The Center of Excellence for Renewable Energy and Storage Technologies (CREST) shows that sulfate ions reduce the amount of free water to increase the lifespan and performance of aqueous batteries

Scientists at King Abdullah University of Science and Technology (KAUST) have uncovered a critical molecular cause keeping aqueous rechargeable batteries from becoming a safer, economical option for sustainable energy storage. Their findings, published in Science Advances, reveal how water compromises battery life and performance and how the addition of affordable salts – such as zinc sulfate – mitigates this issue, even increasing the battery lifespan by more than ten times.

One of the key determinants to the lifespan of a battery – aqueous or otherwise – is the anode. Chemical reactions at the anode generate and store the battery's energy. However, parasitic chemical reactions degrade the anode, compromising the battery lifespan.

The new study shows how free water contributes to these parasitic reactions and how zinc sulfate reduces the amount of free water in the battery.

"Our findings highlight the importance of water structure in battery chemistry, a key parameter that has been previously overlooked," said KAUST Professor and Chair of CREST Husam Alshareef, the principal investigator leading the study.

Free water describes water molecules that are not strongly bonded with other molecules. This state allows free water to engage with more molecules than otherwise, triggering unwanted reactions that consume energy and compromise the anode.

Sulfate was found to stabilize the bonds of free water, acting as what the KAUST team describes as a "water glue", to change dynamics of the water molecules that reduces the number of parasitic reactions.

While the bulk of experiments by the KAUST researchers were done on batteries using zinc sulfate, early investigation has shown that sulfate has the same effect on other metal anodes, suggesting the inclusion of sulfate salts into the battery design could be a universal solution for lengthening the lifespan of all aqueous batteries.

An aqueous battery from the study.

"Sulfate salts are cheap, widely available and chemically stable, making our solution scientifically and economically viable," said KAUST Research Scientist Yunpei Zhu, who conducted the bulk of the experiments.

Aqueous batteries are gaining significant global attention as a sustainable solution for large-scale energy storage and are projected to exceed a market size of $10 billion by 2030. Unlike lithium batteries, which are often used in electric vehicles, aqueous batteries offer a safer and more sustainable option for integrating renewable energy sources like solar power into electrical grids, a key goal for Saudi Arabia's energy transition.

KAUST Professors Omar Mohammed, Osman Bakr, Xixiang Zhang, and Mani Sarathy also contributed to the study.

Alshareef noted that bringing together CREST scientists possessing complementary backgrounds, such as battery design, electrochemical modeling, and experimental tools, such as advanced spectroscopy and microscopy, was critical for the discovery.

"CREST was founded to be a leader in renewable energy innovation in the Kingdom. The dramatic improvement in aqueous battery performance and stability reported here is just one example of what CREST can accomplish by leveraging the high caliber and diverse skills of its members,” he said.