Graphene coatings could help prevent lithium battery fires
16 April 2019
Lithium batteries are what allow electric vehicles to travel several hundred miles on one charge. Their capacity for energy storage is well known, but so is their tendency to occasionally catch on fire – an occurrence known to battery researchers as “thermal runaway.” These fires occur most frequently when the batteries overheat or cycle rapidly.
Graphene coated lithium cobalt oxide - Image: R. Shahbazian-Yassar
With more and more electric vehicles on the road each year, battery technology needs to adapt to reduce the likelihood of these dangerous and catastrophic fires.
In a report in the journal Advanced Functional Materials, researchers from the University of Illinois at Chicago College of Engineering say they have found a way to reduce the risk of fires in lithium batteries by coating them with graphene.
The reasons lithium batteries catch fire include rapid cycling or charging and discharging, and high temperatures in the battery. These conditions can cause the cathode inside the battery — which in the case of most lithium batteries is a lithium-containing oxide, usually lithium cobalt oxide — to decompose and release oxygen. If the oxygen combines with other flammable products given off through decomposition of the electrolyte under high enough heat, spontaneous combustion can occur.
“We thought that if there was a way to prevent the oxygen from leaving the cathode and mixing with other flammable products in the battery, we could reduce the chances of a fire occurring,” said Reza Shahbazian-Yassar, associate professor of mechanical and industrial engineering in the UIC College of Engineering and one of the authors of the paper.
Shahbazian-Yassar and his colleagues knew that graphene sheets are impermeable to oxygen atoms. Graphene is also strong, flexible and can be made to be electrically conductive. Shahbazian-Yassar and Soroosh Sharifi-Asl, a graduate student in mechanical and industrial engineering at UIC and lead author of the paper, thought that if they wrapped very small particles of the lithium cobalt oxide cathode of a lithium battery in graphene, it might prevent oxygen from escaping.
“Graphene is the ideal material for blocking the release of oxygen into the electrolyte,” Shahbazian-Yassar said. “It is impermeable to oxygen, electrically conductive, flexible, and is strong enough to withstand conditions within the battery. It is only a few nanometers thick so there would be no extra mass added to the battery. Our research shows that its use in the cathode can reliably reduce the release of oxygen and could be one way that the risk for fire in these batteries — which power everything from our phones to our cars — could be significantly reduced.”