Researchers at the University of Oxford, led by Professor Paul McGonigal, have reported a new class of organic materials that challenge a long-standing assumption in materials science: that ionic conductivity drops sharply when a material solidifies. Their findings show that it is possible to design solids in which ions move just as easily as they do in liquids, opening up new design space for solid-state devices.
Barclay, J., Williamson, J. M., Litt, H., Cowling, S. J., Shimizu, K., Freitas, A. A., Poppe, S., Sturala, J., Sun, Y., Kohout, M., Avestro, A.-J., Canongia Lopes, J. N., Groves, C., Jones, J. C., & McGonigal, P. R. (2025). State-independent ionic conductivity. Science, 390(6779), 1254–1258. https://doi.org/10.1126/science.adk0786
In most electrolytes, the transition from liquid to solid locks molecules into fixed positions. This structural rigidity restricts the pathways available for ions, which is why solid electrolytes typically conduct far more poorly than their liquid counterparts. The Oxford-led team has demonstrated materials that do not follow this rule. They describe these compounds as state-independent electrolytes, meaning their ionic conductivity remains largely unchanged across liquid, liquid-crystalline, and solid phases.
University of Oxford, led by Professor Paul McGonigal stated,
“We designed our materials hoping that ions would move through the flexible, self-assembled network in an interesting way. When we tested them, we were amazed to find that the behavior is unchanged across liquid, liquid-crystal, and solid phases. It was a really spectacular result—and we were happy to find it can be repeated with a few different types of ions.”
The key lies in the molecular architecture. The researchers synthesized organic molecular ions with a flat, disk-like core surrounded by long, flexible sidechains. The positive charge on each molecule is spread across the central core rather than localized, which weakens the electrostatic attraction to the accompanying negative ions. As a result, the negative ions are not tightly bound and can move through the material with relative ease.
When these molecules solidify, they self-assemble into ordered stacks, forming rigid columns of disk-shaped cores. Around these columns, the flexible sidechains remain mobile. This combination produces an unusual structure: ordered enough to be a solid, yet dynamic enough to maintain continuous ion transport pathways. The sidechains create free volume that allows ions to migrate through the solid in much the same way they would in a liquid environment.
Experimental measurements showed that ionic conductivity remains essentially constant as the material passes through different physical states. According to the research team, this behavior was reproduced with several different ionic species, suggesting that the effect is not limited to a single chemistry. For materials scientists, this provides a concrete example of how molecular design can decouple mechanical state from transport properties.
The work was carried out in collaboration with researchers from the Universities of York, Leeds, and Durham, along with partners in Portugal, Germany, and the Czech Republic. While the study is fundamental in nature, its implications are largely practical. Solid electrolytes that retain high ionic conductivity are a central goal in the development of safer batteries, flexible sensors, and electrochromic devices. Organic materials are particularly attractive in these contexts because they are lightweight, mechanically compliant, and potentially easier to process than many inorganic alternatives.
One proposed use case involves processing the electrolyte as a liquid at a moderately elevated temperature so it can conform closely to electrodes or device structures. Once cooled, it would function as a solid without the usual penalty in ionic transport. This could simplify manufacturing while improving safety by reducing leakage and flammability concerns associated with liquid electrolytes.
The Oxford team is now working to increase the absolute conductivity of these materials and to expand the range of ions they can support. They are also beginning to test the electrolytes in prototype electronic and energy-storage devices. More broadly, the study suggests that the traditional trade-off between solid mechanical stability and high ionic mobility is not inevitable. With careful molecular engineering, solids can be designed to behave, at least in transport terms, much more like liquids.
Adrian graduated with a Masters Degree (1st Class Honours) in Chemical Engineering from Chester University along with Harris. His master’s research aimed to develop a standardadised clean water oxygenation transfer procedure to test bubble diffusers that are currently used in the wastewater industry commercial market. He has also undergone placments in both US and China primarely focused within the R&D department and is an associate member of the Institute of Chemical Engineers (IChemE).
