Accidental discovery could charge up large-scale energy storage systems

The accidental discovery

Two years ago, the PNNL research team found that a naturally occurring compound called fluorenone could improve the energy storage capacity of flow batteries. The team soon discovered that using Fluorenone impacted the energy storage process since it was much slower than commercially available methods.

The team was looking for a way to dissolve fluorenol, an alcohol derivative of fluorenone, in their water-based electrolyte and found that simple sugar called β-cyclodextrin could help. When the team used the sugar in the electrolyte, they also found that the addition boosted battery longevity and capacity.

The researchers then further experimented with the ratio of chemicals in the electrolyte till they achieved a 60 percent increase in peak power. More importantly, the team also found that adding sugar minimized the loss of capacity common with batteries.

The battery was kept operational for extended periods for over a year, during which it charged and discharged on multiple occasions. In addition to increasing the pace of the electrochemical reaction, the β-cyclodextrin in the solution ensured minimal storage capacity loss.

Advantages of flow batteries

β-cyclodextrin is a derivative of starch and is naturally available on the planet. The vast amounts of sugar required, if the flow batteries are deployed at scale, will still not require humanity to dig the Earth for additional resources.

Moreover, it will help create a low-cost energy storage solution that does not use toxic chemicals. The most significant advantage of this discovery is that it will help the researchers deploy the flow battery for many applications, given that it is now comparable to commercially available solutions.

Flow batteries are a highly scalable technology built from a lab bench model to one supporting the grid. The research team is also looking for alternates to β-cyclodextrin since the sugar makes the electrolyte much thicker and less conducive to flow.

Nevertheless, the advantages of the addition still outweigh the drawbacks. In addition to patenting the technology, the team is also looking to use it at grid-level storage next year.

The research findings were published in the journal Joule.

Abstract

Redox flow batteries have a unique architecture that potentially enables cost-effective long-duration energy storage to address the intermittency introduced by increased renewable integration for the decarbonization of the electric power sector. Targeted molecular engineering has demonstrated electrochemical reversibility in natively redox-inactive ketone molecules in aqueous electrolytes. However, the kinetics of fluorenone-based flow batteries continue to be limited by slow alcohol oxidation. We show how strategically designed proton regulators can accelerate alcohol oxidation and thus enhance battery kinetics. Fluorenone-based flow batteries with the organic additive β-cyclodextrin demonstrate enhanced rate capability, high capacity, and long cycling. This study opens a new avenue to improve the kinetics of aqueous organic flow batteries by modulating the reaction pathway with a homogeneous catalyst.