Dual-Site Functional Control Boosts Anode and Cathode Performance for Long-Lasting Zinc–Iodine Batteries

In the rapidly evolving landscape of sustainable energy storage, aqueous zinc-iodine (Zn-I2) batteries have emerged as a compelling alternative to conventional lithium-ion systems. Their promise lies in combining high theoretical energy density with inherent safety features attributed to aqueous electrolytes and cost-effective raw materials. Yet, despite these advantages, the pathway to widespread commercialization remains fraught with formidable challenges rooted in the electrochemical instabilities at the heart of their operation. At the core of these issues are the complex anode and cathode interface reactions threatening both performance and longevity.

Uncontrolled dendritic growth at the zinc metal anode has long been a notorious barrier, precipitating short circuits and rapid capacity degradation. This dendrite formation not only jeopardizes safety but also truncates cycle life, undermining the technology’s viability for grid-scale applications. Concomitantly, the iodine cathode grapples with the so-called shuttle effect—a process in which soluble polyiodide intermediates such as triiodide (I3⁻) and pentaiodide (I5⁻) diffuse away from the cathode, migrating to the anode and causing material loss. This shuttle mechanism fosters irreversible capacity fading and self-discharge, further complicating the energy storage profile.

Addressing this dual-edged dilemma, a pioneering study from researchers at China Three Gorges University, published in the esteemed Nano-Micro Letters journal, introduces a nuanced electrolyte engineering approach—termed “dual-site functional orchestration.” This innovative strategy hinges on a single multifunctional additive, 2-imidazolidone (ELA), architected to simultaneously mitigate the distinct but interconnected instabilities at both electrodes. The molecular elegance of ELA lies in its bifunctional nature, featuring carefully decoupled functional groups designed for targeted intervention.

Central to this approach is the carbonyl (C=O) group within ELA, which selectively coordinates with zinc ions in the electrolyte’s solvation shell. In typical aqueous environments, Zn²⁺ cations are heavily solvated by water molecules, promoting side reactions such as hydrogen evolution through water decomposition. By integrating ELA, the carbonyl oxygen replaces some water molecules around zinc ions, effectively reshaping the solvation environment. This reconfiguration raises the activation energy for water reduction, significantly suppressing the parasitic hydrogen evolution reaction (HER), stabilizing the local pH, and creating a more benign electrode interface conducive to stable zinc plating.

Complementing this molecular solvation modulation, ELA exerts control over the zinc metal’s crystallographic deposition tendencies. Zinc often deposits on high-energy planes such as (100) and (101), which foster dendritic growth due to their energetic favorability for irregular ion attachment. ELA molecules preferentially adsorb onto these reactive facets, sterically “blocking” their accessibility. Consequently, zinc ions are coerced to nucleate and grow along the more stable basal (002) plane. This guided deposition results in a compact, lamellar, and dendrite-free zinc morphology, markedly improving the anode’s safety and cycling stability.

On the cathode front, the imino (N-H) groups of ELA emerge as a chemical anchor against the notorious polyiodide shuttle. These moieties establish robust hydrogen bonding interactions with terminal iodine atoms in dissolved polyiodides. This binding forms a molecular tether that spatially confines polyiodides near the cathode interface, preventing their diffusion into the electrolyte bulk. Insights from in situ spectroscopic analyses reveal that electrolytes containing ELA maintain optical clarity and stability over extended operation, directly attesting to suppressed polyiodide dissolution and shuttle phenomena.

This controlled containment of polyiodides leads to a meaningful reduction in self-discharge—a key determinant in practical battery deployment where energy retention during idle periods is critical. By stabilizing the cathode environment, ELA mitigates active material loss and fosters sustained capacity retention across cycling. This synergistic effect between anodic stabilization and cathodic mooring underpins the enormous longevity gains reported: Zn anodes demonstrating operational lifetimes exceeding 5500 hours at current densities as high as 8 mA cm⁻², and full cells sustaining over 2500 cycles with nearly 80% capacity retention.

Notably, the dual-site functional orchestration strategy embodies a balanced electrochemical ecosystem, where reduction in water activity and suppression of parasitic reactions at the anode are intricately coupled to chemical anchoring of redox-active species at the cathode. This integrated approach outperforms conventional single-site additives or electrode modifications, providing a holistic resolution to complex interfacial challenges. The resulting electrochemical environment stabilizes both electrodes simultaneously, fostering unparalleled cycling durability and efficiency.

The implications of this research extend far beyond zinc-iodine systems. The molecular design philosophy exemplified by ELA—utilizing specific functional groups to independently yet synergistically target electrode instabilities—provides a versatile blueprint for stabilizing other multivalent metal-ion batteries. As the global energy sector intensifies its search for safer, environmentally benign, and affordable alternatives to lithium-ion batteries, such electrolyte engineering innovations stand poised to reshape the future of aqueous battery technologies.

Moreover, the scalability and cost-effectiveness of using 2-imidazolidone as an electrolyte additive offer practical advantages conducive to mass manufacturing. Its bifunctional role negates the need for multiple separate additives, simplifying electrolyte formulation. This streamlined approach not only reduces costs but also minimizes the complexity of electrolyte chemistry, enhancing the prospect of commercial adoption.

In conclusion, the dual-site functional orchestration strategy unveiled by the China Three Gorges University team represents a milestone in battery science, unlocking endurance and reliability in aqueous zinc-iodine systems through precise molecular engineering. By simultaneously modulating zinc anode deposition and confining cathodic polyiodides, this strategy overcomes two of the most pressing challenges limiting aqueous battery technology. As researchers continue to refine and expand upon these insights, the dream of ubiquitous, long-lasting, and safe aqueous batteries powering the renewable energy grid moves closer to realization.

News Publication Date: 24-Mar-2026

Web References: DOI: 10.1007/s40820-026-02144-5

Keywords

Zinc-iodine batteries, electrolyte additive, 2-imidazolidone, dendrite suppression, polyiodide shuttle, aqueous batteries, electrolyte engineering, hydrogen bonding, solvation shell modulation, battery longevity, anodic modulation, cathodic mooring