BATTERIESFlameproofing Lithium-Ion Batteries with Salt
Rechargeable lithium-ion batteries power phones, laptops, other personal electronics and electric cars, and are even used to store energy generated by solar panels. But if the temperature of these batteries rises too high, they stop working and can catch fire. A polymer-based electrolyte makes for batteries that keep working – and don’t catch fire – when heated to over 140 degrees F.
Rechargeable lithium-ion batteries power phones, laptops, other personal electronics and electric cars, and are even used to store energy generated by solar panels. But if the temperature of these batteries rises too high, they stop working and can catch fire.
That’s in part because the electrolyte inside of them, which ferries lithium ions between the two electrodes as the battery charges and discharges, is flammable.
“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 a report published Nov. 30 in Matter.
Huang developed a non-flammable electrolyte for lithium-ion batteries with 19 other researchers at the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University. Their work demonstrated that batteries containing this electrolyte continue to function at high temperatures without starting a fire.
Their secret? More salt.
Salty SAFEty
Conventional lithium-ion battery electrolytes are made of a lithium salt dissolved in a liquid organic solvent, such as ether or carbonate. While this solvent improves battery performance by helping to move lithium ions around, it’s also a potential firestarter.
Batteries generate heat as they operate. And if there are punctures or defects in a battery, it will heat up rapidly. At temperatures above 140 degrees F, the small molecules of solvent in the electrolyte start to evaporate, transforming from liquid to gas and inflating a battery like a balloon – until the gas catches fire and the whole thing goes up in flames.
Over the past 30 years researchers have developed non-flammable electrolytes, such as polymer electrolytes, which use a polymer matrix instead of the classic salt-solvent solution to move ions around. However, these safer alternatives don’t move ions as efficiently as liquid solvents do, so their performance has not measured up to that of conventional electrolytes.
The team wanted to produce a polymer-based electrolyte that could offer both safety and performance. And Huang had an idea.
She decided to add as much as she could of a lithium salt called LiFSI to a polymer-based electrolyte designed and synthesized by Jian-Cheng Lai, a postdoctoral scholar at Stanford University and co-first author on the paper.
