RFBs were first built in the 1940s, and are considered a promising form of large-scale energy storage. Traditionally, they have been made using expensive metals and dangerous acids.
“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,” said Jena University’s Dr Martin Hager, one of the lead authors of a paper on the research.
The new technology, described in the journal Nature, uses organic polymers for the electrodes, with a saline solution as the electrolyte. According to the researchers, these materials are cheaper and safer than those currently in use, yet comparable in efficiency.
“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,” said Hager.
The electrodes of RFBs come in a dissolved form, stored in two tanks to form the positive and negative terminals of the battery. Using pumps, the polymer solutions are transferred to an electrochemical cell, where they are then reduced or oxidized, thereby charging or discharging the battery. The cell is divided in two by a membrane to prevent the two electrolytes from mixing.
“In these systems the amount of energy stored as well as the power rating can be individually adjusted,” said Hager. “Moreover, hardly any self-discharge occurs.”
Tests conducted so far on the team’s battery have shown that it can endure up to 10,000 charging cycles without losing a “crucial amount of capacity”, and the energy density of the system presented in the study was ten watt-hours per litre. The reserachers say the technology is ideally suited to energy storage for large wind farms and photovoltaic power stations, and they are already working on larger and more efficient systems.