A collaborative research effort has cracked a fundamental mystery plaguing a promising next-generation battery material, revealing why so-called “single-crystal” cathodes often fail to live up to their theoretical potential and pointing toward new design principles for longer-lasting, safer batteries.
The study, published in Nature Nanotechnology by scientists from the UChicago Pritzker School of Molecular Engineering (PME) and Argonne National Laboratory, directly addresses concerns over battery lifespan and safety that are critical for consumer confidence in electric vehicles and the broader electrification of society.
“If people don’t trust batteries to be safe and long-lasting, they won’t choose to use them,” said corresponding author Khalil Amine, an Argonne Distinguished Fellow and UChicago professor.
For years, lithium-ion batteries using cathodes made from “polycrystalline” nickel-rich materials (PC-NMC)—clusters of many tiny crystals—have been prone to cracking. As these batteries charge and discharge, the individual crystals swell and shrink, stressing and eventually fracturing the boundaries between them. This degradation leads to capacity fade and, in severe cases, can allow dangerous side reactions and thermal runaway.
To solve this, researchers turned to cathodes made of “single-crystal” nickel-rich oxides (SC-NMC)—solid, unified particles without vulnerable internal boundaries. However, their performance has been inconsistent. The new research reveals the critical error: engineers were applying old design rules to a fundamentally new material.
“When people try to transition to single-crystal cathodes, they have been following similar design principles as the polycrystal ones,” explained first author Jing Wang, who conducted the work during her PhD at UChicago PME. “Our work identifies that the major degradation mechanism of the single-crystal particles is different.”
Using advanced synchrotron X-ray and electron microscopy techniques, the team discovered that cracking in single crystals is not caused by crystal-boundary stress. Instead, it is driven by “reaction heterogeneity”—where different parts of a single particle react at different rates, creating internal strain that eventually causes it to fracture from the inside out.
“We demonstrate that degradation in single-crystal NMC cathodes is predominantly governed by a distinct mechanical failure mode,” said corresponding author Tongchao Liu, a chemist at Argonne.
This new understanding forced a re-evaluation of the essential cathode materials themselves: nickel, manganese, and cobalt. In polycrystalline designs, cobalt, while expensive, is necessary to mitigate structural disorder. The team found that for single crystals, the roles reverse. In their experiments, a cobalt-free, nickel-manganese single-crystal cathode degraded quickly, while a nickel-cobalt version (with no manganese) performed far better, with manganese being more mechanically detrimental in this architecture.
“Not only are new design strategies needed, different materials will also be required,” said Prof. Shirley Meng, who co-supervised the research and directs the Energy Storage Research Alliance at Argonne.
The findings reset the roadmap for developing superior batteries. The immediate next challenge is to find less expensive alternatives that can replicate cobalt’s beneficial stabilizing effect in single-crystal systems.
“Advances come in cycles,” said Amine. “The insights outlined in this collaborative paper will help future researchers… create safer, longer-lasting materials for tomorrow’s batteries.”
By moving beyond outdated assumptions, the research provides a clear scientific foundation for engineering the robust, high-performance battery cathodes required for a sustainable energy future.
