Modified battery separator acts as a "spillway" to prevent fires
Battery researchers place a lot of focus on making the devices safer, and scientists at the University of California San Diego (UCSD) are reporting a promising advance in this area. The team’s newly developed safety feature acts as a “spillway” in lithium metal batteries to stem the flow of electrons that takes place during a failure, preventing a rapid buildup of heat and dangerous fires and explosions.
Lithium-metal batteries hold a great deal of potential in terms of the performance, but are very prone to failure in their current form. This is due to the growth of needle-like structures called dendrites, which form on the anode after battery charging and can pierce through the separator, a barrier between the anode and cathode built to slow the flow of energy and heat.
When this barrier is compromised and the electrons can flow more freely, they generate far more heat and things spiral out of control, with the battery overheating, failing, catching fire or even exploding. Scientists are looking to solve these problems in lithium metal batteries in all sorts of ways, with the use of ultrasound or special protective layers to prevent dendrite growth just a couple of possibilities.
The UCSD team’s solution involves a tweak to the design of the separator component, covering one side in a web of partially conductive nanotubes. When a dendrite forms and pierces the separator, the electrons gather on this web and slowly drain out of the battery, rather than flooding through all at once. The team likens this to the way a spillway works in the event of a dam failure.
“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,” says Matthew Gonzalez, first author on the paper. “That’s the idea with our separator. We are draining out the charge much, much slower and prevent a ‘flood’ of electrons to the cathode. When a dendrite gets intercepted by the separator’s conductive layer, the battery can begin to self-discharge so that when the battery does short, there’s not enough energy left to be dangerous.”
In testing, lithium metal batteries featuring the new separator design gradually deteriorated over 20 to 30 cycles, while batteries with a traditional separator failed abruptly in a single cycle. While they will no doubt be aiming higher than this in terms of performance, the researchers already see real advantages of the design based on these early results.
“In a real use case scenario, you wouldn’t have any advance warning that the battery is going to fail. It could be fine one second, then catch on fire or short out completely the next. It’s unpredictable,” Gonzalez says. “But with our separator, you would get advance warning that the battery is getting a little bit worse, a little bit worse, a little bit worse, each time you charge it.”
The research was published in the journal Advanced Materials.