QUT researchers unlock potential for century-old battery technology to power smart devices

The research, published in the Journal of the American Chemical Society, shows that the voltage increase in a zinc aqueous battery can be achieved without a potentially dangerous hydrogen build up, paving the way for potential development of a safer and cheaper way of powering smart devices.

In some instances, lithium-ion batteries have caught fire due to overcharging or the use of non-compliant charging equipment.

However, aqueous batteries, using a water-based solution as an electrolyte, have largely been used as non-rechargeable batteries and are said to not have the sufficient energy density and life cycle needed for electric vehicles.

Increasing the voltage of an aqueous battery is seen as a major step towards upgrading the technology to allow for broader usage in smart devices.

“Improving the low voltage of rechargeable aqueous batteries is one of the biggest hurdles facing their wide-spread implementation for many uses,” says Professor Ziqi Sun, one of the QUT researchers working on the project.

“In common rechargeable batteries, organic electrolytes are used to fill the space between the anode and cathode, which are expensive, and most importantly, highly flammable,” he says.

“The use of aqueous electrolytes could address the safety issue of lithium-ion batteries, as the aqueous electrolyte is much cheaper and safer. But the use of aqueous electrolyte in rechargeable batteries is very challenging.

“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.”

Fan Zhang, first author on the research paper, notes there is another key challenge in increasing this 1.23V voltage window with an aqueous electrolyte.

“If the applied voltage is higher than 1.23V, hydrogen will generate and lead to swelling of the battery and possible explosion,” says Zhang.

But the researchers are said to have found a way of increasing the voltage in a zinc aqueous battery while avoiding the potentially dangerous hydrogen build up.

The method was inspired by the Marcus Theory for electron transfer among molecules in a solution, which earned Rudolph Marcus the Nobel Prize in Chemistry in 1992.

“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,” says 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.”

Sun sees the research as a step towards a potential rebirth of the old zinc-based aqueous batteries for modern applications, with the technology offering several key advantages.

Zinc ions have twice the charge of lithium ions, therefore offering twice as much energy, while the batteries can be smaller, charge more quickly and offer a recharging cycle that is many times greater.

“The outer sphere electron transfer mechanism paves us a new way to design the high-voltage aqueous electrolytes,” says Sun.

“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 three times better than normal aqueous electrolytes.

“This is a big leap to aqueous rechargeable batteries for industrial production.”

QUT researchers involved in the study are Sun, Associate Professor Dongchen Qi and Fan Zhang, all 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.