From laptops to smartphones to the burgeoning electric car industry, our world is increasingly reliant on rechargeable batteries. But as anyone who’s owned a laptop for more than a few years knows, batteries eventually lose their ability to hold a full charge. Scientists never really understood why this happens, which has made it a hard problem to fix. But according to a pair of recent studies by researchers from the U.S. Department of Energy, published in the journal Nature Communications, we may be closer than ever to a battery that doesn’t degrade.
Working specifically with lithium-ion batteries, commonly used in consumer devices because of their light weight and high capacity, the scientists have mapped the charge and discharge process down to billionths of a meter to better understand exactly how degradation works. They discovered two culprits in battery degradation.
The first: microscopic vulnerabilities in the structure of the battery material steer the lithium ions haphazardly through the cell, eroding the battery in seemingly random ways, much like rust spreads across imperfections in steel.
In the second study, focused on finding the best balance between voltage, storage capacity and maximum charge cycles, researchers not only found similar issues with the ion flow, but also tiny accumulations of nano-scale crystals left behind by chemical reactions, which cause the flow of ions to become even more irregular after each charge. Running batteries at higher voltages also led to more ion path irregularities, and thus a more rapidly deteriorating battery.
It may seem like scientists should have fully understood the battery—a technology that's effectively been around since 1800—decades ago. But Huolin Xin, a materials scientist at Brookhaven Lab and coauthor on both studies, says the winning combination of new technologies only recently became available.
“Many state-of-the-art characterization tools, such as aberration-corrected electron microscopes and new synchrotron X-ray techniques, were not available 10 years ago,” Xin says. But now, he says, they can be applied to the study of lithium-ion batteries.
The new data gives researchers a clearer picture of the how these batteries work, which could lead to longer-lasting batteries in consumer electronics in the not-too-distant future. But, it also presents new problems. Xin says maximizing surface area is important to battery performance, but a larger surface area also likely facilitates degradation.
“To prevent [surface degradation], we can either coat the cathode with a protection layer,” Xin says, “or hide these surfaces by creating boundaries within the micron-sized powders [inside the cell].”
Finding the most efficient, cost-effective ways to do this will be part of a future phase of the research. But Daniel Abraham, a scientist focused on lithium-ion battery research at the Argonne National Laboratory outside Chicago, is skeptical that the new studies represent a real breakthrough. He says mapping work with similar materials has been done in the past, including by his team about 12 years ago. He also believes there may be more to battery degradation than what the new studies have found.
“They’re trying to make a correlation between performance degradation and the pictures that they see, which may not be correct,” Abraham says. “It’s partially the story, but I don’t think it’s the entire story.”
Xin, is more optimistic that the work will lead to battery improvements, not only for future electric vehicles, but for portable electronics as well.
“Lithium-nickel-manganese-cobalt-oxide cathode has recently been identified as the only commercially viable material for next-generation lithium-ion batteries,” Xin says. “By resolving its degradation problem, we can make next-generation batteries smaller and make them charge and discharge more reliably.” The two battery experts do agree though, that for many important future applications, finding a way to make batteries that don't wear out as quickly is just as important as creating batteries that have a greater capacity.
Xin points out that electric car buyers justifiably worry about battery failure after their warranty expires. Abraham notes that while you likely only need a couple of years of performance from your smartphone or tablet battery, for electric vehicles, most owners are looking for a battery that lasts 10 to 15 years. And for use in the electric grid (to store excess energy produced on off-peak hours), batteries should last 30 years or more. That makes building a better battery for your laptop a lot easier than solving longevity problems in other areas.
“It’s good to have a higher energy density, but if you get a high energy density but not a long life, then the commercial viability of those technologies comes into question,” Abraham says. “Whereas, if you can show that you have a new technology and it can last between two and 30 years, that becomes immediately viable commercially.”
While the work of Xin and his colleagues may help researchers create batteries that don’t degrade as quickly, it’s clear that further breakthroughs will be necessary before we’ll see rechargeable batteries that last a decade or more without serious wear.