Tiny Molecules, Big Gains: How Ethylene Glycol Tames Water in Zinc Batteries

Aqueous zinc-ion batteries have long been hailed as a promising candidate for grid-scale energy storage, thanks to their low cost, inherent safety, and the abundance of zinc. Yet their commercial viability has been persistently undermined by a pair of stubborn problems: the growth of zinc dendrites that can pierce the separator and short the cell, and a cascade of water-induced side reactions at the zinc anode that quietly erode performance over time. Now, a team of researchers from West Anhui University, Xuzhou College of Industrial Technology, and East China University of Science and Technology has delivered a remarkably elegant answer to a deceptively simple question: which molecular features actually make an electrolyte additive work?

The study, published in the journal Ionics, is a masterclass in controlled comparison. Rather than adding yet another empirical data point to the dozens of small-molecule electrolyte additives already reported, the researchers deliberately selected three structurally analogous molecules—ethylene glycol (EG), diethylene glycol (DEG), and 1,2-dimethoxyethane (DME)—and tested them in a 2 M ZnSO4 electrolyte. This choice isolates three variables that are normally entangled: the number of hydroxyl groups, the hydrogen-bond donor and acceptor character, and the molecular size. By holding everything else constant, the team could directly rank the hydrogen-bond regulation capability of each additive and trace the molecular origin of the differences.

The results are striking. Using quantitative Gaussian deconvolution of the O–H stretching band in infrared spectroscopy, the researchers measured the fraction of strongly hydrogen-bonded O–H species in each electrolyte. In the pristine solution, that fraction stood at 66.1 percent. Adding EG dropped it to 38.6 percent, DEG to 43.8 percent, while DME barely moved the needle at 59.8 percent. This single number provides a direct, quantitative ranking of how effectively each molecule disrupts the water hydrogen-bond network—the very network that drives the parasitic chemistry at the zinc anode.

To understand why EG outperforms its cousins, the team turned to electrostatic potential analysis, a computational technique that maps the distribution of charge across a molecule’s surface. The analysis revealed a clear structural hierarchy: EG is a bifunctional hydrogen-bond donor and acceptor with the smallest steric footprint of the three, allowing it to engage water molecules from multiple directions without obstruction. DEG retains this bifunctionality but carries a larger molecular body that sterically hinders its approach to neighboring water molecules. DME, meanwhile, is an acceptor-only molecule—it can receive hydrogen bonds but cannot donate them—severely limiting its ability to reorganize the water network.

This molecular ranking propagates consistently through every measurable property of the battery. The desolvation-related activation energy, a key barrier that zinc ions must overcome before depositing on the anode, dropped from 47.0 kJ mol⁻¹ in the pristine electrolyte to just 21.2 kJ mol⁻¹ with EG. Interfacial wettability improved dramatically, with the contact angle falling from 86.1 degrees to 71.7 degrees, meaning the electrolyte spreads more evenly across the zinc surface. Side reactions were suppressed, and zinc deposition became markedly more uniform—each a direct downstream consequence of the hydrogen-bond engineering at the molecular level.

The practical payoff is extraordinary. In Zn//Zn symmetric cells operating at 1 mA cm⁻² and 1 mAh cm⁻², the EG-containing electrolyte sustained cycling for over 1,800 hours. The pristine electrolyte, by contrast, managed only about 170 hours before failing—a more than tenfold improvement in lifetime. In full cells pairing zinc with a NaVO cathode, the EG formulation delivered the highest capacity retention among all tested formulations after 500 cycles at a demanding 5 A g⁻¹ current density.

What makes this work particularly valuable for the field is its identification of practical molecular descriptors. The researchers conclude that the number of hydroxyl groups and the molecular size are the two features that most reliably predict an additive’s hydrogen-bond regulation capability. This transforms additive design from a trial-and-error exercise into a rational, structure-guided process. Chemists can now screen candidate molecules computationally, looking for small, bifunctional donor-acceptor structures with minimal steric hindrance, before ever synthesizing them.

The broader implications extend well beyond zinc batteries. The hydrogen-bond network is a fundamental organizing principle in aqueous chemistry, and the ability to quantify and rank how small molecules reshape it has relevance for supercapacitors, corrosion inhibition, and even biological systems where water structure governs reactivity. The methodology—combining spectroscopic deconvolution, electrostatic potential mapping, and controlled molecular analogs—offers a template that other researchers can adapt to their own electrolyte challenges.

For a technology that could underpin the renewable energy transition, the message is clear: sometimes the most powerful interventions are also the smallest. A few drops of a simple, inexpensive molecule like ethylene glycol, chosen not by accident but by understanding exactly how its hydroxyl groups and compact geometry reshape the water around it, can multiply the lifetime of a battery tenfold. It is a vivid reminder that in electrochemistry, as in so much of science, structure is destiny.

Subject of Research: Unraveling the structure–activity relationship of hydroxyl/ether-based molecular additives for hydrogen-bond network regulation in aqueous zinc-ion batteries

Article Title: Unraveling the structure–activity relationship of hydroxyl/ether-based molecular additives for hydrogen-bond network regulation in aqueous zinc-ion batteries

Article References: Li, P., Jiang, H., Zhu, Y., Lian, Z., Yang, M., Shen, M., Chen, X., Liu, H., & Zhang, D. (2026). Unraveling the structure–activity relationship of hydroxyl/ether-based molecular additives for hydrogen-bond network regulation in aqueous zinc-ion batteries. Ionics. https://doi.org/10.1007/s11581-026-07586-w

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07586-w

Keywords: Unraveling, structure, activity, relationship, hydroxyl, ether-based, molecular, additives, hydrogen-bond, network, regulation, aqueous