A Polymer Cage That Locks Iodine in Place: Flinders University Sends a Zinc-Iodine Battery Past 60,000 Cycles

Researchers at Flinders University in South Australia have built an aqueous zinc-iodine battery that holds up through more than 60,000 charge and discharge cycles while still filling in about three minutes. The result, published in the journal Angewandte Chemie, points to a chemistry that could undercut lithium-ion for the bulky, stationary storage jobs that grids actually need.

The team is not promising a phone that runs for a month or a car with a 1,500-kilometer range. They are promising something the energy transition is short on: a cheap, safe, long-lived cell built from materials Australia already has in the ground.

Why iodine, and why now

Iodine is one of the better-known candidates for rechargeable batteries. Weight for weight, it can hold a lot of energy. Associate Professor Zhongfan Jia, a Matthew Flinders Fellow in the university's College of Science and Engineering, puts the figure at roughly 211 milliampere-hours per gram. That is competitive with the materials inside many lithium-ion cells, and the raw element is abundant and cheap.

The trouble has never been capacity. It has been wanderlust.

In a zinc-iodine cell, iodine species tend to drift where they should not. They dissolve into the water-based electrolyte, migrate across the battery, and react in the wrong place. Engineers call the effect polyiodide shuttling. It bleeds capacity, fouls the electrodes, and kills the cell long before its chemistry has any right to give out. It is the same kind of self-sabotage that has kept many clever battery ideas stuck on the lab bench.

The cage that solves it

The Flinders group's fix is almost absurdly simple. They use a low-cost organic polymer built from cyclodextrins, the ring-shaped sugar molecules already used in food, pharmaceuticals, and cosmetics. The polymer's structure acts like a cage. It locks iodine compounds in place and keeps them from roaming.

That single design choice changes the cell's personality. Charged in seven minutes, the prototype runs at 1.3 to 1.4 volts with a capacity of 200 milliampere-hours per gram across 8,000 cycles. Push the charge time down to three minutes and it clears 60,000 cycles at 150 milliampere-hours per gram. Either way, the battery does not catch fire, because the electrolyte is water, not the flammable organic solvent found in lithium-ion cells.

"This system offers a new approach to mitigate polyiodide shuttling by using polymers derived from inexpensive, biodegradable materials, thereby enabling sustainable and long-lasting aqueous zinc-iodine batteries," Jia said.

Built from what Australia already has

Part of the appeal is geological. Australia holds an estimated 20 to 28 percent of the world's zinc reserves, the largest share of any country. For a nation watching lithium-ion demand strain supply chains and inflate prices, a storage chemistry anchored in local metal has a certain logic.

"As a top global producer and exporter, we can use these zinc resources for safer energy storage, which is important for energy manufacturing in Australia," said Shangxu Jiang, a PhD student in the university's Sustainable Polymers for Energy and Environment group and a co-author of the paper.

The group is now working with industry partners to stand up a prototyping platform, the unglamorous step between a promising result in a journal and a product a utility can bolt to a substation. Their stated aim is a viable alternative to lithium-ion for large-scale storage, not a replacement for the battery in your laptop.

The lithium-ion hangover

The push has a wider context. Demand for lithium-ion cells, from electric vehicles to earbuds, has driven up prices and exposed ugly supply chain and recycling problems. Australia alone generates about 3,300 tonnes of lithium-ion battery waste a year. The national science agency projects that number climbs past 136,000 tonnes by 2036 if nothing changes. Zinc, by contrast, is plentiful, cheaper to refine, and far less likely to burn.

That is why aqueous zinc batteries keep drawing research money even when they trail lithium-ion on energy density. For a grid-scale installation where space and weight barely matter, 150 milliampere-hours per gram with 60,000 cycles and a three-minute top-up looks like a fair trade for a chemistry that will not explode and will not depend on contested supply routes.

Where this fits among battery contenders

Zinc-iodine is one entry in a crowded field of post-lithium ideas. Sodium-ion has attracted heavy investment from Chinese manufacturers chasing a cheaper, safer grid cell. Lithium-sulfur promises high energy density for weight-sensitive uses. Solid-state designs aim to kill the flammable electrolyte entirely. Each has a catch: sodium lags on density, sulfur struggles with cycle life, solid-state fights a brutal manufacturing bill.

The Flinders result attacks the exact weakness that has dogged aqueous zinc batteries. If the cyclodextrin cage holds up outside the lab, the chemistry's combination of cheap inputs, non-flammable electrolyte, and now very long life makes it a credible contender for stationary storage, where lithium-ion's advantages matter least.

The paper, titled "Caging polyhalide anions in polycyclodextrin for long-lasting aqueous zinc-iodine batteries," lays out the mechanism in detail. It is the kind of incremental-but-load-bearing advance that rarely makes headlines yet quietly sets the terms for which batteries get built a decade from now.

What comes next

A 60,000-cycle lab cell is not a gigawatt-hour of installed storage. The team knows that. The next phase is the prototyping platform with industry, the work of proving the cage survives mass production, temperature swings, and the slow grind of real grid duty.

For now, the headline number stands: a water-based zinc battery, charged in three minutes, that still works after 60,000 cycles. In a market obsessed with lithium, that is a reminder that the chemistry that wins the future may be the one we can dig out of the ground next door, not the one we have to ship across an ocean.

Read more on battery technology at Battery Tech and the wider energy-storage picture in our EV and Semiconductors coverage.

Source: Flinders University newsroom announcement and pv-magazine reporting on the Angewandte Chemie study.