With their high energy density and low self-discharge, it’s not surprising that lithium-ion batteries are ubiquitous in portable electronics. They are not without their limitations, however; they are best designed to operate near room temperature and within narrow temperature constraints, shutting down if it’s too cold or too hot. Charging a cell phone, in fact, also raises the temperature inside its battery; Samsung’s extensive recall of the Galaxy Note 7 in late 2016 -- after the devices began overheating and catching fire -- was just one of the latest developments in a string of incidents that have affected a wide range of lithium-ion-powered devices.
Here’s the good news: A recent Rice University study analyzes progress in lithium-ion technology, and makes recommendations for making the batteries more adaptable to extreme conditions. It’s a research area that has not received as much attention as methods for making batteries last longer, or charge more quickly.
"We searched hard to find one paper that talks about all the problems at the same time and what all the individual components experience at extreme temperatures, and we couldn't find one," said postdoctoral researcher Hemtej Gullapalli, co-author of the paper. "Most research involving batteries and temperatures involve management systems: For instance, if a phone is used in cold temperatures, they slow it down a little bit to preserve the battery," he continued. "To make batteries that work from low to high temperatures, scientists have to take the materials perspective to see what temperature is specifically doing to the materials."
In other words, the performance and safety of lithium-ion batteries at different temperatures has a direct relationship to the components that they’re made from. So the team built a comprehensive map of materials used in commercial batteries, including some new materials that show promise for battery applications. Typical energy densities and temperature ranges were detailed for each component; the team was most interested in seeing how batteries perform in temperatures ranging from -60° to 150° C.
This led to some valuable observations. Water-based electrolytes (e.g., lead-acid, nickel-metal hydride) operate only between -50° and 50° C, for instance; molten salt batteries are reliable at temperatures above 90° C. Lithium thionyl chloride can operate throughout the entire range tested, but only operate at peak between 22° and 50° C.
"Building an ideal or a close-to-ideal system requires a thorough understanding of the subtle mechanisms and replacing each delinquent component with a suitable alternative," said Rice materials scientist Pulickel Ajayan. "A trivial component at ambient conditions can change the whole electrochemistry when exposed to high temperatures."
The researchers’ work has the potential to extend the environmental frontiers of commercial lithium-ion batteries. And, it can be surmised, to avoid future explosions.