An Electrolyte with Elevated Average Valence for Suppressing the Capacity Decay of Vanadium Redox Flow Batteries

Abstract

Nafion series membranes are widely used in vanadium redox flow batteries (VRFBs). However, the poor ion selectivity of the membranes to vanadium ions, especially for V 2+ , results in a rapid capacity decay during cycling. Although tremendous efforts have been made to improve the membrane's ion selectivity, increasing the ion selectivity without sacrificing the proton conductivity is still a challenging issue. In this work, instead of focusing on enhancing the membranes' ion selectivity, we develop an efficient valence regulation strategy to suppress the capacity decay caused by the crossover of V 2+ in VRFBs. Despite the discharge capacity of the VRFB with the elevated average valence electrolytes (V 3.68+ ) being slightly lower than that with commercial electrolytes (V 3.50+ ) in the first 35 cycles, the accumulated discharge capacity in 400 cycles is improved by 52.33%. Moreover, this method is efficient, is easy to scale up, and provides deep insights into the capacity decay mechanism of VRFBs.

Titanium Nitride Nanorods Array‐Decorated Graphite Felt as Highly Efficient Negative Electrode for Iron–Chromium Redox Flow Battery

“…Vanadium redox flow batteries (VRFBs) are one of the most successful and widely applied flow battery systems at present. [ 6–10 ] However, the market penetration of VRFBs for large‐scale energy storage is limited by their high capital cost which is due to the use of expensive vanadium redox couples and Nafion membranes. [ 11 ] Considering a base case of a 1 MW‐8 h VRFB energy storage system, the vanadium electrolyte and Nafion membrane respectively account for 53% and 19% of the total VRFB system cost.…”

In Situ Mapping of Activity Distribution of V(II)/V(III) and Onset Potential Distribution of Hydrogen Evolution Side Reaction in Vanadium Flow Batteries

“…[9][10][11] Nonetheless, the limited activity of V(II)/V(III) and the hard-to-eliminated hydrogen evolution side reaction present significant obstacles to the development of VFBs. [12,13] Currently, the characterization techniques commonly employed to investigate the activity and side reactions of VFBs are cyclic voltammetry (CV), [14] electrochemical impedance spectroscopy (EIS), [15] etc. Nevertheless, these methods only provide a global perspective of the electrode, and cannot attain the spatial distribution of activity and side reactions on the electrode surface.…”

“…[ 9–11 ] Nonetheless, the limited activity of V(II)/V(III) and the hard‐to‐eliminated hydrogen evolution side reaction present significant obstacles to the development of VFBs. [ 12,13 ]…”

Self-Assembled Construction of Ion-Selective Nanobarriers in Electrolyte Membranes for Redox Flow Batteries

“…More stable components for the matrix and additives should be considered as well as optimized operation in electrolyte solutions to improve the VRFB performance. 60 In summary, a nanostructured SPEEK hybrid membrane with enhanced proton conductivity and proton selectivity was prepared by an in situ self-assembly strategy. The multiple interactions among SPEEK, PSP, and PW with the confined self-assembly behavior of PSP induce the construction of…”

“…It seems that the certain degradation of SPEEK under the strongly acidic and oxidizing environment with a high electric potential during the test limits the cycling stability. More stable components for the matrix and additives should be considered as well as optimized operation in electrolyte solutions to improve the VRFB performance …”