Searching for a Better Battery

Emily Ryan, a Boston University assistant professor of mechanical engineering, works with graduate student Kathy Dupre (ENG’21) on July 5, 2018. Her research focuses on how lithium batteries deteriorate and how to build stronger ones for our personal tech and green technology. Photo by Jackie Ricciardi

It’s hard not to feel let down when your smartphone’s battery begins to die on you. When new, it can last one—even two days—on a single charge, but a year or two later can barely limp through half a day without a boost. These light and efficient lithium-ion batteries are king in the world of portable technology, able to power items from your smartphone to your smart car. But they also have big shortcomings.

In January 2013, a Japan Airlines Boeing 787 Dreamliner caught fire after landing at Boston’s Logan International Airport and had to be evacuated. A National Transportation Safety Board report found that the culprit was the new fleet’s environmentally friendly lithium-ion batteries. Or more specifically, small seaweed-like deformities growing inside them.

These batteries comprise a positively charged cathode and a negatively charged anode, with a liquid electrolyte in the middle. The electrolyte transports lithium ions, which react with the electrodes to produce electrons that are transported between the electrodes through an outside circuit. While they start off strong, one major contributor to the loss in capacity of these batteries—and thus the strength and length of the charge—are small, fragile lithium dendrites that can grow within them over time. If broken, through dropping your phone for example, the battery can lose capacity, and if the dendrites continue to grow they can cause the battery to short-circuit and potentially to catch fire.

“You can think about it like a sandwich,” says Emily Ryan, a Boston University assistant professor of mechanical engineering. “You’ve got a solid and a solid with a liquid in between.”

Ryan is working on improving the next generation of lithium batteries in her Computational Energy Laboratory. She’s using computational models to find the best plan for suppressing the growth of dendrites and improving the capacity of lithium air and metal batteries.

“In particular, with lithium air batteries it’s thought that theoretically you might be able to get practical energy differences an order of magnitude greater than lithium ion,” she says. “In reality, will we get to that point? Maybe not, but if you have that much potential, it shows there’s a lot of room for growth in terms of getting higher energy density batteries.”

The graphic above shows simulation of dendrite growth on the anode surface of a lithium battery under different electrolyte properties. By suppressing dendrite growth, the battery lasts longer. Photo courtesy of Journal of the Electrochemical Society

Ryan says interest in the dendrite issue has increased significantly over the last five years as technology and research methods have advanced. Researchers have been studying the growth and possible suppression of these dendrites through experimentation at the atomic level, large-scale battery models at the macro level, and in between to gain more insight into the world of these tiny structures.

“At the last Electrochemical Society conference, everybody was talking about this problem,” she says. “It’s an active area that nobody has a good answer for yet.”

Members of her lab have been interested in this issue for several years and have published about half a dozen papers on the topic. What’s unique about their approach, she says, is that they’re using computational models to look at the problem on a mesoscale.

“We’re not looking at each atom, but small volumes of material that contain lots of atoms,” Ryan says.

To put it into perspective, imagine a colony of ants. At an equivalent to the atomic level, you can see the way a single ant’s joints move, or how its small mandibles can lift food. On the macroscale, you can maybe see where the anthill is, but any knowledge about how the ants have created it would have to be inferred, because they are far too small to see. But on the mesoscale, you can see how the ants interact with one another and cooperate to use their individual strength to move in concert to build an anthill thousands of times their size.

“At the mesoscale,” she says, “you can start to resolve an actual dendrite growing.”

One way that Ryan’s lab has done this is through the modeling of a porous material that can be theoretically constructed in the electrolyte layer of the battery to make it harder for dendrites to grow. To grow through this medium, which roughly resembles a level of Pac Man with fragments of parallel barriers, the dendrites would have to frequently twist and turn. Her lab’s research has shown that an obstacle like that could prove effective in slowing the growth and damage of dendrites.

She acknowledges that this kind of research alone won’t solve the dendrite problem, but that’s part of what makes it so rewarding. “We’re trying to add to the development of these new batteries by working with groups,” she says. “We work with people to understand the fundamentals that can then help inform their experiments, their design, or their selection of materials.”

This technology, Ryan says, could one day be used to help power electric cars or better regulate the collection and distribution of renewable energy sources like wind and solar.

“In the field, the push is toward sustainable energy. Every car on the road, every bus, every train is burning fossil fuels and producing greenhouse gases,” she says. “If you can replace the cars with electric vehicles, that could help. In the case of increasing renewables like solar and wind, you’ll want grid-level storage. At night or when there’s no wind, how are we going to get the energy? And if it’s too sunny out and we don’t need all that energy, how could we store it? So, another idea is to have better batteries for grid-level storage.”

Ryan cautions that we shouldn’t expect to see wide commercialization of these batteries anytime soon. Just as lithium-ion batteries were slow to gain popularity and acceptance in the ’80s and ’90s, these batteries will likely need a big backer interested enough in their potential to drive the research forward and introduce the product to the commercial market.

“There will be a specific application that they’re needed for, and that might start it,” she predicts. “I would guess that once you get to that point, you’ll start to have advances in the manufacturing and the cost, and that is when you will see it make its way into the market.”

Sarah Wells can be reached at swells21@bu.edu.