ENGINEERING UNIVERSAL STACKS FOR LONG DURATION ENERGY STORAGE FLOW BATTERIES

Vanadium Flow Batteries (VFBs) have already hit the market with several GW/GWh systems installed worldwide. The growing market demand for long duration energy storage (LDES) systems, linked to the increasing diffusion of renewable sources, requires high-performance and economically convenient technologies. This has led numerous research initiatives across major countries to develop innovative, efficient, accessible, and cost-effective active chemical species for their use in flow batteries. However, there has been comparatively little effort dedicated to advancing high-performance technology to take full benefit from these chemistries. This gap poses the risk that inadequate flow battery engineering may hinder the potential success of emerging new flow battery chemistry or even lead to industrial and commercial failure of start-ups and industries. The goal of this work is to develop an electrochemical reactor that fully harnesses the potential of various chemistries, to allow interested companies to quickly and effectively enter the market. The opportunity to develop a universal stack comes from the fact that different flow batteries share the same active materials, membrane and electrodes, and therefore the same cell configuration. This thesis presents the process for the design, construction and testing of a universal redox flow battery stack, capable of operating with different active chemical species. Polarization curves on a mid-size single cell were obtained to identify high performance commercial active materials, as well as to investigate their chemical stability over prolonged charge and discharge cycles. The experimental analysis was coupled with CFD simulations to evaluate the fluid dynamics of large flow battery cells during full-load charging and discharging under critical conditions, with vanadium electrolyte and organic electrolyte. The fluid dynamic analysis enabled important drivelines to guide the mechanical design of the stack that was performed through advanced CAD software for assembly and tolerance analysis. The stack designed in this work was then hydraulically validated. In the framework of investigating new chemistries, a techno-economic comparison between all-vanadium and all-iron flow batteries was performed. This analysis aims to highlight the potential of all-iron flow batteries as innovative and competitive solutions for LDES applications, while exploring strategies to reduce their production costs. Finally, an investigation on the impact of electrolyte mixing, inside vanadium flow battery tanks, on capacity degradation was performed using various inner tank structures. This thesis represents one of the first studies on the scale-up process for high performance electrochemical stack. In general, the results presented are new and aim to cover the gap between research and industry in view of widespread flow battery commercialization.