UC San Diego nanoengineers have developed a new safety feature that prevents lithium metal batteries from catching fire.
The team led by professor Ping Liu and his Ph.D. student Matthew Gonzalez, have made a clever tweak to the battery’s anode-cathode separator so that it slows down the flow of energy building up inside the battery when it short circuits.
“We’re not trying to stop battery failure from happening,” notes Gonzalez.
“We’re making it much safer so that when it does fail, the battery doesn’t catastrophically catch on fire or explode.”
Lithium metal batteries fail because of the growth of dendrites which pierce through the separator and create a bridge between the anode and cathode, causing an internal short circuit.
When that happens, the flow of electrons between the two electrodes gets out of control, causing the battery to instantly overheat and stop working.
The separator that the UC San Diego team developed essentially softens this blow.
One side of the separator is covered by a thin, partially conductive web of carbon nanotubes that intercepts any dendrites that form.
When a dendrite punctures the separator and hits this web, electrons now have a pathway through which they can slowly drain out rather than rush straight towards the cathode all at once.
Gonzalez compares their new battery separator to a spillway at a dam:
“When a dam starts to fail, a spillway is opened up to let some of the water trickle out in a controlled fashion so that when the dam does break and spill out, there’s not a lot of water left to cause a flood.”
“That’s the idea with our separator. We are draining out the charge much, much slower and preventing a ‘flood’ of electrons to the cathode.”
In tests, batteries equipped with the new separator showed signs of gradual failure over 20 to 30 cycles.
Meanwhile, batteries with a normal (and slightly thicker) separator experienced abrupt failure in a single cycle.
Image and content: David Baillot/UC San Diego