(Invited) Low Cost in Situ Electrosynthesis and Cycling of Quinone Negolytes in a Commercial Flow Battery Stack

Abstract

Aqueous organic redox flow batteries (RFBs) potentially offer greatly lower capital cost relative to vanadium RFBs or even lithium-ion batteries, as they use no critical materials and are instead derived from very inexpensive precursors. To date, the success of organic RFBs as a whole has been hampered by two factors. The first is the high cost of scaling up a new chemistry, as every synthetic step adds cost and complexity and creates waste that must be disposed of. The second is fast degradation of the reactants and has been largely mitigated through various strategies that have recently been reported. The recent results mean that low-cost compounds that may intrinsically have a fast degradation rate, now merit consideration since their fade rate can be lowered significantly.We report the development of an in situ electrosynthesis process, from the lab scale to the ton scale, that creates the organic RFB negolyte from the starting reactants using commercial RFB stacks that have been repurposed as chemical reactors. The yield and purity are even higher than the equivalent chemical process and no further purification or downstream processing is required; the entire process is self-contained and produces zero waste which greatly simplifies scaleup, permitting, and implementation. Moreover, the as-produced material can be immediately cycled as a drop-in replacement for vanadium in RFBs with minimal modification of existing vanadium RFB designs.This unique in situ strategy enables rapid scaling of a new chemistry in a way that supports local manufacture, which is of strategic importance to many governments. Further cost reductions are envisioned if it can be implemented at the customer site -- inside a completed flow battery system -- rather than at a centralized facility.When combined with previous results on reversing the degradation of quinone RFB reactants, the electrosynthetic pathway to producing organic RFB negolytes is the final missing piece of the puzzle in the commercialization of an affordable, practical, and viable organic RFB chemistry.