The FSU Jena research team with the novel redox-flow battery. Left to right: Ulrich Schubert, Tobias Janoschka, Martin Hager. Image: Anne Günther/FSU.
The FSU Jena research team with the novel redox-flow battery. Left to right: Ulrich Schubert, Tobias Janoschka, Martin Hager. Image: Anne Günther/FSU.

Chemists in Germany have developed an innovative redox-flow battery made from organic polymers and water.

Sun and wind are important sources of renewable energy, but they suffer from natural fluctuations: in stormy weather or bright sunshine, electricity production can exceed demand, whereas clouds or a lull in the wind inevitably cause a power shortage. To ensure continuity in the electricity supply and stable power grids, energy storage devices will become essential. So-called redox-flow batteries are a promising technology for solving this problem, but they have one crucial disadvantage: they require expensive materials and aggressive acids.

A team of researchers at the Friedrich Schiller University Jena (FSU Jena), the Center for Energy and Environmental Chemistry (CEEC Jena) and JenaBatteries GmbH (a spin-off from FSU Jena) have now taken a decisive step towards a redox-flow battery that is simple to handle, safe and inexpensive.

“What's new and innovative about our battery is that it can be produced at much less cost, while nearly reaching the capacity of traditional metal and acid containing systems,” says Martin Hager at CEEC Jena. The researchers present their battery technology in a paper in Nature.

In contrast to conventional batteries, the electrodes of a redox-flow battery are not made of solid materials such metals or metal salts, but come in dissolved form as electrolyte solutions. These solutions are stored in two tanks, which form the positive and negative terminal of the battery. With the help of pumps, the polymer solutions are transferred to an electrochemical cell, where they are electrochemically reduced or oxidized, thereby charging or discharging the battery.

To prevent the electrolytes from intermixing, the cell is divided into two compartments by a membrane. “In these systems, the amount of energy stored as well as the power rating can be individually adjusted. Moreover, hardly any self-discharge occurs,” explains Hager.

Traditional redox-flow systems mostly use the heavy metal vanadium dissolved in sulphuric acid as the electrolyte. “This is not only extremely expensive, but the solution is highly corrosive, so that a specific membrane has to be used and the life-span of the battery is limited,” Hager points out.

So for their redox-flow battery, the Jena researchers used an electrolyte made from an organic polymer and a saline solution. The organic polymer resembles polystyrene, but with added functional groups that allow it to accept or donate electrons. No aggressive acids are needed anymore; instead, the polymers 'swim' in the saline solution.

“Thus we are able to use a simple and low-cost cellulose membrane and avoid poisonous and expensive materials,” explains Tobias Janoschka at FSU Jena and first author of the new study. “This polymer-based redox-flow battery is ideally suited as energy storage for large wind farms and photovoltaic power stations,” says Ulrich Schubert, chair for organic and macromolecular chemistry at FSU Jena and director of CEEC Jena.

In first tests, the redox-flow battery could withstand up to 10,000 charging cycles without losing much capacity and demonstrated an energy density of 10 watt-hours per liter. Yet, the scientists are already working on larger, more efficient systems, as well as collaborating with JenaBatteries on commercializing the battery technology.

This story is adapted from material from the Friedrich Schiller University Jena, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.