As countries around the world increase energy generation from renewable — and variable — sources like wind and solar, the need for energy storage solutions increases. Europe has led the way in renewable energy generation, and by the beginning of 2020, for the first time ever, renewable energy provided more than half of the electricity consumed in Germany. Storage solutions mean this green energy could also be used when the sun is not shining on the solar panels or no airflow is driving the wind turbines, which makes suitable energy storage devices indispensable. Researchers at the Friedrich Schiller University Jena (Germany) have recently developed promising new polymer electrolytes for redox flow batteries, which are flexible, efficient, and environmentally friendly. They report on their success in the current issue of Advanced Energy Materials.
Huge potential of redox flow batteries
The new material developed by the Jena chemists is used in so-called redox flow batteries. “In this type of battery, the energy-storing components are dissolved in a solvent and can therefore be stored at a decentralized location, which allows the battery to be scaled as required, from a few millilitres to several cubic metres of electrolyte solution,” said Dr. Ulrich S. Schubert of the Center for Energy and Environmental Chemistry Jena (CEEC Jena) at the Friedrich Schiller University.
Thanks to this flexibility, redox flow batteries generally have great potential to become an important means of energy storage in the future. Until now, however, they suffered from two weaknesses that have prevented their widespread use. The first was the frequent usage of environmentally hazardous and toxic heavy metal salts, such as vanadium dissolved in sulfuric acid, as electrolytes. The other problem was the restriction of the batteries to a maximum working temperature of 40°C, which necessitated the usage of an elaborate cooling system. With the help of the new material, these two problems were solved.
Cleaner, more heat-resistant, more efficient
“We have designed a new type of polymer that is soluble in water, which makes it suitable for use in an aqueous electrolyte, and that contains iron, which provides the ability to store electricity,” explains Schubert. “At the same time, the polymer can cope with a significantly higher temperature of up to 60°C, so that the additional expense for a sensitive temperature management is eliminated.” In addition, during their tests with the new system, the Jena researchers discovered that it also works more efficiently than its predecessors.
This means that electricity can be stored in a non-hazardous, water-based solution, which is then stored temporarily in tanks, and the electricity in the battery can be used again the next day without significant losses or additional effort. Systems of this kind can also be used in warmer regions, such as Africa, India or Brazil. “By improving the energy storage medium, we believe that the redox flow battery is once again in a good position to make an important contribution as the energy storage technology of the future,” says Schubert. “And our development shows once again the great importance of novel polymers for the development of innovative storage methods.”