Aqueous zinc–iodine batteries have attracted intense interest because they combine the inherent safety of water-based electrolytes with the low cost and abundance of zinc and iodine. Unlike many lithium-based systems that rely on flammable organic electrolytes, aqueous batteries are far less vulnerable to combustion. Iodine is also capable of storing a large amount of charge through reversible redox reactions. Yet converting that theoretical potential into a durable commercial battery has proved difficult, particularly when the cell is designed to use the full four-electron iodine reaction.

The key chemistry involves the transformation of iodide through multiple oxidation states, represented broadly as I⁻/I⁰/I⁺. Accessing this four-electron pathway can substantially increase the amount of energy stored per unit of iodine. However, the high-valence iodine species generated during charging are chemically reactive and difficult to control. They can form soluble polyiodides, migrate through the electrolyte, and reach the zinc electrode, where they trigger unwanted reactions. These processes reduce the battery’s efficiency, accelerate self-discharge, and cause active material to escape from the cathode reaction zone.

The zinc anode presents a second major obstacle. During charging, zinc ions must be reduced and deposited back onto the metal surface. If the deposition is uneven, needle-like dendrites or rough, porous structures can develop. Such irregular growth may increase electrical resistance, consume electrolyte, and in severe cases create conditions for internal short circuits. At the same time, water can participate in parasitic reactions at the zinc surface, producing hydrogen and changing the local chemical environment. A successful battery therefore needs to control iodine at the cathode while also regulating zinc deposition at the anode.

To solve both problems, the research team, led by Prof. Chen Zhongwei and Prof. Wang Dongdong, systematically screened nitrogen-containing cationic ligands and identified N-methylimidazolium chloride, or MImCl, as a multifunctional electrolyte additive. Its positively charged MIm⁺ component does not remain confined to one location in the cell. Instead, the cations dynamically migrate between the cathode and anode interfaces as the battery operates, acting as mobile chemical regulators in the two regions where instability is most severe.

At the iodine cathode, MIm⁺ coordinates with reactive iodine intermediates. This coordination changes the local chemical environment around the iodine species and helps stabilize the high-valence forms required for the four-electron reaction. By binding or interacting with these intermediates, the additive can also reduce the tendency of iodine to assemble into soluble polyiodides. Suppressing this shuttle effect is crucial because polyiodides can diffuse away from the cathode, cross the electrolyte, and react directly with zinc instead of contributing to useful charge storage.

The same additive performs a different function at the zinc electrode. MIm⁺ modifies the interfacial environment through which Zn²⁺ ions approach and are reduced onto the metal surface. This encourages more uniform nucleation and growth, helping zinc plate into a smoother and more compact layer. During discharge, the regulated interface also supports more even stripping of zinc. The researchers describe this simultaneous control of iodine chemistry and zinc electrochemistry as “dual-interface coordination orchestration,” because one mobile electrolyte component coordinates the behavior of both electrodes rather than treating them as separate problems.

The results are particularly notable because the team moved beyond small laboratory cells and tested high-loading configurations designed to better reflect practical battery operation. In the reported pouch cell, the strategy sustained the demanding zinc–iodine chemistry over more than 800 cycles while delivering 1.4 Ah of capacity. The stated energy density reached 455 Wh kg⁻¹ when calculated using the mass of the active cathode material. That measurement basis is important: it highlights the performance of the iodine-based cathode chemistry, but it does not represent the full packaged-cell energy density, which would also include the electrolyte, current collectors, separator, casing, and other components.

The study offers a broader lesson for aqueous metal batteries. Rather than relying solely on new electrode materials, the researchers show that a carefully selected electrolyte additive can act as an active participant in battery chemistry, moving to the interface where it is needed and coordinating unstable reaction intermediates. If the approach can be validated under larger-scale conditions, with leaner electrolyte quantities, thicker electrodes, and full-cell mass accounting, it could help close the gap between the impressive theoretical capacity of zinc–iodine systems and the durability required for grid storage. The researchers say the work provides new insights into electrolyte-mediated interface regulation and creates a promising route toward safer, higher-energy aqueous zinc batteries.

Subject of Research: Not applicable

Article Title: Unveiling Dual-Interface Coordination Orchestration for Durable Aqueous Zinc–Iodine Pouch Cells with Four-Electron Chemistry

Web References: https://doi.org/10.1021/jacs.6c11308; https://english.dicp.cas.cn/

References: Journal of the American Chemical Society, DOI: 10.1021/jacs.6c11308

Keywords

Aqueous batteries, zinc–iodine batteries, zinc metal anodes, iodine redox chemistry, electrolyte additives, MImCl, N-methylimidazolium chloride, polyiodide shuttle, pouch cells, energy storage, electrochemistry, zinc deposition, four-electron chemistry

Thermal runaway, a process where an escalating chain reaction within a battery cell causes rapid temperature and pressure increases, often culminating in fires or explosions, represents the most critical safety challenge in the field of energy storage. Traditionally, the design of electrolytes—the medium allowing ion transport within a battery—has centered around developing non-flammable or flame-retardant formulations. However, achieving complete suppression of thermal runaway, especially in commercially relevant, ampere-hour-level sodium-ion cells, has remained unattainable. The newly proposed electrolyte leverages a cleverly engineered polymerization mechanism, triggered by temperature rises, which imparts an unprecedented level of intrinsic safety.

At the heart of this technology is an innovative polymerizable electrolyte chemistry that embodies a synergistic interaction between anions and cations, facilitating a robust solvation effect that optimizes ion mobility. More importantly, when exposed to elevated temperatures indicative of potential thermal events, the electrolyte undergoes rapid in situ polymerization. This process forms a cross-linked, solid-state barrier at the electrode–electrolyte interface. Such a barrier not only physically suppresses deleterious mechanical and chemical interactions between electrodes but also significantly mitigates side reactions that typically liberate reductive gases responsible for initiating thermal runaway.

The meticulous control over these electrochemical and physical interfacial phenomena marks a paradigm shift in battery safety engineering. By preventing the generation of gases and inhibiting the progressive degradation of electrode materials, the batteries demonstrate remarkable resilience under abuse conditions. For instance, the research team subjected the newly developed sodium-ion cells to rigorous nail-penetration tests, a standard to assess battery robustness under mechanical damage. Unlike conventional batteries, which often emit smoke, catch fire, or explode under such stress, these advanced cells passed without any such hazardous manifestations, showcasing no smoke, flame, or explosion.

This achievement signals a major breakthrough in the application of sodium-ion batteries for grid-scale energy storage systems, which demand the highest safety standards due to their large format and energy density. The innovative electrolyte allows for the construction of ampere-hour-level cells—a scale relevant for commercial energy storage—without compromising on essential safety parameters. In addition to safety, the polymerizable electrolyte maintains high ionic conductivity, ensuring that the batteries deliver competitive power and energy densities, a balance notoriously difficult to strike in non-flammable electrolyte systems.

Beyond its mechanical and thermal stability, the electrolyte’s unique design also addresses the chemical stability challenges that plague sodium-ion chemistries. Cross-linked polymers formed in situ effectively seal the interfaces, preventing continuous electrolyte decomposition and electrode corrosion. This stabilization prolongs the cycle life of the batteries, making them not only safer but also more durable—a crucial consideration for renewable energy integration where long operational lifetimes are demanded.

Another key insight from this study revolves around the fundamental relationship between electrolyte flame retardancy and overall battery safety. Previously, the assumption that a non-flammable electrolyte automatically guarantees thermal runaway prevention has been challenged by empirical results. The researchers demonstrate that flame retardancy alone is insufficient; instead, a comprehensive approach that includes interfacial engineering and dynamic polymer chemistry is essential for disrupting the chain of events leading to thermal escalation.

The implications of this work extend to the broader landscape of battery materials and design. The concept of a thermally triggered polymerization mechanism could be adapted to other battery chemistries, including lithium-ion and emerging multivalent systems. This cross-disciplinary innovation offers a blueprint for integrating responsive materials that dynamically alter their phase or chemical structure in response to thermal stress, thereby enhancing intrinsic safety profiles without resorting to bulky external protective systems.

Moreover, this electrolyte addresses the environmental and economic aspects critical to next-generation battery design. Sodium, being abundant and geographically widespread compared to lithium, offers cost and supply chain advantages essential for the scalability of energy storage technologies. By resolving safety concerns, the deployment of sodium-ion batteries equipped with such advanced electrolytes could accelerate decarbonization efforts and support grid resilience with economically viable and large-capacity storage solutions.

While the polymerizable electrolyte system excels in typical operational contexts and abuse tests like nail penetration, further investigations are underway to evaluate its performance under other challenging scenarios such as high-temperature cycling, overcharge conditions, and long-term calendar aging. Understanding the longevity and reliability of the interfacial polymer layers over extended periods will be critical to commercial translation.

The authors also highlight the potential for customizing the polymerizable components to finely tune the electrolyte’s mechanical properties and polymerization kinetics. Tailor-made chemistries could lead to optimized performance envelopes for various battery formats, including pouch cells, cylindrical cells, and even flexible or wearable energy storage devices. Such versatility amplifies the impact of this material innovation across diverse applications.

Addressing the broader context, this research aligns with the global imperative to ensure battery safety as the energy transition accelerates. Incidents involving battery fires in electric vehicles and grid systems underscore the urgency of incorporating intrinsically safe chemistries. The approach championed by Zhang et al. offers a tangible pathway to not only meet but exceed current safety benchmarks, thereby building public trust and regulatory confidence in large-scale battery technologies.

Furthermore, this work underscores the importance of integrating advanced characterization techniques and theoretical modeling in electrolyte design. Sophisticated analyses enabled the delineation of anion–cation interactions, polymerization dynamics, and interfacial phenomena, providing insights essential for engineering next-generation electrolytes. Such cross-pollination of experimental and computational science fosters innovation tailored to real-world safety challenges.

Looking ahead, this polymerizable non-flammable electrolyte could catalyze a new paradigm in energy storage safety that redefines the design ethos of rechargeable batteries. The fusion of chemical intuition and materials engineering illustrated here achieves a holistic remedy to thermal runaway without sacrificing the electrochemical performance needed for commercial viability. As a result, this breakthrough sets the stage for a safer, more sustainable energy future powered by large-scale sodium-ion storage.

In essence, the findings reported by Zhang, Zhou, Wang, and their team propel a transformative leap in battery technology, merging advanced materials design with practical engineering challenges. By solving the persistent issue of thermal runaway through innovative polymerizable electrolytes, they provide a critical breakthrough that promises to redefine standards for energy storage safety and performance globally. This development not only satisfies the stringent requirements of grid-scale applications but also inspires ongoing exploration into dynamic, self-protecting battery environments.

This pioneering work, published in Nature Energy, marks a compelling milestone in the quest for safer portable power and stationary energy storage. The amalgamation of a synergistic solvation environment, thermally triggered polymerization, and interfacial stabilization creates a robust defense against the perils of battery failure modes that have long limited widespread adoption and public acceptance of large-capacity batteries. Its impact resonates through scientific, industrial, and environmental domains, heralding a new era of confident and resilient energy storage technologies.

Subject of Research:
Polymerizable non-flammable electrolyte design to achieve thermal runaway-free sodium-ion batteries at ampere-hour scale, focusing on electrolyte chemistry, interfacial engineering, and safety performance in large-scale energy storage.

Article Title:
Thermal runaway-free ampere-hour-level Na-ion battery via polymerizable non-flammable electrolyte

Article References:
Zhang, J., Zhou, L., Wang, H. et al. Thermal runaway-free ampere-hour-level Na-ion battery via polymerizable non-flammable electrolyte. Nat Energy (2026). https://doi.org/10.1038/s41560-026-02032-7

Image Credits:
AI Generated

DOI:
https://doi.org/10.1038/s41560-026-02032-7

Keywords:
Thermal runaway, sodium-ion battery, polymerizable electrolyte, non-flammable electrolyte, electrolyte flame retardancy, electrode–electrolyte interface, energy storage safety, cross-linked polymer barrier, ion solvation, large-scale battery safety, battery abuse testing