Low-Cost Flow Battery Active Materials for Long Duration Storage
Authors: Saraidaridis James D , Darling Robert M. , Davenport Tim C , Yang Zhiwei 
Published: July 2021

Energy storage capacity is presently dominated by pumped-hydroelectric storage, but the past decade has brought increasing levels of electrochemical energy storage (EES) installations.1 As more EES gets added to the grid, policymakers have recognized the need for longer-duration systems and sought systems that can provide durations of 8+ hours.2
,
3 At these longer durations, redox flow batteries (RFBs) have an advantage over Li-ion systems since the marginal cost of another hour duration asymptotes to the cost of additional active materials and their storage containers, rather than additional cells, packs and modules.

Leading vanadium RFBs have made cost reductions by improving the power density of their energy conversion stacks,4
,
5 but eventually are limited by the relatively high, incremental cost of their vanadium active materials. Switching to lower cost active materials can permit economically feasible long duration RFB systems.6

Raytheon Technologies Research Center has previously reported on the proposed sulfur-manganese (S-Mn) chemistry, which uses active materials based on low-cost sulfur, a waste product of fossil fuel production, and inexpensive manganese, an element presently used commercially in disposable primary cells. The team has implemented electrolyte takeover RFB technology, which has made low-cost S-Mn systems feasible despite crossover-induced precipitation that hampers performance levels.7 This technology implementation has allowed S-Mn sub-scale (20+ cm2) cell operation for 1000+ hours.

Additionally, development of another low-cost chemistry, relying on ligand-coordinated metal centers,8 has showed promising early results. This chemistry, which relies on a more neutral solution pH, brings new challenges, such as managing pH in an environment where small absolute concentration changes have outsized effect, but comes with benefits such as wide electrochemical stability windows.

Techno-economic analysis suggests that these two chemistries present an opportunity to deliver competitively priced long duration EES systems. This abstract will focus on the progress made advancing these two chemistries toward industrial relevance.

Acknowledgements:

The work presented herein was funded by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR000994. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

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