August 13, 2026 Tracer exchange reveals ions can speed up or slow down inside battery solids by Paul Dailing, University of Chicago edited by Gaby Clark, reviewed by Robert Egan Gaby Clark Scientific Editor Meet our editorial team Behind our editorial process Robert Egan Senior Editor Meet our editorial team Behind our editorial process Editors' notes This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: fact-checked peer-reviewed publication trusted source proofread The GIST Add as preferred source Solid-state ionic diffusion and crossover dynamics observed during 6Li-7Li self diffusion or Li-Na ion exchange. . DOI: 10.1038/s41467-026-73937-w Understanding how ions diffuse in solid materials is essential for technologies including batteries, electronics and chemical catalysts, but it has been hard for a simple reason: the materials are solids.
"When we think about diffusion processes in liquids, you drop ink in water and then you see how the ink will spread," said UChicago Pritzker School of Molecular Engineering (UChicago PME) associate professor Chong Liu. "There are a lot more constraints in solids than in liquid environments, so diffusion is not as well-studied." A team led by researchers at UChicago PME and Delft University of Technology (TU Delft) in the Netherlands has pioneered a new way to study coupled multi-ion and electron transport in solids, showing that the picture in solids is more complicated than previously assumed. "Those assumptions break because the self-exclusion and the cross-channel hopping are different for highly confined materials," said UChicago PME graduate and co-first author Gangbin Yan, Ph.D.'25.
"You cannot describe this just using the traditional diffusion model." The team, which included researchers from the Massachusetts Institute of Technology (MIT) and the University of Illinois at Urbana-Champaign (UIUC), created a "tracer exchange" technique similar to the isotope tracking used to follow individual atoms through chemical reactions or cellular processes. Their results were published in Nature Communications. By tracing the paths of sodium and lithium ions as they passed through solid lithium iron phosphate, they found traditional "Fickian" diffusion.
But they also found a complicated web of nanoscale confinement, structural dynamics, regions where one-dimensional channels forced ions to march in single file, regions where chemical reactions or lattice softening rushed ions down the path and other complexities previous models missed. "This work demonstrates that something as apparently well-known and described as diffusion of ions is much more intricate and can transition between different modes," said TU Delft professor Marnix Wagemaker, a co-corresponding author with Liu. "These fundamental insights as well as the methods developed to establish this represent building blocks for better understanding of these processes that are relevant for materials for electrochemical energy storage and conversion." The results establish tracer exchange as a powerful platform for studying diffusion in solids, with major applications for building new batteries, electronics or membranes to extract pollutants or valuable materials from water.
"Fundamental understanding of diffusion in highly concentrated solids can extend the ways we characterize and optimize these systems," said co-first author Pierfrancesco Ombrini, a Ph.D. candidate at TU Delft. "The methodology could distinguish between surface ionic reactions, electronic limitations and solid diffusion in an important material such as lithium iron phosphate (LFP), widely used in batteries and, more recently, in lithium extraction technologies. The same method can be used to evaluate other exchange phenomena, such as hydrogen inclusions in metals or catalysts." KMC simulations for carbon-coated 20nm_Li1.0FP particles during 6Li-7Li ion exchange.
Initially (at t = 0 min), ~7% of the storage sites contain naturally abundant 6Li. Key: 7Li ions (dark blue); 6Li ions (light green); defects (yellow). . DOI: 10.1038/s41467-026-73937-w Roads less traveled Imagine someone meandering aimlessly on a hillside, going back and forth with no destination in mind.
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