A reserach team led by Professor Huang Zhang at Harbin University of Science and Technology recently made significant progress in the research of zinc-iodine aqueous batteries. They proposed an electrolyte additive strategy based on tetramethylammonium iodide (TMAI), which, through the synergistic effect of anions (I-) and cations (TMA+), simultaneously solved three core challenges in zinc-iodine batteries: sluggish iodine reaction kinetics, polyiodide shuttle effect, and zinc dendrite growth. This research not only achieved ultra-long cycle stability of over 5500 hours for symmetric zinc batteries, but also demonstrated excellent performance with almost no capacity decay after 50,000 cycles in the full cell, providing a new approach for the design of high-performance, long-life aqueous zinc-iodine batteries. The article was published as an open access Research Article in CCS Chemistry, the flagship journal of the Chinese Chemical Society.
Background information:
With the global energy structure transitioning towards renewable energy, the development of low-cost, high-safety, and easily scalable energy storage systems has become an urgent need. Aqueous zinc batteries have attracted much attention due to their abundant resources, low cost, and high safety. Among them, zinc-iodine batteries, with their high theoretical capacity (211 mAh g⁻¹) and abundant reserves of iodine , are considered to be a highly promising energy storage system. However, their practical application still faces multiple challenges: the iodine cathode has poor conductivity and slow reaction kinetics, and easily forms soluble polyiodides (such as I³⁻ and I⁵⁻ ) , leading to loss of active material and capacity decay; the zinc anode suffers from dendrite growth and hydrogen evolution side reactions, which seriously affect cycle life; polyiodide shuttle further exacerbates the side reactions of the positive and negative electrodes, resulting in decreased battery efficiency and severe self-discharge. Traditional improvement strategies mostly focus on cathode modification, separator optimization, or single interface regulation, which cannot solve the above problems simultaneously. Therefore, developing an electrolyte additive that can synergistically regulate the interface chemistry of the positive and negative electrodes, improve reaction kinetics, and suppress side reactions has become the key to promoting the practical application of zinc-iodine batteries.
Highlights of this article:
Highlight 1: Core Strategy – "Collaboration" rather than "Individual Combat"
Traditional additive design often focuses on solving a single problem, such as improving kinetics or inhibiting shuttle operation, which can easily lead to unintended consequences. The core innovation of this work lies in utilizing the anion (I-) dissociated from the compound TMAI. Together with cations (TMA+), they play key roles and produce synergistic effects at the positive and negative electrode interfaces, respectively. This "killing two birds with one stone" or even "killing three birds with one stone" design concept breaks through the limitations of single-component functions and achieves multi-target synergistic regulation of complex battery systems through the intrinsic functional complementarity between ions.
Highlight 2: Overcoming the challenges of the cathode – Constructing a new "solid-liquid-solid" iodine conversion pathway
To address the issues of slow iodine cathode reactions and loss of active materials, the research team revealed a unique TMAI-induced solid-liquid-solid conversion mechanism. I⁻ acts as a catalyst, accelerating the conversion of solid I₂ into soluble I₃⁻, significantly improving reaction kinetics. Simultaneously, TMA⁺ acts as a trapping agent, rapidly combining with I₃⁻ to form an insoluble TMA-I₃ solid complex, firmly anchoring it in the cathode region. This process ensures both rapid iodine reaction and fundamentally blocks the dissolution and shuttle pathways of polyiodides, thus achieving a balance between high capacity and high coulombic efficiency.
Highlight 3: Stabilizing the Zinc Anode – Establishing a Dual Protection System of "Electrostatic Shielding + Interface Regulation"
On the zinc anode side, the two ions in TMAI also play a synergistic protective role. TMA+ tends to adsorb at the initial protrusions of zinc deposition, forming a positively charged "electrostatic shielding layer," driving subsequent Zn2+ to deposit uniformly into the depressions and suppressing dendrite nucleation from an electric field perspective. Meanwhile, I- can specifically adsorb on the zinc surface, lowering the zinc deposition nucleation barrier and leading to the growth of a dense, flat zinc deposition layer. Together, they construct a stable double protective layer at the anode interface, significantly improving the reversibility of zinc deposition/stripping.
Highlight 4: Performance Breakthrough – Achieving Ultra-High Stability and Ultra-Long Cycling
Thanks to the aforementioned synergistic mechanism, the battery's overall performance has achieved a breakthrough. In rigorous electrochemical tests, the battery using TMAI electrolyte demonstrated comprehensive superiority: not only did it possess a polarization voltage as low as 90 mV and a high energy efficiency of 92.8%, but its cycle stability also reached new heights. The Zn||Zn symmetric battery achieved a cycle life exceeding 5500 hours, far surpassing the benchmark electrolyte (120 hours). After 50,000 cycles at a high rate of 5 A g⁻¹ , the Zn||I₂ full cell maintained nearly 100% capacity retention, with an average coulombic efficiency as high as 99.95%. Furthermore, the battery's self-discharge rate was significantly reduced, and it also exhibited excellent stable cycling capabilities in a simplified "electrode-less" configuration, demonstrating the powerful practical potential of this strategy.
Summary and Outlook:
This research successfully overcomes the traditionally difficult-to-achieve performance challenges of zinc-iodine batteries in terms of kinetics, shuttle effect, and zinc anode stability through a simple and efficient anion-cation synergistic electrolyte additive strategy, breaking the long-standing " performance triangle " dilemma. This work not only reports a high-performance battery system, but more importantly, provides a universal new approach to electrolyte design: achieving precise control of complex electrochemical interfaces through the synergistic combination of multifunctional ionic components. This concept is expected to be extended to the design of other metal - halogen batteries and even broader energy storage systems, driving the development of next-generation safe and long-life energy storage technologies.
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About the journal: CCS Chemistry is the Chinese Chemical Society's flagship publication, established to serve as the preeminent international chemistry journal published in China. It is an English language journal that covers all areas of chemistry and the chemical sciences, including groundbreaking concepts, mechanisms, methods, materials, reactions, and applications. All articles are diamond open access, with no fees for authors or readers. More information can be found at https://www.chinesechemsoc.org/journal/ccschem .
About the Chinese Chemical Society: The Chinese Chemical Society (CCS) is an academic organization formed by Chinese chemists of their own accord with the purpose of uniting Chinese chemists at home and abroad to promote the development of chemistry in China. The CCS was founded during a meeting of preeminent chemists in Nanjing on August 4, 1932. It currently has more than 120,000 individual members and 184 organizational members. There are 7 Divisions covering the major areas of chemistry: physical, inorganic, organic, polymer, analytical, applied and chemical education, as well as 31 Commissions, including catalysis, computational chemistry, photochemistry, electrochemistry, organic solid chemistry, environmental chemistry, and many other sub-fields of the chemical sciences. The CCS also has 10 committees, including the Woman's Chemists Committee and Young Chemists Committee. More information can be found at https://www.chinesechemsoc.org/ .
