Researchers crack why even advanced batteries for electric cars don’t last long

For years, the race to build better electric vehicle batteries has focused on boosting energy density, cutting costs, and extending range. Engineers believed they were on the right path when they moved towards next-generation materials designed to last longer and crack less. Yet many of these advanced batteries have still shown disappointing lifespans, fading capacity, and in extreme cases, safety risks. Now, researchers at the Argonne National Laboratory and the University of Chicago’s Pritzker School of Molecular Engineering believe they have finally pinpointed the hidden flaw responsible, and the answer overturns some of the most widely accepted rules of battery design.

The research paper published on December 16 in the journal Nature Nanotechnology states that at the heart of the issue is the buildup of stress inside the materials that make up a battery’s cathode, the component that stores and releases energy during charging cycles.

Incredibly small and invisible to the naked eye, such stress causes microscopic cracks over time that slowly exhaust a battery from within. What makes this discovery so important is that the failure of the battery does not happen in the way scientists long assumed, also in terms of the newer “single-crystal” battery materials that were supposed to solve the cracking problem once and for all.

Traditional lithium-ion batteries commonly use polycrystalline nickel-rich cathode materials. These are made of many tiny crystal grains packed together. Each time a battery charges and discharges, these grains slightly expand and contract. Over thousands of cycles of charging and discharging, the motion strains the boundaries between grains, causing them to fracture and form minor cracks. Once those are formed, liquid electrolyte can seep inside, causing unwanted chemical reactions, resulting in oxygen release, and a gradual loss of capacity and exhaustion of the battery.

To avoid this, researchers shifted toward single-crystal cathodes. Unlike their polycrystalline counterparts, single-crystal materials lack internal grain boundaries. In theory, that meant fewer weak points and a much longer lifespan. In practice, however, the results were inconsistent. Some single-crystal batteries degraded faster than expected, puzzling engineers who believed they had already solved the mechanical problem.

The new research shows that the mistake was not the material itself but the assumptions used to design it.

In polycrystalline cathodes, damage accumulates between grains. In single-crystal cathodes, the degradation happens inside the crystal itself. Cutting-edge imaging techniques revealed that chemical reactions during charging do not proceed evenly across a single particle. Some regions react faster than others, leading to uneven expansion and contraction within the same crystal.

That internal mismatch generates stress strong enough to cause cracking, even though there are no grain boundaries involved. This subtle failure mode had largely been overlooked because engineers were still applying design rules developed for older, polycrystalline materials.

The discovery explains why single-crystal batteries sometimes fell short of expectations: they were being optimised for the wrong kind of problem.

One of the most striking findings involves how different metals affect durability. Battery cathodes typically rely on a balance of nickel, manganese, and cobalt. In conventional designs, cobalt has long been associated with cracking risk, even though it helps control other structural issues. Manganese, by contrast, is usually considered helpful and affordable.

When the same logic was applied to single-crystal materials, it produced the opposite result.

By testing experimental cathodes with different compositions, researchers found that manganese actually increased mechanical damage in single-crystal structures. Cobalt, once seen as a liability, improved durability and extended battery life by reducing the uneven internal stresses that lead to cracking.

In other words, elements thought to be harmful turned out to be protective depending entirely on how the crystal is built.

Cracking inside battery materials is not just a performance issue, but when the fractures grow large enough, they allow electrolytes to penetrate deeper into the cathode, which accelerates chemical degradation and raises the risk of overheating. Even without sudden huge failures, the slow loss of structural integrity reduces range and forces earlier battery replacement.

For electric vehicles to gain wider trust, batteries must be both safe and long-lasting. Consumers are far less likely to embrace electrification if they worry about rapid degradation or rare but serious failures. By identifying the real degradation pathway in single-crystal cathodes, this research provides a clearer path toward batteries that age more predictably and safely.

The findings do more than explain why earlier designs underperformed—they also point the way forward. Single-crystal batteries cannot reach their best performance by copying material recipes from older technologies; instead, their makeup must be tailored to the unique stresses they experience, even if that means rethinking which elements should be used in the cathode. Although cobalt still delivers useful stability, its high cost is driving efforts to find more affordable alternatives, guided by a much deeper understanding of how internal stresses form and spread at the microscopic level.

Advancements in battery technology seldom occur in a straight path. Solutions frequently uncover additional issues, which subsequently propel the next surge of innovation. By revealing this concealed issue, researchers have now removed one of the major barriers to creating safer, more durable electric vehicle batteries, and in the process, they have altered key principles that dictate how future energy storage systems will be developed.