New cathode chemistry reduces self-discharge in grid-scale zinc-iodine batteries

Researchers at the University of Adelaide have used a microscope to understand how water-soluble zinc-iodine batteries are powered, and discovered a way to improve their performance.

Rechargeable aqueous zinc batteries are growing as an alternative to large lithium-ion energy storage systems due to their low cost, affordable density, and high safety.

However, traditional iodine cathode hosts are often slow to react and have poor electrochemical reproducibility, so a research team led by Professor Shizhang Qiao, dean of the Department of Nanotechnology in the School of Chemical Engineering, explored the use of ferrocene in the cathode.

Their findings were published in the journal Nature Chemistry.

“The conversion of iodine in aqueous zinc-iodine cells is accompanied by a shuttle effect of polyiodide, while the conversion of ferrocene, an organometallic compound, can lead to polyiodide precipitation, which leads to lower self-discharge,” said Professor Qiao, who is also director of the Center for Energy and Catalytic Materials.

“Because ferrocene is composed of low-cost elements, it has favorable scalability and can be low-cost in large-scale production.

“Simulation results show that incorporating ferrocene reduces the total cost of the battery by 9% compared to without ferrocene.”

Professor Qiao said that the use of ferrocene virtually eliminated the shuttle effect, a common problem in zinc-iodine batteries, where the intermediate polyiodide dissolves in the electrolyte and shuttles between the positive and negative electrodes.

“Using ferrocene not only increases energy density but also lowers overall cost, making coupling a practical, economical and scalable strategy to advance aqueous zinc-iodine battery technology,” said Professor Qiao.

“Our findings also show that the active mass of the cathode can reach 88%, minimizing the capacity loss of the inactive host.”