Nano engineers at the University of California, San Diego have developed a safety feature that prevents lithium batteries from rapidly heating up and catching fire during an internal short circuit. Researchers led by Liu Ping, a professor of nanoengineering at the University of California, San Diego, and his doctoral student Matthew Gonzalez, published a paper in Advanced Materials detailing their work.
Lithium metal batteries have great potential in terms of performance, but are prone to failure in their current form. This is due to the growth of a needle-like structure called a dendritic crystal, which is formed on the anode after the battery is charged and can pierce the separator, which is formed between the anode and the cathode A barrier that slows down the flow of energy and heat.
When this obstacle is broken and the electrons can flow more freely, they generate more heat and things can get out of control, causing the battery to overheat, fail, catch fire, or even explode. Scientists are seeking to solve these problems in lithium metal batteries in various ways, where the use of ultrasound or special protective layers to prevent dendrite growth are just a few of the possibilities.
The team made clever adjustments to the part of the battery called the separator. The separator acts as a barrier between the positive and negative sides of the battery. In this way, when the battery is short-circuited, the accumulated energy (that is, heat) inside the battery will flow. Slow down.
The first author of the paper, Gonzales, said: "We are not trying to prevent battery failures. We just make the battery safer so that when it fails, the battery will not catastrophically catch fire or explode."
After repeated charging of lithium metal batteries, needle-like structures of dendrites will appear on the anode. Over time, the dendrites grow long enough to penetrate the diaphragm and build a bridge between the anode and cathode, causing an internal short circuit. When this happens, the flow of electrons between the two electrodes gets out of control, causing the battery to immediately overheat and stop working.
A baffle invented by a team at the University of California, San Diego has substantially alleviated this phenomenon. One side is covered with a thin, partially conductive carbon nanotube network that can intercept any dendrites that form. When a dendrite pierces the membrane and hits the carbon nanotube network, the electrons have a channel, and they can be discharged slowly instead of rushing directly to the cathode.
Gonzalez likened the new battery separator to a spillway on a dam. He said: "When the dam begins to break, the spillway will be opened to allow some water to flow out in a controlled manner. In this way, when the dam really breaks and overflows, there is not much water to trigger The flood. This is the idea of our separator, which greatly reduces the discharge speed of the charge and prevents the electrons from "flooding" to the cathode. When the dendrite is intercepted by the conductive layer of the separator, the battery will start to self-discharge, so when the battery is shorted Time, there is not enough energy to create danger. "
Other battery research efforts have focused on making separators with materials strong enough to block the penetration of dendrites. But one problem with this approach, Gonzales said, is that it only prolongs the inevitable result. These separators still need to have holes for ions to pass through for the battery to work. So when the dendrites finally pass, the short circuit will get worse.
In tests, lithium metal batteries with new separators showed signs of gradual failure over 20 to 30 cycles. At the same time, the battery experienced a sudden failure with a normal (and slightly thicker) separator in one cycle.
"In a real-life use-case scenario, you wouldn't have any advance warning about the impending failure of the battery. The first second may be fine, the next second will catch fire or be completely short-circuited. This is unpredictable," Gonzalez Say. "But with our splitter, you will be warned in advance."
Although the study focused on lithium metal batteries, the researchers said the separator could also be used for lithium ion and other battery chemical reactions. The research team will work to optimize the commercial use of the separator. The University of California, San Diego has applied for a temporary patent for research.