Development of a Vanadium Redox Flow Battery Operating with Thin Membrane Coupled with a Highly Selective and Stable Silica‐Based Barrier Layer

Vanadium redox flow battery (VRFB) is a very promising solution for large-scale energy storage, but some technical issues need to be addressed. Crossover, i.e., the undesired permeation of vanadium ions through the cell separator, causes capacity loss and self-discharge. Low-cost and highly selective separators are thus required to improve the competitiveness of this technology. This work investigates the use of silica nanoparticles in an innovative selective layer to improve membrane selectivity and reduce its thickness. 1.5 mu m thick barrier layers composed of 1100EW Nafion ionomer with silica (approximate to 3-13 nm diameter) and Vulcan XC-72R (approximate to 40 nm) nanoparticles in different proportions are directly deposited on 50 mu m thick Nafion membranes. The barrier layer composed only of silica nanoparticles reduces the self-discharge due to crossover by 5 times and increases the average efficiency of the battery. Finally, during more than 1000 h of operation, the barrier layer on a 25 mu m Nafion membrane demonstrates excellent stability, working with a constant coulombic efficiency higher than 99% and a capacity decay rate comparable with a thicker Nafion membrane, thus enabling the use of thinner membranes in VRFB, allowing an estimated 8% stack costs reduction with respect to NR212.Using silica nanoparticles in the barrier layer allows for the improvement of its selectivity, reducing the self-discharge of a vanadium redox flow battery by 5 times compared to the supporting membrane, without affecting efficiency. Due to its high selectivity and stability, the barrier can also be used coupled with a thin membrane, enhancing energy efficiency and reducing battery costs.image (c) 2024 WILEY-VCH GmbH