Ultrasonic Spray Coating for the manufacturing of a selective layer for flow batteries: From the analysis of ink composition to component scale-up

Developing highly selective separators that can effectively mitigate vanadium crossover is crucial for improving Vanadium Redox Flow Batteries (VRFB), which can play a key role in tackling the challenges set by future energy scenarios. This work presents the development of the barrier, a selective layer directly deposited on the membrane, using Ultrasonic Spray Coating (USC). Ultrasonic Spray Coating is characterized by excellent flexibility, allowing for easy deposition on any kind of substrate and enabling the tuning of the barrier ink composition. Moreover, as a commercial and already scaled-up technique, USC is suitable for the large-scale manufacturing of the barrier layer. Indeed, this work demonstrates the development of the barrier through USC starting from lab-scale to a size more representative of real applications. The composition of the ink and the deposition process were investigated to define the best ink composition and best combination of deposition parameters for the barrier scale-up. The barrier was directly deposited on Nafion^TM NR212, successfully reducing the capacity decay of the battery and the net vanadium flux by around 30 % without penalizing efficiency. Finally, the barrier layer effectively mitigated cross-over losses also at larger scale, with improved battery efficiency when deposited on a thinner membrane (Nafion^TM NR211).