Affordable viologen batteries: a promising alternative to vanadium

A researcher is assembling an organic material-based flow battery-1. Credit: Korea Institute of Energy Research.

Researchers at the Korea Institute of Energy Research have developed a new, more affordable technology for large-capacity energy storage systems, known as redox flow batteries.

Led by Dr. Seunghae Hwang, the team improved these batteries’ performance and lifespan by introducing special functional groups to replace the expensive vanadium currently used.

As renewable energy sources like solar and wind power become more common, there is a growing need for efficient long-term energy storage systems.

These systems must store excess electricity generated during sunny or windy conditions for more than eight hours and release it when needed.

Redox flow batteries are ideal for this because they have a low fire risk and a lifespan of over 20 years, much longer than lithium-ion batteries.

Currently, vanadium is used in redox flow batteries, but its limited supply makes it expensive. Researchers are exploring alternatives like viologens, which are organic compounds made from abundant elements such as carbon and oxygen.

Viologens are cheaper but have issues with low solubility and instability during repeated charging and discharging.

To address these problems, Dr. Hwang’s team added functional groups to viologens. These groups, which act like assembly blocks, improve the solubility and stability of viologens. They introduced sulfonate and ester groups that interact well with water, helping viologens disperse better in the electrolyte solution.

Additionally, they added alpha-methyl groups that twist the molecular structure, preventing unwanted reactions and increasing efficiency.

The new viologen-based redox flow batteries showed remarkable improvements. They had more than twice the energy density of vanadium batteries. After 200 charging and discharging cycles, these batteries maintained a coulombic efficiency of 99.4% (the ratio of discharge capacity to charge capacity) and a capacity retention of 92.4%, proving their enhanced performance and stability.

Dr. Hwang emphasized the importance of developing cost-effective and long-lasting redox flow batteries to support renewable energy and combat climate change. The research team’s innovations make these batteries more affordable and durable, bringing them closer to early commercialization.

These findings were published in the journal ACS Applied Materials and Interfaces, marking a significant step toward making renewable energy storage more practical and widespread.

This new technology could help drive the transition to cleaner energy by making storage systems cheaper and more efficient.