Zinc–iodine battery delivers double performance of lithium-ion batteries

Researchers at the University of Adelaide have developed a new dry electrode for aqueous batteries which delivers cathodes with more than double the performance of iodine and lithium-ion batteries.

“We have developed a new electrode technique for zinc–iodine batteries that avoids traditional wet mixing of iodine,” said the University of Adelaide’s Professor Shizhang Qiao, Chair of Nanotechnology, and Director, Center for Materials in Energy and Catalysis, at the School of Chemical Engineering, who led the team.

“We mixed active materials as dry powders and rolled them into thick, self-supporting electrodes. At the same time, we added a small amount of a simple chemical, called 1,3,5-trioxane, to the electrolyte, which turns into a flexible protective film on the zinc surface during charging.

“This film keeps zinc from forming sharp dendrites—needle-like structures that can form on the surface of the zinc anode during charging and discharging—that can short the battery.”

Aqueous zinc–iodine batteries offer unparalleled safety, sustainability, and cost advantages for grid-scale storage, but they suffer from performance issues compared to lithium-ion batteries.

The team published their results in the journal Joule.

“The new technique for electrode preparation resulted in record-high loading of 100 mg of active material per cm²,” said the University of Adelaide’s Han Wu, Research Associate, School of Chemical Engineering, from the team that worked on the study.

“After charging the pouch cells we made that use the new electrodes, they retained 88.6% of their capacity after 750 cycles and coin cells kept nearly 99.8% capacity after 500 cycles.

“We directly observed how the protective film forms on the zinc by using synchrotron infrared measurements.”

High iodine loading and a robust zinc interface mean much more energy can be stored in each battery at a lower weight and cost. This could bring zinc–iodine batteries closer to real-world use for large-scale or grid storage.

There are several advantages of the team’s invention over existing battery technology:

• Higher capacity: the dry electrodes pack more active material than wet-processed ones, which typically top out below 2 mA h cm⁻².
• Lower self-discharge and shuttle loss: dense dry electrodes reduce iodine escaping into the electrolyte and degrading performance.
• Better zinc stability: in situ protective film prevents dendrite growth, giving much longer cycle life.

“The new technology will benefit energy storage providers—especially for renewable integration and grid balancing—who will gain lower-cost, safer, long-lasting batteries,” said Professor Qiao. “Industries needing large, stable energy banks, for example, utilities and microgrids, could adopt this technology sooner.”

The team has plans to develop the technology further to expand its capabilities.

“Production of the electrodes could be scaled up by using reel-to-reel manufacturing,” said Professor Qiao. “By optimizing lighter current collectors and reducing excess electrolytes, the overall system energy density could be doubled from around 45 watt-hours per kilogram (Wh kg⁻¹) to around 90 Wh kg⁻¹.

“We will also test the performance of other halogen chemistries such as bromine systems, using the same dry-process approach.”