Breakthrough Discovery in Next-Generation Flow Battery Design Sets New Records

A team of scientists from the Pacific Northwest National Laboratory, funded by the Department of Energy, has achieved a remarkable feat in flow battery technology. Through a groundbreaking experiment, they have enhanced the capacity and durability of a flow battery by an astounding 60%. The key to this breakthrough lies in the incorporation of a starch-derived additive called β-cyclodextrin, commonly used in food and medicine. This extraordinary achievement has the potential to reshape the future of large-scale energy storage.

The researchers from the Pacific Northwest National Laboratory (PNNL) have made a significant stride in the field of flow battery design by utilizing β-cyclodextrin, a readily available food and medicine additive derived from starch. Their study, published in the prestigious journal Joule, demonstrates that the flow battery exhibited consistent energy storage and release capabilities for over a year of continuous cycling.

In a record-setting experiment, the researchers harnessed the power of a common food and medicine additive to significantly augment the capacity and longevity of the next-generation flow battery design. The flow battery, optimized for electrical grid energy storage, demonstrated an exceptional ability to store and release energy throughout continuous charge and discharge cycles over a period exceeding one year.

Ruozhu Feng, a flow battery researcher, posing with the ingredients for a long-lasting grid energy battery. (Credit: Andrea Starr, Pacific Northwest National Laboratory)

The study, recently published in Joule, marks the first successful utilization of a dissolved simple sugar, β-cyclodextrin, a starch derivative, to enhance battery longevity and capacity. Through a series of experiments, the scientists fine-tuned the chemical composition until the battery exhibited a remarkable 60% increase in peak power. The battery was subsequently subjected to continuous cycling for over a year, with the experiment ending only due to failure of the plastic tubing. Remarkably, the flow battery experienced minimal loss of capacity during this extended period. This study represents the first laboratory-scale flow battery experiment to report over a year of continuous use with negligible capacity degradation.

Moreover, the β-cyclodextrin additive is the first to expedite the electrochemical reaction responsible for storing and releasing flow battery energy. This process, known as homogeneous catalysis, allows the sugar to catalyze the reaction while dissolved in the liquid electrolyte, rather than being applied as a solid to a surface.

According to Wei Wang, the principal investigator of the study and a long-time battery researcher at PNNL, “This is a brand new approach to developing flow battery electrolyte. We demonstrated that it is possible to use a completely different catalyst designed to accelerate energy conversion. Furthermore, since it is dissolved in the liquid electrolyte, it eliminates the risk of solid dislodgment and system fouling.”

Flow batteries, as their name implies, consist of two chambers containing different liquids. They charge via an electrochemical reaction and store energy in chemical bonds. When connected to an external circuit, they release the stored energy to power electrical devices. Unlike solid-state batteries, flow batteries employ two external supply tanks that continuously circulate liquid electrolyte, serving as the “blood supply” for the system. The size of the electrolyte supply tank directly correlates with the energy storage capacity of the flow battery.

At a larger scale, flow batteries can serve as backup generators for the electric grid. They are a critical component of decarbonization strategies aimed at storing energy from renewable sources such as wind, solar, and hydroelectric power. One of the advantages of flow batteries is their scalability, ranging from laboratory-scale to city-block-scale installations.

The need for new types of flow batteries arises from the demand for large-scale energy storage, which acts as an insurance policy against disruptions in the electrical grid. As electricity generation increasingly relies on renewable energy sources like wind, solar, and hydroelectric power, the requirement for flow battery facilities is expected to grow. These facilities can minimize disruptions and restore service during severe weather or periods of high demand. However, existing commercial flow battery facilities predominantly rely on costly and hard-to-obtain mined minerals such as vanadium. Consequently, research teams are actively seeking alternative technologies that utilize abundant, easily synthesized, stable, and non-toxic materials.

Imre Gyuk, the director of energy storage research at the DOE’s Office of Electricity, emphasizes the necessity for a sustainable approach, stating, “We cannot always dig the Earth for new materials. We need to develop a sustainable approach with chemicals that we can synthesize in large amounts—just like the pharmaceutical and food industries.”

The work on flow batteries forms part of a larger program at PNNL focused on developing and testing new technologies for grid-scale energy storage. This effort will be accelerated with the opening of PNNL’s Grid Storage Launchpad in 2024.

In their pursuit of an effective flow battery, the research team at PNNL, comprising organic and chemical synthesis experts, capitalized on the availability of materials already used in other industrial applications. The team sought a straightforward method to dissolve more fluorenol in their water-based electrolyte, which was modestly achieved with the β-cyclodextrin additive. However, the true benefit of this sugar-derived additive lay in its surprising catalytic ability.

To unravel the complex chemistry behind this new flow battery design, the researchers collaborated with Sharon Hammes-Schiffer, a leading expert in chemical reactions from Yale University and co-author of the study.

The sugar additive, as explained in the research, accepts positively charged protons, thereby balancing the movement of negative electrons during battery discharge. While the details are intricate, the concept is analogous to sugar sweetening a pot, facilitating the completion of the chemical reactions involving other components.

The study represents the next generation of a PNNL-patented flow battery design first described in the journal Science in 2021. Although the initial breakthrough demonstrated the effectiveness of another common chemical, fluorenone, as a flow battery component, its slow reaction rate compared to commercialized flow battery technology required improvement. This recent advance positions the battery design as a potential candidate for scaling up.

Simultaneously, the research team continues to refine the system by exploring alternative compounds similar to β-cyclodextrin but with smaller molecular structures. Despite the drawback of increased viscosity, akin to honey, the advantages of β-cyclodextrin outweigh this limitation.

The research involved a multidisciplinary team of scientists, including Ying Chen, Xin Zhang, Peiyuan Gao, Ping Chen, Sebastian Mergelsberg, Lirong Zhong, Aaron Hollas, Yangang Lian, Vijayakumar Murugesan, Qian Huang, Eric Walter, and Yuyan Shao from PNNL, along with Benjamin J. G. Rousseau and Sharon Hammes-Schiffer from Yale University, in addition to Ruozhu Feng and Wei Wang.

The team has submitted a patent application to protect their innovative battery design in the United States.

This study received support from the DOE Office of Electricity through its Energy Storage Program and internal research investments via the Energy Storage Materials Initiative at PNNL. The Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the DOE Office of Science, Basic Energy Sciences, facilitated mathematical calculations that elucidated the capacity boost of the battery. Additional computational and imaging studies were conducted at the Environmental Molecular Sciences Laboratory, a national scientific user facility situated at PNNL.

Frequently Asked Questions (FAQs) about flow battery design

More about flow battery design

• Pacific Northwest National Laboratory
• Department of Energy
• Journal Joule
• Flow Batteries – Energy Storage Association
• Renewable Energy – U.S. Energy Information Administration
• β-Cyclodextrin – PubChem