Electric cars already have comparable range to gasoline and diesel cars, but batteries have an extra problem: they degrade in time. Now, a new study led by researchers from Dalhousie University in Canada suggests there could be a better way. The researchers found that “single-crystal electrodes” could power electric vehicles (EVs) for millions of miles over decades. In other words, EV battery degradation would no longer be a practical concern.
The electrification of our transportation and energy systems depends on reliable, long-lasting batteries. In fact, batteries are one of the biggest bottlenecks slowing down this transition. Lithium-ion batteries have revolutionized energy storage, but their performance declines after years of use.
By US law, the lithium-ion batteries powering EVs on the road need to be able to hold 80% of their original full charge after 8 years in operation. Many scientists feel like that’s not enough. If batteries could last for decades, it would be a game changer not just for cars, but for our electricity use as well. Used batteries could get a second life in grid energy systems, storing wind or solar energy.
This is where single-crystal electrode batteries come in.
These batteries use materials composed of individual, large crystalline structures, while traditional batteries typically consist of aggregated polycrystalline particles. In the new study, a team led by Toby Bond assessed the durability of commercial, single-crystal batteries. The researchers found them to be much more durable than conventional batteries.
Durable, single-crystal batteries
The single-crystal battery was extensively cycled over six years, completing more than 20,000 cycles, equivalent to 8 million kilometers of EV use. After all this, it was at 80% capacity — the capacity conventional EV batteries typically reach after 2,400 cycles. After 2.5 years, the single-crystal batteries retained 96% of their capacity.
The researchers also characterized what happens inside the batteries as they suffer wear and tear in realistic conditions.
“The main focus of our research was to understand how damage and fatigue inside a battery progresses over time, and how we can prevent it,” says Toby Bond.
High-resolution computed tomography (CT) scans revealed extensive cathode microcracking in heavily cycled cells. The charging and discharging of the battery essentially force the lithium atoms in the battery material apart. This causes expansion and contraction of the material, which results in cracks. “Eventually, there were so many cracks that the electrode was essentially pulverized,” Bond says.
These cracks disrupt the electrode’s structural integrity, reducing active material and creating dead zones where lithium ions can no longer flow. Single-crystal cathodes, by comparison, exhibited far less cracking, reinforcing their potential for more durable batteries. “In our images, it looked very much like a brand-new cell. We could almost not tell the difference.”
The research also suggests that surface coatings and electrolyte additives can mitigate degradation. Alumina coatings and carefully selected additives were shown to slow the degradation. Notably, partial-depth cycling (up to 25% DoD) also reduces degradation compared to full-battery cycling, which suggests that charging the battery more often can be a good idea.
The technology already exists
The good news is that this type of battery is already here. It’s not commonly used in electric cars and its production is not scaled, but the technology does exist. This new study just described a better methodology to assess how well it works.
The researchers emphasize the importance of studying commercial cells under realistic conditions (as was done here). By using real-world commercial cells rather than lab-constructed ones, the study ensured that the results applied to actual usage conditions. While lab-built cells provide useful data, they often fail to replicate the nuanced degradation patterns seen in the field.
“I think work like this just helps underscore how reliable they are, and it should help companies that are manufacturing and using these batteries to plan for the long term,” Bond adds.
From single-crystal cathodes to optimized cycling strategies, the insights gained from this work are good news for our goal of a more sustainable, electrified world. As these findings make their way into commercial applications, the promise of more efficient and durable EV batteries comes closer to reality.
“We really need these vehicles to last as long as possible, because the longer you drive them, the better its improvement on the carbon footprint is,” says Bond.
The study “The Complex and Spatially Heterogeneous Nature of Degradation in Heavily Cycled Li-ion Cells” was published in the Journal of the Electrochemical Society.
