Building a better battery

In the last few decades, electric cars have gone from a curiosity in the auto market to a powerhouse that is sending shockwaves throughout the industry. In the U.S., sales spiked by two-thirds in 2022 with more than 807,000 cars purchased, according to a Wall Street Journal report.

Electric vehicles accounted for 5.6% of new car and light truck registrations in the U.S. last year, a significant increase from 3.1% in 2021.

The lithium batteries currently used in electric vehicles allow drivers to travel hundreds of miles on a single charge. While their energy storage capacity is well known, they also gained a reputation for periodically catching on fire, which is known as “thermal runaway.”

The increase of electric vehicles on the roads has driven the need for new innovations in battery technology to prevent – or at least reduce – thermal runaways. One leader in this charge is Professor Reza Shahbazian-Yassar, of mechanical and industrial engineering at UIC, and his team of researchers who are developing lithium batteries that will make electric vehicles safer, more efficient, and able to travel for longer distances between charges.

Improving the separator

The researchers are focusing on the separator technology in batteries. Separators are used to prevent the positive and negative electrodes from touching each other, which would create a spark and lead to a fire.

“Our work has been to add functionality to these separators,” Shahbazian-Yassar said. “Right now, separators don’t have any job apart from physically separating the positive and negative electrodes. We want the separator to be multifunctional.”

To achieve this, the researchers developed technology that will allow them to replace the graphite anode, which is currently used in lithium-ion batteries, with a lithium metal anode.

“Owing to its lightweight and high capacity, lithium metal is the ultimate anode for future high-energy-density rechargeable batteries,” said Vahid Jabbari, a graduate student working under the direction of Shahbazian-Yassar in the Nano Engineering Laboratory at UIC.

The team has been working on ways to make sure the lithium is able to deposit uniformly over the lithium metal anode because lithium tends to deposit in the form of needle-like structures called dendrites. These dendrites can lead to fast capacity loss and degradation, lowering the life cycle of lithium batteries.

A needle structure going from one electrode to another would also allow the positive and negative sides to touch each other and create a short circuit between them, causing failure, fire, or even an explosion. These needles are preventing the widespread use of lithium metal batteries, which have higher energy density than their commonly used lithium-ion counterparts.

“What we have done is add a coating to the separator that is able to regulate the lithium movement, and it’s making sure that the lithium deposition is uniform and level,” Shahbazian-Yassar said. “We wanted to remove the needle-like structures within the two electrodes and make them planar, and the coating technology that we have developed at UIC is able to make that happen.”

The coating utilizes graphene oxide, a two-dimensional material that stands out for being strong, flexible, and light. It is estimated that it is 200 times more resistant than steel and five times lighter than aluminum. With these properties, graphene appears to have all the characteristics to develop a safer and lighter battery.

“The graphene oxide materials – due to their inherent atomic structure and atomic properties – are able to guide the lithium through the battery and make sure that when it passes to the anode side, it deposits in a planar morphology,” Shahbazian- Yassar said.

“Our technology suppresses lithium dendrites by the confinement of lithium at the interface with the graphene oxide layer, which is spray-coated over a porous polypropylene separator at the interface with a lithium metal anode,” Jabbari added. “The graphene oxide and its strong binding to the lithium metal surface confine lithium metal growth and enforce its lateral growth rather than dendritic growth.”

With this development, the researchers see their breakthrough as a major game changer for the electric vehicle industry.

“Safety in current lithium batteries is still an issue in terms of fires and explosions. We’re confident that our coating can control lithium deposition, prevent thermal runaway, and add to the safety of current batteries and next-generation batteries,” Shahbazian-Yassar said.

Supercharged performance

In addition to safety, the researchers are estimating additional benefits that will impact performance. Computer modeling and simulations have shown that using lithium metal separators will reduce the weight of the battery packs by approximately 20% to 30%.

“In terms of the mileage, we estimate that the next-generation batteries with our separators can add hundreds of miles to the range of the batteries, which is a significant improvement,” Shahbazian-Yassar said.

“The electric vehicle industry is interested in batteries with fast charge and discharge and a long cycle life. Replacing the graphitic anode with lithium metal would significantly increase the energy density and power density of lithium batteries,” Jabbari said.