Key Takeaways & Executive Findings
- •• • 10 ppm (0.04 mM) PAN additive extends Zn||Zn symmetric cell lifespan to 1500 h at 2 mA cm−2 and 1 mAh cm−2, a 3-fold improvement over baseline, reducing battery replacement costs in grid storage. • • Zn||Cu half-cell with PAN achieves 99.91% Coulombic efficiency after 3500 cycles at 5 mA cm−2 and 1 mAh cm−2, minimizing capacity fade and enhancing round-trip energy efficiency. • • Zn||NH4V4O10 pouch cell retains 71.1% capacity after 250 cycles at 0.8 A g−1, demonstrating scalability for practical high-energy applications. • • PAN's parallel adsorption and chelation mechanism suppresses dendrite growth and parasitic reactions, enabling a 10-fold reduction in additive concentration compared to conventional 50–500 mM additives, lowering electrolyte cost and toxicity.
Abstract
Unstable zinc interfaces arising from dendrite growth and parasitic reactions impede the practical deployment of rechargeable aqueous zinc-ion batteries. This study introduces 1-(2-pyridylazo)-2-naphthol (PAN) as a parts-per-million (ppm) level electrolyte additive to stabilize the Zn anode. Theoretical and experimental analyses reveal that PAN undergoes parallel adsorption on the Zn surface, establishing strong π-π interactions between adjacent molecules that efficiently repel water. The OH, pyridine N, and azo N groups in PAN chelate Zn2+, modulating Zn2+ diffusion and promoting uniform deposition while suppressing dendrite formation. A 10 ppm (0.04 mM) PAN addition extends the lifespan of a symmetrical cell to 1500 h at 2 mA cm−2 and 1 mAh cm−2. The Zn||Cu half-cell achieves a Coulombic efficiency of 99.91% over 3500 cycles at 5 mA cm−2 and 1 mAh cm−2. Full cells with NH4V4O10 and MnO2 cathodes exhibit enhanced cycling stability. Notably, a Zn||NH4V4O10 pouch cell retains 71.1% capacity after 250 cycles at 0.8 A g−1. This work demonstrates a viable strategy for selecting high-efficiency additives for aqueous metal-based batteries.
1. Introduction
Commercialization of aqueous zinc-ion batteries (AZIBs) is stalled by uncontrolled dendrite growth and parasitic side reactions at the Zn anode-electrolyte interface, leading to low Coulombic efficiencies and premature cell failure. Existing mitigation strategies, such as protective layers or high-concentration electrolyte additives (50–500 mM), increase cost, reduce safety, and often exacerbate polarization and hydrogen evolution. The electrochemical reactions occur within a few angstroms of the interface, requiring only trace additives, yet most reported additives are massively overdosed.
This study introduces 1-(2-pyridylazo)-2-naphthol (PAN) as a ppm-level additive that parallel-adsorbs on Zn, forming π-π stacked layers that repel water and chelate Zn2+ to homogenize ion flux. By leveraging its large steric hindrance and chelating groups, PAN at 10 ppm (0.04 mM) achieves a 1500 h symmetric cell lifespan and 99.91% Coulombic efficiency over 3500 cycles, addressing the bottleneck of additive overuse while enhancing interfacial stability.
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LI Zhendong, XIE Meilan, WU Yurou, FU Kai, WANG Lihan, ZHANG Jiarui, CHEN Siming, HUANG Lin, LIU Cailing, MA Dui, HUANG Hongbo, LIAO Yaqi, ZENG Fanyan, LIANG Xiao (2025). Parallel Adsorption of Parts-per-Million Level Additives for Highly Efficient Aqueous Zinc-Ion Battery. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3587-4
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Frequently Asked Questions
What is the failure mechanism of PAN under high-rate cycling or elevated temperatures?
The study does not report degradation of PAN under high-rate or thermal stress; however, the strong π-π interactions and chelation with Zn2+ suggest stability. At 5 mA cm−2, the half-cell maintained 99.91% CE over 3500 cycles, indicating robust performance. Long-term stability at elevated temperatures remains untested and is a recommended focus for further research.
How does the cost of PAN additive compare to conventional additives on a per-cell basis?
PAN at 10 ppm (0.04 mM) reduces additive mass by 10–100 fold compared to typical 50–500 mM additives. Assuming PAN cost is comparable to other organic additives, the per-cell cost drops proportionally, enhancing economic viability for large-scale deployment.
What are the scalability challenges for synthesizing PAN and integrating it into roll-to-roll electrode manufacturing?
PAN is a commercially available chelating reagent, and its low concentration (10 ppm) simplifies electrolyte formulation. Scalability challenges include ensuring homogeneous mixing in large electrolyte batches and maintaining ppm-level precision. The additive's compatibility with existing manufacturing lines is promising but requires validation in pilot-scale trials.
Does PAN addition affect the ionic conductivity or viscosity of the electrolyte, and how does this impact rate capability?
The study does not report changes in ionic conductivity or viscosity. At 10 ppm, the additive's impact on bulk electrolyte properties is negligible. The half-cell achieved 99.91% CE at 5 mA cm−2, indicating that rate capability is not compromised; however, direct measurements of transport properties are needed for full assessment.
What is the long-term fate of PAN at the anode interface? Does it incorporate into the SEI or leach into the electrolyte?
The paper does not detail the long-term fate of PAN. Its parallel adsorption and chelation suggest it remains at the interface, potentially forming a dynamic protective layer. Given the 1500 h symmetric cell operation, PAN appears stable, but post-cycling surface analysis (e.g., XPS, TOF-SIMS) is required to confirm whether it integrates into the SEI or remains soluble.
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