Researchers at Argonne National Laboratory and the UChicago Pritzker School of Molecular Engineering (UChicago PME) have identified the source of a long-standing battery problem linked to fading capacity, shorter lifespans, and in some cases fires. The findings clarify why certain advanced lithium ion batteries break down faster than expected and how those failures might be reduced.
The work, published in Nature Nanotechnology, explains how extremely small internal stresses can build up inside battery materials and trigger cracking. These effects are especially important for batteries used in electric vehicles and other high demand technologies, where durability and safety are critical.
“Electrification of society needs everyone’s contribution,” said one of the corresponding authors Khalil Amine, Argonne Distinguished Fellow and Joint Professor at UChicago, “If people don’t trust batteries to be safe and long-lasting, they won’t choose to use them.”
Why New Battery Materials Fell Short
For years, engineers have struggled with cracking in lithium ion batteries that use polycrystalline nickel rich materials (PC-NMC) in their cathodes. These materials are made of many tiny crystal grains packed together, and repeated charging and discharging can cause them to fracture. To avoid this issue, researchers began shifting toward single-crystal nickel rich layered oxides (SC-NMC), which lack those internal grain boundaries.
Despite the promise, single-crystal cathodes did not always perform as well as expected. The new study explains why. The research was led by Jing Wang during her PhD work at UChicago PME through the GRC program, under the joint supervision of Prof. Shirley Meng’s Laboratory for Energy Storage and Conversion and Amine’s Advanced Battery Technology team.
The team found that design rules developed for polycrystalline cathodes were being incorrectly applied to single-crystal materials. That mismatch, they discovered, was at the heart of the performance problems.
Through the GRC program and UChicago’s Energy Transition Network, Wang collaborated closely with national laboratory scientists and industry partners to push the research forward.
“When people try to transition to single-crystal cathodes, they have been following similar design principles as the polycrystal ones,” said Wang, now a postdoctoral researcher working with UChicago and Argonne. “Our work identifies that the major degradation mechanism of the single-crystal particles is different from the polycrystal ones, which leads to the different composition requirements.”
Rethinking Battery Design and Materials
The findings challenge both traditional battery design strategies and assumptions about which elements help or hurt performance. In particular, the study reshapes the understanding of how cobalt and manganese influence mechanical failure inside batteries.
“Not only are new design strategies needed, different materials will also be required to help single-crystal cathode batteries reach their full potential,” said Meng, who also directs the Energy Storage Research Alliance (ESRA) at Argonne. “By better understanding how different types of cathode materials degrade, we can help design a suite of high-functioning cathode materials for the world’s energy needs.”
How Cracks Form in Battery Cathodes
In polycrystalline cathodes, charging and discharging causes the stacked particles to repeatedly expand and contract. Over time, this motion can widen the boundaries between grains, much like how cycles of freezing and thawing damage road surfaces.
“Typically, it will suffer about five to 10% volume expansion or shrinkages,” Wang said. “Once an expansion or shrinkage exceeds the elastic limits, it will lead to the particle cracking.”
When cracks grow large enough, liquid electrolyte can seep inside. This can trigger unwanted chemical reactions and oxygen release, raising safety risks including thermal runaway. Even without dramatic failures, the gradual result is capacity loss, as batteries slowly lose their ability to hold the same amount of charge.
Single-crystal cathodes do not contain grain boundaries, so researchers initially expected them to avoid these problems. Instead, they found that degradation still occurred, but for a different reason.
A Different Failure Mode Inside Single Crystals
The Argonne and UChicago PME team showed that damage in single-crystal NMC cathodes follows a distinct mechanical failure process.
“We demonstrate that degradation in single-crystal NMC cathodes is predominantly governed by a distinct mechanical failure mode,” said another corresponding author, Tongchao Liu, a chemist at Argonne. “By identifying this previously underappreciated mechanism, this work establishes a direct link between material composition and degradation pathways, providing deeper insight into the origins of performance decay in these materials.”
Using multi-scale synchrotron X ray techniques and a high-resolution transmission electron microscope, the researchers observed that reactions inside single-crystal particles do not occur evenly. Different regions react at different speeds, creating internal stress within a single particle rather than stress between multiple grains.
Opposite Material Needs for Single-Crystal Batteries
In polycrystalline cathodes, engineers carefully balance nickel, manganese, and cobalt. Cobalt tends to promote cracking, but it also helps reduce a separate issue known as Li/Ni disorder.
To test how this balance changes in single-crystal materials, the team built and evaluated two experimental designs. One used nickel and cobalt with no manganese, while the other used nickel and manganese with no cobalt. The results flipped conventional thinking. In single-crystal cathodes, manganese caused more mechanical damage, while cobalt actually improved durability and extended battery life.
Cobalt remains costly compared with nickel and manganese. Wang said the next challenge is identifying more affordable materials that can deliver the same benefits cobalt provides.
“Advances come in cycles,” Amine said. “You solve a problem, then move on to the next. The insights outlined in this collaborative paper will help future researchers at Argonne, UChicago PME and elsewhere create safer, longer-lasting materials for tomorrow’s batteries.”
