Validating Membrane Ageing Protocols: A Real‐World Perspective on Vanadium Redox Flow Battery Degradation

Membranes are essential for an efficient and stable long‐term operation of the vanadium redox flow battery (VRFB). Membrane degradation is one of the main limiting factors for VRFB lifetime because of the resulting increase in electrolyte crossover and self‐discharge. Understanding membrane degradation is crucial for the lifetime extension of VRFBs. Most studies concerning membrane degradation are based on artificial ageing. In contrast to that, this study examines membrane samples from commercial stacks and compares them to pristine and artificially aged membranes. Performance tests are conducted to determine the membrane resistivity, ion‐exchange capacity, and vanadium permeability. The influence of ageing on characteristic cell parameters, like coulombic and voltaic efficiency, is determined in battery cell tests. Furthermore, the membrane materials are compared by light microscopy, scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy. In summary, this study reveals that artificial ageing and real‐world ageing lead to similar changes in the physical properties of the membranes. However, it is shown that membranes in large‐scale battery systems age inhomogeneously while artificial ageing leads to more evenly degraded membranes.