What causes batteries to explode? How to reduce the explosion accident rate?

In order to reduce the risk of battery fires, some research institutions have designed carbon nanotubes for the battery's conductive plate, the anode, which can safely store large amounts of lithium ions, thereby reducing the risk of fire. In addition, the researchers also said that this lithium battery with a new anode structure charges faster than batteries currently on the market.

Juran Noh, a graduate student in the Department of Materials Science, said: "We have designed a next-generation anode for lithium batteries that can continuously generate high currents and allow devices to charge faster. In addition, this new structure prevents lithium from accumulating outside the anode, which can cause Over time, lithium can cause accidental contact between the components of the battery poles, which is one of the main causes of battery explosions."

When lithium batteries are used, charged particles move between the battery's poles. The electrons released by the lithium atoms move from one side of the battery to the other. When the battery is charged, the lithium ions and electrons return to the pole where they were originally.

Therefore, the properties of the anode (the electrical conductor containing lithium ions) play a decisive role in the properties of the battery. One commonly used anode material is graphite, in which lithium ions are inserted between graphite layers. However, Noh said this design limits the number of lithium ions the anode can store, and even requires more energy to pull the ions out of the graphite when charging.

There is a more dangerous problem with this type of battery. Sometimes, lithium ions do not deposit evenly on the anode. Instead, they accumulate into clumps on the anode surface, forming tree-shaped structures that become dendrites. Over time, the dendrites can grow and eventually puncture the material that separates the battery's poles, causing the battery to short out and potentially set the device on fire. Growing dendrites also affect battery performance because they consume lithium ions, making them unable to generate electrical current.

Another anode design would use pure lithium metal instead of graphite, Noh said. Lithium metal anodes contain much higher energy density per unit than graphite anodes. However, since dendrites also form, they can render the battery useless in the same way.

To solve this problem, the researchers designed anodes made of carbon nanotubes, a highly conductive lightweight material. Such carbon nanotube scaffolds contain spaces or holes that allow lithium ions to enter. However, such structures cannot be combined with lithium ions smoothly.

So the researchers made two more carbon nanotube anodes with slightly different surface chemistries, one with a large number of molecular groups that can bind to lithium ions, and the other with the same molecular groups but in smaller amounts. The researchers built batteries using such anodes to test whether they had a tendency to form dendrites.

As expected, the researchers found that scaffolds made solely from carbon nanotubes did not bind well to lithium ions. Therefore, although few dendrites are formed, the battery's ability to generate large currents is also affected. On the other hand, scaffolds with too many molecular groups will form many dendrites, thus shortening the battery life.

However, carbon nanotube anodes with the right number of molecular groups can prevent the formation of dendrites. In addition, large numbers of lithium ions can bind together and diffuse along the surface of the stent, thereby enhancing the battery's ability to continuously generate large currents.

The researchers say the anode's current handling capacity is five times higher than that of commercial lithium batteries. Furthermore, this capability would be useful for large batteries that need to be charged quickly, such as those used in electric vehicles.