In 2018, Li et al. of Nankai University and, nearly simultaneously, Bai et al. writing in Nano Research, demonstrated the basic design of a rechargeable zinc-iodine battery using an aqueous electrolyte. Iodine is one of the simplest molecules exhibiting reversible electrochemical behavior, with a theoretical capacity of 211 mAh/g. Because the electrolyte is aqueous, there is no fire risk, and the materials are inexpensive. As a candidate for large-scale power storage—that is, "grid-scale storage" connected to the power grid to absorb fluctuations in renewable energy—this battery system rapidly attracted research attention. By January 2023, more than 100 papers had been published on the topic.
However, this system had a structural flaw. During charge and discharge, iodide ions () react with iodine molecules () to form triiodide ions () and pentaiodide ions (). These polyiodides are highly soluble in water. The dissolved polyiodides pass through the separator and migrate to the negative electrode side, where they undergo irreversible reactions with the zinc metal. The result is loss of active material at the positive electrode, progressive self-discharge, and corrosion of the zinc anode surface. This phenomenon is known as the "shuttle effect," also familiar from lithium-sulfur batteries, but it is particularly severe in aqueous zinc-iodine batteries.
Early batteries suffered substantial capacity loss after just a few hundred to a few thousand cycles. As of 2018, reported cycle life was around 1,500 cycles. For grid-scale storage, batteries are expected to sustain daily charge-discharge cycles for over 20 years. A simple calculation puts this at more than 7,000 cycles, and considering economic viability, a lifespan in the tens of thousands of cycles is desirable. Suppressing the shuttle effect was the single biggest obstacle blocking practical deployment of this battery system.
Finding a Cavity Size That's "Neither Too Tight Nor Too Loose"
A research team led by Associate Professor Zhongfan Jia (Matthew Flinders Fellow) in the Department of Chemistry at Flinders University took on this challenge with an unexpected material: cyclodextrin (CD).
Cyclodextrins are a family of cyclic oligosaccharides obtained by enzymatically breaking down starch. There are three types—α-CD, β-CD, and γ-CD—each with a different cavity diameter. They are used routinely as ingredients in food additives and cosmetics, and are biodegradable and inexpensive. Their structure has a distinctive property: the outer surface is hydrophilic, while the inner cavity is hydrophobic. This "host-guest chemistry," in which specific molecules are captured within the hydrophobic cavity, has been widely studied in fields such as drug delivery and functional materials.
Jia's team applied this host-guest chemistry to the design of a battery cathode. They cross-linked cyclodextrins into a polymer (polycyclodextrin, polyCD) and used a composite loaded with (potassium triiodide) as the cathode material. By encapsulating polyiodides within the cyclodextrin cavities, dissolution into the electrolyte is physically suppressed. At the same time, because entry and exit from the cavity are reversible, the redox reactions of iodine that drive charging and discharging themselves are not hindered.
What matters here is the choice of cavity size. The research team compared all three types—α-CD, β-CD, and γ-CD. Computational chemistry analysis performed by Zhipeng Pei (co-first author), who belongs to the group of Professor Michelle Coote at Flinders University, together with experimental results, revealed that α-CD binds polyiodides too strongly, making release difficult, while γ-CD has a cavity too large for stable encapsulation. β-CD has just the right binding energy to strike a balance—"caging" polyiodides while still releasing them when needed. In his own LinkedIn post, Jia described this result as: "α-CD is too tight, γ-CD is too loose, β-CD is just right."
This discovery of the "optimal size" is not merely a performance improvement; it clearly demonstrates a design principle in which the strength of host-guest interactions determines battery performance—providing the field with a methodological guideline.
Capacity Barely Fades Even Beyond 60,000 Cycles
Let's look at the performance figures. The following data are compiled from the paper (Shangxu Jiang, Zhipeng Pei, Yanlin Shi, Kai Zhang, Justin M Chalker, Sara J Fraser-Miller, Michelle L Coote, Zhongfan Jia, Angewandte Chemie International Edition, 2026, DOI: 10.1002/anie.6010682) and the pre-publication ChemRxiv preprint (DOI: 10.26434/chemrxiv.15001257/v1).
| Condition | Capacity (mAh/g) | Cycle count | Capacity decay per cycle | Charge time |
|---|---|---|---|---|
| 2-electron storage, 8C (1.67 A/g) | 205 | 8,000 cycles (95% of initial capacity retained) | 0.0006% | ~7 min |
| 2-electron storage, 23C (4.2 A/g) | 182 | 30,000 cycles (84% retained) | 0.0005% | ~2.6 min |
| 2-electron storage, 6.2 A/g | 149→148 | over 60,000 cycles | near zero | ~3 min |
| 4-electron storage, 4C (1.4 A/g) | 356 | 9,000 cycles (93% retained) | 0.0008% | ~15 min |
| 4-electron storage, 8.3 A/g | 250→205 | over 60,000 cycles | 0.0003% | ~7 min |
Two-electron storage refers to the standard mode utilizing the redox reaction between and (theoretical capacity: 211 mAh/g). Four-electron storage is an extended mode that additionally exploits the reaction between and (theoretical capacity: 422 mAh/g); the research team stabilized the species by adding ZnBr, achieving long life even in this high-capacity mode.
Particularly notable is the capacity retention observed in cycling tests beyond 60,000 cycles. In the 2-electron storage mode, capacity declined from an initial 149 mAh/g to 148 mAh/g after 60,000 cycles. The drop of just 1 mAh/g translates to a per-cycle decay rate of 0.0001% or less. Even in the 4-electron storage mode, the decay rate remains at only 0.0003%. Total operating time exceeded 3,300 hours.
The operating voltage is about 1.3 V in 2-electron storage mode, while a plateau at roughly 1.6 V appears for the / reaction in 4-electron mode. The preprint reports that under the best conditions, an energy density of 500 Wh/kg and a power density of 2,000 W/kg were achieved (likely calculated on an active-material basis).
Comparison with Competing Approaches
Countering the shuttle effect in zinc-iodine batteries is not a challenge unique to this study. Below, representative recent competing studies are compared with the present results.
| Study (journal, year) | Method | Capacity (mAh/g) | Cycle count | Decay rate per cycle |
|---|---|---|---|---|
| Flinders University, Jia et al. (Angew. Chem. 2026) | Poly(β-CD) cathode host | 149 (2e, at 60,000 cycles) | over 60,000 cycles | ≤0.0001% (2e) |
| Yan et al. (Energy Storage Materials, 2026) | DMImCl ionic liquid additive (4-electron) | 405.2 (initial, 1 A/g) | over 60,000 cycles | 0.00058% |
| Zhang et al. (Materials Today Energy, 2025) | BES buffer additive | 83.14% retained | 50,000 cycles | not reported |
| Energy & Environmental Science (2024) | Superhalide solvation structure | 127 (5.0 A/g) | 45,000 cycles | ~0.0003% |
| PEO binder (J. Colloid Interface Sci., 2025) | Charge-transfer complex-forming binder | 154.6 (20C) | 33,000 cycles | 0.00018‰ (=0.0018%) |
The Flinders University approach achieves cycle life comparable to or exceeding that of competing methods, while being differentiated by using a starch-derived, biodegradable polymer as the material. Unlike approaches relying on ionic liquids or specialized electrolyte additives, this method can construct the cathode material itself from an inexpensive, naturally derived polymer, potentially offering advantages in both cost and environmental impact.
On the other hand, Yan et al.'s 4-electron battery has a higher initial capacity of 405.2 mAh/g compared to this study's 356 mAh/g (4-electron, 4C), but the present study also demonstrates stability beyond 60,000 cycles in 4-electron storage mode, giving it a distinct advantage through host-material design for extending battery life.
A Structural Difference from Lithium-Ion Batteries
The target application for this battery is not electric vehicles or smartphones. Because it uses an aqueous electrolyte, its voltage is limited to 1.3–1.6 V, falling short of the 3.6–3.7 V typical of lithium-ion batteries. In terms of volumetric energy density as well, aqueous batteries are at a disadvantage compared to lithium-ion batteries (up to 500 Wh/L).
However, what grid-scale storage demands is not energy density but rather safety, cost, and lifespan. Lithium-ion batteries, which use organic solvent electrolytes, carry a fire risk, and fire incidents at large-scale storage facilities have been repeatedly reported. In Australia, approximately 3,300 tons of lithium battery waste is generated annually, and this is projected to exceed 136,000 tons by 2036. Aqueous zinc-iodine batteries are nonflammable, and their materials—zinc, iodine, and starch—are all common substances.
A technical assessment report from the DOE (U.S. Department of Energy) identified cycle life and material durability as the biggest challenges for zinc-based batteries. The figure of over 60,000 cycles achieved here presents one answer to this challenge.
What Australia's Zinc Resources Mean
Co-first author Shangxu Jiang (a PhD student at Flinders University) frames Australia's zinc resources in a strategic context. According to 2025 data from Geoscience Australia, Australia ranks first in the world for zinc resources, holding 27% of the world total, and third in production, at 9%. In contrast to the current concentration of lithium processing in China, zinc offers the possibility of completing the entire chain from sourcing to processing domestically.
Jia states that they are "jointly building a prototyping foundation with industry for large-scale storage using aqueous zinc-iodine batteries." The transition from laboratory coin cells to practical, large-format cells will be the next stage.
Remaining Challenges and Untested Assumptions
The paper itself acknowledges certain limitations. After disassembling the cell following cycling tests beyond 60,000 cycles, some loss of the zinc foil anode was observed. The research team assessed this as "an acceptable level of zinc corrosion for over 5,900 hours of charge-discharge operation," while noting the need to apply anode protection strategies in future device development.
Additionally, the reported energy density of 500 Wh/kg is a figure stated in the preprint and appears to be a theoretical value calculated on an active-material-only basis. It does not represent the value for the entire cell, including separator, current collectors, and packaging. Energy density in a practical cell would be substantially lower than this figure.
In 4-electron storage mode, coulombic efficiency drops to 95%. This is thought to be because is smaller in size than , leading to somewhat greater leakage from the cyclodextrin "cage." Compared to the 99.5% efficiency in 2-electron storage, an efficiency-related challenge remains for practical deployment.
Furthermore, all of this data was obtained using small, laboratory-scale cells. Verification under practical conditions—such as large-area electrodes, high loading amounts, and temperature fluctuations in real-world environments—has not yet been reported. While prototype construction with industry partners is reportedly underway, until those results are made public, whether the figure of 60,000 cycles will be reproduced in an actual device remains an open question.