Flow batteries are a promising storage solution for renewable energy but they often suffer degraded energy storage capacity after many charge-discharge cycles, requiring periodic maintenance of the electrolyte to restore the capacity.
By modifying the structures of molecules used in the positive and negative electrolyte solutions, and making them water soluble, the team engineered a battery that loses only 1% of its capacity per 1000 cycles.
"Lithium ion batteries don't even survive 1000 complete charge/discharge cycles," said Professor Michael Aziz.
The key to designing the battery was to determine why previous molecules were degrading so quickly in neutral solutions. By first identifying how the molecule viologen in the negative electrolyte was decomposing, the team could modify its molecular structure to make it more resilient.
Next, the researchers turned to ferrocene for the positive electrolyte. By functionalising ferrocene molecules in the same way as with the viologen, the team turned an insoluble molecule into a highly soluble one that could also be cycled stably.
"This work on aqueous soluble organic electrolytes is of high significance in pointing the way towards future batteries with improved cycle life and lower cost," said Imre Gyuk, director of energy storage research with the US Department of Energy. "I expect that efficient, long duration flow batteries will become standard as part of the infrastructure of the electric grid."
