UMD Researchers Revive Old Chemistry to Create Safer Zinc Battery

A team of researchers from the University of Maryland's A. James Clark School of Engineering have created a water-based zinc battery that is simultaneously powerful, rechargeable, and intrinsically safe. The new aqueous zinc battery could eventually be used in consumer electronics, as well as in extreme conditions to improve the performance of safety-critical equipment and vehicles used in aerospace, military, and deep-ocean environments.

Together with colleagues at the U.S. Army Research Laboratory (ARL) and National Institute of Standards and Technology (NIST), UMD engineers used metallic zinc – an element used in 1799 in the very first battery – to crank up the energy of their own 2015 advance in battery technology. That previous UMD advance used a novel and safe water-in-salt electrolyte to replace the flammable organic electrolyte used in conventional lithium-ion batteries.

The team’s peer-reviewed paper based on their latest research was published April 16 in the journal Nature Materials.

"Water-based batteries could be crucial to preventing fires in electronics, but their energy storage and capacity have been limited – until now. For the first time, we have a battery that could compete with the lithium-ion batteries in energy density, but without the risk of explosion or fire," says Fei Wang, a jointly appointed postdoctoral associate at UMD's Clark School and ARL, and first author of the paper.

Fei Wang cites numerous, highly publicized battery fires in cell phones, laptops, and electric cars as examples of the clear need for a safer battery that can provide comparable, or even better, performance than current lithium-ion batteries.

The team’s new highly concentrated aqueous zinc battery also overcomes disadvantages of conventional zinc batteries, such as: the capacity to endure only limited recharging cycles; the damaging growth of tree-like crystal structures, known as dendrites, during usage and recharging; and the sustained water consumption that results in the need to regularly replenish the batteries’ electrolyte with water.

"Existing zinc batteries are safe and relatively inexpensive to produce, but they aren't perfect due to poor cycle life and low energy density. We overcome these challenges by using a water-in-salt electrolyte," says Chunsheng Wang, UMD professor of chemical and biomolecular engineering and corresponding author of the paper.

Through their collaborations, the researchers identified the fundamental cause in zinc batteries of irreversibility – a phenomenon observed in rechargeable battery usage where the amount of charge a battery can deliver at the rated voltage decreases with use – and found a novel solution.

"Because most water molecules in the new electrolyte are strongly bonded by the highly concentrated salt, the water in the aqueous zinc battery's electrolyte will not evaporate in an open cell,” explains Chunsheng Wang. “This advance revolutionizes zinc–air batteries, which are powered by oxidizing zinc with oxygen from the air, such as those used in energy grid storage."

Joseph Dura, a physicist at NIST and co-author of the paper says, "Zinc batteries would provide a powerful and inexpensive means of energy storage if they could be rechargeable. This research uncovered ways to control which molecules in the electrolyte surround the ions that move back and forth in a battery when storing and releasing energy. Here, the co-authors applied this knowledge to make a highly rechargeable zinc battery which could offer a low-cost, safe alternative for consumer electronics, cars, and electrical grid storage."

The research team says this battery technology advance lays the groundwork for further research, and they are hopeful for possible future commercialization.

"The significant discovery made in this work has touched the core problem of aqueous zinc batteries, and could impact other aqueous or non-aqueous multivalence cation chemistries that face similar challenges, such as magnesium and aluminum batteries," says Kang Xu, ARL fellow and co-corresponding author of this paper.