in Redox Flow Battery

Qingtao Luo,¹ Liyu Li, ² Zimin Nie,¹  Wei Wang,¹ Xiaoliang Wei, ¹ Feng Chen, ¹Bin Li,¹ Guan-guang Xia,¹  Baowei Chen, ¹ Zhenguo Yang,² Sprenkle Vincent¹

¹ Pacific Northwest National Laboratory, P. O. Box 999, Richland, WA 99354, USA

² UniEnergy Technologies, LLC, 4333 Harbour Pointe Blvd SW, Unit A, Mukilteo, WA 98275, USA

Among the different RFB systems, the all-vanadium redox flow battery (VRB) is probably the most promising and extensively researched flow battery system.^1-3 However, severe capacity decay of VRBs was reported by several groups. Although the capacity fading mechanism is not entirely understood by the VRB research community, the inevitable crossover of vanadium ions across the membrane may play a significant role in causing the capacity fading during cycling.⁴Therefore, it is of great importance to investigate the transport behaviors of vanadium ions across the membrane, which may also shed light on the VRB capacity fading mechanism. The reactions between transported vanadium ions and native vanadium ions, however, make this study very challenging. In this work, flow batteries with vanadium and iron redox couples as the electro-active species were employed to investigate the transport behavior of vanadium ions in the presence of an electric field. It was shown that the transport of vanadium ions was affected by a combination of different factors, such as the charge/discharge process, current density, and SOC. The electric field accelerated the positive-to-negative and reduced the negative-to-positive transport of vanadium ions in the charging process and affected the vanadium ion transport in the opposite way during discharge. With the increase of current density, the effect of promoting or suppressing to the vanadium ions transport is further enhanced. At each given current density, the vanadium ion transport rate, in general, demonstrated a trend of decreasing with the increase of SOC.

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