Batteries naturally lose their ability to hold a charge over time, which is why older phones run out of power faster. While this is a common issue, the reasons behind it have not been fully understood—until now.
An international team of researchers, led by an engineer from the University of Colorado Boulder, has uncovered the root cause of this battery degradation. Their discovery could lead to the creation of better batteries, allowing electric vehicles (EVs) to drive farther and last longer, while also improving energy storage systems essential for the transition to clean energy.
The research, published in *Science* on September 12, reveals insights that could reshape battery technology. Michael Toney, the lead author and a professor of Chemical and Biological Engineering, explained, “Our work advances lithium-ion batteries by pinpointing the molecular-level processes responsible for their degradation.” Better batteries, he stressed, are critical for moving away from fossil fuels and toward renewable energy sources.
For years, engineers have been working to develop lithium-ion batteries—the most common rechargeable batteries—without cobalt. Cobalt is a costly and rare material, and its mining, particularly in the Democratic Republic of Congo, raises serious environmental and human rights concerns. Many of these miners are children, making the need to find alternatives even more pressing.
Researchers have experimented with other materials like nickel and magnesium to replace cobalt in batteries. However, these alternatives often lead to higher self-discharge rates—when a battery loses energy due to internal chemical reactions, causing its capacity to degrade faster. This problem limits the lifespan of most EV batteries to about seven to ten years before they need replacing.
Toney, who is also a fellow of the Renewable and Sustainable Energy Institute, and his team set out to find the cause of this self-discharge. In a typical lithium-ion battery, lithium ions move between the anode and cathode, generating the electric current that powers devices. Charging the battery sends the ions back to the anode.
Previously, scientists believed that not all lithium ions returned to the anode during charging, which reduced the battery’s capacity. However, using advanced X-ray technology at the U.S. Department of Energy’s Argonne National Laboratory, Toney’s team discovered that hydrogen molecules from the battery’s electrolyte were moving to the cathode. These hydrogen molecules took up spots normally reserved for lithium ions, reducing the battery’s ability to hold a charge and weakening its overall performance.
In the U.S., transportation is the largest source of greenhouse gas emissions, accounting for 28% of the country’s output in 2021. As automakers push to reduce emissions by moving from gasoline-powered vehicles to electric ones, challenges like limited driving range, high production costs, and short battery life remain. Most electric cars in the U.S. can travel about 250 miles on a single charge, which is just 60% of what gasoline cars can manage.
Toney believes this new discovery could address these challenges. “Consumers want EVs with a long driving range,” he said. “Low-cobalt batteries could help, but we need to make sure they don’t degrade too quickly.” Reducing cobalt content also helps lower costs and addresses ethical concerns tied to cobalt mining.
Now that researchers understand how self-discharge happens, they can develop solutions to prevent it, such as coating the cathode to block hydrogen or using different electrolytes. “This knowledge allows us to guide the battery chemistry community on what improvements are needed,” Toney concluded.
With this breakthrough, the future of EVs and energy storage could soon look brighter, paving the way for more sustainable and efficient technologies.
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