The All-Vanadium Redox Flow Battery is a promising technology for solving the problem of cost-efficient and safe large-scale storage of renewable energies [1]. One key component of the batteries, which alters the performance and long-term stability of those systems, is the membrane. For this purpose, Nafion based membranes are often used. However, these membranes are high in cost and show a significant capacity fading and reduction of coulombic efficiency mainly due to crossover of vanadium species [2]. One way around this is to use commercially available, low-cost materials with positively charged ammonium groups, which can effectively repel positively charged vanadium species due to the Donnan exclusion effect [3, 4].

In this work we present novel anion-exchange blend membranes comprised of a commercially available and water-soluble ionomer and a PBI blend matrix, which can be used in All-Vanadium Redox Flow batteries. For this approach the water-soluble ionomer was modified to achieve solubility in organic solvents and miscibility with the matrix polymer. The resulting membranes show good mechanical properties even at high IECs and can be modified in a wide range of properties by adjusting the amounts of ionomer and matrix polymer and/or by the addition of crosslinking agents.

The above-mentioned membranes were characterised ex-situ by using EIS, NMR spectroscopy, IR spectroscopy, DMA, TGA, tensile tests and permeability tests. In addition, first promising in-situ characterisations were performed in a VRFB single-cell test station.

Literature

[1] Fan, X; Liu, B; Liu, J; Ding, J; Han, X; Deng, Y; Lv, X; Xie, Y; Chen, B; Hu, W; Zhong, C.: Battery Technologies for Grid-Level Large-Scale Electrical Energy Storage. Trans. Tianjin Univ. 2020, 92 – 103.

[2] Düerkop, D; Widdecke, H; Schilde, C; Kunz, U; Schmiemann, A.: Polymer Membranes for All-Vanadium Redox Flow Batteries: A Review. Membranes 2021.

[3] Xi, J; Wu, Z; Teng, X; Zhao, Y; Chen, L; Qiu, X.: Self-assembled polyelectrolyte multilayer modified Nafion membrane with suppressed vanadium ion crossover for vanadium redox flow batteries. J. Mater. Chem. 2008, 1232.

[4] Mohammadi, T; Kazacos, M.: Modification of anion-exchange membranes for vanadium redox flow battery applications. Journal of Power Sources 1996, 179 – 186.