In a groundbreaking advance that promises to reshape the future of energy storage, a research team led by Professor Huang Zhang at Harbin University of Science and Technology has unveiled a novel electrolyte additive strategy for aqueous zinc-iodine batteries. This innovative approach harnesses the synergistic interplay between anions and cations derived from tetramethylammonium iodide (TMAI) to simultaneously address three of the most persistent challenges plaguing zinc-iodine battery technology: sluggish iodine reaction kinetics, the polyiodide shuttle effect, and zinc dendrite formation. Their work not only surmounts these obstacles but also establishes a new paradigm for electrolyte design, achieving ultra-long cycle life exceeding 5500 hours in symmetric zinc cells and demonstrating near-perfect capacity retention after 50,000 cycles in full cells.
Zinc-iodine batteries have long been hailed for their theoretical promise, boasting a high specific capacity of 211 mAh g⁻¹ and leveraging iodine’s abundant availability. These attributes position them as a front-runner for safe, cost-effective, and scalable energy storage solutions crucial for integrating renewable energy sources. However, their practical deployment has been hampered by intrinsic material and electrochemical limitations. The iodine cathode, despite its high capacity, suffers from inherently poor electronic conductivity and sluggish redox kinetics. This leads to the formation of soluble polyiodides—intermediates like I₃⁻ and I₅⁻—which dissolve into the electrolyte, migrate between electrodes, and degrade cell performance through a phenomenon known as the shuttle effect. Concurrently, the zinc anode is vulnerable to dendritic growth and parasitic hydrogen evolution reactions, which compromise cycle life and safety. The complex interplay between these factors has rendered traditional single-faceted improvements insufficient.
The ingenious breakthrough in this work lies in the deliberate exploitation of the dual ionic components of TMAI—tetramethylammonium cations (TMA⁺) and iodide anions (I⁻)—to enact complementary and mutually reinforcing functions at both the cathode and anode interfaces. Rather than treating each challenge in isolation, the team embraced a holistic “collaboration” strategy that transforms these ions into multifunctional agents, unlocking synergistic mechanisms that simultaneously enhance reaction kinetics, suppress deleterious shuttle processes, and stabilize zinc plating behavior. This conceptually transformative approach encapsulates a shift from piecemeal additive use to integrated interface engineering through ionic synergy.
At the cathode, this additive orchestrates a novel solid-liquid-solid iodine conversion arc. Traditionally, iodine reduction suffers from slow solid-state I₂ to I₃⁻ conversion kinetics. The iodide anion acts as a catalytic species, accelerating the dissolution of solid iodine into soluble triiodide ions, effectively bypassing kinetic bottlenecks. Meanwhile, the cation TMA⁺ promptly complexes with I₃⁻, precipitating as an insoluble TMA-I₃ solid that remains anchored in the cathode region. This engineered immobilization not only halts polyiodide dissolution and diffusion across the electrolyte—thereby quashing the shuttle effect—but also maintains the electrochemical activity of iodine species, balancing capacity retention with coulombic efficiency. This refined “solid-liquid-solid” reaction pathway represents a meticulous orchestration of phase transformations underpinning superior cathode performance.
On the opposing anode side, the TMAI additive extends its protection via a sophisticated dual-layer passivation schema. Positively charged TMA⁺ cations preferentially adsorb on nascent zinc protrusions, forming an electrostatic shield that modulates local electric fields. This shields active sites from uneven Zn²⁺ deposition, steering ion flux toward more uniform plating in micro-scale valleys, thereby impeding the initiation and propagation of zinc dendrites—primary causes of cell failure and short-circuiting. Complementing this, iodide anions adsorb distinctly onto zinc surfaces, effectively lowering the nucleation barrier for zinc deposition. This facilitates the growth of a dense, flat, and compact zinc layer. Together, these mechanisms synergistically construct a robust, self-regulating double protective interphase that enhances the reversibility and safety of zinc plating and stripping processes.
The culmination of these multi-faceted advancements manifests in remarkable electrochemical performance metrics. Cells incorporating the TMAI additive exhibit remarkably low polarization voltages—approximately 90 millivolts—reflecting rapid reaction kinetics and minimized overpotentials. Energy efficiency peaks near 92.8%, indicative of lower intrinsic losses during charge-discharge cycling. Most strikingly, the symmetric Zn||Zn cells demonstrate unprecedented cycling lifespans surpassing 5500 hours, vastly exceeding conventional electrolytes which typically sustain only around 120 hours under similar testing conditions. In full Zn||I₂ configurations, capacity retention nears 100% after an extraordinary 50,000 cycles at a formidable rate of 5 A g⁻¹. The average coulombic efficiency stabilizes at an astounding 99.95%, underscoring the efficacy of shuttle suppression and surface stabilization schemes. The self-discharge behavior is also markedly attenuated, reflecting the electrolyte’s ability to preserve stored charge over extended periods.
Adding another dimension to the practical viability of the approach, the team tested their system in simplified configurations devoid of traditional electrodes—so-called “electrode-less” cells—still achieving stable and efficient cycling. This suggests the strategy’s broader applicability and robustness, with potential for diverse architectural adaptations in next-generation battery systems. The facile, one-step additive introduction to the aqueous electrolyte further enhances scalability prospects, while avoiding the complexity and cost of extensive electrode material modifications commonly employed in prior efforts.
The conceptual innovation in this research transcends the immediate zinc-iodine system, offering a blueprint for exploiting multifunctional ion pairs to fine-tune and harmonize interface chemistry in complex electrochemical energy devices. By harnessing intrinsic ionic complementarity and their distinct adsorption behaviors, it becomes feasible to orchestrate multi-target advances—including kinetic acceleration, shuttle suppression, and dendrite inhibition—simultaneously. This integrative strategy may well be broadly translatable to other metal-halogen couples, such as zinc-bromine or metal-sulfur chemistries, catalyzing a new generation of scalable, durable, and high-performance aqueous batteries.
From a broader energy landscape perspective, the importance of safe, affordable, and environmentally benign energy storage solutions is escalating as renewable energy sources proliferate globally. Zinc-based aqueous batteries, exemplified by the newly optimized zinc-iodine system, are emerging as front-runners in fulfilling grid-scale and decentralized energy buffering roles. Their use of earth-abundant, non-toxic materials mitigates supply risks and environmental concerns inherent to lithium-ion technologies, positioning them as sustainable alternatives. The present electrolyte design paradigm—centered on ionic synergy—addresses fundamental electrochemical constraints that have historically limited aqueous zinc battery commercialization, ushering in renewed optimism for their wide-scale deployment.
This work also reinforces the critical, sometimes underestimated role of electrolyte chemistry in governing battery performance. While electrode materials often receive primary attention, the electrolyte and its additives wield profound influence on interfacial reactions, ion transport pathways, and degradation mechanisms. Strategic molecular engineering of electrolyte constituents, especially through multifunctional ion pairs, stands as a powerful tool for tuning battery interface properties and kinetics. Moving forward, continued exploration of synergistic ion interactions may unlock further transformative breakthroughs, potentially enabling aqueous batteries with unmatched energy densities, cycle lives, and safety profiles.
Published as an open access article in CCS Chemistry—the flagship journal of the Chinese Chemical Society—this study exemplifies international scientific collaboration and dissemination aimed at addressing global energy challenges. The reported findings are poised to stimulate extensive interdisciplinary research spanning electrochemistry, materials science, and chemical engineering, accelerating innovation toward safer and longer-lasting energy storage solutions. As renewable energy integration intensifies and electrification expands, such advancements could play a pivotal role in achieving low-carbon, sustainable energy futures worldwide.
In summary, the research led by Professor Huang Zhang deftly solves the notorious “performance triangle” problem of zinc-iodine batteries through a simple yet elegant synergistic anion-cation additive approach. By fundamentally reengineering electrode interfaces via multifunctional ion complementarity, they have achieved a rare trifecta: dramatically improved reaction kinetics, effective shuttle suppression, and robust anode protection. This milestone inspires a fresh vision for electrolyte design and battery architecture, signaling a new era where complex electrochemical interfaces are precisely controlled through cooperative ionic chemistry. The ripple effects of this work will undoubtedly resonate deeply across the evolving energy storage landscape, catalyzing safer, more efficient, and more sustainable battery technologies worldwide.
Subject of Research: Not applicable
Article Title: Synergistic Anion-Cation Pair Additive Unites Shuttle-Suppressed and Kinetics-Accelerated I2 Chemistry for Aqueous Zn Batteries
News Publication Date: 7-Jan-2026
Web References:
https://www.chinesechemsoc.org/journal/ccschem
http://dx.doi.org/10.31635/ccschem.025.202506944
Image Credits: CCS Chemistry
Keywords
Batteries, Electrochemistry, Zinc-Iodine Batteries, Electrolyte Additives, Ion Synergy, Energy Storage, Aqueous Zinc Batteries, Polyiodide Shuttle Suppression, Zinc Dendrite Inhibition, Electrochemical Interfaces, Reaction Kinetics, Sustainable Batteries
Tags: aqueous zinc-iodine batterieselectrolyte additive strategieshigh capacity zinc batteriesiodine reaction kinetics improvementpolyiodide shuttle suppressionrenewable energy storage solutionsscalable energy storage technologiessynergistic anion-cation additivestetramethylammonium iodide electrolyteultra-long cycle life batterieszinc dendrite preventionzinc-iodine battery technology
