Helmed by QUT, the team has published their research in the prestigious Journal of the American Chemical Society, demonstrating a way of improving the voltage of aqueous zinc-ion batteries.

Aqueous zinc-ion batteries are a type of rechargeable battery with a water-based electrolyte.

Most rechargeable batteries in common use have organic electrolytes, not aqueous. Organic electrolytes are expensive and highly flammable.

Aqueous electrolytes are cheaper and safer and have been more than a hundred years in non-rechargeable batteries.  

“But the use of aqueous electrolyte in rechargeable batteries is very challenging,” explained Professor Ziqi Sun, from the QUT School of Chemistry and Physics and Centre of Materials Science.

“Because of the low reducing voltage of water (1.23V), the aqueous batteries usually have low voltage window and thus low energy density – which means inferior battery performance compared with the normal organic rechargeable batteries.”

“Improving the low voltage of rechargeable aqueous batteries is one of the biggest hurdles facing their wide-spread implementation for many uses,” said Professor Sun. 

The problem with increasing the voltage in an aqueous battery, according to Fan Zhang, first author on the research paper, is that “if the applied voltage is higher than 1.23V, hydrogen will generate and lead to swelling of the battery and possible explosion,” which is less than ideal. 

Professor Sun explained that the researcher’s way of circumnavigating these potentially explosive side effects was inspired by the Nobel-Prize winning Marcus Theory for electron transfer among molecules in a solution.

“In our work, we applied an organic compound called catechol into the aqueous zinc sulphate electrolyte, which changes the electron transfer model from a normal inner sphere transfer in electrolyte to an outer sphere transfer model,” said Professor Sun. 

“In simple terms, this means that catechol compound transfers an electron to the Zinc ion, which results in the water molecules being more stable and the potentially dangerous hydrogen reaction is controlled.”

It may be beyond the common comprehension but in even simpler terms, these researchers – including Professor Ziqi Sun, Associate Professor Dongchen Qi, and Fan Zhang from the School of Chemistry and Physics, Professor Ting Liao and Professor Cheng Yan from the School of Mechanical, Medical and Process Engineering and Dr Aaron Micallef from the Central Analytical Research Facility – have put us a significant step closer to having batteries that are not only cheaper and safer, but can charge faster, hold more charge, have a recharging cycle life of many times greater.

“The outer sphere electron transfer mechanism paves us a new way to design the high-voltage aqueous electrolytes,” Professor Sun said. “The use of this new types of aqueous electrolyte improves the voltage window for two folds higher and enhances the overall battery performance for 1.5 to 3 times better than normal aqueous electrolytes.”

Don’t head out to the stores with aqueous rechargeable batteries on your list yet though. This scientific breakthrough may still take a while to trickle down to consumers.

However Professor Sun is pleased and proud.“This is a big leap to aqueous rechargeable batteries for industrial production.”