Stanford's extra salty electrolyte makes for flameproof batteries
Researchers are working to improve battery technology in all kinds of ways, and among the most important is addressing the issue of flammability. Scientists have cooked up a new electrolyte recipe that tackles this in a highly promising way, leaning on extra salt content to circumvent problematic chemical reactions.
Lithium-ion batteries in our phones, laptops and electric vehicles carry some risk of fire because they generate heat as they operate. We’ve seen many interesting approaches to managing that risk, including integrated flame retardants, warning systems that alert users to overheating, and kill switches that shut the device down before that can happen.
Many promising solutions center on the combustible liquid electrolytes that carry the electrical current between the battery’s two electrodes. Defects and rising temperatures can cause these electrolytes to swell up and/or ignite, which can then result in flaming smartphones or electric vehicles. This process normally kicks off at around 140 °F (60 °C), where solvents in the electrolyte begin to evaporate and turn from liquid to gas.
“One of the biggest challenges in the battery industry is this safety issue, so there’s a lot of effort going into trying to make a battery electrolyte that is safe,” said Rachel Z Huang, a graduate student at Stanford University and first author of the new study.
Huang and her colleagues at Stanford and SLAC National Accelerator Laboratory have developed a battery that is able to endure high temperatures without catching fire. The novel polymer-based electrolyte incorporates a high amount of lithium salt called LiFSI, which constitutes 63% of its total weight. Counter-intuitively, this was paired with flammable solvent molecules, with the two forming a symbiotic relationship that benefits the battery’s safety and performance.
The solvent molecules enable the electrolyte to conduct ions and perform to the same level as a conventional electrolyte, while the high concentration of salts anchor those molecules, preventing their evaporation and, in turn, fire. The team’s non-flammable electrolyte was put to the test in a lithium-ion battery, which was able to safely operate from room temperature all the way up to 212 °F (100 °C).
“This new finding points out a new way of thinking for polymer-based electrolyte design,” said Zhenan Bao, a professor at Stanford University. “This electrolyte is important for developing future batteries that are both high energy density and safe.”
One key feature of the team’s new electrolyte is that it has a gooey form similar to conventional electrolytes, which means it can be integrated with existing battery parts unlike other experimental, non-flammable electrolytes. The team sees particular potential in electric vehicle applications, where batteries could be packed more closely together without the risk of overheating. This would equate to improved energy density and greater range.
“This very exciting new battery electrolyte is compatible with the existing lithium ion-battery cell technology and would make big impacts on consumer electronics and electrical transportation,” said study author Yi Cui.
The research was published in the journal Matter.