Thorny issue plaguing lithium-ion batteries laid bare in new study

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Lithium dendrites, i.e. tiny crystalline thorns that grow off of lithium-ion battery anodes during charging, have been a persistent challenge for the world's most widely used form of energy storage. "Dendrites can penetrate the battery's separator, causing catastrophic short circuits and safety hazards," said Qing Ai, a former research scientist at Rice University who is a first author on a new study published in Science that reports for the first time exactly how these tricky structures behave inside batteries. "Despite decades of study, the fundamental nanomechanical properties of lithium dendrites remained a mystery—until now."

Most materials exhibit entirely different properties at the nanoscale than they do in bulk. Researchers suspected lithium dendrites—which measure just hundreds of nanometers in diameter and are more than a 100 times smaller than a strand of human hair—are likewise different from bulk lithium, which is soft and ductile, meaning it deforms significantly before breaking in response to physical force.

However, exact knowledge of how lithium dendrites behave in batteries was lacking. Beyond the challenge of scale, there was also the problem of access: What scientists needed to know was the behavior of lithium dendrites formed within the battery's native chemical environment, yet their mechanical properties had never been directly measured.

"Our work addresses this critical knowledge gap by directly probing the mechanical strength of individual dendrites harvested from the real battery," said Jun Lou, Rice's Karl F. Hasselmann Professor of Materials Science and Nanoengineering and co-corresponding author on the study.

To test lithium dendrites' mechanical response, Rice researchers and collaborators at the Georgia Institute of Technology, University of Houston and Institute of High Performance Computing in Singapore examined their behavior while making sure the entire process took place in a carefully engineered protective environment. Using high-resolution electron microscopy, they observed the deformation of individual dendrites under controlled stress in real time.

"This experiment was highly challenging because lithium is extremely reactive—exposure to even trace amounts of air alters its chemistry and structure," said Boyu Zhang, a Rice doctoral alum and co-first author on the study. "To enable the quantitative study of lithium dendrites, we developed customized sample preparation and mechanical characterization platforms for such delicate work."

"To perform these challenging experiments, we developed an airtight transfer box to house the in-SEM nanoindenter, with significant support from the Rice University Shared Equipment Authority (SEA)," said Hua Guo, who led the nanomechanical testing and served as a co-corresponding author.

With the help of the specialized air-free chamber and precise nanomechanical probes, the research team was able to achieve direct, individual measurements of the fragile structures. These unprecedented measurements provide important insights into how lithium dendrites respond to the physical stresses within a battery cell.

"Contrary to common assumptions, we found that lithium dendrites exhibit unexpectedly high strength and brittle behavior under mechanical stress," Lou said.

Lithium dendrites, it turns out, are rigid, microscopic structures resembling nanosized needles or whiskers. Inside the battery cell, they get enveloped in a minute layer of solid electrolyte interphase as they form. This coating enhances their structural rigidity, explaining how they can pierce separators or even stiff solid electrolytes. This same encasement prevents the dendrites' lithium core from deforming plastically; as a result, the "lithium icicles" are prone to snapping under stress, leading to the formation of isolated "dead lithium" fragments.

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The University of Houston team, led by professor Yan Yao, played a critical role in the study by performing operando SEM imaging to observe brittle fracture of lithium dendrites within operating solid-state cells.

"By seeing these dendrites snapping in real-time as the battery operates, we confirmed the brittle nature persists whether the dendrites are grown in liquid or solid electrolyte systems," said Yao, a professor in the Department of Electrical and Computer Engineering and co-corresponding author.

"This work provides a potential explanation for why certain protective layers fail to arrest lithium dendrite growth," said Xing Liu, an assistant professor at New Jersey Institute of Technology and co-first author on the study. "It is a useful mechanical framework that could help the research community develop more effective strategies for improving the safety and reliability of high-energy storage systems, including those for electric vehicles and renewable energy grids."

Publication details

Qing Ai et al, Strong and brittle lithium dendrites, Science (2026). DOI: 10.1126/science.adu9988. www.science.org/doi/10.1126/science.adu9988

Journal information: Science

Provided by Rice University