Nano engineers at the University of California, San Diego have developed a safety feature that prevents lithium metal batteries from rapidly heating up and catching fire when an internal short circuit occurs. Researchers led by Liu Ping, a professor of nanotechnology at the University of California, San Diego, and his doctoral student Matthew Gonzalez published a paper in the journal 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 dendrite, 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 Barriers can slow down the flow of energy and heat.
When this barrier is broken and electrons can flow more freely, they will generate more heat, and things will run 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. The use of ultrasound or special protective layers to prevent dendrite growth are just a few of the possibilities.
The team made ingenious adjustments to the part of the battery called the separator. The separator is the barrier between the positive and negative electrodes of the battery. In this way, when the battery is short-circuited, the energy (that is, heat) accumulated inside the battery flows Slow down.
Gonzalez, the first author of the paper, said: "We are not trying to prevent battery failure. We just make the battery safer so that when it fails, the battery will not catch fire or explode catastrophically."
After the lithium metal battery is repeatedly charged, a dendritic needle-like structure will appear on the anode. Over time, the dendrites grew 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 is out of control, causing the battery to overheat immediately and stop working.
The partitions invented by the research team at the University of California San Diego basically alleviated this phenomenon. One side is covered with a thin, partially conductive carbon nanotube network, which can intercept any formed dendrites. When a dendrite pierces the membrane and hits the carbon nanotube network, the electrons have a channel, and they can be slowly discharged instead of rushing directly to the cathode.
Gonzalez likens the new battery separator to the spillway on the dam. He said: "When the dam starts to break down, it will open the spillway and let some water flow out in a controlled way. In this way, when the dam really breaks and overflows, there is not much water to trigger Flooding. This is the idea of our separator, which greatly reduces the rate of discharge of charges and prevents electrons from "flooding" to the cathode. When the dendrite is intercepted by the conductive layer of the separator, the battery will start to discharge itself, so that when the battery is short Time, there is not enough energy to create danger. "
Other battery research efforts have focused on making separators with materials that are strong enough to block dendrite penetration. But Gonzalez said that one problem with this approach is that it only prolongs the inevitable result. These separators still need to have holes to allow ions to pass in order for the battery to work. Therefore, when the dendrite finally passes, the short circuit will become worse.
In the test, the lithium metal battery with the new separator installed showed signs of gradual failure over 20 to 30 cycles. At the same time, the battery and a normal (and slightly thicker) separator experienced a sudden failure in one cycle.
"In a real-life use-case scenario, you won't have any advance warning that the battery is about to fail. The first second may be okay, the next second will catch fire or be completely short-circuited. This is unpredictable," Gonzalez Say. "But with our separator, you will be warned in advance that the battery is getting worse, getting worse, getting worse, every time it is charged."
Although the focus of this research is on lithium metal batteries, the researchers say that this separator can also be used for lithium ion and other battery chemical reactions. The research team will work to optimize the commercial use of the separator. UC San Diego has applied for a temporary patent for research.