Researchers Identity a New Method to Dramatically Boost Battery Lifetime

Researchers at Harvard University have been developing an organic aqueous flow battery for many years, but despite this, they have encountered a major challenge—the organic anthraquinone molecules that fueled their revolutionary battery were gradually decomposing over time, decreasing the battery’s long-term usefulness.

Now, headed by Roy Gordon, the Thomas Dudley Cabot Professor of Chemistry and Professor of Materials Science, and Michael Aziz, the Gene and Tracy Sykes Professor of Materials and Energy Technologies at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), the researchers have discovered the mechanism behind the decomposition of molecules and how this decomposition can be mitigated and even reversed.

The death-defying molecule is called the “zombie quinone” in the laboratory but it is also known as DHAQ in the researchers’ paper. The molecule can be produced on a commercial scale in the most cost-effective manner. The rejuvenation technique developed by the team reduces the battery’s capacity fade rate by at least a factor of 40, while allowing the battery to be composed fully of economically-priced chemicals. The results of the study have been reported in the Journal of the American Chemical Society.

Low mass-production cost is really important if organic flow batteries are going to gain wide market penetration. So, if we can use these techniques to extend the DHAQ lifetime to decades, then we have a winning chemistry.

Michael Aziz, Gene and Tracy Sykes Professor of Materials and Energy Technologies, Harvard John A. Paulson School of Engineering and Applied Sciences

This is a major step forward in enabling us to replace fossil fuels with intermittent renewable electricity.

Roy Gordon, Thomas Dudley Cabot Professor of Chemistry and Professor of Materials Science, Harvard John A. Paulson School of Engineering and Applied Sciences

Gordon, Aziz, and their group have been working on the development of economical and safe organic aqueous flow batteries since 2014. Their aim was to store electricity from irregular renewable sources like solar and wind and supplying it when the sun is not shining and the wind is not blowing. Molecules called anthraquinones are used by the researchers’ batteries. These molecules are made up of naturally abundant elements like oxygen, hydrogen, and carbon, for storing and releasing energy.

Initially, the investigators believed that the molecules’ lifetime depended on the number of times the battery was charged and discharged, similar to solid-electrode batteries, for example, lithium ion. Conversely, in reconciling unpredictable results, the team found that the anthraquinones are decomposing gradually over the duration of time, irrespective of the number of times the battery has been utilized. The researchers observed that the extent of decomposition depended on the molecules’ calendar age, and not how frequently they have been charged and discharged. That finding spurred the team to analyze the mechanisms through which the molecules were decomposing.

We found that these anthraquinone molecules, which have two oxygen atoms built into a carbon ring, have a slight tendency to lose one of their oxygen atoms when they’re charged up, becoming a different molecule. Once that happens, it starts of a chain reaction of events that leads to irreversible loss of energy storage material.

Roy Gordon, Thomas Dudley Cabot Professor of Chemistry and Professor of Materials Science, Harvard John A. Paulson School of Engineering and Applied Sciences

Two methods were discovered by the researchers to prevent that chain reaction. The first method involved subjecting the molecule to oxygen. The researchers discovered that when the molecule is exposed to the atmosphere at just the right part of its charge-discharge cycle, it captures the atmospheric oxygen and changes back into the original anthraquinone molecule—as if it is returning from the dead. Through this method, a single experiment was able to recover 70% of the lost capacity.

In the second method, the researchers discovered that whenever the battery is overcharged, conditions are created that speed up decomposition. If this overcharging is avoided, the battery’s lifetime can be extended by a factor of 40.

“In future work, we need to determine just how much the combination of these approaches can extend the lifetime of the battery if we engineer them right,” stated Aziz.

“The decomposition and rebirth mechanisms are likely to be relevant for all anthraquinones, and anthraquinones have been the best-recognized and most promising organic molecules for flow batteries,” added Gordon.

This important work represents a significant advance toward low-cost, long-life flow batteries. Such devices are needed to allow the electric grid to absorb increasing amounts of green but variable renewable generation.

Imre Gyuk, Director, Office of Electricity Storage Program, Department of Energy

The study was co-authored by Marc-Antoni Goulet, Daniel P. Tabor, Daniel A. Pollack, Liuchuan Tong, and Eugene E. Kwan, all from Harvard; and Alán Aspuru-Guzik of the University of Toronto; and Susan A. Odom of the University of Kentucky.

The Energy Storage program of the U.S. Department of Energy, the Advanced Research Projects Agency – Energy, Harvard SEAS, the Innovation Fund Denmark, and the Massachusetts Clean Energy Technology Center supported the research.

With help from Harvard’s Office of Technology Development (OTD), the team is looking for commercial partners to upgrade the technology for industrial applications. A portfolio of pending patents on innovations in flow battery technology has been filed by Harvard OTD.