Ellen Phiddian
Cosmos science journalist
Flow batteries promise longer-lasting and safer grid energy storage than their lithium-ion counterparts. But, while they don’t need lithium, commercial examples still currently need metals to work, with the highest-performing being vanadium.
Now Chinese researchers have developed a class of carbon-based materials that can work in a flow battery.
They’ve published their findings in Nature Sustainability.
The research revolves around organic redox-active molecules (ORAMs): carbon and hydrogen-based molecules (hence “organic”), which can perform chemical processes of reduction and oxidation (hence “redox”).
These compounds have been highlighted as possible ways to make flow batteries, but most of them have been too unstable and too reactive with air to work long-term.
The researchers approached the problem with a series of compounds based on naphthalene, an oil- or coal-derived substance which is commonly used as a chemical feedstock and moth repellent.
They were able to make these naphthalene-based substances with a simple process, using electrochemistry.
These compounds dissolved easily, which is important because flow batteries use liquid to store and transfer energy.
And they were stable in air, lasting for at least 40 days without any signs of decay.
The team made a flow battery in the lab with their naphthalene-based materials. This battery ran for 22 days, and more than 600 charge-discharge cycles, also without any signs of decay or reduction in capacity.
The process was easy to scale: the researchers made 10kg of material in the lab.
When they trialled pilot battery stacks with scaled-up amounts of material, they could operate them for 270 charge-discharge cycles over 27 days. The batteries retained 99.95% of their capacity per cycle.
“This study is expected to open a new field in the design of air-stable molecular for sustainable and air-stable electrochemical energy storage,” says senior author Professor Xianfeng Li, a researcher at the Dalian Institute of Chemical Physics within the Chinese Academy of Sciences.
