Most conventional batteries today work thanks to redox reactions of metals. The metal electrodes used in these devices can be expensive and are often toxic for the environment.

“When designing our ‘green’ battery, we were inspired by the important role of quinones (a class of organic compounds) in nature,” says team leader Guihua Yu. “We used hydroquinone aqueous solution as the liquid cathode and graphite in an aprotic electrolyte as the anode. The redox reaction occurring in the device mimics the bioelectrochemical process that quinones undergo in nature and our novel energy storage system combines the concept and advantages of lithium-ion batteries and redox-flow batteries, while going beyond conventional ‘intercalation’ electrode materials.”

High working potential and high energy density

According to the researchers’ measurements, the new metal-free battery can provide a high working potential of 3.4 V, is stable over hundreds of testing cycles and has a higher energy density compared to conventional vanadium-based flow batteries. What is more, the device works thanks to reactions of earth-abundant materials and shows promise for meeting the system capital cost target of $150 per kWh set by the US Department of Energy,” team member and first author of this study Yu Ding tells nanotechweb.org.

The concept of the new device could also be extended to designing other types of metal-free batteries in the future, he adds. “For example, the properties of such a battery can be modified by changing the electrolyte solvent, and the structural diversity of organic materials could allow us to tailor the electrochemical activity and redox potential by functionalizing them with certain chemical groups.”

Indeed, the researchers are now planning to functionalize hydroquinone with hydrophilic groups, such as sulphonic moieties, to further improve their battery’s energy density. “By designing such metal-free batteries using organic electroactive materials, we hope to move the frontiers of the ‘atom economy’ in green chemistry to the field of energy storage,” says Yu

The battery is described in Angewandte Chemie International Edition DOI: 10.1002/anie.201600705.