Mar 13 2020
At the University of California San Diego (UC San Diego), scientists have devised a new, safety feature that stops rapid heating of lithium metal batteries and thus prevents them from catching fire in the event of an internal short circuit.
UC San Diego nanoengineers developed a separator that could make lithium metal batteries fail safely so that they do not rapidly overheat, catch fire or explode. Image Credit: David Baillot/University of California San Diego Jacobs School of Engineering.
The researchers had ingeniously adjusted the portion of the battery known as the separator, which acts as a barrier between the cathode and anode, allowing it to slow down the energy flow (and thus heat) that accumulates within the battery when it experiences a short circuit.
Headed by UC San Diego nanoengineering professor Ping Liu and his PhD student Matthew Gonzalez, the researchers have described their work in a paper published in the Advanced Materials journal.
We’re not trying to stop battery failure from happening. We’re making it much safer so that when it does fail, the battery doesn’t catastrophically catch on fire or explode.
Matthew Gonzalez, Study First Author and PhD Student, University of California San Diego
Frequent charging of lithium metal batteries causes them to fail and this can be attributed to needle-like structures—known as dendrites—that grow on the anode. Over time, these dendrites grow sufficiently long to penetrate via the separator and form a bridge between the cathode and anode, resulting in an internal short circuit.
When this short circuit occurs, the electrons flowing between these two electrodes go out of control and cause the battery to rapidly overheat and cease working. This blow is essentially softened by the new separator developed by the UC San Diego researchers.
A thin and partly conductive web of carbon nanotubes covers one side of the separator. This web intercepts any dendrites that are formed. When a dendrite strikes this web after puncturing the separator, this provides a pathway to electrons through which they can gradually drain out instead of rushing directly towards the cathode.
Gonzalez evaluated this novel battery separator against 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 prevent a ‘flood’ of electrons to the cathode.
Matthew Gonzalez, Study First Author and PhD Student, University of California San Diego
Gonzalez continued, “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.”
Other efforts made on battery research aim to produce separators from materials that are sufficiently robust to prevent dendrites from penetrating through; however, one drawback of this method is that it simply extends the inevitable, stated Gonzalez.
But such separators still need to have pores that allow ions to pass through so that the battery can operate. Hence, when the dendrites finally make it through, the internal short circuit would be even worse. Instead of blocking dendrites, the researchers at UC San Diego sought to alleviate their effects.
Tests were conducted in which lithium metal batteries integrated with the novel separator, displayed signs of slow failure across 20 to 30 cycles. In the meantime, batteries equipped with a standard and somewhat thicker separator experienced sudden failure in just one cycle.
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. 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.
Matthew Gonzalez, Study First Author and PhD Student, University of California San Diego
While this work targeted lithium metal batteries, the new separator can also be used on other battery chemistries, including the lithium ions, stated the research team. The researchers will further work to improve the new separator for commercial applications. UC San Diego has also filed a provisional patent.
The study is titled “Draining Over Blocking: Nano-Composite Janus Separators for Mitigating Internal Shorting of Lithium Batteries.” Co-authors of the study include Qizhang Yan, John Holoubek, Zhaohui Wu, Hongyao Zhou, Nicholas Patterson, Victoria Petrova, and Haodong Liu from UC San Diego.