Rechargeable Zinc batteries come back with water-based electrolytes

Technology News |
By Nick Flaherty

The team led by researchers at A. James Clark School of Engineering at the University of Maryland combined old battery technology – metallic zinc – with a new water-based aqueous electrolyte. 

“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,” said Fei Wang, a jointly appointed postdoctoral associate at UMD’s Clark School and the US Army Research Laboratory (ARL). The team also included researchers from the US National Institute of Standards and Technology (NIST) and the paper was published in Nature.

Such an aqueous zinc battery could be used in consumer electronics and safety-critical applications in aerospace, military, and deep-ocean environments.

“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,” said Chunsheng Wang, UMD professor of chemical and biomolecular engineering.

Zinc batteries suffer from low coulombic efficiency (CE) and dendrite growth during plating/ stripping, and sustained water consumption. The new approach uses lithium salts at high concentrations and produces deliver 180 Wh/kg while retaining 80% capacity for over 4,000 cycles using a LiMn2O4 electrolyte. Using oxygen as the cathode in a zinc-air design delivers 300 Wh/kg (1,000 Wh/kg based on the cathode) for over 200 cycles.

The researchers identified the fundamental reason causing irreversibility in zinc batteries and found a way to alter the structure of positively charged zinc cations. This can also be used with magnesium and aluminium battery systems.

“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. 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,” said Chunsheng Wang.

“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 team 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,” said Joseph Dura, a physicist at NIST.

“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 aluminium batteries,” said Kang Xu, a ARL fellow.

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