Researchers from the Energy Storage Research Department at the Korea Energy Research Institute have found an alternative for vanadium, an important component of redox flow batteries, an active area of ​​research around the world.
The study found that vanadium, which is mined from the ground, can be replaced by readily available molecules made of carbon and oxygen.
Renewable energy technologies such as wind and solar energy can only be implemented on a large scale if a suitable energy storage solution is available. This storage solution can help overcome the intermittent nature of the technology’s power generation and deliver power when needed, even when the sun isn’t shining or the wind isn’t blowing.
A reliable energy storage solution should be able to hold a charge for more than eight hours and readily deliver it when demand increases. Redox flow batteries are a highly preferred solution in this area.
Why are redox batteries so good?
Redox flow batteries are electrical cells that store energy in an electrolyte instead of an electrode, as in lithium-ion batteries.
Redox batteries are better than lithium-ion batteries because they can have a flexible arrangement, which greatly reduces the risk of fire. Battery performance can be easily increased by increasing the size of the reservoir.
The absence of phase changes in the solid state ensures that the battery has a longer life and provides excellent energy performance even after two decades of operation.
The only downside to a redox flow battery is that it uses vanadium, which is not a rare earth mineral but is already used in commercial processes and has limited supplies. To avoid a similar fate to lithium, scientists are looking for more abundant substitutes for vanadium and have found them in viologens.
How are viologens useful?
Viologens are organic compounds made from abundant elements such as carbon and oxygen that do not need to be mined. Previous research into the use of viologens as a substitute for vanadium faced the obstacle of low solubility in the electrolyte.
Lower solubility of viologens leads to lower battery energy density and instability in charge and discharge processes. To overcome these obstacles, the researchers introduced functional groups into viologens that fit into these organic molecules, like building blocks, and improved their stability.
The research team used sulfonate and ester functional groups, which are water-friendly, making them easier to disperse in the electrolyte.
The addition of functional groups also solved another problem with the use of viologens. Their molecular shape is similar to a sandwich, and occasionally two layers of viologens are combined, making them unsuitable for holding a charge.
The researchers added alpha-methyl functional groups that prevent the two viologens from combining and ensure that they are always available for energy storage. The end result of adding these functional groups was that the researchers achieved an energy density twice that of a flow battery made of vanadium.
After 200 charge-discharge cycles, the researchers found that their new battery demonstrated 99.4 percent coulombic efficiency and 92.4 percent capacity retention, both indicators of improved performance and stability.
The results of the research were published in the journal ACS Materials and Interfaces.
ABOUT THE EDITORIAL
Ameya Paleja Ameya is a science writer based in Hyderabad, India. A molecular biologist at heart, he traded the micropipette for writing about science during the pandemic and doesn’t want to go back. He enjoys writing about genetics, microbes, technology and public policy.